The Stovebolt Site Forums The Shop Area Engine Shop 235 timing settings

Ive searched the timing posts and read quite a few... seems that setting timing by vacuum, or advance timing until you hear ping when loaded are the two most common methods... I haven't found any posts that specify a certain timing setting (except repeating the factory setting of 2-4 BTDC) my question is when the engine has been timed using these methods what is the actual advance (in degrees BTDC) as seen on a timing light? I have timed mine using the vacuum method and I have approx. 14 degrees BTDC as indicated on my timing light.

This seems high to me.... what timing are you guys getting/running?

The vacuum gauge timing method is for people who just don't know any better.

Measure it with a micrometer
Mark it with chalk
Cut off with an ax

That's a rough equivalent of timing with a vacuum gauge. Use a delay-flash timing light and set the initial timing to 5-8 degrees BTDC. Then check the centrifugal and vacuum advance to be sure it's working smoothly and repeatably. The "listen for a ping and retard until it goes away" is a little better, but not a great deal. One degree of over-advance once the "sweet spot" for torque is found robs as much power as 5 degrees retarded from that point, so err on the side of "not enough" if you're unsure of where to set the timing.
Jerry

Jerry is not leading you astray here when he says make sure the centrifugal and vacuum advance are working properly. I just finished rebuilding a 2403 (55-62) distributor. It was dirty and a little cruddy on the outside but not any worse then some I have seen. The breaker plate area was typical, some accumulated dirt/dust, oil mist. Put it on the sun machine for an initial check out and the advance showed to be very delayed. So the 2-3 degrees at 350 Distributor rpm (700 engine rpm) was actually not starting until 600 distributor rpm, and it stayed that way with the max advance not happening until nearly 1200 rpm over when it was supposed to be fully in. When I got it all apart, found a lot of built up old oil, sludge and dirt accumulated on the bottom of the advance plate, rusty advance weights that were sticking and not working, and everything gummed up. So you could set the timing on that distributor a thousand times and the motor will still not run correctly.

Once I got it apart I rebuilt the advance assembly, got everything cleaned up, new parts, relubricated, repaired and back into specification, got it back on the machine and it tested in perfect specification. Now you can get the initial timing set up.

Just as an fyi, with a good working distributor, I set my modified 261 up initially for about 4 degrees BTC (using an anolog dial back timing light) and ended up at 8.

I have tried the advance to ping method also, as well as vacuum, as well as setting timing where it seems to run best... each method gave a different timing setpoint when checked with a timing light. The motor is a 1962 261. the distributor is in good condition, vacuum/centrifugal advance seems to work properly (as checked on dial back timing light at diff rpms)

overall I have no problems with how the motor runs but it seems like having a target range for setting timing would allow for checks and better repeatability when doing tune ups.. it just doesn't seem like "custom" settings should be required.

I have run the motor from 4BTDC to the 14BTDC noted above ... it runs a little better at the higher advance settings but doesn't seem to idle as smooth at low rpm with the more advanced settings.. again...not a problem just observations

what timing settings work best for you guys?.... whats your timing set at?

Mike, let's just give up and quit giving reasoned answers with facts and figures to back them up! The best part of pounding one's head against a wall is that it feels so good when you stop!
Jerry

"Mike, let's just give up and quit giving reasoned answers with facts and figures to back them up!"

Go ahead and give up... Ive asked for input on what actual timing everyone is running as measured by timing light... I get innuendos about my abilities, feedback on accuracy and inaccuracy of methods to set timing, I should check distributor condition, and now your opinion that you are banging your head against the wall responding to valid questions..

as far as facts and figures... I don't see any from HRL - just the same "1 degree over advanced causes as much power loss as 5 degrees retarded"... read that 1000 times in my post searches... maybe you can explain how you set timing in your circle track days... about as relevant as the rest of your responses.

