The Stovebolt Site Forums The Shop Area Engine Shop 235 engine detectives wanted

Scenario: rebuilt 58-59 235 engine with 2500 miles on rebuild,30wt non-detergent oil, lean jet on Rochester carb, 48 suburban driven at 5300-8000' elevation, good compression. Symptom: engine runs fine when cold, begins to run rough when fully warmed up at 55 mph. Pretty much always at the same distance from home. It sounds louder from the exhaust pipe and the engine vibrates a bit kind of like running on only 5 cylinders but it actually has pretty good power. I originally thought ignition but now I'm leaning towards valves. It sounds like excess pushrod to rocker arm clearance except this engine has hydraulic lifters and makes no such noise when cold. I've already done a valve adjustment using companion cylinder method. Defective lifter? Sticking exhaust valve? I checked the exhaust manifold thermal spring when we started with our winter-blend gasoline here and my carburetor started vapor locking on me- at 65 degrees outdoor temperature! The spring is sticking the diaphragm in the manifold in warm-up position. I detached the spring and drove the truck with the manifold diaphragm wide open and it still had no effect on the rough running although my carb percolation problem greatly diminished. My best guess is an exhaust valve sticking in the valve guide that fully releases when the engine cools off.
So, engine detectives, where do I go from here? What clues did I leave out? Thanks!

Put a vacuum gauge on and see what it says. That will help you confirm if you have a sticking valve. You could always do a hot compression test. Is this a truck engine or a passenger car engine?

I have put a vacuum gauge on it and see no fluctuation- when I'm back home and the engine has settled down, after cooling off a bit. Still hot though. I have also done a hot compression test recently and get readings between 116# to 130#. I haven't been able to check it while the disruption is actually going on- frustrating! This engine was ordered through an auto parts chain where you supply a core and they send back another engine that is already rebuilt and in their inventory. So I don't know if it is a truck or car engine, but I suspect a car.

If the engine has hydraulic lifters, it most likely is a car engine. Although, a 58-59 truck 235 block is drilled for hydraulic lifters and someone could have changed the cam/lifters.

What is the engine serial number (pressed into the block to the rear of where the distributor goes into the block)? A re-builder might have changed the code, but see what you have.

Serial # F623B.I remember asking for solid lifters and was told at the time that all 235 engines already came with hydraulic lifters. Regarding the vacuum reading, I suppose I could set up the intake manifold with the proper fitting and pull over to the shoulder of the interstate and get a reading when the engine is acting up at its worst.

F623B
F = Flint, MI plant
6 = June
23 = 23rd day
B = Powerglide car engine

Hydraulic lifers were standard in Powerglide car engines.

No truck 235 came with hydraulic lifers/cam.

That's an interesting fact. How does car vs. truck affect the diagnostics?

It confirms you have a car engine:"So I don't know if it is a truck or car engine, but I suspect a car."

It does not affect the diagnostics for a hydraulic lifter engine. Presumably you correctly adjusted the lifters.

Pre '68 Dave is one of the 235 engine experts. Most likely he'll check in with some advice.

I would start by pulling each plug wire off, one at a time, with it running, to see if you can detect one or more cylinders that are not doing there job when the problem occurs.
If two cylinders feed by the same intake port are week you will want to look for a vacuum leak at that port.
It would also be nice to plumb a vacuum gauge to watch while driving, to see if it is a valve problem.

I have tried pulling the plug wires and it seems that #2 cylinder doesn't make much difference whether it is connected or not. But once again, that's at home after most of the symptoms have settled down. Another argument for roadside diagnosis as the problem is occurring. I had the intake and exhaust manifolds off yesterday while checking out the manifold heat valve/vapor lock situation and noticed signs of gasoline leaking down the sides of the block below the intake manifold ports. Also, bubbles showed up near the middle intake port with the engine idling after reinstallation. Do I need an additional sealant besides the metal foil-like gasket? How does a vacuum leak contribute to this problem? I come back to this manifold heat valve thing because the shop manual says that the excessive lean mixture caused by the heat valve stuck in the "on" position can cause sticking valves. I should add that for the most part the engine runs at the 180 degrees called for by the thermostat.

