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Thread: R90/6 cylinders and pistons: What will interchange? R100/?

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    R90/6 cylinders and pistons: What will interchange? R100/?

    This is what I would like to do: My R90/6 smokes a little more, struggles a little more, etc. I would like to refresh the top end. However I would like a little more guts so I would like to swap out the cylinders and pistons for those from an R100/whatever. Can I swap out cylinders/pistons from some of the later models in order to take advantage of the nikasil cylinders? Maybe a better question is what WILL NOT bolt on? Can I still use the R90/6 heads with an R100/? and also would anybody recommend a place that you can send your heads out to to freshen them up (newer hardened valve seats,etc.)? Thanks for your brain power and expect even stupider questions to follow! Bob h.

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    What year R90/6? Beginning with the 1976 models, the engine case opening increased from 97 to 99mm. Thus swapping can be an issue if you're on the wrong side of this.

    I would think that use of an R90 head with later pistons might not get you everything you need when considering piston shape (squish bands or not) not to mention the different sized carbs. You're going to be pulling in more air, so there needs to be some consideration there, too.

    I just did a top end on my /7. I used Ted Porter for my head refurb. My cylinder was out of spec and I chose not to try and go 1st over. I ended up buying from Ted the Sienbenrock 1000cc kit for my bike. I really like what it did to the way the bike runs.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    I think I'm on the right side of this, I have a '76. The Siebenrock kits look mighty tempting the only problem is money. Although I am very hansom, I'm not very wealthy. I'm not ruling out the possibility of a Siebenrock kit it is just that hiding the $1000 expenditure from my wife would be more work than actually going out and earning the extra $1000.

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    Certainly, money is at the heart of it. If you can get used parts for cheap and they don't need any work, that might be the way to go. But my guess is after the cost of the cylinders, pistons, rings, wrist pins, possibly some machine work to get things in shape, you're still going to spend some money. You just have to see which works out the best.

    I'd like to hear someone else weigh in on the mixing of R90 heads with R100 pistons/cylinders.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Didn't the 900s and 1000s have the same valve diameters? 42mm intake, 40mm exhaust? Weren't the heads the same for both 900s? Squish bands? Would have to be measured? Someone must have the info at the ready.

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