'66 327 in C20 issues

[pjb155]

I've been having serious issues with the 327 in my 66 C20 pickup.

all i know about the engine is that the block is also from 66 and the size matches the build sheet, so could well be matching.

At idle, it runs ok and revs reasonably but somewhat resisting to rev high. Under load i'm having constant backfiring and sometimes blowing back through the carb. Power is so limited the truck struggles to accelerate at all in 4th gear (1.00) and as i'm driving a bit further even struggles in lower gears, making it basically undriveable.

It used to run much better (or less bad), but an oil leak resulted in a short highway drive with no oil pressure with loud ticking noises as a result which went away after refilling with oil (20w50). I'm not sure if the issues started immediately after this "little" incident.

I ran some tests to see if I could identify the issue(s):

InsHg at idle 14" steady
BTDC timing 5° adv with vac advance plugged at idle
cranking compression around 80 psi on all cylinders variation +-10 psi
cylinder leakdown test indicates some leaking via the cylinder walls / piston rings into the crankcase, but is still in the "low leakage" range on my leakdown tester.
Fuel pressure 4 PSI at idle, 3 psi at high rev (stationary)

I know the compression is very low but i'm not sure if this is causing the symptoms or if i could avoid putting in a crate engine or going for a full rebuild...

Distributor cap & rotor, coil are all new. it has a 4bbl carb which has a triangular tag on it with T02512511 and E6 on it, i haven't been able to find anything on this, and therefore have not touched the carb apart from the mixture screws.

thanks for posting your views

[PGSigns]

You are not going to make any power at all with the motor in that condition. Then what happened in the motor with no oil in it is any ones guess. I would say it is time to either rebuild or replace.
Jimmy

[geezer#99]

You could do a couple things.
Take some pics of your motor for us with the air cleaner off.
And bump your timing up to 14 btdc and see if that helps.

And tell us your method for doing a compression test.

[jchav62]

I agree. Bump up the timing to 10 - 14 degrees. Also double check your firing order and make sure no wires are crossed for some reason. Check for vacuum leaks as well.

[TJ's Chevy]

Tight valves will do that to.

[pjb155]

thanks, will check all that and post some pics when I can

[63C20]

there is no such thing as the motor not matching the vehicle. you removed so of your cam material, and burned your rings and lost some compression due to oil out. 60 psi is half of what it should be

[cadillac_al]

If your compression gauge is accurate then your engine is about dead. I would think positive and try the gauge on another engine to see if it is really accurate.

[crazy longhorn]

Lack of oil pressure, is not good & could be the source of your problem....but, I would ask if you had the carb opened up/breather off , when you did the comp test? If not, try that again, or check the gauge on another engine as mentioned above? If it looks a little better, I will go back to what Geezer stated (12-14 initial on the timing) . See if that works better? Longhorn

[GRX]

Bell shaped cylinders, worn cam lobes, stuck rings, weak valve springs, and various other unsavory things.

[pjb155]

thanks for all the ideas!

some pics of the engine, starting to think more about a replacement engine, i have a 3970010 block available in the area (belgium) at a reasonable price.

I will still try the timing approach tomorrow & i can test the (new) gauge on something in much better condition.

in the second last picture, the lead without the dust cap on the distributor goes to the #1 cylinder.

[pjb155]

Originally Posted by geezer#99

You could do a couple things.
Take some pics of your motor for us with the air cleaner off.
And bump your timing up to 14 btdc and see if that helps.

And tell us your method for doing a compression test.

removed the lead between coil & distributor, removed 1 spark plug at a time then connect (new) pressure gage, crank about 4-5 rotations and get the max reading from the gage.

[PGSigns]

Pull all 8 plugs and tie the throttle wide open during the test. Don't forget to release it after the test. Put the gauge in a cylinder and spin the engine 5 or 6 turns and go tot he next hole. Do it dry.
Jimmy

[geezer#99]

Pull all the plugs and block the carb wide open. That'll be more accurate.

[68gmsee]

After you do all the recommended checks and it still has low power, replace the cam. Some of the cams in these old engines were notorious for going flat on you after 80k or higher mileage on them. Back in the old days, I replaced a few of them for lack of power and sputtering and just plain not running well.

[cadillac_al]

Since you plug wires are in an unconventional pattern you may have one crossed somewhere. That usually leads to backfiring under power. If your compression is accurate it may never run right anyway.

[Dead Parrot]

How long was your 'short' no oil pressure drive? If more the a couple of km, probably damaged the engine/cam.

If the proposed replacement block is a newer model then your current, you will need new accessory brackets. Sometime in the early 70's, Chevy switched the Alt to the passenger side. Something more to research before installing a replacement engine.

[Captainfab]

A short water pump and it's accessory drive, including the drivers side alternator mounting, can be installed on any year Gen I small block. Just because an engine may have come from the factory with a long water pump and a passenger side mounted alternator, does not mean it has to stay that way. It is more important to use the style that fits the vehicle correctly.

Originally Posted by Dead Parrot

How long was your 'short' no oil pressure drive? If more the a couple of km, probably damaged the engine/cam.

If the proposed replacement block is a newer model then your current, you will need new accessory brackets. Sometime in the early 70's, Chevy switched the Alt to the passenger side. Something more to research before installing a replacement engine.

[pjb155]

I had a look at the replacement block, it was even worse than what I have :-), and had code CRX on it, meaning just 145 hp (when it was new).

The no-oil drive was definitely more than a few kms/mls...

I tried the compression test on the existing block with all plugs removed & carb wide open with fully charged battery, showing only a ~5psi improvement. Bumping the timing made it run with considerably less backfiring etc, but very VERY low power still.

Plug wire order is triple checked and ok. I noticed that all plug wires were "offset" by 2 places counterclockwise compared to what is prescribed by engine manuals, but also the rotor angle is different (so this may balance each other out).

I will do a last attempt by doing everything as per manual + with new points/condenser and plugs.

Is there any way to check cam condition without removing it? I have an 8mm borescope available.

[geezer#99]

Easiest way to check cam is remove valve covers and watch the rockers looking for any that don't move much or the same as the rest.
Your position of #1 wire is working fine. Leave it like that until you've done the plugs and points.

And what's wrong with the replacement block?
Could be a good foundation for a rebuild.

[pjb155]

Originally Posted by geezer#99

And what's wrong with the replacement block?
Could be a good foundation for a rebuild.

I did a leakdown test and the loss was even bigger than on the block in the truck now. If i have to do a rebuild then I'd also prefer to stick with the matching engine to the car.

[pjb155]

after replacing the ignition with HEI (which i wanted to use anyway for a potential replacement block), new spark plug wires, oil change, new spark plugs and more advanced timing, adjusting the valves and checking engine ground, it now runs perfectly fine with even some decent power.

i really don't know what exactly the problem was, but it seems to be solved now!

thanks a lot for your advice & suggestions

[geezer#99]

Likely the hei was the best change.

Did you use a dedicated 12v supply to the hei?

[pjb155]

i replaced the resistor wire which used to run to the coil with a normal one and used that to power the HEI.

[chris mc bride]

IMO what why or how is out of way.With that low CC its time to yank it and do full rebuild.Its a 327 which one BAD A$$ engine and well worth cost. Maybe dump the heads for some with harden seats and more compatable with unleaded gas.