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Old 08-27-2014, 01:32 AM   #1
windsurf OP
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late barrels on earlier cases

I know the later barrels with O ring aren't supposed to fit the earlier cases, however does anyone know if that is only due to the larger section where the o rings sits? If so I could just turn it off in the lathe instead of modifying the cases.
I realise that you can't use the o ring but obviously the early engines didn't have them anyway.
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Old 08-27-2014, 07:45 PM   #2
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Yep. It's been done a lot.
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Old 08-29-2014, 07:01 AM   #3
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So what would be best, to machine the barrels to fit the smaller opening of the old cases or to enlarge the casing opening to fit the newer barrels. Assuming an engine is already stripped to a bear engine casing...which options to choose?
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Old 08-29-2014, 11:19 AM   #4
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Originally Posted by gorma900 View Post
So what would be best, to machine the barrels to fit the smaller opening of the old cases or to enlarge the casing opening to fit the newer barrels. Assuming an engine is already stripped to a bear engine casing...which options to choose?
It isn't stripped at the moment which is why I would like to just turn the barrels down if possible.
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Old 08-29-2014, 12:11 PM   #5
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Apparently either is about the same to the machinist depending on what machines he has available. There was one done a year ago, about, here that the machinist told the rider to pick, either one. You might ask the machinist which he recommends.

I always thought that turning the barrels would be easier but I'm not a machinist and I've not had this job done.

The real problem is finding a machinist to do the job. Some will turn the job down I think. Get a price up front.

If the block is done the machinist may want it stripped before doing his work and that would be more work for you?
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Old 08-29-2014, 06:10 PM   #6
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Does anyone have a pic of what the later model barrels look like? The step that needs to be machined off. A before and after shot would be best thanks.

Mal
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Old 08-29-2014, 06:28 PM   #7
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There is a step on later cases. There is also a smaller bore and corresponding spigot size. The spigot size from 1970 thru 1975 are 97 mm. In 1976 the spigot was larger. It became 99 mm. The first 99 mm barrels are different from the later 99 mm barrels. This difference is the step I think.

What year block do you have?
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Old 08-29-2014, 06:50 PM   #8
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Turn the barrels...

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Old 08-29-2014, 08:08 PM   #9
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If I had the choice, it would be to bore the cases, but I suspect that this would take a lot of set up time for the machinist, while turning the cylinders is a reasonably easy task.
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Old 08-29-2014, 09:42 PM   #10
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Given the choice, I'd do the block. But it also depends on what cylinders you have in mind. If they're liter barrels, there's not a whole lot there, and they're aluminum if nikasils. I'd definitely go with boring the block if bumping up to a liter.
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Old 08-30-2014, 06:59 AM   #11
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The motor is a 1979 R80 and I have barrels and pistons from a 1993 GSPD. I would just turn them down on the lathe at home. I dont especially want to pull the whole motor apart to enlarge the case openings.
I know Motobins do a 1000cc conversion with lighter pistons that evidently bolts onto the earlier cases without any machining and uses the original 800cc heads. I would like to use what I already have if it's only a matter of an hour or so lathe time.
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Old 08-31-2014, 12:40 AM   #12
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The 79 block already has the larger holes - no issue what-so-ever!

Bolt it all together and be done with it.
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Old 08-31-2014, 07:56 AM   #13
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The 79 block already has the larger holes - no issue what-so-ever!

Bolt it all together and be done with it.
Ah, no.

The later nikasil barrels have a ridge or shoulder that fits a corresponding recess in the later blocks.

That ridge/shoulder needs to be turned off to fit earlier 99mm blocks.

Here's a pic showing the recess in the block of a '92 R100GSPD.


Lornce screwed with this post 08-31-2014 at 08:25 AM
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Old 08-31-2014, 08:12 AM   #14
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The ridge needs to be turned down to fit early blocks that take a 99 mm spigot with no ridge. If the bike is pre 1976 then the entire spigot needs to be turned down to fit a 97 mm bore.

If you will, Three spigot size/shapes to deal with. 97 mm from 1970 thru 1975. 99 mm 1976 thru the end of Airheads but the ridge is a later variation. (sorry I don't know the year)(wish I did)
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Old 12-22-2014, 03:31 AM   #15
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I managed to fix it quite easily in the end with 78 100RS barrels, pistons, heads carbs and 40mm exhausts. Obviously this lot bolted straight on without any machining - but thanks for the advice.
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