Hey Everyone,

I have been working to reseal pretty much everything on my 1981 C3, 4 Speed, all original so I have the CCC system still intact.

when I replaced the crank seal I went ahead and replaced the timing set, “while I’m there” sort of deal. I still had the factory aluminum/plastic gear set from the factory that looked quite good with 80k miles on it, some I dentation but the chain looked worse for wear than the nylon gears. The chain was loosy goosy, so glad I got it replaced with a cloyes double roller (non adjustable, stock replacement).

anyways! My question;
if I installed the timing gear one tooth off, would my distributor timing also be too far off to idle well?

let me explain;
when I start the car, it start well enough, idles and dies, I have to feather the throttle to keep her alive, I don’t think the choke it working but I am in AZ and it’s a beautiful 72 degrees right now (sorry back easters). What worries me is a slight pop/backfire from the carb as I am feathering the throttle, when the motor warms up a little it idles well and does not pop or backfire anymore …

am I being paranoid and second guessing my timing chain work?

the CCC carb is original, a little leaky with a busted choke (parts are there but doesn’t seem to work).

my thought is if I changed the chain and installed a tooth off, without removing my distributor, then ignition timing will be too far off to idle? I also removed the ignition plug so the distributor wouldn’t have any ignition advance from the “computer”.

Lastly, I just want this motor buttoned up and running right until I can replace the carb and distributor with Holley Stealth components …

thanks guys!

 

if you install timing set One tooth off ... the cam timing is Off and must be corrected

so, your distributor aka ignition timing may be correct for the piston position but incorrect for the valve position ... or vice versa.

suggest you first re-install the timing set and ensure it's correct; then check distributor/re-install it.

 

I believe it IS correct … but as a sanity check, I am thinking if it was 1 tooth off, the ignition timing wouldn’t let it start and idle well after warm up. Remember, I did NOT move or remove the distributor. Just a sanity check. I did line up the dots on the gears.

i am getting the manifolds ceramic coated, so I cannot start it now.

 

If that chain was loose I would have at least went back and set the timing again

 

I agree, if you put your chain on one tooth off your engine would run terrible everywhere. the slack in the old chain and lack of the slack in the new chain could easily throw your timing off by 5 degrees or more.
Who wouldn't recheck ignition timing after replacing a timing chain.
Get your timing light out and reset your ignition timing.
Then repair that choke!

 

We are drifting a little off topic …I have shorty headers getting coated right now, I started it after I finished buttoning up the car and those were my observations. It also popped before the timing chain. Again, just a sanity check.

when I get my exhaust back from the coaters I’ll return the distributor. OF COURSE !!!

I have a new HEI from AC delco and new edelbrock 1904 quadrajet ready to go. But contemplating just going Holley EFI (sniper or terminator stealth).

 

OF COURSE!!! I will be retiming it when I get my manifolds back for the powder coaters. I was just inquiring my suspicions after my preliminary observations.

as I understand it, factory timing sets were retarded a few degrees for emissions, my new timing set would restore timing, that alone would change ignition timing as well as the cam timing…

 

is either valve cover off? you can eyeball check cam timing with #1 or @6 valves and the timing mark.bump motor until exhaust vakve is open. then bump it quickly or turn motor with a wrench and watch the valves on 1 or 6. as exhaust is just finishing closing and intake is just starting to open, timing mark should be on TDC if a tooth off timing mark will be 10 degrees off with 36 tooth top geat and about 7 degrees off with 42 or 44 tooth upper gear. you can rock engine back and forth watching the 2 valves to get the center spot where they are both a tiny bit open.

 

curious; did you buy the new 1904 recently ? if so, where ?

 

DITTO.... If the motor is timed straight up like it should be it's very likely that somebody at some junction advanced the timing in relation to the retarded timing from the cam. So what was 12 degrees BTDC is now 15 degrees. Go reset your timing.

 

HA! I wish!!! These were a great option back in the day … however I bought a couple on eBay, one that was mounted but never used and one used lightly, but slightly crusty, bought for spare parts …

I was thinking of selling all my carbs to fund a sniper EFI swap …

https://www.corvetteforum.com/forums...ck-1904-a.html

 

I agree , however I believe since the car ran fine when warmed up, I’m assuming CAM timing is good. I mentioned above that my manifolds are getting ceramic coated, when they come back I can re install the exhaust and retime …

 

Cam timing and ignition timing are related but only cam timing can affect ignition timing....ignition timing cannot affect cam timing. That said.....do a compression check.....you should have around 140psi....if not then it is off. You can have the cam off but the rotor will never hit the cap in the right spot because it physically cannot...regardless of which way you spin it. When I do a chain....I do them dot to dot then turn the crank 360 so both are 12 o'clock.....I do this because you will remember doing this.....setting the dots together is foolproof.....turning the crank one revolution makes you remember you did it.
Stock CCC 1981 spec for timing is 4 degrees with the breakout plug pulled......why are you setting it to 15 degrees? 6 or 8 is all the stock CCC will handle......

Jebby

 

HA! I see we have to play the same games for “sanity” … I meant to take a stinking picture so I’d remember it was done right, but I like your method of doing a full rotation as a mental “bookmark”. I was just surprised about the backfire when starting, but timing may have slid a few degrees from the new tightened up chain.

Honestly I haven’t looked up the timing specs, it’s on the hood but waiting for a few parts before I can fire it up again.

I can do a compression check, that’s easy enough… thanks for that tip

 

and to follow up, I have 150psi, cold, 5 cranks, open throttle, no oil squirted in bore. I only did one cylinder, but I’ll pop off the carb and do them all before I put my exhaust manifolds back on … see how healthy this iron lug is.

I was reading and it seems that retarded can timing should produce low compression and advanced can actually show high compression??? Someone said 190psi or so???

 

Maybe a little but not 190psi….

Jebby

 

But at least 150psi sounds typical? 81 stock L48, excuse me, L81 …

 

Yes….150 is a healthy 8.5 to 1 engine with a small cam….

Jebby

 

Ericshere03 OP

PM Sent

 

well as per your advice I went ahead and did a full leak down test of all cylindersCold engine, sat for a month, no oil added, 5 cranks, carb lifted off manifold



1 - 149
2 - 150
3 - 156
4 - 156
5 - 149
6 - 157
7 - 145
8 - 162
6 and 8 were my over achievers. I ran 8 again because of it being such an outlier and got 157. So no idea … almost splitting hairs here anyways.

id say things look normal. When I get my parts I’ll be buttoning her up and hopefully hitting the road!