The Stovebolt Site Forums The Shop Area Engine Shop Chevy 235 ignition timing (1956)

i am wrapping up the punch list on my 56 project and noticed that the distributor didn't move when the engine is rev'd - so i replaced the vacuum advance mechanism. that was straightforward enough. As far as timing it, i followed the manual and set the static timing to have the rotor pointing at cylinder one when it was at 0 deg TDC. the pointer was pointing at the ball in the window by the starter as expected. The engine started, but was a little rough. Then i tuned the engine using a vacuum gauge, adjusting the distributor for max vacuum. When I completed this task, then engine was running well, but the steel ball was no longer visible in the window because i believe i advanced the timing such that it isn't visible in the window when the timing light is triggered on cyl 1.

do others observe this situation on their engines? Should I expect problems? the shop manual suggest that the engine should run at 0 deg TDC, but for me that is just not the "sweet spot"

thanks for any ideas/comments

Mine seemed to run best when the pointer was around the triangle ( BB not in window of bell housing ) stamped into the flywheel. I'll be interested in what others have to say as well.

Search the forums on the word timing and you will get a few thousand hits.

The marks on the flywheel are a good place to start.

Setting the timing with a vacuum gauge, adjusting the distributor to maximum vacuum at 2000 rpm will give a good timing setting.

Another technique that is quite good is to advance the timing until you hear engine knock when accelerating. Then, retard the timing until there is no ping upon accelerating.

I like the vacuum technique because it is easier and quicker to do, and because I also use use vacuum for adjusting the carburetor mixture.

Vaccume method is the better option. never had any luck with the BB in the flywheel. Mounted a vaccum gauge right to the manifold where the wiper used to be and set timing and carbs very easily.

From what I read in your post, I take it that your timing light does not have an advace knob on it, correct? That would explain why you're not seing the BB in the flywheel. Nothing wrong with the method you used, as others mentioned, it is a good option.
I've found that with modern gas, these engines like a bit more advance than the original specs. I'm running 15 degrees advanced on mine, but I do not have a vacuum advance unit on my distributor (aftermaket Mallory).

Happy Birthday, Bill

I have found that timing with a vacuum gauge works best if you use a tachometer along with the vacuum gauge, as follows:

1. Vacuum gauge and tach connected (vacuum gauge connected to manifold vacuum, not ported vacuum, which is the distributor source), engine at normal idle speed--500-600 RPM.

2. Advance the distributor until either the RPM or the vacuum reaches a peak- it doesn't matter which reaches a peak first. Stop advancing the distributor at that point.

3. Retard the distributor until the vacuum drops 1"Hg. You're done, but don't forget to tighten the distributor clamp.

If the engine speed is considerably higher after the adjustment, adjust the idle speed and do the timing procedure again.

Its been my observation that setting the timing at the highest vacuum more often than not leaves the timing several degrees advanced, which may result in detonation, depending on the engine and all the variables that affect detonation.

Also, I would not run the engine at 2000 RPM as suggested previously, because ported vacuum (distributor vacuum) will be applied to the vacuum advance at that throttle position unless you have the distributor vacuum line disconnected. Also, the mechanical advance mechanism is likely to be operating at that engine speed (1000 RPM for the distributor).

If memory is correct, the triangle setting mentioned previously was used on 1959 and later 235 engines to provide 5° advanced timing from TDC. The ball represents TDC, which I think was a carry-over from the hand-crank days, when you didn't want any spark advance while you were pulling on a hand crank. (You pulled upward on the crank and avoided pushing downward.)

Another point of history, but immaterial to the original question, the crank jaw was first removed from the 1959 235 engines, even though the jaw hadn't been accesable for several years prior. I don't remember when the passenger cars could no longer be hand-cranked, 1948 and later, I believe, but the AD trucks though 1953, and maybe through the first series 1955 models could be hand-cranked- if you kept your wits about you and you wished to do so...

Hope this helps.

Harvester

I'm hoping this is what i need to to get my engine running again, except i have no clue on what to do or where to start. What happened was my dad was backing the truck into a dark shed and he caught the wall with the box of the truck and the engine stalled, ever since that happened the engine will turn over but won't fire at all. Do you think the timing is my problem or something internal in the engine?

Harvester said "Also, I would not run the engine at 2000 RPM as suggested previously, because ported vacuum (distributor vacuum) will be applied to the vacuum advance at that throttle position..."

On an old Rochester model "B" there aint no above throttle butterfly vacuum port or "spark port". The distributor gets its vacuum from a port BELOW the throttle butterfly--thus it is getting full "manifold vacuum" at all times. This "ported spark advance" system was not around on Chevys prior to 1968, the first year of smog era carbs (thus no mo' model "B"s around either).

My Rochester B distributor vacuum source is ported on my 55.2 3100 truck with a 235 engine. No vacuum at idle, only after the throttle is opened.

This is correct, no vacuum at idle with a Model B.

Did it.amazing it worked, timing dead on.also cleaned that engine block drain (plugged up) kept at it for 2 hours and nothing but black stuff came out,then it started to flow thanks stove bolt..