The Stovebolt Site Forums The Shop Area Engine Shop Dual exhaust dilemma

So my heat riser is stuck pretty hard and I've spent a week soaking it in PB Blaster while tapping each side with a hammer back and forth with no major moves toward it unsticking. I can feel a little lateral movement, but not much else, and I'm feeling like I may have to split the manifolds to see what is going on so I can fix it.

This got me to thinking about just going with the dual Fenton or William's exhaust and be done with the heat riser all together. So I started digging on the internet and found what I thought was a deal that had to be too good to be true - National Chevy Association has William's headers and full header back exhaust with glass-packs for $600. Thinking it was too good to be true, I came back to the bolt and found it had already been thoroughly reviewed and this kit does seem to be too good to be true!! (see thread below).

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1034037/1.html

Since that thread is from 2014, has anyone lately found a good complete package for dual exhaust? From what I have read here, the best sound is the straight through duals and glass packs with no crossover or shared muffler. I can find Fenton headers and a nice looking header-back exhaust package from Patrick's, but not a straight through system. Do most just go to a muffler shop and have them build a header back exhaust? That just sounds more expensive.

I know this subject has been talked about several times here, but I am hopeful there is a good kit out there somewhere.

Thanks,
mark

Have you tried heating your riser? I heated it and after it cooled, used more pb on it. It eventually came loose. I also used attempted to turn it gently to get her loose.

Chris

Chris

With the possible exception of the original Corvette split exhaust with the built-in heat riser, stovebolt header systems seem to create more problems than they solve. I haven't seen a really good approach to supplying intake heat with any of the aftermarket dual exhaust systems.
Jerry

Why don't you just cut off the shaft and remove the riser and faghedaboudit?

I got my setup from Langdon's and added a water heat rise from them. You can run straight pipes but I have a crossover. I have been running this set for over 10 years. My mufflers are Flomasters.

Depends on what you want to do here. If you are sticking to the stock intake manifold, why not just dig up an exhaust manifold with a working heat riser. If you are set on dual exhaust, Fentons are the one choice but you have to do your homework, they do not fit on every application. Same for Williams. The other alternatives are the cheap so called headers on ebay. Some of these are even made out of stainless steel. Not really a true tube header but does the trick. Finally, Clifford Headers. these are true tube headers, a little pricy but available and useful. I have run Clifford long tube headers for nearly 40 years. Love them really but no longer made.

As for heat, I have run dual carb set ups with no heat and with heat. Heat runs better. I have tried exhaust heat (copper tubes from the fentons to the underside of the intake) and water heat (302 gmc lower therm housing on a 235/261-has water outlet on drivers side of motor in addition to one on the pass side) where you run hot water to the bottom of the intake and then back into the cooling system. Hot water runs better.

As for an exhaust system, from the dual outlets to the mufflers, I have always had to make them up to fit the application. Get around the clutch linkage, and the best way to cross over for a true both side dual set up. I have seen others run them both down one side. Looks pretty cool, but not for me. For tail pipes, cars are easier because you just use dual v8 tail pipes (if the cars came with a v8) or custom depending on what kind of money you want to spend. I have also used two stock tail pipes and cut one up and rewelded it back together to get it to fit on the other side when no dual tail pipe exists. Trucks are similar in that there may not be a pass side tail pipe available so I tinker a bit. I have seen some of the universal dual kits but have not used any myself.

No can do. That would put full-on heat to the intake and result in horrible performance once the engine reaches operating temperature.
It is possible to just leave it alone if it is stuck in the closed position, but it would not work well in cold weather, and will lead to unburned gas pouring down past the rings while the intake is cold, leading to ruining your oil, and destroying bearings before their time.
Maybe you are referring to the V8 style one on the passenger side exhaust pipe below the manifold.
Carl

Right 52Carl, the stuck heat riser is what got me started on fixing my exhaust or going dual. I believe that the stuck riser (in the heat on position) is leaning out my fuel mixture. I'll see if I can borrow my buddies torch and try to get it to pop loose, but catching things on fire or cracking the manifold by applying too much heat are concerns for me. I want to avoid taking the manifolds apart, but it is stuck pretty hard right now, so if heat doesn't work, I may have to open it up. Finding a replacement manifold with a good valve is another choice, but I'd want to see what I am dealing with on mine first and see if I can fix it before I buy a new one.