OK, I hooked up a vacuum gauge and went for a ride. Vacuum needle was steady until fully warm and then rapidly vibrated +or- 1/2 inHg when the exhaust noise and vibration began at 55mph. I tried pulling the plug wires one at a time and it seemed like #2 made the least difference when pulled. But not a huge difference on any of them. I tried spraying starting fluid around the intake ports and carburetor base while idling and didn't notice any increase in rpm. Engine idle when fully warm fluctuates from 14 down to 13 on the vacuum gauge and I can hear a correlation between loss of vacuum on the needle and exhaust pipe noise volume increase. Exhaust pipe sucks up a piece of paper when engine misses. Overall, the truck ran better today than it has before disconnecting the manifold heat spring.
Does this sound like a finicky #2 exhaust valve?

I would be inclined to readjust the valves. If they are too tight, they might start to not fully seat when up to temp and running at full pressure. If set a bit loose there will be no harm, just a bit of clicking. If the running issues is resolved then you can adjust them until the noise just goes away. It might click a bit when it is cold but the valves will fully close. If there are no intake leaks, and the carb is adjusted correctly you will be just fine. The vacuum readings you posted would indicate the valves are not fully closed when up to full temp.

That sounds like a good idea Steve. I'll try it. Thanks to all who have responded and I'm still open to alternate theories. Dave

An intermittent miss causing the paper to get sucked into exhaust could also be caused by a sticking valve. Gummed up valve guide, or slightly bent valve stem are possibilities.

I readjusted the valves today and I can report that I must have been in too much of a hurry when I did them last time. I found several needing better adjustment. I haven't had a chance to test drive yet, but I'm hopeful that this is the answer.

Another update in the continuing soap opera. The valves continue to fluctuate as before when warmed up, but the exhaust noise is much less and the pipe no longer sucks a piece of paper. So the valves are improved but not fully well. There could conceivably be a bent valve stem on this rebuilt engine, but the valves appear very clean and I doubt they're varnished up. But I experienced the "running on 5 cylinders" bit again as I neared the end of the test run. This comes and goes. Not every time I drive but always warmed-up when it happens. I'm back to ignition again. I pulled the insulating boots back from each plug wire and yanked each wire, one at a time, with the engine at idle. Each cylinder was firing. The spark could jump maybe a 3/8" gap at each plug but is yellow rather than blue. The coil, cap, rotor, points, and condenser are all new and I've tried 2 different sets of used wires with no difference in performance between the 2 sets. Is there a temperature-dependent ignition problem here or are valves still the culprit? I'd like to think that now that the valves are adjusted better (or at least the best that I can adjust them) they'd seat themselves with additional driving. I'm running out of ideas.

How fresh is the rebuild? Mine took about 4,000 miles to break in and settle down. Now it runs smooth as silk.

I'm at about 2600 miles spread over 3 years on the rebuild. I'm ready to live and let live with the valves for a while to see if they break-in some more. It's the intermittent, rough, "5- cylinder" performance issue that has me concerned now. When the engine is running well it has plenty of power. When it starts running rough, I have to downshift the transmission just to climb a small hill and it sounds like I've lost a cylinder. That yellow spark from wires to plugs yesterday looked unhealthy to me. I suppose that I could start changing out electrical components one at a time and watch for an improvement.

Both coils and condensers can start to break down when they worm up.
Have you checked to see that you are getting good oil to the rockers?

"I have put a vacuum gauge on it and see no fluctuation- when I'm back home and the engine has settled down, after cooling off a bit. Still hot though. "

Drive with the vacuum gauge hooked up. What is doing in your garage is not the symptoms you are troubleshooting.

