Motorcycle Repair: FLH burning oil, blown head gasket, hole ring

Question
QUESTION: Hi Mike

Bought a FLH year 77 a while ago . 1200 cc .It had top ends done recently.
Then after a while i discovred that it was leaking oil out on front cylinder , - between top end and cylinder .

So we got a blown head gasket :) spark plug was oily burnt

I took the things apart .

Piston measures 87 mm in diameter (im Danish you know ... metric system ) :) which means ? what size do i then have in cylinder ... ? still 1200 cc ?
well ,- it looks like head gasket was blown at one of the cylinder bolts , - a clear passage was visible on the gasket .

Valves clearly carbonized of burnt oil . Top of piston clearly carbonized of burnt oil.
Theres a "ring" around the cylinder/chamber wall that fits up into the top end ..... it looks like oil has been burnt "over" that ring ???the hole ring is full of carbonized oil... which looks like that this ring obviosly doesnt fit completly tight up into the top end !! It was clearly James gasket that was used ... maybe the thickness of this gasket affects that the ring on  the cylinder doesnt get properly up into the top end ?

I poured gasoline on the closed valves to see if they are leaking ... they were not leaking , no gasoline got away

I poured gasoline on the top of piston in the cylinder , - to see if it ran beside the pistonrings , -  .... it did not ..

Next thing to check is the nylon bushes for oil leaking by there ,-  at the valve guides ? Is there an easy trick for this ?

Where do you think the oil is coming from into the ignition spark area combustion chamber ?

Another thing is .... when does a piston look worn out ? My piston looks "used" at top sides  and bottom sides of it .. at the surface .. you know ... i know a piston is "oval" in shape ..

No burns down at sides of piston .... which indicates okay tolerances ???

Please help :)

Regs
C

ANSWER: First, you have a 1200. Standard bore is 3.438. Yours is 3.425.
Now what you need to do is mic the skirt of the piston and then, using a bore mic, check the cylinder. The cylinder has to be bigger than the piston or it will lock up. You are allowed .0025. If the cylinder is bigger than that then you have to bore the cylinders to the next bigger piston and hone it. Micing it is the only way you will know if its in tolerence.
Same thing with the valves. You have to mic the valve and then the valve guide to see if they are within tolerence.
Good luck and happy riding
Mike

---------- FOLLOW-UP ----------

QUESTION: Hi mike
Thanks

Do you think its possible to buy new pistons at same size as the old ones , and just replace them in the cylinders ?

What do you think about the carbonation over the ring as i describe ?

regs
C

Answer
If the cylinders are to big you will not accomplish anything. You need to mic the pistons and cylinders. That is the only way to do it correctly.
All shovel pistons will get some carbon on them. It is due to incomplete burning of the fuel.
Your oil burning is either from oil getting past your rings or oil getting through the valve guides.
Good luck and happy riding
Mike