I suggested setting the initial timing to 5-8 degrees BTDC as a starting point- - - -same as Mike did- - - -and then explained that the centrifugal and vacuum advance measurements are much more important than the initial setting- - - -just like Mike did. If that's not sufficient for a specific timing suggestion, I'm not sure what would be. We set the round track engine timing on a run stand with a bellhousing mounted water brake dyno, and checked it on a chassis dyno occasionally. What, exactly, else are you asking for?
Jerry

Well, I do not know any better.

I have no problem reading/hearing/respecting (in awe, usually) these more sophisticated (and, possibly/probably, more accurate techniques).

However, I still use a "modified" "timing using engine vacuum" technique
on my Stovebolt engines. The modification is described in step 6.

Saves time and saves equipment cost.
No need for an electrical outlet or battery.
The same vacuum gauge (and same connection) is used to quickly/easily set carburetor mixture.

My 235/261 engines seem to start easily and run like tops.

It is, however, good to know how the pros do it.

Easy now, lol. Here is the thing. Custom settings are necessary no ifs ands or buts. The gasoline that was sold when the shop manuals were written is not the fuel we have available to us now, i.e., the unleaded, alcohol infused, additive laden stuff we are calling gas. Winter blend, summer blend, fall blend. It flashes off at different points, evaporates its volatiles more easily, hygroscopic water absorption at room temperatures, all kinds of stuff. All of those factors now have to be taken into consideration with these old cars. That is why it is so very important that all of the ignition periphery be pretty spot on in order to dial in the motor to run its best and get some consistency. Thus, the mechanical advance must be pretty spot on. That means not just working, but working as it should. My example above was to show you that I could get to the max mechanical advance, but it would not come in when it was supposed to. At that point, there is no way to accurately time the motor for optimum running. If you have the same issue, and its not uncommon with these distributors at near 60 years and older, neither the ping method nor the vacuum method, nor the dial back light method or any other method will get you any consistency. So, you need to first sort out the specifications. When I get home tonight I will look up my Sun and AEA specification charts for your 62 motor and see where the mechanical advance starts, intermediate and full are supposed to be. Set your motor at TDC, and using an analog dial back light, confirm whether the mechanical advance is working correctly within specification at the appropriate rpm ranges. If its way off, then you need to address that first. If its within specification, start advancing in 2 degree increments until you hit the point where the motor is running smoothly and not pinging when you put a load on. See where that is.

As Jerry noted, its usually, but not always, in the 5-8 degree BTDC, depending on the fuel you are running, the altitude you are at, and the condition of the distributor. Mine ended up at 8 degrees but I am gonna play with it some more this season. You may very well end up with something less or more then what I am running. I know that quite a few use the vacuum method. I myself do not care for that method as every time I try it I end up with total timing that is too much which messes with all kinds of things, idle quality, drivability. Same for the ping method. Lots use it with good results. I have not had good results. No opinion on those methods one way of the other, just my own way of approaching timing on these motors. I have been at this since I was 16 with these old style motors, 41 years now, so I tend to stick what works for me.

Jerry is quite correct, too much advance is just as power robbing as being retarded (and I am saying that in the politically correct mechanic speak, lol) notwithstanding that the motor is seemingly running fine and not pinging. So choose a method, timing light, ping or vacuum, stick with that method, confirm the distributor function and sort out where your motor likes to be with the fuel you are running. Happy tinkering.

For 62, the timing is 5 degrees before tdc on a stock motor at idle (475-500 rpm). The mechanical advance comes in as follows: 0-2 degrees at 375 distributor rpm (double this figure for engine rpm), 5-7 at 750 distributor rpm, 10-12 at 1450, and 13-15 at 1875. For a total of 32-36 degrees advance, depending on the fuel and what the motor likes, might be more or less.