My thought of having a true dual exhaust instead of dealing with the old riser may have come and gone knowing that there is no guaranteed bolt on perfect fit that is cheap (cuz I'm pretty cheap). Stock seems like it is the best engineered solution and I just want to drive knowing I have things set up right. The heat riser/lean condition is also making some valves stick, so I want to get the riser valve working so I can clear up the sticky valves and not invite more of that side effect. Cruising around with a chuff, chuff, chuff sound isn't how you want to show your work.

Seems like when you own one of these vehicles, if you haven't touched or repaired/worked on everything yet, you will at some point.... I have learned way more than I wanted too, but am enjoying learning how to sort it all out. thanks for everyone's help!
mark

I just got my kit from Waldron's out of Centerville MI. I've only mocked it up so far but it looks good and the woman I worked with on the phone (Ruth I think her name was) was super helpful and actually knew about the products they were selling. I had mine shipped by a local carrier and was able to get just the dual exhaust (no mufflers or manifolds) delivered for about $400 total.

Another option would be to go old school and split the original manifold. It's not all that difficult to weld in a blocker plate between the front and rear sections of the exhaust manifold and add a second exhaust flange to the front section. It solves the manifold heat problem by using the original heat riser valve, and it looks period-correct when somebody looks under the hood.
Jerry

Even after all the work of installing the dual exhaust, I really doubt the engine or you will know its on the truck. It's a lot money just for noise, and if you haven't been around a straight six with glass pack mufflers, I suggest you ride in one before investing the money.

Heat up the manifold around the shaft on both sides, let it cool, then do it again. Add candle wax to the shaft the second time, it should melt and flow into the gaps pretty fast. Add the wax once you shut off the torch.

Sulli: about every 3 or 4 years I have to unstick that manifold heat butterfly valve on a 216. I had good luck by first cleaning the exposed "shaft" on both the weighted and coiled spring sides where the shaft enters the manifold. I used a Dremel wire brush, or a thin sandpaperstrip to lightly shine & buff the shaft clean first. That shaft often does have a small bushing that it rides into on the manifold.
As another version of Joes' candle wax method ....
I then use heat from a soldering iron , or small torch, to heat shaft and then rapidly cool that area with a few drops of Kroil. That Kroil should "suck" along the shaft and help free the bind as the shaft cools. I would caution that twisting the weighted end too much may snap the shaft, and watch for mushrooming the little slot on the coil spring end as you gently tap the shaft side-to-side.

{52Carl, I'm confused if the manifold butterfly is removed, isn't that permanently "heat off" ?}

Dual exhausts on a stovebolt are like dual carbs- - - -eye candy for people who are lousy at physics. There's no point in having huge links in a chain that's held together by a few loops of baling wire in the middle- - - -the cylinder head!
Jerry

Carl,

Like Bart said, removing the shaft & riser, is an option.

Removing the shaft & heat riser valve does not put "full-on" heat to the intake.
Just the opposite.
It opens up the exhaust manifold, and turns the "heat-off" the (intake) from the preheating process.

If the valve sticks in the "heat-on" position, the valve is "closed". NOT GOOD!
Closed directs the hot exhaust gases to the intake manifold when the engine is cold.
Closed = heat on the intake.

If the valve sticks in the "heat-off" position, the valve is "open",
and directs the exhaust gases away from the intake manifold to the exhaust manifold.
Open = heat off intake.

In 1954, Chevrolet "determined that manifold heat control valve operation
is neither necessary nor desirable under normal temperature and operating conditions"........

"the heat control valve spring has been reversed so as to hold
the valve continuously in a "heat-off" position".

"If preheating of the incoming charge is desired for extreme cold weather
operation", reverse the spring.

If you look at the really great Lugnutz video he did, this riser is a primitive, iffy feature. Due to convection and conduction and the fact that heat rises, in my opinion, there is not enough difference in open and closed. There are thousands of stuck open and stuck closed risers across America. Nothing horrible is happening. So if I had this I would cut it off until a better solution is found $600 plus dollars later. I believe there could be an insulator under carb. All those castings will be real hot, eventually, no matter the riser. Too much false science is being placed on a low tech flapper. Have not seen documented facts to support faulty heat riser serious motor damage. Just hearsay speculation. The poster has not reported any performance issues with the motor.

