Compression Question

k20_chevy · 06-29-2009, 04:24 PM

Hi guys,

So I have a 81 Chevy k20 with a 350 4-bolt main and its blowing blue smoke. I know its my rings.

Here are my compression results (dry only): *edit: I did this with a cold engine (not at operating temps)
1 - 120 2 - 100
3 - 95 4 - 100
5 - 85 (oil on plug) 6 - 95
7 - 95 8 - 95

So from your experiences how bad off am I? It's my mud truck, just wondering if I will get 8 more Friday's out of it.

I'll take any opinions

leolkfrm · 06-29-2009, 04:43 PM

put 15-40 in it keep it full, check the oil when pushing it hard, and plan on a rebuild at the end of the season

k20_chevy · 06-29-2009, 04:45 PM

I definitely plan on a rebuilt. Never thought about trying heavier oil.

stumpuller454 · 06-29-2009, 05:13 PM

gm states that if the compression is 70% of the highest cylinder let her run, but your getting on the low side, it`ll run for as long as you want you`ll just start losing power and consuming more oil later on.

k20_chevy · 06-29-2009, 05:15 PM

Quote:

Originally Posted by stumpuller454

gm states that if the compression is 70% of the highest cylinder let her run, but your getting on the low side, it`ll run for as long as you want you`ll just start losing power and consuming more oil later on.

Yeah, i know. my old dodge had 30 psi per cylinder before i s******* it and used about 2 qrts. of oil a week. It still ran though

leolkfrm · 06-29-2009, 07:16 PM

might want to throw a bottle of lucas in the oil, for the ten bucks its worth the try

k20_chevy · 06-30-2009, 06:07 AM

I will try the lucas too.

bradrhale · 06-30-2009, 06:47 AM

i wold say do the test again at operating temps. the engine runs better at temp which seals better also. you will more than likely get different numbers when you do this. 85 is a good little step from 120.

k20_chevy · 06-30-2009, 09:02 AM

Yea I can do it again. I'm sure my #5 cylinder is bad since the spark plug was covered in oil when I was pulling them out.

bradrhale · 06-30-2009, 10:57 AM

if blowing out blue smoke, could be a future ring job, valve job or valve seal job. with the lower compression, i would lean to a valve or ring.

06-29-2009, 04:24 PM	#1
k20_chevy Senior Member Join Date: Apr 2009 Location: Lorain Posts: 82	Compression Question Hi guys, So I have a 81 Chevy k20 with a 350 4-bolt main and its blowing blue smoke. I know its my rings. Here are my compression results (dry only): edit: I did this with a cold engine (not at operating temps) 1 - 120 2 - 100 3 - 95 4 - 100 5 - 85 (oil on plug) 6 - 95 7 - 95 8 - 95 So from your experiences how bad off am I? It's my mud truck, just wondering if I will get 8 more Friday's out of it. I'll take any opinions __________________ 1981 Chevy K20 3/4 ton 4x4. 350 with th400 trans. 33x12.5x16 Super Swamper SSR. open D44 front and 14-bolt rear with detroit locker. 3" body lift. Last edited by k20_chevy; 06-29-2009 at 04:28 PM. Reason: forgot something*

06-29-2009, 04:43 PM	#2
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 4,300	put 15-40 in it keep it full, check the oil when pushing it hard, and plan on a rebuild at the end of the season __________________ 4 wheels move the body 2 wheels move the soul B.W.A.I

06-29-2009, 04:45 PM	#3
k20_chevy Senior Member Join Date: Apr 2009 Location: Lorain Posts: 82	I definitely plan on a rebuilt. Never thought about trying heavier oil. __________________ 1981 Chevy K20 3/4 ton 4x4. 350 with th400 trans. 33x12.5x16 Super Swamper SSR. open D44 front and 14-bolt rear with detroit locker. 3" body lift.

06-29-2009, 05:13 PM	#4
stumpuller454 Senior Member Join Date: Dec 2007 Location: Grande Prairie, AB Posts: 2,043	gm states that if the compression is 70% of the highest cylinder let her run, but your getting on the low side, it`ll run for as long as you want you`ll just start losing power and consuming more oil later on. __________________ SUPERCHARGED 454 K2500 GMC! 450hp and 600ft/lbs http://www.youtube.com/watch?v=WJ27RJHfJKE "sailing with Captain Morgan often!"

06-29-2009, 07:16 PM	#6
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 4,300	might want to throw a bottle of lucas in the oil, for the ten bucks its worth the try __________________ 4 wheels move the body 2 wheels move the soul B.W.A.I

06-30-2009, 06:07 AM	#7
k20_chevy Senior Member Join Date: Apr 2009 Location: Lorain Posts: 82	I will try the lucas too. __________________ 1981 Chevy K20 3/4 ton 4x4. 350 with th400 trans. 33x12.5x16 Super Swamper SSR. open D44 front and 14-bolt rear with detroit locker. 3" body lift.

06-30-2009, 06:47 AM	#8
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 8,028	i wold say do the test again at operating temps. the engine runs better at temp which seals better also. you will more than likely get different numbers when you do this. 85 is a good little step from 120.

06-30-2009, 09:02 AM	#9
k20_chevy Senior Member Join Date: Apr 2009 Location: Lorain Posts: 82	Yea I can do it again. I'm sure my #5 cylinder is bad since the spark plug was covered in oil when I was pulling them out. __________________ 1981 Chevy K20 3/4 ton 4x4. 350 with th400 trans. 33x12.5x16 Super Swamper SSR. open D44 front and 14-bolt rear with detroit locker. 3" body lift.

06-30-2009, 10:57 AM	#10
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 8,028	if blowing out blue smoke, could be a future ring job, valve job or valve seal job. with the lower compression, i would lean to a valve or ring.

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