Help! Uneven Compression on New Motor

[///M5]

At the machine shop right now checking the spec and roundness.

Just thought I would close the thread out with a conclusion.

Thanks for all the help everyone!

 

[///M5]

Back from machine shop. I have to admit it had me sweating, but the machinist said he barely touched it and the clearances are still well within spec.

 

[mbrick]

Thanks for posting after you found the root cause. Do you think the ring was bent when installing on the piston?

Is it a coincidence the aluminum transfer is below the bent ring end?

Did you change the jetting between the first post to the photos ones on page 3 after the teardown? The Mag side still looks lean. PTO looks OK, on the safe side of rich.

John Ziegler - good call on this one with your prediction!

 

[///M5]

Thanks for posting after you found the root cause. Do you think the ring was bent when installing on the piston?

Is it a coincidence the aluminum transfer is below the bent ring end?

Did you change the jetting between the first post to the photos ones on page 3 after the teardown? The Mag side still looks lean. PTO looks OK, on the safe side of rich.

John Ziegler - good call on this one with your prediction!

The bent ring was definitely my fault, I must have caught it when dropping the cyls and not noticed. The aluminum transfer was on the bottom because the stuck ring was cocking the piston to one side, so that the skirt on the opposite side was rubbing the cyl wall the whole time.

I have not changed jetting jet. I went through the carbs before I reassembled and they are super clean inside and out, I made sure all the passages were clear, and adjusted them to the same specs. After a break-in run over the weekend I'm still lean on the Mag, and good on the PTO. Right now Im at 1-1/2 turns out on the highs with 142.5 main jets, and 1 turn out on the Lows with 75 Pilot. Im going to try another half turn on the MAG, but I still don't understand why that cyl is burning leaner.

I tested comp again and now I am at around 190 on both cyls with the MAG reading about 5 psi lower, which I attribute to the rings still wearing in.

 

[mbrick]

You should wait for the experts to chime in on the jetting, because that's not me.

As a reference, stock 701 H is 1-1/8(F) and 1-1/2(R) showing they expect one cyl to run slightly leaner. Opposite of your lean Mag though?

 

[Fro Diesel]

I have some 82mm rings i will send ya fo free. Send me an address if you need them still