As far as I always thought, if the numbers went up with oil in the cylinder during a compression test it was bad rings/ringlands for sure.

WRONG

If you have low compression, your block might be fine! It could be in the cylinder head.

If the valves aren't seating properly, you will loose compression and burn oil, just like having bad rings or cracked ring lands. Adding oil to a compression test can help seal the valve seat, rasing compression temporarly


So before you yank the pistons out of what could be a perfect block, check your head

 

i guess no one cares

 

i care

 

how would the oil get onto the valve seat to seal it if u just poured it into the spark plug hole?

 

yea, how much oil are you pouring in?

 

heres a simple solution, perform a leak-down test after the compression test and you will find more accurate and distinguishable results.

 

yep of course,
leakdowns should be able to diagnose very well.

but the problem is most ppl don't have compressed air handy.. nor do ppl want to pay 50-150bux for a ld tester

 

or after you pull the head sit it on its side and fill the intake/exhaust ports with water

 

huh. Ignorance at its best...hehe j/k.

Adding oil doesn't show your head is fubbared. A leak down test is the ONLY way.

The oil test will ONLY test for how well the rings are sealing.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bryson &raquo;</TD></TR><TR><TD CLASS="quote">huh. Ignorance at its best...hehe j/k.

Adding oil doesn't show your head is fubbared. A leak down test is the ONLY way.

The oil test will ONLY test for how well the rings are sealing. </TD></TR></TABLE>

If the oil test shows higher compression, it could be the valve seats, not the rings!



either way compression tests suck, the only real way to know anything is to do a leak down test

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by adictionbass &raquo;</TD></TR><TR><TD CLASS="quote">yea, how much oil are you pouring in?</TD></TR></TABLE>

like a capfull

it raised compression in my #3 from 90psi to about 130psi

the rings and block were fine, it turned out to be a bad valve seat

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Sketch_hs &raquo;</TD></TR><TR><TD CLASS="quote">

If the oil test shows higher compression, it could be the valve seats, not the rings!



either way compression tests suck, the only real way to know anything is to do a leak down test </TD></TR></TABLE>


A cap full of oil shouldn't make any difference with the valve seat.

did you do the compression test with this same block, AFTER you "fixed" the seat? That is the only way you could say with any such evidence that it actually was the seat.

How exactly are you determining that the rings are fine?

A good rule of thumb from my experience is...

Compression test to check the condition of the block
Leak down test to check the condition of the head

Of course either test can tell you somethings wrong with the head, block or both but mainly thats how they should be approached.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Sketch_hs &raquo;</TD></TR><TR><TD CLASS="quote">

If the oil test shows higher compression, it could be the valve seats, not the rings!



either way compression tests suck, the only real way to know anything is to do a leak down test </TD></TR></TABLE>

no.....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Sketch_hs &raquo;</TD></TR><TR><TD CLASS="quote">

If the valves aren't seating properly, you will loose compression and burn oil, just like having bad rings or cracked ring lands.


So before you yank the pistons out of what could be a perfect block, check your head

</TD></TR></TABLE>

this isnt true either other then the fact that it will loose compresion.... it will not burn oil from this and will not be just like a cracked ringland .....

 

Exactly.

People often forget too that the oil ring does little to hold compression. You can have a fubbared oil ring and burn a crap load of oil, but still have great compression.

 

interesting, i did the oil drop thing too and my #4 compession went from 90 to 130 as well but my dad thinks its the rings, im not burning any oil though. just lost compression on the #4. but if you pull a sparkplug wire out the #4 when its running it doesnt do much and wehn you pull any other it almost wants to die.

What do you think is wrong with mine then? i havent driven it for a month now

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by T3T495GSR &raquo;</TD></TR><TR><TD CLASS="quote">interesting, i did the oil drop thing too and my #4 compession went from 90 to 130 as well but my dad thinks its the rings, im not burning any oil though. just lost compression on the #4. but if you pull a sparkplug wire out the #4 when its running it doesnt do much and wehn you pull any other it almost wants to die.

What do you think is wrong with mine then? i havent driven it for a month now </TD></TR></TABLE>

rings, and/or ring lands. it also doesn't have to burn oil for the rings to be fubbared. that just means the oil ring is doing its job, and your valve seals are working.