I ran it for a little bit with the valve cover off, Dave, and saw the rockers beginning to oil but I didn't watch it long enough to see each and every rocker get oil before I put the cover back on. The temperature gauge in the instrument cluster reports an engine temp of around 180 degrees. So the cooling system is doing its job. I have other coils and condensers that I know are good that I can borrow from other vehicles for test purposes.
I have driven it twice, pfarber, at highway speeds over maybe 10 miles each time with the vacuum gauge hooked up and wired to my dash so that I could watch it while driving. I can see how it can be confusing to keep track of all the different reports of test drives that I've spoken of. My reports of the vacuum gauge needle fluctuating rapidly by +/- 1/2 inHg are based on real road miles driven.
Again, my thanks to all of you that have been helping me to figure this out.

A "yellow" spark is normal unless you're running metal-core plug wires. The "it needs a hot blue spark" advice is at least 50 years out of date, but some of the people who give that advice have no idea why they're saying it, they're just repeating an "old mechanic's tale" they learned from some oldtimer who didn't know what he was talking about, either. Any radio-frequency suppression wire will change the color of the spark, and make the carbon contact button in the center of the distributor cap last three times as long in the process.

Are you doing the suggested hydraulic lifter adjustment that's in the service manual? Try using half as much preload on the lifter after the slack is taken out of the linkage. Some manuals recommend as much as 1 1/2 turns of lifter preload- - - -I believe that's way too much.
Jerry

Ok, here are a couple of new pieces to the puzzle. I forgot to mention that last year, my rocker arm shaft literally broke in two while running down the interstate. It broke off at the rear pedestal and temporarily disabled #6 exhaust valve. I replaced it with a used one from a 216 engine I had sitting around since it seems to be the same part. I took off the entire rocker assembly today and measured the used and new shaft (the front half that didn't break) with a micrometer. The used shaft has up to .002" wear on it but the rockers don't seem sloppy at all. The engine was doing its noisy valve thing before the rocker arm shaft broke and has done it since. This was only 1300 miles ago but seems like an eternity since it was last year.
I noticed today that I have a bluestreak DX-70 condenser on this engine instead of the DX-90 that I have on my other 235 engines so I changed it out. But given the info to forget about the blue spark thing, perhaps that has no practical effect.
As for valve adjustment, I used your companion cylinder method, Hotrod, only I used the opening of the points in the distributor to find TDC for each cylinder. This time I tightened 3/4 turn from pushrod snug tension. All the rockers are oiling properly. Unfortunately, I was pretty sloppy at finding TDC last time, and had one valve that was overtightened to 2 1/2 turns. That was probably the exhaust valve that sucked paper at the tailpipe. That has since cleared up as well as the excessive exhaust noise volume, but as you say, Denny, the damage may have already been done.

To summarize where I'm at with this before moving on, having maladjusted/ possibly burnt valve(s) coupled with marginal high-altitude fuel issues MAY explain all the issues that I've been having with this 235 engine. When this engine gets into "running on 5 cylinder" mode, it could be the gasping of fuel starvation just short of stalling out or a valve sticking temporarily. Or there could be something else going on as well. I'll just have to see.
Thanks everybody for your help! Dave

I wouldn't be surprised if you have a tight valve, when things get hot it's sticking.

