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happypig
08-24-2010, 10:24 AM
After 5500 trouble free miles on a completely rebuilt 46 knuckle engine (74"). I started to hear a slight noise in the front cylinder… before I got home the noise was louder (piston slap) and I could hear a squeak. Pulling the top end off I found the piston pin bushing had turned in the connecting rod and the front piston and cylinder were scuffed. Everything looked normal in the rear cylinder.
I had the front cylinder bored out 0.010” over and installed a new piston, rings, piston pin, and bushing. The rear cylinder was honed and a new set of rings installed. I drove the bike less than 20 miles and started hearing a noise like a leaking head gasket. Before I could pull over the bike started losing power and shut off. I couldn’t turn the engine over with the kicker until it cooled down. The front cylinder was quite cool... the rear was very hot.
I pulled the rear cylinder off last night. The head gasket was blown and the rear piston and cylinder are scuffed. I haven’t removed the piston yet, but the pin is squeaking in the bushing. Both times I dismantled the engine, the piston, cylinder, rod, etc seemed quite dry… though this could be from the heat.
Does anyone have any idea what might have caused this? Could the turned piston pin bushing in the front cylinder and the blown head gasket in the rear cylinder just be two isolated incidents?
Thanks.

Jim

koanes
08-25-2010, 07:49 AM
It sounds like you are having problems with oiling or you have a very lean fuel mix causing the heat to build. Having wrist pin bushing seizure would point towards oiling trouble.

happypig
08-25-2010, 07:56 PM
Thanks Kyle... I agree it does look like a problem with oiling. Any idea what could cause a lack of oil to the cylinders.

It sounds like you are having problems with oiling or you have a very lean fuel mix causing the heat to build. Having wrist pin bushing seizure would point towards oiling trouble.

MJW
08-25-2010, 11:13 PM
Was the slot in the bushing aligned for oil passage to the pin? (before she spun) Possibly a dirty jet causing a new lean mix? Manifold leak?

happypig
08-26-2010, 05:50 AM
Thanks MJW.
The slot in the bushing was aligned when the engine was assembled.
It is possible there was a manifold leak. I am using peek seals... and I didn't test for leaks when it was assembled the last time. The engine started, idled and ran flawlessly right up to end.
The plugs don't look like the gas mixture was too lean.


Was the slot in the bushing aligned for oil passage to the pin? (before she spun) Possibly a dirty jet causing a new lean mix? Manifold leak?

T. Cotten
08-26-2010, 11:40 PM
Happy Pig!

Shame on you for not testing upon assembly.

If you did not find heat signatures within the combution chamber, then certainly the problem came from below.

If I had something to bet,
it would be upon an un-straighten'd-and-align'd rod.

But then never does only one thing go wrong at a time......!

....Cotten

happypig
08-29-2010, 12:11 PM
Thanks Cotton... I almost didn't admit to not checking the carb for air leaks...LOL.
I'm not seeing any heat signatures in the combusion chamber...
The rods were checked before reassembly...


Happy Pig!

Shame on you for not testing upon assembly.

If you did not find heat signatures within the combution chamber, then certainly the problem came from below.

If I had something to bet,
it would be upon an un-straighten'd-and-align'd rod.

But then never does only one thing go wrong at a time......!

....Cotten

happypig
08-30-2010, 03:12 PM
Thank you all for your help...

The problem has been resolved. The pinion shaft bushing had turned in the gear cover shutting off the oil flow through the shaft into the cases.

Jim