SOHC.co.uk Forums > CB350/400
CB400/4 ENGINE STRIP, ASSESSMENT AND REBUILD BY JULIE - NOW COMPLETE
Green1:
I was thinking about the damaged pistons today and remembered my 2stroke Go kart had almost identical damage except the rings stayed in one piece. It was running far to lean due to a damaged diaphragm.
My brothers KH125 did exactly the same thing when his mates fiddled with the carb aswell
K2-K6:
Now there's a bunch of people that work more closely with detonation Mick. They often use different shaped combustion head shapes with differing squish bands to control it.
It's often seen on isolated or any number of cylinders on V8 cars running high power setups. It's by no means odd to get some cylinders to detonate and some not even when all running through one carb.
Those applications they try and get all the spark plug electrodes facing the same way in the heads to avoid any masking of the spark if not facing the flame advance direction of combustion.
mike the bike:
How did the piston rings get like that I wonder. I can understand them snapping when installed, or when the barrels are fitted, but once fitted, how would they break?
K2-K6:
I think you're entirely right Mike.
If you look at the pistons and the witness marks that have been carved out of them by the rings then you can see in some of them where the piston land material has let go, this has resulted in the part of the ring that's still attached to bend and flex in an arc which has cut a corresponding hole at its free end that looks like a metronome.
To me this illustrates that the piston material went soft through heat and prior to the ring being broken. Under extreme heat exposure the rings can anneal as well. Spring steel is annealed by heating up over critical temperature, but not melting, then leaving to cool gently over a period of time. As opposed to hardening via heat and sharp quenching.
Nurse Julie:
Thanks for answering Mikes question K2-K6. I have been thinking all day about the reasons for the broken rings. I was swaying between the damage to the top of the pistons causing the rings to break or the rings breaking first and leading to the damage to the top of the pistons. But, my extremely limited knowledge of these things, which quite honestly, would fit on the back of a postage stamp, meant I did not know the answer for certain. I was hoping someone like you would come along to explain....and you did. Thank you.
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