1940 Buick 320 cam timing

[kgreen]

I've got a rough running engine after a total rebuild.  Haven't run a vacuum gage yet, but will this weekend.  In thinking of all the possibilities I wonder if the 320 cu in engine would even run if the timing chain was off by one tooth; anyone know?

 

The engine starts, revs fine, but has a skip and occasional backfire and doesn't like to idle smoothly or at a lower more appropriate RPM of 650-700.  New plugs and wires.  Grounding the plug shows a great spark.  New points and condenser, gap checks out at 0.015.  Timing is close enough that the engine will start fairly easily and continue to run and adjusted so that I have a higher engine speed.  I've improperly installed the flywheel with the timing marks off so conventional timing measurement is not available.  The engine belongs on a convertible where there is a heavy vacuum demand when the top is operated and an improved chance for vacuum leaks.  Carb was rebuilt, but by me so I could suggest that I goofed something there.  Compressions on all cylinders is great and uniform.  Valves adjusted correctly and checked.  I've run the engine for a total of probably 20-30 minutes by now so some wear in has occurred. 

 

I'll run the engine with a vacuum gage this weekend as suggest by another member here; thanks Greg as always.  I'm trying to think of all possible options before I dig back in this weekend.  Any ideas that you think I should pursue?

[Matt Harwood]

As you may know, the timing chain in my Lincoln was off by two teeth. It still ran reasonably well, but it wasn't happy and got really hot. It's certainly possible that yours could be off a bit, which would cause all kinds of mischief that's hard to trace.

 

I'm also thinking that setting up the timing gears on the Buicks is unusual. It isn't as easy as "line up the two dots" like on most cars. I think you have to make sure the dots on each gear are pointing at 3 o'clock or something like that. It would be easy for a shop unaware of that fact to do it incorrectly and simply line up the dots like every other engine. But that might also make the cam timing so far off that it would not run, I don't know.

 

Here are pages from the service manual with some information, particularly showing the timing marks.

 

Edited March 20 by Matt Harwood (see edit history)

[Gary W]

From my '37 manual:

 

 

The timing chain has marks that are exactly 10 LINKS apart.  These must align with the marks  on the gears.

 

 

 

 

The book on the left, my actual engine on the right displaying the proper alignment of the timing chain.

Edited March 20 by Gary W (see edit history)

[Rusty_OToole]

One way to check this is by finding the crossover point of the cam in relation to the crankshaft. First you must verify or mark TDC on the crank pulley. Then using dial indicators, find the spot where intake and exhaust valves are open the same amount. One will be opening, the other closing, and a very small rotation will change the measurement. The crossover point should be at or near TDC. Like a couple of degrees.  If it is way off you have a problem.

 

Incidentally advancing the cam enhances low speed cylinder filling, retarding it helps at higher speed. This is an old stock car racer's trick. But they would advance or retard the cam a couple of degrees at a time using an offset bushing or key.

Edited March 20 by Rusty_OToole (see edit history)

[EmTee]

How did you adjust the valve lash?  Is it possible one or more may be too tight?  I'd probably start by setting #1 piston at TDC and measure the cold lash.  When I set mine cold I used 0.019" instead of the hot value (0.015").  Roll the motor through the firing order and see whether any were too tight, as those may not be closing completely when hot.  At this stage, too loose (within reason) is better than too tight.  If the valves are quiet now I'd be suspicious that they may be too tight.

 

If you do see a number of valves too tight at the TDC for each piston, pay attention to which valve (I or E).  If it looks like all of one type are tight, then the cam gear might possibly be off a tooth.  If I began to suspect that as a possibility I would set-up a dial indicator on each rocker arm and look at where the "foot" of each cam lobe lands with respect to TDC of the piston.  I'd be looking for an offset one way or the other.  If things seem to line up, I'd eliminate other possibilities before pulling the timing cover off.

[SPS700]

Back fire sounds like mixed plug wires. Cam timing find tdc with #1 plug out. Then valve cover off check #8 for over lap