R60 to R75 barrels.

[bluboxer]

Good day all,
I am trying to determine if a R60/5 barrel can be bored out to 750cc. Anyone done this?
Alan

[Garnet]

R75 standard pistons are 82mm. You need to measure the OD of the steel liner. It will need to be at least 85mm OD to be safe. It will cost a lot more than a normal bore job do drill out the 6mm to get to 82.

[Max Headroom]

I recently did an R60/5 - 750cc conversion for a guy. He's owned the R60/5 for 30 years, (bought it in the USA on an extended trip as it happens) and he had assumed that the 26,000mi on the speedo was original when purchased. When the bike began using lots of oil recently at 46,000mi, he pulled the barrels off and brought them to me for measuring. They were too worn to accept a re-ring successfully, so i suggested a s/h set of low-mileage 750 pistons, barrels, heads and carbs I had in stock as a cheaper alternative to reboring with new o/s pistons. He agreed, and is very happy with the result.

I'm not certain that the R60 barrels can be machined out to suit 750cc pistons successfully, 'cos the barrels are a different casting. I am fairly sure we considered that option and discarded it.

P.S. As an aside, we now reckon that the true mileage is probably 146,000mi, given the amount of wear in the R60 bores and even that is based on the uncertain assumption that the speedo is original . . .

[bluboxer]

Thanks for your comments.
My problem is that I have a NOS set of stock pistons and at 300 bucks ea. for pistons it is a shame that I can't do anything with them.Maybe this is why I got them for a song!

[Duane Ausherman]

From some distant memory, I seem to think that the steel casting doesn't have parallel outsides. I think that a bore to 82 mm will break through. I have no proof, or have tried it.

I would not try it. I could be wrong.

[Major Softie]

From some distant memory, I seem to think that the steel casting doesn't have parallel outsides. I think that a bore to 82 mm will break through. I have no proof, or have tried it.

I would not try it. I could be wrong.

I don't know about breaking through, but the different thicknesses can lead to a waviness in the cylinder wall if it's too thin. I know that's been a reported problem even for some going to +2 or (especially) +3 oversize bores.

[bluboxer]

Well that answers that,thanks for the help.
Now,is there a company that can install new liners?

[Garnet]

Well that answers that,thanks for the help.
Now,is there a company that can install new liners?

Yes there is, I just don't have it at my finger tips, someone will chime in.

Did you ever mesaure the thickness of the steel liner? And is the spigot part that goes into the block all steel, or is the outer part of the spigot aluminium?

[wirewrkr]

From some distant memory, I seem to think that the steel casting doesn't have parallel outsides. I think that a bore to 82 mm will break through. I have no proof, or have tried it.

I would not try it. I could be wrong.

Actually Duane the older cylinders do have parallel liners, I cut one in half last year as well as an hour-glass shaped R80 cylinder.
the liner on the R60 is 5mm (ish) all the way through, boring to 82 would leave way too little meat. Probably distort.
Same on the R80, at it's thinnest point it was around 5mm.
Somewhere in my computer I still have the pics.
We successfully have bored Std R80 cylinders up to std R90. (85-90mm)
any more would be foolish.
Also still have the jugs, but they are lost in the mess, as I just moved.