Things have taken an unpleasant, new turn. Last night at 55 mph, the usual fluctuating valve condition blossomed into an intake valve sticking open and resulting in the sound of exploding combustion coming from under the hood. The vacuum gauge wired to my dash went wild. It was intermittent in proportion to the amount of gas pedal I was feeding it. After a mile or two, the explosions went away and I was able to limp home at reduced power. Perhaps I should have pulled over to the roadside and just sat there with the hood up instead of motoring on, but having no cell phone with which to call a tow truck I kept going. This is the first time that intake valve(s) have been affected versus exhaust.
So now I'm back to Pre68Dave's question about oiled rockers. As I mentioned earlier, I changed out the rocker arm shaft that broke last year with a used one. The actual wear on the used shaft is about .001" rather than .002". The front 1-3 cylinder rockers (new shaft) all oil nicely and evenly at idle. The back 4-6 cylinder rockers (used shaft), not so evenly. #6 intake flows like crazy while #5 exhaust barely at all based on the amount of oil exiting the top vent in each rocker. The re-builder pinched off the tube on the center oil connector to boost pressure to the rockers. I disassembled the rocker arm and shaft assemblies today to make sure that they were identical on both sides, Both new and used shafts have the slight flat milled surface on the bottom. I noticed that the inner oil groove on #6 intake lines up with the pressurized oil hole in the shaft explaining the mini-geyser of oil coming from that vent hole. I cleaned out some crud from the vent holes of the other 4-6 rockers and they oil better now. Is it normal for #6 intake to flow a lot more than the others? My new theory is that partially blocked oil flow to the rear rockers could be responsible for them seizing up at high speed when hot and causing the valve havoc. I've noticed before that there is increased lifter/pushrod noise when the engine is acting up but maybe that's because the rockers are partially frozen.
Does this seem likely?
After almost getting stranded on the interstate last night, I'm now reluctant to take off on a long journey without having changed anything substantial on the engine.

How long since the engine has had a valve job? If you've got sticky valves, it's most likely problems with the guides, not the rocker arms. Unless I'm missing something here, it sounds like it's time to pull the head and fix things right, instead of doing a bunch of Band-Aid patches.
Jerry

This is a freshly rebuilt engine with 2600 miles on it.

In that case, it sounds like your machine shop has done a poor job of fitting the valves to the guides. It's not possible to use modern engine tight clearances on the older ones- - - -the valves get hot and sticky if they don't have enough clearance.
Jerry

That is my worst case scenario. This engine was purchased through Checker Auto Parts in July, 2003 and sat covered in my garage until installation in summer, 2011. So the 12 month warranty came and went before it went a mile. I had the entire rocker assembly loosened while in storage so the valve springs wouldn't become fatigued. I've been trying the Band-Aid patches to rule them out before disassembling a new engine. I've been HOPING that these valves would loosen up with some miles on them but haven't seen any improvement yet. I'm going to try another Band-Aid and add some Marvel Mystery Oil to the gas. What the heck!

I'd stop trying to find a quick fix. You going to end up with everything in a bushel basket if you keep running it. Do as Jerry suggests and get the head off and see whats going on.

I'm with Don. I've made that mistake with motors in the past: trying to will away the issues or fix them with tweaks.

The problems you've been describing are serious and I'd hate to see you do further damage.

The head needs to come apart so you can get answers to the following

• Are all valve stems straight
• Get valve stem diams for all
• Get valve guide I.D. for all
• Is valve/guide clearance sufficient
• If valves or guides were replaced, are the materials compatible. Nitrided valves like different guide material than SS valves than stock valves. Guides come in many different material compositions.
• Are your spring heights and seat-off pressures correct?
• Are oil passages clear and all are passing sufficient lube
  

In other words. . . a full inspection / valve job.

Jason

If you know which valve is sticking I would pull the oil seal from that valve and run it like that for a while. You can reinstall it later.
This also gets me wondering if umbrella seals were used. In some cases they can starve the valve of oil and cause problems.

I can't pin down a particular valve. Sometimes intake, sometimes exhaust. And I can't pin down a particular set of circumstances except warmed up at high speed- most of the time. A couple weeks ago, after the warm engine valve sticking scenario had run its course, the symptoms went away for most of the remainder of a 100 mile 40-50 mph trip to the salvage yard. Just enough to give me some false hope. I appreciate the honest feedback about this from you all. Dave

See if all of the valve springs are installed right-side-up (closely wound coils go on the bottom).
Carl

You may want to confirm that you are getting oil from each rocker.
You may also want to remove all the valve seals until you are sure all are broken in well. It may smoke a little on start up but will not hurt anything.

