Engine Timing Help
 

I bought a ready-to-run 327 from a individual. A few years later I have it in my pickup and it's running, but it's not running as well as I expected. It will idle smooth-ish, but with an irregular, subtle hiccup. The engine also lacks the power I expected it to have.

The engine is supposed to be built close to the specs for a 300hp 1963 Corvette 327. Here's is the other info I was given:
1. roughly 10:1 compression ratio
2. comp cam 12-234-2
3. 76cc open chamber heads'
4. Pertronix ignitor 1 and flamethrower 1.5 ohm coil

Here's what I've observed when I try to tune this engine:
1. The engine requires a ridiculous amount of advanced timing--in the neighborhood of 40deg while idling without vac advance.
2. If I try to back timing to where I think it should be, the motor bogs and dies around 10deg BTC.
3. I'm getting decent vacuum of about 16.5 when warm and idling at 750rpm.
4. The 6" factory-style balancer is not spun. The keyway and the timing mark align perfectly as I understand a 327 should.
5. The timing sprocket dots are aligned, and the crank sprocket is using the neutral/factory (circle mark) keyway. Chain is new and tight.
6. I have swapped out the intake for a different one, and discovered there was probably a vacuum leak there, but I think I have solved that with a new intake and better installation.
7. Pertronix says their system either works or it doesn't work at all, so since it works at an odd timing, they are directing me to other areas.
8. I found the breaker plate ground wire was loose where it grounds to the vac advance assembly, but after cleaning and tightening that connection nothing changed.
9. I'm running 91 octane fuel currently.

What could cause this?
1. Any other easy things I can check?
2. My carb is too big for the motor (Holley 700cfm), working on changing this but haven't yet. Could that cause this in any way?
3. I haven't clocked the cam, is it possible I have a different cam than I was told?

Re: Engine Timing Help
 

Ben,
Have you run a compression test???
76 cc heads on even a .030 over 327, yield a fuzz over 8:1 compression ratio. If you had 64 cc heads (as per original), it would be a hair over 9:1.

That cam should function in your engine, but could be considered a hair large. Competition XE cams are praised here quite often. I'm not one of them though...

If the timing gears are off, or the cam is ground off, these would contribute to what's going on...

The 700 cfm carb should not be a problem, part throttle running only uses half the carb...
Degreeing a camshaft on installation is a must these days. Most of the aftermarket parts are made off shore, and it can be a pain find out that the part in your engine was not properly made (timing sets...)

Pertronix distributors can have problems, also...Do you have an original points distributor???

Jeff

Re: Engine Timing Help
 

I would verify the timing marks 40 degrees is a lot.
Jimmy

Re: Engine Timing Help
 

I think there have been 2 or 3 variations of SBC timing mark placements on the timing cover. Possible the one on your motor doesn't match how the balancer/cam was installed.

IMO - Step 1 is verify TDC for #1 matches the balancer mark vs the indicator.

I know you said the balancer ring hasn't shifted but might put a mark that goes from the outer ring, across the rubber and to the inner ring. Any movement will show up fairly quickly.

It really sounds like the engine is in good shape and what you have is a timing indicator problem. With the current setup, go to 45 or 50 indicated on the initial timing. If it runs and sounds even better, pretty much a confirmation of an indicator issue and not an internal problem.

Re: Engine Timing Help
 

Is your vacuum advance disconnected when you are setting timing?
Have you Triple checked firing order?


Agreed. You should verify your timing marks.
Disconnect your battery and Pull #1 spark plug.
Turn the motor over slowly with a breaker bar (clockwise from the front).
You should be able to slip a small screwdriver in the plug hole and feel the piston coming up.
If you're very careful, you should be able to get really close to TDC. Close enough to verify timing marks.
Don't worry about compression or exhaust. We just want to verify that your timing indicator is accurate.

Re: Engine Timing Help
 

Jeff, the engine is .030 over and the builder told me he used 11:1 TRW forged pistons. Does that get me close to 10:1? I've run compression on all the cylinders and they all came in at 150-170 psi. I'm working on converting my distributor to points to see if that makes a difference.

