Compression Test

[FreeBeeTony]

After cleaning the pistons and cylinders (see before and after pics below). I installed the heads and adjusted the valves.
Exhaust/Intake manifolds are not installed. The numbers were not good. All cylinders ~30PSI.
I thought maybe it was the gauge. Went to Autozone and borrowed a different gauge. No different except #1 came up to ~120 after about 10 revolutions.
I am soaking the cylinders in Trans fluid/ acetone mixture hoping I can free up the rings.

Any other suggestions?

​@Bondo achris

 

[Scott Danforth]

make sure your valves are adjusted properly. do a leak down test.

however may be pulling the motor to rebuild.

 

[Bt Doctur]

Not to bust your bubble but I dont think you will be freeing up anything looking at the before pic.
Assuming you drained the block before installing the heads so as not to wet the head gaskets, and ran a tap to clean the threads for the head bolts ,and correctly torqued the bolts in the correct pattern and value and you only read 30 psi.

 

[FreeBeeTony]

BT Doctur.......yes to all of your questions.
scott Danforth.....will check valves....pretty sure they are adjusted properly.

 

[Bt Doctur]

a leakdown test would be better , loosen the rockers so valves are closed, make a fitting from a old sparkplug (remove the porcelain and tap for 1/4 inch pipe, install short hose and air fitting) or compression gauge hose and inject air.and listen

 

[Bondo]

Ayuh,.... Don't look good Tony,....

My guess is, a leak-down test will show the rings are shot,....

 

[Rick Stephens]

If not mistaken, this was an over 600 hour motor. Can't feel too bad about needing to do the cylinders and pistons, the end result will slide a smile onto your face. Note: usually cheaper to buy V8 worth of oversize pistons and ring sets than a V6 worth. Another note, this is a great time to pressure test your cooling system, make sure you don't have a crack anywhere before spending on the block.

 

[FreeBeeTony]

No Title

LeakDown Test:

​1) Loosened rockers to close valves.
2) Applied 85# of pressure........seems to hold???

Am I doing something wrong?

​

 

[Bt Doctur]

If you pressurized the cylinder and did not hear hissing in the crankcase vents and it is holding pressure you should be able to get a compression reading over 30 psi. How tight did you adjust the valves from 0 lash?

 

[Scott Danforth]

remember lash is the free-play up and down of the push-rod. zero lash is when there is no more vertical wiggle. not zero spin. you can rotate pushrods with your finger tips even as the valve starts to open.

adjustable rockers with hydraulic lifters are 3/4 turn past zero lash (puts you about middle of the plunger stroke)

 

[FreeBeeTony]

I went 1/2 turn after 0 lash.

 

[FreeBeeTony]

Just re- checked the valves and re- adjusted.............guess I was too tight.
​Now getting ~156-160 on #1 & #2!!
Need to re-adjust the rest and re-verify.
​The adjustment seems very sensitive.........I am going to use the compression gauge as a check as I adjust.
​Can/should you adjust for maximum PSI using the compression gauge?

 

[Lou C]

Might be getting lucky there. I read a bunch of articles on adjusting valves on these engines and the confusion seems to in 2 areas:
How to determine zero lash
How much to tighten after zero lash.

I followed the procedure in my OMC shop manual and really took my time with the zero lash part. I used up and down movement of the pushrod with the weight of the socket and ratchet off the rocker nut. Then went 1 turn more as the book said. Results: normal comp test results & no valve lifter noise. Just be careful with the zero lash part. Spinning the pushrod gives a false reading and can cause the valves to be too tight.

here's what I got for a hot comp test:
1 160
2 160
3 175
4 165
5 160
6 165

​also keep in mind that cold comp test results will be different. If the rest of them come up to those 2, then finish the re-assembly and run it and see what you got.

 

[FreeBeeTony]

Bought a leak-down tester from Harbor Freight tonight.
Gonna perform a real leak-down test this w/e.
Need to decide if I should pull it or not.

Boat isn't a show-stopper.....more of a battle wagon.
Strong hull........sea worthy.
​Have been considering building a stroker if the opportunity presented itself..........
This may be my opportunity.
​I want to and I don't want to..............make any sense???

I will report my findings.
If I decide to pull it............
It will be another thread and have a whole lot of more questions.

 

[FreeBeeTony]

While watch youtube videos of leak-down testing I think I now know why I was holding 85# of pressure.........
​I was using the hose from the compression tester that had a Schrader valve! Air never got to the cylinder.

 

[Lou C]

Aha! that's why the readings were almost the same!
​Keep us updated. Even if you have to pull the engine, its still worth the rebuild because the engine was always closed cooled. And the boat is a Grady, that will always be worth more than some of the lil lake boats that people run (like mine!)

 

[FreeBeeTony]

Conducted a leak-down test tonight...........
​Cylinders 1,3,5,& 7 showed > 75% leakage.
Next step is to pull the engine.............may be an interesting winter!

 

[QBhoy]

Can you feel a strong pressure through oil fill cap hole with hand when turning her over