85 FLTC So finally got time to start tearing into the engine the other night. Everything was going good until..... see attached I took the rear jug off and saw this! Just wondering if anyone has ever encountered this before? The jug it self is perfect I can still see the cross hatch pattern. This was a barn find so I knew going into it I would more than likely run into something eventually. The rest of the top end is pristine just this back piston. Should I continue with tear down and split the case to see what else I might find? Just looking for some insight here. You guys have been great on advice that is why I am reaching out.

 

Without any input from the rider of this bike my first guess would be detonation as the culprit, and the cause of that could be be a number of things. It don't look like anything foreign went through this lung. Do you have any info on what this engine was acting like prior to the teardown?

 

Photo of the plug would help. Ceramic and the electrode. Photo of the head also. A plug that has peppering (small black dots) on the insulator is a sign of detonation. Those dots are aluminum deposits. Do you see peppering on the ceramic?

Is this the condition of the piston as you pulled the head & barrel, or have you removed carbon build-up before the photo was taken? Absence of carbon may indicate a lean condition or very little run time.

Seeing the piston damage alone would not prompt me to tear it down further.

Here's a sample of damage caused by detonation. Look familiar?

 

as long as the bottom end feels tight ... no slop in the rods or crank ... there would be no reason to split the cases

 

A small piece is stuck in the valve relief, the valve may have hammered it.
Did you happen to do a compression test before tear down? With those domed pistons, and the wrong cam, the compression ratio may be out of range for pump gas, .
You can plug info in here and calculate compression
http://www.bigboyzheadporting.com/EVOComp.htm

 

Detonation for sure, if that was a forged piston it looks like an old beat up cast now.. That looks like at least 11-1 piston that had either too much timing not enough fuel or the squish was too big. Don't believe it was set up right..

As said if you have a FSM check the rods if within spec leave it alone.. Wonder what cam was in there along with head work.. pics would be nice as well as mileage, model and year..

 

85 fltc 35,000 miles. I have not cleaned anything up these were raw photos as I took apart the ole girl. I do not know how it ran before buying it. I know the owner but it was his sons. I will try and see if he knows anything. So here is the real question would I just be $ ahead and just buy new stock heads and jugs and be done? The front jug and piston are really clean I will take pics later of that. Thanks for all the help so far.

 

I agree with the detonation remarks, but that chunk missing looks like it tried to ingest something like a air cleaner nut or bolt? (sparky0496 first pic). Anything going on with the combustion chamber in the head? YD
EDIT: OK now I see the pics of the head...

 

Definitely a bit of pepper on that porcelain.... As for the heads they're untouched. They look pretty much stock and definitely blew out a head gasket. Somebody was using OEM style head gaskets.. They should have went to an MLS. I think you'll be okay to get the heads worked. I don't understand why somebody would up the compression like that and not at least go to bigger valves doesn't make sense.. Because the combustion chambers look stock the squish was actually pretty big which probably helped create more detonation. You can have them worked no problem... You don't need to get another set of heads... But take them to your local Indy and let him make that decision but they look pretty good to me.. looks to me your damage is minimal so I would think a bore in a set of pistons and you'd be good to go..

 

Thanks so much for all of the insight guys! I will update later on this issue. I just want to run a stock setup not into more power anymore just wanna cruise down the road and enjoy life on life's terms.