O-360 pistons

caryr · #1 08-11-2009, 06:37 AM

These are from a O-360 200 SMOH

What do you think caused this?

osxuser · #2 08-11-2009, 10:02 AM

It looks like it got kinda hot. For 200 hours, it also looks like there was quite a bit of blow-by. I'm guessing that it was an overhauled cylinder/piston at 200hr not NEW? If it's new, you definitely need to contact the manufacturer... if their still in business.

My initial diagnoses would be poor inspection at overhaul, assuming it wasn't new.

664781 · #3 08-11-2009, 10:07 AM

Cary,
Looks like an inclusion or void in the raw stock. If the other pistons came from the same batch I would change them out. Mfg. flaw.

mahlon_r · #4 08-11-2009, 10:41 AM

Cary,
The erosion/ burning on the piston, in the last picture, looks like damage from
detonation. Too hot intake air, bad gas, low octane gas, advanced ignition
timing, wrong heat range plugs could be the cause among other things. The ring
looks like it broke due to being stuck from carbon build up in the ring land.
That is normally caused by too much heat cooking the oil causing the carbon
build up. The ring land can breaks due to the ring breaking.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully
helpful to you. Please use the information provided responsibly and at your own
risk."

caryr · #5 08-11-2009, 11:03 AM

all the rings were intact. the part laying out in the pic is a piece of the land.

It was a NEW Superior Millenium cylinder/piston/rings.

I think Superior is gone, isn't it???

I was running on the lean side of normal for some time before I rejetted it last spring.

enlarging the main carb jett inproved the temp issues. but the damage may have already been done.

I am thinking mechanical fracture also. Bad piston machining?? Maybe I broke it sliding assembly into cylinder?? But both #3 and #4 ???? Maybe not.

erosion in the area could have happened after the blow-by started. explosion going to weakest path.

Inside of the cylinder looks very good. almost new. valves look good.

F1Boss · #6 08-11-2009, 02:39 PM

Detonation: look how the carbon/lead deposits wrap around the side of the piston. Keep those CHTs below 400F (lean OR rich) and there won't be any detonation....

If you want to run LOP, I'd recommend 2 things:
A good engine analyzer w 4 cyl EGT & CHT
Fuel injection

Kinda hard to do it without both on the engines we run, unless your engine happens to be round.

Fix it, and move on. And, remember that 400F CHT limit.

Carry on!
Mark