If I have to agree, I agree with Carl that stuck closed is better. If closed means flapper diverting to tail pipe.

I do see a semantics issue here. I myself was confused until I saw the Lugnuts video. Open/closed can be seen differently. I am taking the road that, at rest/cold, the flapper is open, letting the exhaust blow on the bottom of the intake. Then when the bimetal spring gets hot, it sort of "closes" off or diverts the flow down toward tail pipe.

Tom, view this and see if your explanation is OK.

Lots of good input, and heat with a Kroil or wax seems like it's the preferred way to unstick the riser, so I'm going to try the torch this weekend and see if I can make it happen. I just got back from running it in the driveway to see if engine heat along with some penetrating oil would do its thing, but no luck. Will keep at it.

Performance issues:
1. Once the engine is warm, there is a noticeable chuff chuff exhaust sound that to my untrained ear is either a miss, or a valve issue (burned or sticky). I could be way off on my diagnosis, but I honestly have no way to tell for sure. So tonight, I pulled the valve cover while it was running, and the rockers had oil coming out of the weeps right away. I did not notice any valves that seemed to be hanging up. I'm not sure if one can tell if a valve is sticky by watching them run, but they looked like they were working fine. I spun all the rods with my fingers before I started it and all felt straight and smooth with no wobbling off center from the rocker, so I don't think have any bent rods.

2. When idling, I can feel the engine randomly bumping, like it is fighting itself. It's not sewing machine smooth, and the bumping becomes more random and more pronounced when the revs are up. I basically have an all new ignition set up.... The only thing I have not replaced is the distributor cap (which looks good) and I have not replaced the distributor itself, but plugs, wires points, condenser and coil are all new. It is a 6 volt set electrical system for now. I statically timed it to be 5 degrees, then gave it two more degrees for a total advance of 7. The vacuum advance is also new and is I have observed it to be functional

3. When I noticed that the heat riser was stuck in the heat-on mode, and read what the Chevy manual said about this condition, I thought the heat riser was contributing to #1 and may have been the answer to my plugs telling me that the fuel mixture was lean. The Chevy manual says if the valve is stuck in the heat on position, it will cause the gas mixture to expand (lean out) which can lead to detonation, overheating and sticky valves. I am no expert by any means just trying to do my homework and figure it out.

To be honest, adding a dual exhaust was on my wish list (guess I'm a sucker for eye candy and noise) and I was trying to convince myself that the stuck riser was a way to validate (and convince the wife) that I needed a dual set up... At the same time I'd be eliminating the dang flapper valve, but I am back to reality, and am determined to make the stock set up work.

On performance gains:
I don't have any illusions about a dual exhaust system turning a 95 hp vintage farm engine into a fire breathing beast, just thought it would be fun and eliminate the sticky flapper ;-). The truck as it is now, seems to hold its own in traffic but the chuff chuff exhaust sound has me concerned.

I am a fan of good engine noises and would rather listen to that than the radio.

Yes, I agree it can be confusing & now I'm confused.

Quoted from the repair manual...
"valve may stick in either the "heat on" or "heat off" position.

"If it sticks in the "heat on" position,
it will result in poor engine performance, overheating and detonation."

"On the other hand, if it should stick in the "heat off" position,
the heat will be turned off the intake heat riser at all times and result in poor performance,
particularly while the engine is warming up and driving at lower speeds."

To me, "heat off"(as quoted from the manual) is the same as removing the flapper completely.
And If you remove the flapper, the flow is now open and the hot gases go out the tail pipe.

Am I understanding this correctly?????

Sulli, I think you have a really good attitude and good natural knowledge of trucks and motors. Your plans and conclusions are well thought out. Good work.
I will follow your progress with an interest to learn.

Nope, sorry to say. "Heat off" means the flapper is redirecting the flow away from intake and down the pipe. I think you got that OK. Removing the flapper (which I sort of said off handed "faghedaboudit", has a consensus here of no-no) will allow the "so called heat" to heat up the intake on it's way out even though the passage down tail pipe is fully open also. That is much closer to "heat on". Some heat (XX%) will swirl, flow against and around the carb base mass on it's way out. Putting "heat on" it.

