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Old 05-12-2012, 09:34 PM   #1
DiabloADV OP
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Is my cylinder toast?

I've been tearing down a 74 R90/6. It's been good news at every step...heads are in great shape. Clutch looks new. Conrods feel perfect. One cylinder had a greasy smear on it -- evidence of when it sat for five years. Like a little puddle of fuel had sat there and left a varnish.

I got around to soaking and cleaning that cylinder and the smear of varnish turns out to be etching of the metal.




It's not deep, but it is a definite etching of the surface. Feels rough to the touch.

Am I screwed here? BTW -- these are R100 cylinders that I found in my R90 bike, and I hear that R100 cylinders are not to be overbored. What's my next step (if these are toast)? Find new cylinders? R90? Look for a Nikosil set...? HELP.
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1974 R90/6 w/1050 kit. Motor only. Seeking a frame.
1970 R60/5

'91 Bill Holland Steel w/Dura Ace
'01 Z3 3.0 Coupe. The Clownshoe.
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Old 05-12-2012, 09:41 PM   #2
Wirespokes
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It's not hard to find cast iron R100 cylinders. And they're not expensive either. The cylinders can be bored, but you'd better make sure the shop has bored BMW cylinders before, otherwise they might give you back trash.

That said, I'd get them nikasil plated. They can plate to match your pistons.

Otherwise, replace them with a good set of nikasils - they come up fairly often for a couple hundred bucks.
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Old 05-12-2012, 09:47 PM   #3
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Don't all the Nikasil cylinders (there are two sets of 100's on ebay right now -- '83 and '88) have the bigger spigot step that won't fit in my '74 /6 case?

As for plating/fixing mine, who is capable of the proper procedure? Any suggestions...?
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1974 R90/6 w/1050 kit. Motor only. Seeking a frame.
1970 R60/5

'91 Bill Holland Steel w/Dura Ace
'01 Z3 3.0 Coupe. The Clownshoe.
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Old 05-12-2012, 09:51 PM   #4
Tosh Togo
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Quote:
Originally Posted by DiabloADV View Post
... As for plating/fixing mine, who is capable of the proper procedure? Any suggestions...?
California nikasil plating
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Old 05-12-2012, 10:04 PM   #5
Wirespokes
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Quote:
Originally Posted by DiabloADV View Post
Don't all the Nikasil cylinders (there are two sets of 100's on ebay right now -- '83 and '88) have the bigger spigot step that won't fit in my '74 /6 case?

As for plating/fixing mine, who is capable of the proper procedure? Any suggestions...?
If you're running R100 cylinders, then you've already got the larger spigots. The 74 took the smaller ones, but the block could have been modified to accept 76 and newer cylinders.
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Old 05-12-2012, 10:33 PM   #6
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The spigots on mine are definitely 97mm, not the later 99mm.

I think maybe I have R90 cylinders, bored out to 100. The pistons are marked 93.97 (1000cc) but the cylinders have a 9 stamped on them, opposite the "KS" raised imprint. Don't the 100 pistons have a "10" stamp?

To get a set of Nikasil R100 cylinders to fit, I'd have to have the spigot on the cylinder machined, I suppose...?
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1974 R90/6 w/1050 kit. Motor only. Seeking a frame.
1970 R60/5

'91 Bill Holland Steel w/Dura Ace
'01 Z3 3.0 Coupe. The Clownshoe.
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Old 05-12-2012, 10:35 PM   #7
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I suppose I could buy these, and have them bored to match my pistons...?

http://www.ebay.com/itm/BMW-R90-6-Cy...sories&vxp=mtr

Thoughts on that...?
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1974 R90/6 w/1050 kit. Motor only. Seeking a frame.
1970 R60/5

'91 Bill Holland Steel w/Dura Ace
'01 Z3 3.0 Coupe. The Clownshoe.
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Old 05-13-2012, 02:45 AM   #8
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I didn't think it was possible to bore R90 cylinders as far out as R100es. Much more likely that someone had the spigors matched to the smaller bore in the block. I think it is more common to have the spigots turned instead or boring the block. But to be sure you will have to check, is the block bored or the spigots reduced? Maybe you have an R100 engine with R90 badges on it. Check serial # above dipstick hole?

