I installed a Comp Cams XE262 and when I checked my timing after my 20 minute run it was 38 degrees BTDC. I tried to set it to 10 to 14 initial but the engine wouldn't run. The closest that I was able to get it was 18 degrees. I was so wound up that I removed the timing cover thinking that I missed the match up of the gears. They were in accordance to the installation instructions for a "straight up" installation. Prior to installing the Fluiddmpr I checked the keyway and 0 point on the 2 to insure that there would be no change in the timing marks. Using a vacuum gage at an intake manifold port I get best vacuum at 38 degrees BTDC at idle.
Where have I gone wrong?
Where do those that have the same cam have thier initial timing set at?
Thanks for any help.

 

Is your vacuum advance connected to manifold vacuum and if so disconnect it and see where your timing is.


[Modified by MotorHead, 11:29 PM 11/3/2001]

 

Sorry, forgot to mention that the vacuum advance was disconnected. I haven't even installed the hose yet, just left the fitting capped until the mechanical is set.

 

OUCH!! :eek:
38 degrees to start with!!
Wouldn't that mean yer getting about 50 degrees total??? :eek: :eek:
That kind of advance is like a :smash: coming down on yer piston as its coming up.
Did you install the cam with or without a degree wheel??
'Cause you might've installed it too retarded in relation to the crank, and that's why you need to advance it soo much.
From what I've read about the XE268 (similar to your 262) the cam is installed with a 4 degree advance built-in.
Are you sure everything is okay??
I REALLY think that you are running WAY too much timing on your motor.

 

i'd guess you installed the distributor a little too retarded.

 

Have you fiddled with your carb yet??
I use a vac gauge to set idle mixture, NOT TIMING.
This was in a previous post somewhere... or was it in the Summit catalog Q&A section???
I suggest you get your car to run, then slowly dial back the timing to about 15 degrees, all the while dialing in yer carb to keep things smooth.
I had to do a lot of fiddling to get my 383 to start, and stay running once I put her together.

 

I have a CC 268. Advance @ idle is about 16 degrees with no vacuum advance - I check total advance, using a dial back timing light, and get a maximum of 35 degrees @ about 2700 rpm. With vacuum advance connected, I get a total advance of about 50 degrees.

How does the way the cam is installed in relation to the crank have any effect on the timing? The cam gear that drives the distributor is, for want of a better word, symetrical. It meshes with the gear on the distributor in any position. Ignition timing is only controlled by the position of the rotor in relation to the distributor cap terminal.

If, as you say, the keyways and '0' marks on the damper lined up, you have an ignition problem.

Your distributor weights and springs are working correctly?

 

Adjust your valves and then try to set your timing. Misadjusted valves can cause the engine to die out at otherwise normal settings. Another less likely thing is the possibility that your harmonic balancer outer ring slipped a little causing mis-readings. But do the valves first, as you should anyway using the running engine method!

 

glen242-- I was told to be careful in trusting the TDC marks on timing gears, and to always use a degree wheel to verify the cam installation. If you have the #1 piston at TDC, the crank should be at 0 degrees, however, if your cam is installed incorrectly (bad timing marks, or other cause), the timing of the valves wont syncronize with the piston position.
The XE268 that we both have, is machined with a 4 degree advance in the cam lobes. Comparing to a (lets say) stock cam, you'd have to install the XE268 4 degrees retarded in relation to the crank, to get a perfect synchronization between valves and pistons.
I don't remember which, but I think its retard the cam in relation to the crank to get top end hp., and advance the cam in relation to the crank to get torque (or vise versa)

 

I just found it...
From Chevy Hi-performance Dec '01...
Question
I just bought the latest issue of CHP, and I was browsing through your ignition and carburetor tuning section. Why don't you use a vacuum gauge to set the timing? Wouldn't that theoretically work since you're looking for the most vacuum attainable? You could go on and tune the carburetor with the vacuum gauge still attached.
Answer
It's great that we've got you thinking. Wouldn't it be easy to set the timing with the vacuum gauge? You are right that you would like to have the highest vacuum possible for the best idle quality, however, as soon as you put a load on the engine it wouldn't be very happy! It would detonate itself to death. The only way you can come close to doing what you have suggested is with a computer-controlled vehicle. If you had the ability to generate a spark table for your computer on an engine dyno, have optimum spark advance at idle, and could spark the engine by its load, you would have everything. We were able to do this on the GM ZZ4 350 H.O. emissions package for the third generation Camaros. The spark curve has an idle advance of 28 degrees. It continues to have this amount of advance at part throttle and light loads, but when the engine is loaded at slow engine speeds, we retard the spark to keep the engine out of detonation.

 

I guess that I didn't read that soon enough. I tried setting the idle with a vacuum gage. Best reading was at about 40 degrees and 17 inches of vacuum. 20 degrees of advance is 15 inches of vacuum.
Could there be an air leak at the intake manifold causing this?

 

Set timing about 12-16 BTDC & all in by 1800-2500. Use the timing light !
Use the vac. guage to set carb. mixture.

:cool:

 

I MIGHT be able to get the engine to run at 16 degrees BTDC but it's too rough and unstable to do any adjustments. I haven't tried too much mixture adjustments. I did turn the screws out 1/4 turn trying to keep the motor from dropping 350 RPM when going in gear.
I just finished putting thread tape on my vacuum port behind the carb. and on the Brake vacuum fitting at the rear of the carb. I really didn't expect more than about 15 or 16 inches of vacuum though and that's what I had before taping.
Owning a Corvette sure is exciting! :smash:

 

If you used Comp Cams anti-pump up lifters, you can not set your valves by the book- if you did are way too tight. You can set w/ it running.

 

Uh-Oh! Excuse me for a moment. Gotta go to the garage.
My lifter box says P/N 812-16. They don't call them anti-pump up. How do I tell? They were set to 0 gap then tightened 1/2 turn with the engine off. No tapping so I was happy.

 

Back 'em up about a half turn & pretty soon you will have your car running like a CORVETTE.

:cheers:

 

I vary the timing sometimes but right now I believe I have it at 14 initial, 34 total and about 16 degrees of vacuum advance for around 50 degrees at cruise.

 

'75 383 ElkGrove:

I agree with what you say. I was trying to point out that it doesn't matter how the cam was installed, advanced, retarded, or straight up it will not effect your ignition timing. As you state, cam installation will only alter the relationship between the cam and the crank.

It was stated that the marks and keyway location were the same on the old and new damper and the marks on the timing gear set were aligned, so the problem seems to be elsewhere. I don't believe that you can be that far off, where the car doesn't run right, by relying on the marks on a quality timing gear set. I know degreeing the cam is ideal, but not everyone has a degree wheel or wants to purchase one for one time use.

 

Thanks for the specs. from your motor Nastee. After following Ganey's advice and backing the valve adjustment off 1/2 turn from my original setting it sounds like a sewing machine now but I was able to get the timing back to 16 BTDC. Once I had it there I fiddled with the idle mixture screws to get a smooth idle. My vacuum is only 15 inches at idle, but I'm close enough to have somthing to work with.
Thanks for all your help guys! I owe you one when we meet :cheers:


[Modified by 1979toy, 11:29 AM 11/4/2001]

 

I have the Xe262 with the same lifters that you have. I'm running @ 37 deg @about 2700 to 2800 rpm's. Runs great. I have the 650 Demon and when I set the 4 corner idle screws with the vaccum gage it ready started to idle smooth and sounds great. Good luck.