So now I'm acting like Mr. expert riser man.....not. Many on the web say it's OK without the flapper. Yo, I gotta stick with my Stovebolt boys and say leave it in....and do what I want on my motors.

If you remove the flapper, you will replicate the "heat on" position. The flapper in the closed position deflects exhaust away from the intake manifold.
Carl

For what its worth ,in the process of freeing up my flapper on my 235 with heat I managed to destroy the temperature sensitive spring which probably has a proper name, so I wired up the flap in the closed position so as not to over heat the carb. I noticed no side effects in town but once I hit the highway and started climbing some long grades the throttle response got a little weird as in when shifting gears and taking my foot of the gas peddle the rpm was slower on dropping. I checked under the hood to see if the return spring had fallen off but I found instead a frost like substance at the base of the carb like one might find on air condition fittings when working hard . I rewired my flapper to about half way between open and closed and this seams to have cured the problem until i replaced the spring thingy.
I mentioned this event to some other people who suggested frosting would not occur , but it sure looked like frost to me.

If you pull the manifolds apart and study on the flapper a bit, you will see it should stay in place. The exhaust will flow better out of the manifold due to the flapper valves design. It directs the flow around the corner and out the opening. Without the flap, the exhaust will still get out, but it will also bunch up under the intake. Does this hurt anything, probably not, but performance minded folks sure wouldn't want a restriction like that.

If you absolutely can't get it to move, leave it alone, it will not cause any problems with performance. My 250 has been running for years without a spring on the valve.
I suspect you might have a vacuum leak, they can cause all kinds of mysterious problems, lean being one of them.

Sulli : for the chuff-chuff and randomly bumping of the engine , have you tried using a vacuum gauge to detect a problem ?

One way to reduce heat with the flapper removed is to make a blockoff plate in the same shape as the gasket between the manifolds. Sure miss my former co worker who did a fabulous job of splitting stock exhausts.

Might as well jump in too LOL.

The heat flapper works in my 49 216 thusly:

Cold engine: The bi-metal spring is at it's full compressed state which pulls the flapper valve "open" and directs at least half the exhaust gases up into a chamber just under the imtake mainfold directly under the carb. This heats the chamber and cast surfaces around it. One of these surfaces is the bottom of the intake manifold. When fuel/air dropletts hit this surface the heated base plate helps to atomize the fuel/air mixture which makes for a better more complete ignition. This also lessens excess fuel into the cylinder which can make it's way past the rings diluting the crankcase oil.
The counter weight on the other end of the flapper rod has it's rounded side up.

Warm engine: As the engine warms up the bi-metal spring starts to lose it's tightness and begins to unwind a little. This relieves it's spring pressure on the flapper valve which begins to "close". Due to the design of the counter weight and flapper valve the on rushing exhaust gases help to close it further and as the spring tension lessons the gasses continue to push the flapper closed as they exit.
In the closed position exhaust gases are redirected straight out the exhaust pipe and greatly lessens the amount of hot gases that get into the heat chamber under the intake manifold.

Engine at operating temp: The bi-metal spring is at it's weakest point and is applying very little to ziltch spring pressure to the flapper valve. This allows the counter weight and exiting exhaust gases to hold the fllapper valve in the closed position. Most if not all exhaust gases are directed straight out to the exhaust pipe and only minimal gases get around the flapper into the heat chamber under the intake manifold.

I've noticed that the flapper will still try to open some on my 216 when it's warmed up to operating temp at idle but when I increase the rpm from idle the gases will fully close the flapper and keep it closed for as long as the rpm is higher than idle. Once rpm is dropped back to idle the flapper will move alittle towards open but not fully like when it's cold. It could be that the bi-metal spring is alittle too taught but I've left it like this for going on 22k miles and the 49 3100 with a very tired 216 avgs 12.5 mpg and starts and runs all year long, all 4 seasons reliably.

re. OP. What position is the flapper stuck? Open (weight round side up) or close (weight round side on it's side).

Being stuck closed is better than stuck open but a working flapper is best.
Good luck
Dave

Wasn't a "flapper" a party girl in the Roaring 20"s? If she's still "working" she must be doing it at a nursing home! If she's 100+ years old, she must be quite a gal!
LOL!
Jerry

She's very spry LOL...