There actually is a way to make a pretty accurate SWAG at ignition timing using a vacuum gauge, but the procedure doesn't even remotely resemble the urban legend that's promoted here. Disconnect and plug the vacuum advance line at the distributor, set the engine speed to 2,000 RPM or a little higher, and attach a vacuum gauge to the port in the intake below the carburetor (full manifold vacuum). Advance the timing until the vacuum peaks and then begins to drop, then turn the distributor housing back and forth until the highest reading is achieved. That method is MUCH more effective than trying to do the adjustment at idle. Not correct by any means, but better than some of the other methods.
Jerry

Thanks, Jerry

I'll try that the next time and do comparison runs, and report back here.

When setting the timing is the bb on the fly wheel TDC ?

Depending on the engine size and year of manufacture, the BB can be several degrees advanced from TDC, and it's not always the same distance. It is an ignition timing mark, not a true TDC indicator. It's "close, but no seegar". There is a straight line TDC mark on some flywheels, but it's not the BB.
Jerry

I deleted my earlier post, that had incorrectly stated information.

As Jerry posted, the bb/BB is the timing mark.
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0619.htm

Timing on stovebolt engines cold be at TDC, or before TDC, or after TDC, depending on the engine and year.

For the 55-57 235 motors the bb is TDC for timing purposes. Now whether it is accurate or not on any given motor is another story. I have had them dead nuts, others a little off, some totally off. So when I am building a 55-57 235/261, I will set the motor up at tdc (which I do with the head off and a piston stop and degree wheel, or if in a pinch you can line up the dots on the cam and crank gears, this is tdc for No. 6, then rotate the motor 180 degrees and that is tdc for no. 1) and then mark the back of the crank flange. Then when I go to install the flywheel, I can look to see where the bb is relative to tdc, and remark the flywheel if need be. Others have a bb but also various markings for setting the timing, a triangle or line for instance where the timing is set some degree in advance (I forget off the top of my headbut that might be 59 or something later) as the timing settings changed from time to time, from application to application, and even depending on whether the car or truck was a Canadian model.

What kind of crankshaft are you running with #1 and #6 180 degrees apart?
Jerry

I am probably not being articulate enough here, lol. As you know, No. 1 and 6 are on the same stroke plane, that is they move up and down at the same time. So when you initially install the cam and you line up the dots on the crank and cam gear (both dots at about 5 o'clock), No. 6 is at tdc compression stroke. Now, rotate the motor one full turn (one turn for the crank, 1/2 turn for the cam) so that No. 1 cylinder is now coming up on its compression stroke. The dot on the cam gear should be 180 degrees opposite the crank dot, so crank dot is at 5 oclock and the cam dot is at 11 oclock for something pretty close to tdc for No. 1.

55-57 235 cars and/or truck 235 and/or 261 BB is TDC - is that the timing spec is TDC for those engines in those?

My understanding us the bb/ball is TDC/TC in any year where a ball is present on the flywheel, but the ball is not necessarily the timing spec. TDC (the ball) was the timing spec in some years.

Regarding no ball in a flywheel, I have also seen such flywheels on later USA 235 and/or 261 engines (I do not know the years/years).
UC/UDC is marked and a timing mark is scribed/labelled on those flywheels.

yes, tdc out of the shop manual but if you look at the Sun tune up Charts or the AEA tune up Charts, they suggest a couple of degrees of advance, but the shop manual identified the bb as the tdc mark for timing purposes. So I have always set the 55-57 motors up for TDC, confirmed the bb placement, then using the bb installed the distributor with the rotor pointed at No. 1, fired the motor and made adjustments from there to get it running its best. Yep, I think you are spot on with the later flywheels. I don't think I have one handy otherwise I would go look but its one of the reasons I like to identify TDC when I am building the motor, and then set the flywheel up from that point, just in case. Truth be told, I had to learn how to do this quite a few years ago in the early 80s when I first installed a Clifford (made by McLeod) steel flywheel and which I discovered at a most inopportune time did not come marked in any way. Young and silly but I paid the price for that one, lol. Btw, McLeod will still make you a steel flywheel as they still have the blue prints to do it, but crazy sort of expensive in the range of 600.

