Piston Upgrade to a R75/5?

[Chuey]

Since you have to farm out the work, why not go to one of the recognized experts? I had Ted Porter do the machine work on my R90S and he sure seems to know what he's doing. I don't know if Robert Grauer does cylinder boring but if he does, he'd be another person worthy of trust.

Chuey

[jjwithers]

Buying a used set of Nikilsil r80 cylinders and Pistons, would be cheap enough, lots of people are fitting 1000 cc seibenrock cylinders and Pistons to 800s. You will have to relieve the crankcase opening.

R80 cylinders will not fit in a R75/5 case. Different spigot hole sizes.
I'd go with Siebenrock but I want to build this engine on the cheap.
I'm hoping I can keep my cylinders, bore them to match some larger pistons, and get this bike back on the road.

[Roy Gavin]

My 75/7 was bored out to 900cc about 10 years ago, with no problems, but the guy who did it was an airhead and had a rig set up, with both torque and heating being applied.

I have also seen two sections through BMW barrels, one of them had a ribbed Alfin finned liner, the other just a cast in parallel sleeve, and would think the Alfin barrels would take to boring a bit better, but you would want them hot while reboring.

[robert]

My 75/7 was bored out to 900cc about 10 years ago, with no problems, but the guy who did it was an airhead and had a rig set up, with both torque and heating being applied.

I have also seen two sections through BMW barrels, one of them had a ribbed Alfin finned liner, the other just a cast in parallel sleeve, and would think the Alfin barrels would take to boring a bit better, but you would want them hot while reboring.

So, do you heat the piston, bore guage, cylinder, boring bar and the hone to the same temp. while this is all happening?

[Roy Gavin]

Air cooled cylinders will distort when they are heated, as it is virtually impossible to cool them evenly, even with ducted fan cooling.

So you heat / torque plate them to try to replicate the distortion in a running motor - it probably isn't going to be perfect but it will be better than trying to bore them cold/untorqued, which doesn't seem to work at all well.

[robert]

Air cooled cylinders will distort when they are heated, as it is virtually impossible to cool them evenly, even with ducted fan cooling.

So you heat / torque plate them to try to replicate the distortion in a running motor - it probably isn't going to be perfect but it will be better than trying to bore them cold/untorqued, which doesn't seem to work at all well.

You didn't answer my question.

[Chuey]

Does the factory heat cylinders when they bore and hone them as they are making them in the first place?

Chuey

[Major Softie]

Air cooled cylinders will distort when they are heated, as it is virtually impossible to cool them evenly, even with ducted fan cooling.

So you heat / torque plate them to try to replicate the distortion in a running motor - it probably isn't going to be perfect but it will be better than trying to bore them cold/untorqued, which doesn't seem to work at all well.

You didn't answer my question.

Your question appeared to ridicule the idea, and he responded quite accurately to that. The specific answer to your question is: no. The cylinder is heated to the temperature it is designed to operate at, and the mill is kept at the temperature it is designed to operate at - both for the same reason.

Does the factory heat cylinders when they bore and hone them as they are making them in the first place?

Chuey

Good question, Chuey, but the thinner the sleeve gets, the more important one might imagine this to be. The factory might well have bored them hot, but I really don't know.

[robert]

........The cylinder is heated to the temperature it is designed to operate at, and the mill is kept at the temperature it is designed to operate at - both for the same reason......

If you heat the cylinder you would have to heat the piston, micrometer, and bore guage to exactly the same temperature
all the while it is being machined for correct piston fit. Don't think you want to be wearing oven mitts around operating machinery.

[Major Softie]

........The cylinder is heated to the temperature it is designed to operate at, and the mill is kept at the temperature it is designed to operate at - both for the same reason......

If you heat the cylinder you would have to heat the piston, micrometer, and bore guage to exactly the same temperature
all the while it is being machined for correct piston fit. Don't think you want to be wearing oven mitts around operating machinery.

I understand your point about the piston, but the part about the measuring tools is obtuse.