Compression after new piston rings

[mikekolbus]

Folks
Installed rings in a 1960 Johnson 3 HP and I am getting 20 psi when checking compression, I am puzzled cylinders honed up cleanly and bore dimensions are to spec. I got this engine for little investment so I wonder if the previous owner could have opened the Engine and installed the pistons backward. The pistons are installed with the high flat area on the intake side of the block
Any thoughts would be appreciated
Mike Kolbus

[aquasonic]

Mike, the sloped side of the piston is the exhaust side. The stepped side of the piston is the intake side.

[Buccaneer]

Mike, from what you describe, it sounds like your pistons are installed correctly.
When you spin the flywheel over by hand, does feel like there’s only 20 psi
compression? If so, there would be very little or no rebound or “bounce”
on the flywheel. Does your compression gauge test out okay on a known
good engine?

Prepare to be boarded!

[dave-bernard]

Did you resurface the head?

[mikekolbus]

Folks
the pistons are correctly installed, I am checking every box. next is the verify the accuracy of my compression tester, and then I will resurface the head. I will let you know the results. I appreciate the ideas and this club is an excellent group of talented and experienced people.
thanks
mike kolbus

[frankr]

20psi is virtually no compression. I suspect a faulty gauge or improper procedure.

[Tubs]

A "Boathouse Repair" is one that done without having tools or the skills to do it properly.

• This reply was modified 4 years, 4 months ago by Tubs.

[fleetwin]

Did you check/clean the head bolt/block threads? Perhaps the threads are messed up and the bolts aren’t really tightening the head before reaching the 60-80PSI torque spec.
Why is it that you pulled the powerhead down and replaced the rings? Were the cylinders scuffed/scored? Were the rings stuck? Did you check the ring end gap like Tubs spoke of? How much did you “hone” the block? Over honing tends to leave the cylinders over size.
Hopefully, this is just a case of a bum compression gage. Or, perhaps the head/block needs resurfacing, bolts/threads cleaned up….I’m assuming you used a new head gasket. You should probably replace it again if you pull the head off.
Post some pictures if you pull the head again…
Like others have said, 20PSI is virtually nothing…..Can you feel some compression when you rotate the flywheel?

[outbdnut2]

If your compression gauge has a hose and the check valve is at the gauge instead of at the motor end, you can read 20 to 40 pounds depending on the diameter of the hose. On small cylinder engines, the volume of the gauge hose is significant, and adds to the volume of the cylinder. The longer the hose and the bigger the inside diameter; the lower the compression reading.

That being said, I’ve never seen one read below 30 pounds, but I imagine there are longer hoses out there.

If that’s the kind of gauge you have, See if it starts and runs.
Dave

• This reply was modified 4 years, 4 months ago by outbdnut2.

[Mumbles]

Possibly the motor isn’t being spun over fast enough or enough times with both spark plugs out and the flywheel mounted. Was the head gasket installed? I’ve seen this happen in the past. The long, flat ramp on the piston goes towards the exhaust side.

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