KNOCK HELP!!
#1
KNOCK HELP!!
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?
#2
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Re: KNOCK HELP!!
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
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
#3
Re: KNOCK HELP!!
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
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#8
Re: KNOCK HELP!!
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!
#9
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Car: 84 TA orig. 305 LG4 "H" E4ME
Engine: 334 SBC - stroked 305 M4ME Q-Jet
Transmission: upgraded 700R4 3200 stall
Axle/Gears: 10bolt 4.10 Posi w Lakewood TA Bars
Re: KNOCK HELP!!
Let me guess - centerbolt valve covers and Vortec heads?
Did you get the narrow body rockers?
Did you get the narrow body rockers?
#10
Re: KNOCK HELP!!
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?
#11
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Re: KNOCK HELP!!
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
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
#13
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Re: KNOCK HELP!!
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
GD
#16
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Re: KNOCK HELP!!
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
How was it pre-lubed before startup?
GD
#18
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Car: 84 TA orig. 305 LG4 "H" E4ME
Engine: 334 SBC - stroked 305 M4ME Q-Jet
Transmission: upgraded 700R4 3200 stall
Axle/Gears: 10bolt 4.10 Posi w Lakewood TA Bars
Re: KNOCK HELP!!
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?
#20
Supreme Member
Re: KNOCK HELP!!
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.
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.
#21
Supreme Member
Re: KNOCK HELP!!
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?
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?
#22
Re: KNOCK HELP!!
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
#25
Supreme Member
Re: KNOCK HELP!!
what size bearings are in it now?
how's the crank look?
getting good oil pressure?
how's the crank look?
getting good oil pressure?
#27
Supreme Member
Re: KNOCK HELP!!
.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?
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?
#28
Supreme Member
Re: KNOCK HELP!!
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.
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.
Last edited by redneckjoe; 05-10-2017 at 05:03 PM.
#30
Supreme Member
Re: KNOCK HELP!!
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.
#31
Re: KNOCK HELP!!
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
#35
Re: KNOCK HELP!!
I know its always best to replace rings once you pull your pistons, but do you think i could get away with using the old rings and re-clock them of course