Well, thanks to Volfandt's easy to read, detailed post,
I finally see the "light".

In the cold position, the flapper counter weight has its rounded side up.
In this position the flapper is "open" to the intake manifold,
and redirects some of the exhaust gases to heat the mixture.

Open & Closed was the issue for me........

Since the flapper is located in the exhaust manifold,
I thought it was opening & closing the exhaust manifold.

But instead it's referring to opening & closing off the intake manifold.

That's how I got it bass ackwards.
Thanks for clearing this up.

I'm just glad the old "flapper girl" is still working....
she is quite a gal and her rounded side is always up when she is cold.

Soggy, I just got back from fiddling with the vacuum gage. After starting and closing the choke, it was idling close to 600 rpm, and had some slight bumping, but when I adjusted it down to 550 rpm, it was smooth and holding 21hg with no noticeable movement on the vac gauge. When I increased throttle and held it at constant high rpm (tested several different rpms), the engine had noticeable bumpping and had corresponding dips in the vacuum gage. The dips were in about the 1hg range, so they weren't big. Is that simply an ignition related misfire and not a mechanical thing? As noted before everything except the cap and dizzy are new. When I replaced the wires, I did not get the solid core set, so I'm not sure if that affects anything.

Looking at my counterweight, I think she might be half cocked...? (see pic) I tried the heat up the engine and douse the riser valve with penetrating oil again with no luck tonight. Even after hitting it with penetrating oil, once it is heated up, I can't even feel the slight lateral movement that I get when it is cold. Will try the torch thing this weekend and if that doesn't work, I may be learning about removing and installing the manifolds. It will be a good opportunity to paint them anyhow.

I like HRL's idea of splitting the original in two, and the pics of the modified original with the block off look pretty nice.

The traditional method of "manifold splitting" doesn't actually cut it into two pieces. A slot is sawed or ground into the manifold runner just ahead of the heat riser area, and a piece of steel or cast iron is cut to fit the slot and welded inside and out to block off most of the manifold runner. Some people choose to make the split slightly leaky to allow a little bit of exhaust gas transfer from front to rear; others block it off entirely. Then a second flange is added to the front section for another pipe. You'll need to observe all the cast iron welding precautions- - - -proper alloy welding rod, pre and post heating, peening the weld beads for stress relief, and then bury the manifold in a pile of sand to cool down slowly and prevent cracks. Fun and games! I just recently found some nickel-allow wire for my MIG welder but I haven't tried welding any cast iron with it yet.
Jerry

Sulli ; From your description of the initial vacuum test , I don't suspect your engine chuffing is a result of that stuck manifold heat riser. Maybe , but ...
I feel it might be possibly more electrical ignition related. Double check for any goobers on the the little cam lobes inside the distributor, and look at any pattern on the faces of the ignition points (any arcing.) Free and smooth travel on the vacuum advance and centrifugal weight mechanisms. And get a new distributor cap before the huge amount of work (and expenses) of spitting manifolds.

That tiny 1hg dip on the vacuum gauge could be a minor sticky valve, dirty valve face, or more likely an electrical miss.
Your pics of that counter weight on the shaft looks to me like the manifold heat riser (flapper) is stuck in the "heat off" position ?
If it's stuck, I prefer the "heat off" and I would take time to get the engine to operating temperature (takes about 20-40 minutes at idle ~70degrees F). Your water temp gauge will show hotter water sooner than the actual temperature of the engine oil. Testing at engine normal operating temps for vacuum is better.

I have seen that butterfly flapper get really stuck from the inside of the manifold. Carbon and corrosion on the shaft. Once you do remove the manifolds you can likely unstick that valve once and for all; without the expense and labor of dual exhaust.
At this stage I would not twist or bang on the heat riser shaft too much that you would damage it. Keep diddling with it by drops of Kroil when hot & cold , and a gently side-to-side tapping and gentle rocking & twisting. May take a few weeks of engine heating and cooling cycles. Cheap to try.
Just my opinion, others may have another good direction to take.

