Is this a sign of overheating or is this the way a piston with lots of miles should look? The smallest feeler gauge I have is .008 inch. That's the one I've got inserted into the ring. Very snug fit. Won't fit into any of the other ring grooves so i will have to invest in a smaller set feeler gauge. The manual says .003 - .005 inch.

 

.008 is on the loose side my guess its probably .0065 with the correct feeler gauge - as you said its a tight push in fit - hair is .007 thick

overheating always involves the thrust side of the piston has damage usually the back side of the front piston

you might what to replace them after you have the cylinder roundness checked - a bore gauge is the only way to see if its round

 

History-In the old days we could shim rings .
Your pistons are shot.
Most real engines want no more the .004
No matter what HD allows, don't listen.
Get new.
You will anyway once the bore is trued up.

 

I would gat a pair of vernier calipers and measure the ring lands and then measure the rings.. I'll bet you'll find the outer edge of the ring has a very tiny lip and is thicker than the inner part of the ring that goes into the land... Anyone know what the ring thickness should be? It might help the OP to determine if it's just rings... Pistons might be ok.. And yes, as john indicated about the bore, You should have it checked....

 

Have a machinist with a proper dial bore gauge measure the bores and check for taper. The piston is done and the bore is tapered (rings wear on bores).

When it's top end time on any ancient air cooled bike (my personal fossils are HD and British and I'm an old multibrand mechanic) it's typical best practice to do a rebore and valve job for longevity. Ring jobs alone on all sorts of engines were common when the US was poor but are rightly rare today because they are a short-term fix.

Check your connecting rod bushings and bottom end since the top end is off.

 

It's been over 30 years since I have torn an engine down, don't recall seeing pistons with such a 'burnt' look. I've got access to dial bore gauges. I'm planning on a complete rebuild. There is a LOT of play in the connecting rods. I've already ordered the first 'special tool' i need which is the pinion gear puller ( and a smaller set of feeler gauges ). I appreciate all the help, thanks

 

There is either a shine to that pic, or that piston had a slap going for it.

 

actually that is quite normal - the rod stroke ratio is 1.87 and the rod is 7.440 long the thrust side front and back always gets that mainly because the cam grind of the piston is steep - its the way they do it

 

Not sure i understand this "rod stroke ratio"? If the rods are 7.440" long and i divide by 1.87 that tells me my stroke would be 4" (3.9786) My stroke is actually 4.25". What part am i not understanding correctly?

 

Yea after a LOT of miles, and I, and we have to presume he is not asking about pistons and overheating in that situation.
So if these are in a newer rebuild there is a LOT of wear going on there.
I kind of sort of perhaps understand Rod ratio- Currently putting halve inch longer rods in this other HIPO engine we have going together here.
The longer the better usually.