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On my 95 R100 Ive fitted a 336 cam and nice extracter and sports muffler in place of the standard collector box,anyway its goes well strong from 4000 thou up.But now Ive got a pair of earlier heads with 44mm inlet valves(mine are 42mm)Im thinking of trying them on but first I,ll put back the stanard 308cam as Im concerned about the valves clipping with the longer overlap 336cam,also will be putting in a pair of 9.5 comp pistons.So basically what Im asking is what would be the best combination 42mm /336 cam or 44mm/308cam the pistons are going in whatever as its only 8.5 at present
Cheers mitch

You didn't say what the engine is to be used for so "best" will vary.

If you are building an all out racing motor (4000 rpm and up) go with big valves, big cam, free breathing exhaust, 40 mm carbs and more compression ratio always helps. If you are building a touring motor, go with the small valves and intake runners, 32 mm carb, use the 336 cam if it is the newer one with the 3 degrees advanced timing (intake closes 6 crank degrees sooner than the earlier cams) stock exhaust and 9.5 compression. If it's for a commuter in town..same as touring except 308 cam and stock compressiom.

I should of said the bike will be used for touring so I will try it leaving the 336 in with the smaller valves and the standard 40mm bings.When the pistons arrive whats a good way of measuring the depth of the valve cut-outs against the standard BM piston,I want to measure off the gudgeon pin (wrist pin.us) as the crown and skirt lenth will be different .The pistons are from Motor-Israel, bit late to ask now but any bad reports.

mitch wrote:I should of said the bike will be used for touring so I will try it leaving the 336 in with the smaller valves and the standard 40mm bings.When the pistons arrive whats a good way of measuring the depth of the valve cut-outs against the standard BM piston,I want to measure off the gudgeon pin (wrist pin.us) as the crown and skirt lenth will be different .The pistons are from Motor-Israel, bit late to ask now but any bad reports.

95 standard carbs were 32mm weren't they?

40mm on mine

Don't know what measuring tools you have.

Put a wrist pin in each side of the piston. set each pin in a vee block sitting on a flat plate (piece of granite cabinet top will do) use a height gauge to measure the difference between the top of the wrist pin and the bottom of the valve pocket. Do this with the old and new piston. Compare the two dimensions.

The 336 cam and big valve combo works, and well ...
but not necessarily without some planning & modification.
Information here: courtesy of John Falkoner

I would not assemble an engine on the basis of trusting knowledge gained from internet hearsay –
MEASURE operating clearances for yourself to know that what you got will work.

A wealth of information thanks a lot!

Pity someone hadn't sent the cam installation instructions to Wossner - the pistons that they supply to M.I. have square cut valve pockets and on my GS didn't maintain the squish band parallel.