Nice job of etching in that cylinder. It's too deep to hone? Looks it from here but can't be sure.
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Old 05-13-2012, 07:29 AM   #9
Wirespokes
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Quote:
Originally Posted by DiabloADV View Post
The spigots on mine are definitely 97mm, not the later 99mm.

I think maybe I have R90 cylinders, bored out to 100. The pistons are marked 93.97 (1000cc) but the cylinders have a 9 stamped on them, opposite the "KS" raised imprint. Don't the 100 pistons have a "10" stamp?

To get a set of Nikasil R100 cylinders to fit, I'd have to have the spigot on the cylinder machined, I suppose...?
It does seem you've got the 900 cylinders, bored to a liter. You're right, the 9 indicates 900cc.

To fit the newer nikasils would require machining the block.
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Old 05-13-2012, 09:20 AM   #10
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Originally Posted by Wirespokes View Post
To fit the newer nikasils would require machining the block.
Or...is it easier (for the machinist) to trim the spigot? I don't care either way...just wondering what the shop would prefer to do.
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1974 R90/6 w/1050 kit. Motor only. Seeking a frame.
1970 R60/5

'91 Bill Holland Steel w/Dura Ace
'01 Z3 3.0 Coupe. The Clownshoe.
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Old 05-13-2012, 02:18 PM   #11
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Apologies for the interruption but a quick noob question please. What is meant by the term spigot here? I have googled but haven't come up with an appropriate def for this discussion.
Very interesting discussion btw
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Old 05-13-2012, 03:51 PM   #12
disston
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The cylinders, wherein reside the pistons and rings, are stuck on the side of the engine block. The cylinder studs, screwed into the block, then pass thru the cylinders and then the cylinder heads and the rocker arms and are capped by the nuts that hold the whole thing on the side of the engine block. It would maybe shift around except the bottom of the cylinder is smaller than the portion you see. This smaller part is caller the spigot. There is a hole bored in the side of the block and the spigot fits inside this hole. From 1970 thru 1975 model years the spigot is 97 mm in diameter. From 1976 thru the end of production of the Airheads the spigot diameter is 99 mm.

What often happens is the engine needs work and there has to be a new pair of cylinders found for an engine. You are limited by the style, size, of the block in question. With an early block the simple way to repair is find a pair of 97 mm cylinders and proceed from there but the older parts are getting harder to find. So not so simple. The 99 mm cylinders will fit the early block if the spigots are machined to 97 mm. Or the block can be bored to accept the larger spigots. This in a nut shell is what needs to happen. It gets a little more complicated sometimes.

You'll see many pictures of cylinders around here, I don't have one for you at the moment but look at the base of the cylinder that mates to the block and you'll see the smaller area, below the fins, this is the spigot.

BTW, how do you get over 1,500 posts and not know what a spigot is?
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Old 05-13-2012, 03:54 PM   #13
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Is it easier (for the machinist) to machine the block or the spigot? What's the right choice here?
__________________
1974 R90/6 w/1050 kit. Motor only. Seeking a frame.
1970 R60/5

'91 Bill Holland Steel w/Dura Ace
'01 Z3 3.0 Coupe. The Clownshoe.
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Old 05-13-2012, 04:09 PM   #14
disston
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I think the shop, machinist, that does the work is the one to ask. We have machinist around here in Airheads but maybe nobody wants to answer for somebody else's work. I think this comes up regularly but I've never seen a post about the details of getting it done, and who did it, except when somebody did his own one off machine.

Consider this. It comes down to money, how much should you pay, what will a machinist charge for either of these operations? I don't know the answer to that either but I think it is high and a lot of people who have considered doing this thought it was a great idea till they heard what it cost.

When you find out please let the rest of us know.
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Old 05-13-2012, 04:36 PM   #15
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I'll visit a machine shop this week and let everybody know what I've learned.
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1974 R90/6 w/1050 kit. Motor only. Seeking a frame.
1970 R60/5

'91 Bill Holland Steel w/Dura Ace
'01 Z3 3.0 Coupe. The Clownshoe.
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