Little advice re:r100 cylinders

[lrz]

Howdy all; been working quite a lot,not riding,etc; hope everyone is well.

For a variety of reasons I'm thinking to swap my current 100/7 cylinders for another(used) pair.

What can I use?
For example, would the post '81 nikasil cylinders be appropriate? (I understand these would need the correct rings/pistons)

Or do I need pre-'81 ?

Or will any/all stock 1000cc cylinders work?

[mattcfish]

Howdy all; been working quite a lot,not riding,etc; hope everyone is well.

For a variety of reasons I'm thinking to swap my current 100/7 cylinders for another(used) pair.

What can I use?
For example, would the post '81 nikasil cylinders be appropriate? (I understand these would need the correct rings/pistons)

Or do I need pre-'81 ?

Or will any/all stock 1000cc cylinders work?

Post 81 Nikasils would be great. Your pistons will work if they are the right size for the new bores, you need to change to Nikasil compatible rings.

[vanzen]

I think that there may also be an issue of the large "O-Ring" used on the base of the Nik Cyls,
and the lack of a chamfer cut into the spigots of the early case ...

[Rob Frankham]

Your pistons will work if they are the right size for the new bores, you need to change to Nikasil compatible rings.

I think we need to qualify that a bit. There are no fewer than 6 different piston sizes for the 1978 1000cc engine. Thats three for standard bores and three for first 1st oversize. 2nd oversize wasn't recomended for 1000cc engines but it was done by some rebuilders which potentially makes 9. The chances that the pistons you have will fit the later cylinders are, therefore not good.

Rob

[mattcfish]

I think that there may also be an issue of the large "O-Ring" used on the base of the Nik Cyls,
and the lack of a chamfer cut into the spigots of the early case ...

Roger that. My aftermarket Nikasil Barrels were made without the o-ring groove. They were designed to be mounted without base shims either...just the appropriate silicone sealer. Couldn't o-ring jugs be mounted to earlier R100 cases using the same method (sans o-ring)?

[mattcfish]

Your pistons will work if they are the right size for the new bores, you need to change to Nikasil compatible rings.

I think we need to qualify that a bit. There are no fewer than 6 different piston sizes for the 1978 1000cc engine. Thats three for standard bores and three for first 1st oversize. 2nd oversize wasn't recomended for 1000cc engines but it was done by some rebuilders which potentially makes 9. The chances that the pistons you have will fit the later cylinders are, therefore not good.

Rob

If he somehow happens to have the original R100 pistons (no bore over), then his chances are much better. I don't have the figures in front of me http://w6rec.com/duane/bmw/engine.htm. The Nikasil barrels require a tighter fit than iron bore....finding the right barrels for the old pistons would require some accurate measurements. Luckily, used piston/barrel
sets come up on eBay pretty regularly.

[John Falconer]

The chamfer is important. If you don't do it the Nikasil barrels won't seat properly, and the flat surface of the flange won't come in contact with the corresponding milled area on the crankcase. You can do it, without removing the crank, carefully with a scraper (from back in poured babbit main and rod bearing days) but it would be crazy to try and to it with the motor in the bike; at least too much for me.

[mattcfish]

The chamfer is important. If you don't do it the Nikasil barrels won't seat properly, and the flat surface of the flange won't come in contact with the corresponding milled area on the crankcase. You can do it, without removing the crank, carefully with a scraper (from back in poured babbit main and rod bearing days) but it would be crazy to try and to it with the motor in the bike; at least too much for me.

Sounds like a can of worms. Maybe this is a better route if you want Nikasil on an older block. http://www.motoren-israel.com/product_i ... -1980.html

[Major Softie]

How come they fit R75/6, R75/7, but not /5? What change causes the difference?

[mattcfish]

How come they fit R75/6, R75/7, but not /5? What change causes the difference?

Bikes before 9/1975 have 97mm instead of 99mm cut outs in the block. But all is not lost, you order this kit.....http://www.motoren-israel.com/product_i ... -1975.html
That's what I needed. Very happy with the results.