If I had some ability to post photos I would post a couple of these Sun and AEA charts as I have them for 55 through 62. They are actually a tremendous resource. The AEA charts are better then the Sun Charts in my opinion and they actually cover the charging system, ignition, and all manner of specifications, as well as part numbers for all of the parts. There is a guy on eBay right now that sells them. I think the sun charts start around 56 (no 55) the AEA goes back a little further but I am not sure how far. If there is any interest, I would be happy to take photos of these charts if someone would post them for me.

For reference (and, comparison) purposes:

1941 216 & 235: 5 degrees BTC Before Top Center / Before Top Dead Center
1953 car 216: 2 degree before TC, and car 235: 2 degrees after TC
1953 truck 216: 5 degrees before TDC, and truck 235: 0 TC - DC - TDC
1954 car & truck 235: 2 after TC, and truck 261: 5 before TC
1956 (and 1957) truck 235 and 261: TDC Top Dead Center
1959 truck 235: 2 BDC, Before DC) and truck 261: TDC
1962 truck 235: 5 degrees BTC/BDC, and 26: TDC

I understand what you were trying to say, but the way you expressed it was a little confusing. 360 degrees on the crank is 180 at the cam, but getting the dots aligned perfectly when they're not facing each other is a SWAG at best. If the head is off, finding TDC is pretty simple- - - -just watch the piston as it comes to the top, or use a "positive stop" over the piston and split the difference. That's how we set up the degree wheel when we checked John's new cam when we built his 261 a while back.
Jerry

I confuse myself sometimes, lol. But yes, I use a piston stop and a degree wheel when the head is off. It’s a must with some of the cams I have used in these motors. I have never actually had a cam that was ground incorrectly and I have been through quite a few over the years so I have been lucky that way. My first was a Chet Herbert regrind. He used to advertise any regrind for 39.00. That cam is still in the motor that I built around 1980. Ran great. I beat on that motor pretty good and never missed a beat. Currently in the back of my garage. Clifford cam (way way too much cam, still have that one, over 300 duration and .512 lift. That cam was hard on everything and was not a great cam, mostly because I was still in the bigger is better mode back then which is never a good approach, lol. That cam will get a regrind pretty soon I think. moon did one for me years ago, it was ok, not great, sig Erson also, who was probably Cliffords source. The last four have come out of schneider. They have been great to work with. Problem now is finding new cam blanks. With the lifts in the .480 and up range, (current cam is .492 lift, 280 duration) and pistons at near 0 deck, I have to degree the cam in and check the intake valve to piston clearance (I do it the Isky way with checking springs and a dial indicator on the valve retainer). Learned that the hard way also. 1984, new motor, Fresh head, did not check, first fire, promptly bent all 6 intake valves. I still have the receipt for that one, lol. The fellow who had just done the head poured solvent into thenports and it all ran out. He was the one who showed me how to check with clay. The dial indicator came later.

But when the head is not off and you are without the right tools and stuck needing something a little more shade tree, you can do it by the dots and get pretty close. Close enough to get the distributor in and the motor fired up any how. I actually use the dot method just to confirm I am on the compression stroke for no. 1 when setting the motor up for tdc.

I use a spark plug shell with a piece of all thread tapped into it as a "head-on" positive stop. On a stovebolt engine the rod needs a 45 degree bend in it to get into contact with the piston and a lock nut on top of the plug shell.

One round track roller cam on a 350 had a quick enough rate of lift that the closest piston to intake valve clearance happened at 25 degrees ATDC. That one was running 1.6:1 ratio rocker arms and it needed a rev kit to combat valve float. "Idle" speed was 2000 RPM. Below 2K it didn't load up or lope, it just quit running. It smoothed out at 3K and it was still building torque when we quit doing dyno pulls at 7500. It would come off the #4 turn at 3K, and accelerate all the way down the straightaway of a 1/2 mile banked oval.
Jerry