PGSigns and Dead Parrot, my understanding is that all SBC cranks have the keyway aligned with the #1 journal. And since my balancer has a timing mark aligned with the keyway, I think I should be seeing the timing mark in the 1:30 o'clock region (minus whatever BTC timing I need). Currently the balancer's timing mark is appearing on top (12:00) when the engine is running best. When the motor is tuned by ear and for max vac and the balancer is rotated to align with TDC, the rotor is way past #1 under the cap. I've verified TDC on piston #1 a couple of times with a couple different methods. This issue has been consistent (not moving) through a lot of troubleshooting steps and about 150 road miles.

Harley: Vac is disconnected when setting timing (and there is no vac coming through the ported carb fitting when idling anyway). I have triple-checked firing order for my engine. When I adjusted the valves they all went in the expected order when rotating the crank.

Re: Engine Timing Help
 

A lot of Chevy engines around late 70,s early 80,s had timing marks straight up. You had to view between the water pump (long pump) & the timing cover. I also believe you have a miss match of parts. With the modifications you have on the engine, the specified marks are not much use any how. Set the timing to where it runs the best. If it pings on a hard pull set it back some. If it kicks back when you go to start it it is also too much. You can usually set it by feel. Also the on damper shone in the photo it appears the outer ring has shifted. The outer ring is generally even with the hub.
George

Re: Engine Timing Help
 

The compression test is a good sign!

There are several variations of balancer diameters, and timing cover tab locations. The tab location and specific balancer have to go together (obviously).
The fact that your keyway and mark on the balancer are aligned are good also.

When the #1 piston is at top dead center. on the compression stroke (just after the intake valve closes) the balancer mark should be exactly at zero on the timing tab.

Without knowing the exact part number of the piston, it could be tough to know what your exact compression ration is. THe end compression ratio is dependent of the combustion chamber volume. THere's not as many domed 327 pistons available these days as there had been, but it would be nice to know more. You could get one of those flexible scopes and look into a cylinder. You'd at least be able to tell if you have domed pistons, or not...

To tune the engine without regard to the timing marks...Advance the timing until the engine pings under a load, then back it off some see how it drives...
Of course do the advancing a little bit at a time, you will have to drive it each advancement to see if you get any pinging.

Wish I was closer...

Re: Engine Timing Help
 

Here is a good wiki on timing tabs on the small block. The only way to find out what you really have is to verify tdc. You will need to pull all the plugs get a piston stop. Put in the piston stop and hand turn the engine till it hits the stop. Put a mark on the damper at the zero mark on the tab. Now rotate the crank the other way till it stops and put another mark on the damper. You true tdc mark is the center between the two marks. Untill you do that your not going to get a true timing.
Jimmy
https://www.crankshaftcoalition.com/..._TDC_lines_SBC

Re: Engine Timing Help
 

So the engine likes a lot of timing at idle and you are using ported vacuum? That doesn't compute. Sometimes people used a B28 vacuum control for high performance 327's. It comes in pretty early. Here is some good specs on vacuum controls.

http://outintheshop.com/faq/Vac%20Adv%20Spec.pdf

Re: Engine Timing Help
 

Yep, this appears to be the case for my engine. I've checked for TDC by using a piece of wire as a lever with one end in the plug hole. Everything I've checked says that my timing mark & tab agree with the rest of the engine at TDC. Mechanically speaking, everything agrees. But when I run the engine, it requires gobs of advanced timing to be happy.

PGSigns, thanks, that wiki is where I've gotten some of my info. I haven't found anything on that page that points to my problem. If anything, it confirms my situation doesn't add up because it says 1) all SBC cranks have a keyway aligned with #1, and 2) my damper is right for my timing tab. I and a local hot rod shop have both found TDC and we both think the marks agree with TDC, but you're right: getting a hard stop would be more precise.