Thanks Soggy, I’ll get a new cap and rotor, clean up/lube the cam lobes and go over the points/dwell again to see if that helps with the misfire.
One thing I am second guessing myself on is the valve adjustment I did a while back. An earlier thread in this forum was asking about flywheels -TDC and the ball actually being 5 degrees advanced (not tdc). I am pretty sure that after i warmed the engine by driving around town, I adjusted the valves with the flywheel on the ball (5 degrees advanced) so my valves are probably tighter than they should be, right?
One quick question on sticky valves, will it hurt anything to hit them with some kroil or sea foam deep creep to help unstick them?
I’m out of town now, but after I replace the cap and rotor, I’ll look at readjusting the valves and hope to have some good results.
Mark

Sulli : I think I'm (unintentionally) helping you drift from the original subject title of dual exhaust. To get a more clear picture of your problem, what engine do yo have in your truck and is it stock?

My summary opinion on your quest for a dual exhaust as a solution to engine roughness --- I would check a bunch of other possible problem sources first before determining that the exhaust manifold flapper is giving you that much performance head aches. Going to duals can be expensive, separating the manifolds to clean the flapper shaft can be dirty labor (with the chance of busting those manifold studs!)

On your ignition timing question: Chevrolet has had a long tradition on those Stovebolt 6 engines of using an embedded ~3/16ths BB-like ball to set the "initial" ignition timing. They did this so the little BB thing could be spotted easily with a neon timing light. {Chevrolet engineers found that ignition timing with the engine running was preferred because it compensated for the slop (back lash) in the timing gears, and distributor gear & distributor cam. Especially on early IL-6 Chevies. To see if the distributor cam lobes were OK, #1 cylinder was first timed to the BB, then the neon light was switched to #6 cylinder: and if the fixed pointer still linedup ... dist cam was basically Ok.}
That little BB is only starting place for your ignition timing, you MUST tweek the setting a bit for the octane of your gas and your engines ambient running conditions. My 51' 216 runs (pulls hills & starts, drives highways etc) best @ ~7-8 degrees advanced from TDC. Finally, TDC is often referenced on the old stovebolt flywheel with the symbol UIC (upper line center).

Note that "valve timing" is NOT the direct same as "ignition timing". Setting the valve tappet lash on your engine is setting the clearance SPACE between the rocker arm and the valve stem. It will clatter if too loose, it can cause valves to burn and loose engine power if too tight.
.
Yes, using SeaFoam or Marvel Mystery added to engine oil to try and get valves un-sticky is a tried and true practice attempt. It will not cure worn or deformed parts, it may unstick a varnished area.

No, I think the ignition is a good place to start working on the misfire, and I will keep fiddling with the heat riser, but just as a secondary thing now. (I have a 1954 stock 235 with a Rochester B). Once I’ve gone back through the ignition and tested it on the road, I would go back and check the valve lash at TDC instead of the ball. I was mistaking the ball for TDC and adjusting valve lash with the ball in the needle. If I’m thinking correctly, setting valve lash on the ball would mean I have set them too tight because the valves would not be fully closed, correct?
On the dual exhaust, I think there are several great responses from everyone about where to either find a dual exhaust kit and options for headers. Also, it sounds like if one wants to go dual exhaust, there will likely be some necessary “adjustments” required for whatever option you choose. I’m hopeful now that I can get the engine smoothed out and keep working on the riser without pulling the manifolds off.
Thanks to all, and I’m hopeful I’ll get things smoothed out and unstuck!
Mark

The "UC" mark on the flywheel will allow you to find an accurate TDC position, but it's only accurate for two cylinders- - - -#1 and #6. Getting the other 4 cylinders exactly on TDC is a wild guess situation unless you use something like the "companion cylinder" method of assuring the cylinder you're adjusting is actually on the base circle of the cam. I've explained that so often my fingers cramp up just at the thought of doing it again- - - - -do a site search for "Companion cylinder valve adjustment"!
Jerry

Jerry, thanks for pointing me in the direction of the companion cylinder method of adjusting valve lash, and apologies for not doing my homework. We need you to keep us inliners - in line!