OK, I'm about to reveal my ignorance here so be it. Dave, you've made a couple references to rocker oiling and valve oiling. I get the basic idea of pressurized oil fed from the rocker shafts to lubricate the motion of the rockers. I see that manifested as oil flowing from the vent holes in the top of each rocker. As of now, all are oiling correctly in that way after I cleaned the vent holes. Is there some other kind of rocker oiling that I should be looking for? As for valve oiling, what would that look like if the valve seals are preventing oil from leaking down through the cap? Where else would the oil come from if not the top? Because I can't say from memory that I've seen oil on the valve stems. And if I did find a spring installed upside down, Carl, or I wanted to pull the valve oil seals out temporarily, Dave, how would I go about it without pulling the head and using a valve-spring compressor? I'd really like to understand these concepts.

The combination of the rubber O ring under the split valve keepers and the sheet metal shield over the top of the valve spring deflect oil away from the top of the valve guide. Enough oil should splash off the spring to lube the valve stem if the clearance is correct. Some people add a "positive valve stem seal" or an umbrella-type seal, but they don't eliminate the O ring and the sheet metal shield when they do. That starves the valve stem for oil, and the valve galls in the guide and/or sticks.

IT IS ABSOLUTELY ESSENTIAL FOR A TINY BIT OF OIL TO GET PAST WHATEVER SEALING SYSTEM IS USED!

The valve cannot operate in a bone-dry condition, especially if someone fits the clearance too tight. With the crankshaft locked with a couple of pairs of vise grips on the flywheel, air pressure can be put into the spark plug hole to keep the valves seated while the spring and/or seals are removed, or a long piece of sash cord or 1/4" nylon rope can be pushed into the cylinder through the spark plug hole, then the piston is pushed up against the cord by turning the crankshaft, trapping the valves in the closed position. Just be sure to leave enough cord hanging out of the plug hole to fish it back out! Most parts stores sell or rent an on-the-car valve spring compressor that can be used with the head installed.

Look up a K-D Tools #2078 valve spring compressor. It's the classic tool everybody else copied.

Jerry

First thing tomorrow I'll take a closer look at the whole valve oiling situation. I was under the impression that the valves lubricated from the fuel (like leaded fuel in the old days). That's why I was thinking Marvel Mystery Oil in the gas. I've been oblivious to the need for engine oil on the stems and haven't been looking for it. Thanks Jerry. Dave

Lucas oil treatment is a very good additive that might help. It makes the oil stringy and sticky which could help stick it to the valve stems. To me, it sounds like a oiling problem, and the valves are sticking when hot. The guides maybe on the verge of being to tight, but since it runs so good when cool, I doubt you have any burnt or bent valves. Once bent always bent, same with burnt, you will hear it in the intake or exhaust, these two problems do not go away on there own. Running with out the oil shields and or seals should add more oil to the stems, at 2600 miles, they should be pretty well broke in already, so all you can do is add more lubricant to see what happens.

Try going up one jet size in the carb, a little richer mixture should help cool the valves.

I would bet you are right about the altitude and fuel supply being a big part of your problem. If you had a thermocouple on the exhaust pipe, I would bet you would see some high temperatures right as it starts acting up. Thats how I found a problem with a head I worked over on my 250. Climbing hills under a decent load, it would go lean and really run terrible. With a thermometer and thermocouple on the head pipe, I could see the temp spike and peg the 1000 degree thermometer. Under normal driving, the pipe would run in the 750 to 800 degree range.

Working on the side of the road is not a good idea, but, if you can get puller over and get the valve cover off fast enough, you just might be able to pin point the problem. One or two rocker arms should be very loose, if they all check ok, then the problem lies with a bad lifter pumping up holding the valve off seat. This will be harder to see. It was mentioned before to back the adjustment off to zero lash + 1/4 turn or so. If you can get them to zero lash, the lifter can pump up fully and still not hold the valve open. They might be noisier when cold, but it's a good test to try if you run into a dead in.

Joe