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General Category >> Rubber Side Down! >> Cylinder PSI goes from 135 to 240 w/oil... WHAT!?
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Message started by Bobbert on 03/28/12 at 15:01:49

Title: Cylinder PSI goes from 135 to 240 w/oil... WHAT!?
Post by Bobbert on 03/28/12 at 15:01:49

~~I just replaced my exhaust seals a week ago cause I've been burning white smoke.~~ Im ~~still~~ burning burning oil like none other (10 ml/mile) so I just did a compression test.

135 PSI straight
240 PSI with a tablespoon of oil deliberately poured in the cylinder

It's obvious my rings are bad... but is a 100 PSI difference really possible!??

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by Kris01 on 03/28/12 at 17:40:06

I'm no expert but 240 psi sounds extremely high...even with the oil sealing the rings. Shouldn't compression be a lot lower?

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by verslagen1 on 03/28/12 at 17:49:50

What seals did you replace?

do mean the valve stem seals?

I worked on one that the seals were missing... and yeah it'll burn a lot of oil.

and i gotta wonder if you sucked in a lotta that oil.
that will drive up the compression if the cylinder is full of oil.

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by Bobbert on 03/28/12 at 18:19:07

657661607F7274767D22130 wrote:

A week ago, I replaced both exhaust valve stem seals because I was blowing white smoke on startup and losing oil. The bad seal was the one that we had replaced way back when. After replacing the exhaust valve stem seals, there is no white smoke on startup but I'm still burning oil. After replacing the stem seals I went on a 300 mile run and was replacing 500 ml of oil every 50 miles.

No major oil leaks anywhere on the case, so I did a dry compression check and got 135 PSI. Then I put a little bit of oil directly into the cylinder through the spark plug hole to test the rings. PSI went up to 240.

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by Retread on 03/28/12 at 21:58:23

This is natural, you are sealing the cylinder with oil.. I like to do a leakdown test on low compression readings before teardown.. Basically you put your engine on TDC, and put compressed air into the cylinder through sparkplug hole.. Hold that pressure and listen for leaks exhaust side, intake side, and crankcase pressure, this will give you an idea of what and where the problem is.. Service limit on compression is 110#...

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by thumperclone on 03/28/12 at 21:59:42

SSM (edited quote to save space)
compression pressure
standard
142-200 psi
limit
114 psi
low compression may indicate any of the following:
excess cyl wall wear
worn piston or rings
rings stuck in the grooves
poor seating of valves
defective head gasket

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by Bobbert on 03/28/12 at 22:58:06

So what you're saying is 135 is below standard but not requiring ring replacement?

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by LANCER on 03/29/12 at 04:01:57

you have replaced the valve stem seals
if you want to cover the bases you can pull it apart, hone the cyl and put new rings on the piston, and do a valve job
I had a valve job done at a local NAPA machine shop a couple yrs ago and it was about $50
honing the cyl should be very cheap too or you could buy a hone at Sears or NAPA and do it yourself with a drill
these are low cost and will eliminate any leaks

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by Routy on 03/29/12 at 05:33:28

But if the cyl wall is worn beyond .010-.015, new rings mite not hold end gap tollerences ?? You can get away w/ worn walls (cyl taper) providing the ring end gaps are held in check. But that don't mean piston slap won't be keepin time w/ some of the music nowdays ! :-/

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by justin_o_guy2 on 03/29/12 at 05:57:28

How many miles on that thing?

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by LANCER on 03/29/12 at 08:38:46

202F352E323427252D2334460 wrote:

Yes. I neglected to include the "assumption" that the cylinder had been checked and that it was within tolerances for the stock bore.

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by Bobbert on 03/29/12 at 10:00:59

4C5355524F4879497941535F14260 wrote:

How many miles on that thing?

somewhere around 45k. hard to tell w/o an odometer

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by justin_o_guy2 on 03/29/12 at 15:48:31

I spose that enough passes of the piston up & down in the jug to cause some wear,, you can probably hand the machinist enough $$$ to buy a new ID mic to get him to let you borrow his to measure up & down in the bore..

Title: Re: Cylinder PSI goes from 135 to 240 w/oil... WHA
Post by k9500winmag on 03/29/12 at 19:53:13

Nobody touches my mics, and ya dont want to know how much they are, but i would prob just measure for someone for free if i was free at the moment. Ive always got walkin jobs that i dont bother to charge people for. They usually come.back for business then.