Al, thanks for the document--very informative and the kind of explanation I have been needing to find. However, given that the ported vacuum port on my carb does not pull any vacuum at idle and it's disconnected while I'm setting timing, I am not sure how that could be contributing to my issue. Feel free to spell it out if I'm missing something.

Re: Engine Timing Help
 

Could a dizzy being one tooth off cause this?

Re: Engine Timing Help
 

Cam out of time?
I noticed the crank gear is adjustable, is it in the correct slot?
Was the camshaft degreed when it was installed?

Re: Engine Timing Help
 

CW, I've tried engaging the distributor gear with the cam gear at different teeth, all that does is allow different ranges of adjustment when you turn the distributor body/cap. There isn't a "correct" tooth to hit with these.

Harley, the crank sprocket is set at the neutral position, not advanced or retarded. I haven't put a clock on the cam--that's something I will look at if I have to pull the timing cover or engine again. For now I've ordered a dead stop that I can use to find TDC more precisely.

Re: Engine Timing Help
 

When you use the piston stop be sure to extend the marks that you make on the balancer down onto the hub close to the crank snout. Easy to see if balancer is moving on you that way.
I use this stuff to mark with.
Goes on easy and stays on forever.


https://www.amazon.com/Bic-Wite-Out-.../dp/B0041IJ4NG

Re: Engine Timing Help
 

Most engines prefer full manifold vacuum. I use ported vacuum once in a while if an engine doesn't seem to like a lot of timing at idle. I'd say give that 327 some more timing at idle.

Re: Engine Timing Help
 

I don’t understand how this would play into my problem with initial timing, which doesn’t use the vac advance?

Re: Engine Timing Help
 

I never used to have a timing light so it was all by ear. If you can't make it run well that way then there must be another problem somewhere. Distributor turns freely with not too much up and down play?

I had a problem with Petronix once in a six cylinder Delco distributor. I thought it was firing between the cap electrodes. Maybe I didn't have the rotor seated properly but when I queried them on it I sent in the old one and they sent me a new one. That old Rambler 232 runs really good now.

Re: Engine Timing Help
 

Hi Vince, this is what I’m looking into now. I ordered a new distributor because I found end play (up & down) was out of spec, and i also found some side-to-side play at the bottom bushing. Will receive it after Christmas.

Re: Engine Timing Help
 

I was also wondering about the cam phasing, being off. Would not be first time that has happened.
That can be checked using a degree wheel. Not easy when engine is installed in vehicle. Would need to get exact cam specs form cam manufacturer...

Re: Engine Timing Help
 

Maybe I've missed something in the posts, but just to confirm with you: when the camshaft timing dot is at the 6 o'clock position, and the crankshaft timing dot is at the 12 o'clock position, the engine is at TDC (Top Dead Centre) firing the #6 cylinder, not #1. If you have the dots lined up as in the first post, and you dropped the distributor in so that the rotor is pointing to #1 plug wire terminal, you've found your problem.

If you have already discussed this in this thread, my apologies.

Re: Engine Timing Help
 

Hi Jeff, I have the cam card from Comp (attached). I didn’t have a degree wheel when I removed the timing cover the first time, but now I wish I had taken the time to do that!

raceman, you are correct. TDC happens when my engine has both dots at 12 o’clock. I posted the pic with the dots next to each other because it’s easier to see.

Everyone: I got a dead stop and put the timing mark questions to rest. Here’s a pic of my stop marks on either side of the balancer timing mark. I think this shows my timing mark is synced with TDC.

Re: Engine Timing Help
 

Is that pic with the piston against the stop on clockwise rotation?
Attachment 2072549

Re: Engine Timing Help
 

Hi Harley, this pic was taken just after I made my second mark, which was the BTDC mark. Normally that’s the first stop mark a person would make, but I did the BTDC mark after the ATDC mark. Yes, the piston was resting against the stop as it was 7deg away from—and on its way to—TDC. The ATDC stop falls exactly 7deg on the other side of my balancer timing mark.

Re: Engine Timing Help
 

JFYI each line is 2 degrees.