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Old 01-26-2013, 02:10 PM   #1
flexfoot OP
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R90/6 Engine Issues

1974 R90/6 with 140k miles. Needs timing chain replacement in addition to valve/cylinder work. I sent the heads and cylinders to Randy Long. He can repair the heads OK, but the cylinder and pistons are out of spec. First over size pistons are $365. each..... OUCH! Cylinders need boring also. I was thinking that spending nearing $800.00 for pistons is not an option.
Any thoughts? i was considering a 1000cc kit for $1200. Does that make sense? I am on a budget, and I really don't have big bucks for this. Will R90S pistons work? Thanks in advanced for your wisdom!


Steve
74 R90/6 sidecar
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Old 01-26-2013, 03:31 PM   #2
bmwrench
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There are several options, but one that you should probably rule out is the Siebenrock kit. They don't offer-as far as I can see-a small spigot cyinder. Another option is plating the cylinder back to standard. That runs $200.00 plus per cylinder.Then you'll need rings, too. You could try to find some used oversized pistons, or a set of low-mileage standard cylinders. Or you could get a set of my 92mm pistons. Yes, R90S pistons will work, too.
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Old 01-26-2013, 04:46 PM   #3
Kai Ju
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Used ?

http://tinyurl.com/bc8ku9h
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Old 01-26-2013, 06:04 PM   #4
disston
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There are several things that you may do. To get started understand first off what you are dealing with. The Airhead type 247 engine went through many changes in the 25 years of manufacture and one of the first changes of a major concern you have run smack dab up against. The engine you have uses the 97mm spigot cylinders. From the beginning with /5s and through model year 1975 all the Airheads have the 97mm cylinders. Then beginning in model year 1976 the cylinder spigots got bigger and the holes in the block for the cylinders to mate with got bigger. In 1976 until the end of production the spigots are 99mm. The Ebay auction posted by Kai Ju will not work. Unless a bunch of expensive machine work is done. (more on this later)

You may get lucky and find a used set of cylinders and pistons but these items are getting harder to come by and many times the cost of this used stuff is not a bargain. It happens but you need to know what you are doing and even then it's a gamble that something bought on the web is truley what it is represented to be.

I would look for a first or even second over sized used set of pistons. Your current cylinders can be bored for these and if good enough pictures are taken you should be able to see the condition of pistons. You mentioned a set of R90S pistons? This would work and give more compression. The cylinders would need boring to fit. You may want to add a shim or two to the base but consider all the factors first.

Sometimes riders want to put the much later Nikelsil cylinders on these early bikes with the 97mm spigots. The spigots can be turned down if a knowledgeable machinist is found willing to do the work. It is apparently not as easy or cheap a job as it sounds like to us novices.

Tell us more about the R90S pistons?
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Old 01-26-2013, 07:21 PM   #5
testa d'aria
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The Siebenrock kit is available for the 97mm opening. Not cheap, but it is an option.
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Old 01-27-2013, 02:39 AM   #6
chasbmw
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Go to the Motoren Israel website in Germany, they sell 1st and 2nd oversize modern lightweight pistons for the 900s, I have them fitted to my R90 and it is a very smooth engine. The compression ratio is highish at 9.5:1. The cost of a pair of pistons is around 360 euros including 19% tax, if you are ordering from outside Europe you don't pay the tax.

Worth thinking about
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Old 01-27-2013, 08:10 AM   #7
DiabloADV
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Quote:
Originally Posted by testa d'aria View Post
The Siebenrock kit is available for the 97mm opening. Not cheap, but it is an option.
I got the 97 kit for my r90. It was around $850 shipped. Cylinders, pistons, rings, pins, clips, gaskets... About the same price as pistons, pins, rings and machine work.
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Old 01-27-2013, 02:09 PM   #8
flexfoot OP
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R90/6 Engine Issues

Thanks, guys for all the info. I can purchase first oversize pistons for $740/pr from Capital Cycle, but heck, that is still a small fortune. Then I have to have the cylinders bored and nikasiled. The coating alone is $400. for the pair plus boring is two hundred bucks. Then I need rings, wrist pins, clips, gaskets etc. What would you do in my situation? Thanks in advance for all your combines wisdom...........


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Old 01-27-2013, 03:27 PM   #9
disston
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New pistons come with rings and wrist pins. Always. If somebody is trying to sell you new pistons with out rings and wrist pins there is something wrong. Don't buy. Evan CC knows this. Make sure Tommie verifies your order if you order from them. Order over the phone. Don't call too late in the day. And tell Tommie I said Hello. The name is

Charlie
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Old 01-27-2013, 04:42 PM   #10
flexfoot OP
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R90/6 Engine Issues

Is there a place in the USA to buy the Siebenrock kit? I don't see the 97mm, 1974 kit on Motoren-Israel.
Thanks.



Steve
74 R90/6 sidecar
09 F650GS Twin
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Old 01-27-2013, 05:03 PM   #11
testa d'aria
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I bought mine from the Beemershop. Ted Porter will answer any questions you might have before or after your purchase - very helpful. The version he sells includes the ss pushrod tubes. Plug and play, although you'll need the larger pushrod tube seals as well as gaskets.
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Old 01-31-2013, 05:16 PM   #12
flexfoot OP
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R90/6 Engine Issues

I have purchased a pair of used pistons off the IBMWR site. Hopefully they are good. The plan is to have the cylinders nikasiled and hopefully everything will turn out OK. I have Randy Long in Honeybrook,PA doing the machine work. I understand he is the best.



Steve
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