Over the winter I have been buying parts to carb swap the good ol' 91 trans am. I threw a cam in it considering it was out and a torque converter, got some vortec 906 heads at a swap meet, got new springs, pushrods, guide plates, 1.6 rockers. Got a Weiland intake, summit distributor, threw a carb on it.. easy stuff right? Go to start it up last week. Fired right up.. had good oil pressure, set timing and went to bed. Next day I went to start it and it was knocking hard, but it changed with timing advancement or retarding. I could get it to where it would almost stop but it was still there. Started pulling it apart and found out the local auto parts store have me 2 diffrent types of plugs, I don't think that's the problem but what do you guys think?

 

Well probably get a matched set of plugs in there. If you set the timing then probably can rule that out. You can usually isolate which cylinder is knocking by pulling plug wires one at a time.

Since you swapped the cam and went to 1.6 rockers - make sure nothing in the valve train is smacking. What's the lift on the cam?

Being that it changes with timing though - that kinda makes me think it's something related to ignition or a specific cylinder. Rod knocks will go away if you pull the associated plug wire which means they will also change pitch and severity by changing timing.

I would be cutting open the oil filter (with a proper filter cutter) to check for metal flake, etc. It's worth it as a precaution against wasting more time or doing more damage.

GD

 

I'll get a new set and try that, the cam is a comp xe 276. .502/.510 lift with 1.5 rockers. I drained the oil and I didn't see anything, I might pull the motor to get the pan off to just double check every thing in the bottom end, but what makes me think it's not bottom end is when it was running and I adjusted timeing to get the knock away it wasn't a steady knock, it seamed like it was all over the place

 

Also pulled the valve covers too and nothing is hitting

 

Were the heads machined for that much lift? Vortec heads are only good for .420 lift without modification. You could have bent the pushrods.

GD

 

There all machined down to accept a bigger lift

 

Change the plugs, check for bottom end condition.

Can you go back to the old distributor?

GD

 

I'll pick up some plugs tonight, the old distributor was computer controlled, I've only got this 1 hei dizzy. I'll keep you informed, thanks for the great info!

 

Let me guess - centerbolt valve covers and Vortec heads?
Did you get the narrow body rockers?

 

I have the narrow body rockers, I just pulled the bottom end apart and the main bearings have very dark oil on the and it's fresh oil, the rod bearings had clear oil on them?

 

Can you post pics of the bearing condition?

Did you cut open the filter to check for metal? That's usually an easier first step and will catch more than just mains/rods - metal from cam bearings and other places that are harder to check will end up there too.

GD

 

I actually can't find a local store that sold a filter cutter, I'll get some pictures up

 

Well - you can use one of those really old school can openers - like for camping. Just don't use a saw that makes filings or cuttings. You want tear or shear it apart so you don't possibly contaminate it. Use gloves for sure. Keep it inverted so anything collected in the bottom stays there.

GD

 

 

Looks like a haze on the bottoms of the bearings, it's not a glare from the camara

 

How much run time on those? If that's just startup and only a few hours run time that would seem concerning to me. I've pulled down engine builds after relatively short runs - had a turbo build that ran lean due to clogged up injectors from some kind of tank contamination and a ferociously powerful fuel pump that blew a hole in the filter element...... cracked the cylinder wall from lean detonation. Bearings still looked new after 5,000 miles of this abuse.

How was it pre-lubed before startup?

GD

 

It's all stock bottom end, motor has 155k on it. I primed the oil pump for quite some time before starting it

 

Did you do the prelubing with a proper shaft that seals the oil galleries at what would be the bottom of the distributor shaft? Did you observe any oil pressure gauge while doing this?

 

Ah that would be normal wear for that age and mileage then. Button that up it looks fine. Must be either spark knock (cheap HEI distributor?) or valve train related since that's what got touched.

GD

 

Ahh the fun of downgrading engine management systems.

How old is the gas in it? You said you did it over the winter have you tried topping it off with some fresh stuff?

Check the basics make sure the distributor is lined up properly and not off a tooth, put in a fresh set of matched plugs.

What is your initial and total timing? How was it measured.

 

just my guess;
it looks like it may have spun a rod bearing at one time? how does the crank look? it's possible that somebody had the crank cut and not re-sized the rods. just threw in some new bearings.
have you MIC'd the journals? what size are the bearings?

how's the wrist pins?

 

All the rods have those black marks that looks like they spun, I don't know if that's normal? Haven't micd the crank yet, wrist pins slide in and out but no up and down play

 

Gas say all winter, that might be a problem also. Im going to throw some bearing in it, new gaskets and new plugs, reset timing and give it a go

 

*same gas from the winter

 

what size bearings are in it now?
how's the crank look?
getting good oil pressure?

 

.010 bearings, crank looked great, 45-50 psi oil on cold start

 

.010 on rod and mains?
i had a shop cut a crank and give me the wrong size bearings before. but that was my fault for not double checking everything.

is the cam out? or can you see the cam bearings? usually you can stick a zip-tie through the hole in the main up to the cam bearing. the holes should line up. if the cam bearing spun, it could be starving the bottom end possibly? i'm no master engine builder, but maybe a builder could verify that? i think some cam bearings have a groove cut around them too?

 

http://www.hotrod.com/articles/0411r...-installation/


from link;

As a case in point, earlier small-block Chevy blocks might feature only an oil-feed hole that aligns with the main cap oil passage, in which case the cam bearing’s oil hole must align with the saddle’s oil hole.

 

010 on rods, don't remember the mains, I'll pull the cam and try that method, I'm down to do anything to figure out if it's bottom end or not

 

it's worth checking. we at least know somebody cut the crank at one time in the past. how good of a rebuild and cleaning could be a mystery. sure hope ya figure it out and let us know what you find.

 

Alright, so I got all the gaskets and bearings I needed, I bought a oil pump too considering I'm this far, I also figured I'd be a good idea to re ring my pistons, i got some e-377k rings from the auto parts store, the top compression ring fits but the lower compression ring doesn't fit, the ring itself is too big? Does anyone know a ring set I can get for a 91 standard 350 bore rings that are already filed? Thanks

 

Rings often have to be gapped..... It's kinda rare to not have to do any gapping.

You can gap them with a diamond points file.... carefully.

GD

 

 

Oh that's a horse of a different color. You can measure the old rings and call Hastings. That would probably be my first step.

GD

 

 

In all likelihood they would be fine if they are regular cast rings. I don't hone cylinders (unless they have been bored) and rings always seat just fine for me. But I do replace them because they are cheap.

GD

 

Fired it up today and runs like a top!! Sounds great, need to reset my rocker arms. Thanks for all the help to finish this not so easy project!!

 

 

Did you find the source of the knock?

Also what rings did you end up needing?

GD