So I got back in town tonight, and checked the lash with the engine cold (you can roll your eyes now) to see how .006 and .018 felt (I was hoping for them to feel looser cold) and I did have about three of 4 valves that felt tight or snug with these settings. This tells me that they would only get tighter when the engine warms up, so I focused on adjusting them. I also did a search on cold engine valve adjustments, and found two camps, one says use the factory settings cold, then re-do the valve adjustment after running it on the road for 45 minutes, and the other camp says to add about .002 (.008 intake and .020 exhaust in my case), then run it and check the valves again. I opted to go with adding .002 to make sure I was on the safe side. Again I have a 54 stock 235.

I practiced the companion method, but I was not able to come close to landing on the UC mark when rocking 1 or 6, so it must take a better trained eye to see the intake valve just begin to rock. (Rocking valves on 6 to hit UC on 1 and vise versa). I went with the method where you set UC on #1 with the needle and check all the valves that are closed, then find UC for #6 and check the other 6 closed valves.

Checked the points gap and it was right on .016, so tomorrow, I'll get the new rotor and cap, then run it and see what happens. The plugs looked fine and only one gap was a little off. If I get the bumping engine symptom again tomorrow, I'll start pulling plug wires one at a time to see if the miss goes away on a certain plug then check that wire for continuity, and if that wire looks good maybe get another set of plugs.

With a cam as mild as a stock stovebolt engine has, the exhaust valve actually gets completely closed before the intake starts to move. On #1 and #6, the UC mark will get past the pointer before you see any movement on the intake rocker. On engines with very radical racing cams, the only way to get a good adjustment is to find the split overlap point and then adjust the cylinder halfway around the firing order. Fortunately, you've got almost the entire power stroke to work with before the clearance on the stovebolt exhaust valve begins to close up. so there's a huge margin of error before there would be an incorrect adjustment induced by missing the mark a little. The main advantage to companion cylinder adjustment is that it works on any engine with an even number of cylinders, with solid or hydraulic lifters. On odd-numbered engines like an Audi 5 cylinder or maybe a GEO Metro 3 cylinder, just find the rocking point, then turn the crankshaft one more turn and adjust!
Jerry

Thanks Jerry, I don't feel so bad now, and am glad to know there is some wiggle room doing the companion method with the stock engine setup.

I didn't get to fiddle as much as I wanted today due to rain, but I did get it running smooth at low RPMs. It started bumping again around 1,000 or 1,100 and kept bumping as revs increased. Things I did today:

1. New distributor cap
2. New rotor - didn't use it because the fit was sloppy
3. Checked the mechanical advance by pushing the rotor clockwise (didn't know you could do that), and it rotated then rebounded back, so it seemed to be functional
4. Checked resistance in all plug wires (coil wire too) all had good constant resistance numbers on the multimeter
5. Checked distributor for wobble, and there was some. I could see it change the points gap, but twisting the grease cup made it feel solid so I figure that is what it's supposed to do
6. Changed the points gap to be .18 instead of .16

I wanted to confirm the dwell was right then reset the timing by vacuum today since I adjusted the points, but it was rainy and I wasn't able to go warm up the engine to do a proper adjustment.

So I'm guessing maybe the plugs themselves need to be replaced, or I have slightly sticky valves? Maybe going over the timing after a good warmup might fix things? I'm stumped, the plugs have maybe 5 hours of run time.

About my original post - I was ultimately concerned that the engine is running lean (plugs are bone white) and thought that was caused by an overheated intake due to the stuck heat riser. What else can cause it to be lean if I have good vacuum - 21hg at sea level?

White spark plugs aren't necessarily an indication of "too lean" like we learned decades ago. The "tan to chocolate brown" color that indicated proper mixture back then was caused by lead deposits on the plugs. No lead- - - - -little to no color change until the mixture gets so rich the plugs go black and sooty. A white plug with a glassy appearance or blisters on the porcelain tip indicates a dangerously lean condition- - - -on the verge of burning valves lean. Increasing the point gap also advances the timing because the points open sooner, and that's when the coil fires. For every degree of distributor rotation sooner that the points open, the crankshaft timing advances two degrees. Increasing the point opening by .001" probably advances the timing 5 degrees or so. Better recheck the timing, if you're using a light. If you're doing the "best vacuum at idle" thing, or listening for detonation on a long uphill pull, it's a waste of time to do anything other than make a ballpark guess to get the engine to run well enough to tinker with it. It's sort of the "Measure it with a micrometer- - - -mark it with chalk- - - -cut it with an axe" method!
Jerry