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Old 04-11-2013, 11:43 AM   #1
Fast Idle OP
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Short Valve Guides? Help

I bought new valve guides for my 1974 R90/6 and they are 47mm long as compared to the originals at 54mm. I checked a few BMW suppliers and it appears they are all listing the short guides #11 12 1 338 708 for my /6. The shorter guides are used in the R90S and the /7's. Has anyone used the short guides in their /6 and did you re-profile the ports to get rid of the voids left by the short guides? I've searched and searched and can't find any mention of this issue on any forums.
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2002 R1150 GS
74 R90/6- Restored
69 Triumph Daytona 500- Survivor
1970 Honda SL100
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Riding as much as my old frame will allow!

Fast Idle screwed with this post 04-11-2013 at 03:06 PM
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Old 04-11-2013, 07:51 PM   #2
supershaft
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When I use to do valve jobs I used nothing but the shorter guides in all the models. BMW figured out that about the only thing super long guides down into the port do is obstruct port flow. Most all the support a guide offers is top side. They are the same length on on top where it matters. IMO, you are better off with the shorter ones.
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Old 04-11-2013, 08:12 PM   #3
bmwrench
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The longer guides disappeared long ago, and most of the aftermarket ones are dimensionally close to the short ones.

Mine are a bit longer than BMW's and I am considering lengthening the upper end of them. First I'll need to see how much room there is, and if it's enough to be worthwhile.
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Old 04-12-2013, 01:05 AM   #4
Fast Idle OP
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Thank you guys for the response, I could not find any info on this anywhere and really appreciate the input. I've installed the shorter guides and will proceed on re-profiling the port runners to match the shorter guides. I'm thinking just enough to match them up. There is a small void created where the guide does not reach into the runner far enough.


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2002 R1150 GS
74 R90/6- Restored
69 Triumph Daytona 500- Survivor
1970 Honda SL100
- Survivor
Riding as much as my old frame will allow!
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Old 04-13-2013, 08:42 AM   #5
Plaka
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Quote:
Originally Posted by Fast Idle View Post
Thank you guys for the response, I could not find any info on this anywhere and really appreciate the input. I've installed the shorter guides and will proceed on re-profiling the port runners to match the shorter guides. I'm thinking just enough to match them up. There is a small void created where the guide does not reach into the runner far enough.


Personally I wouldn't bother. You want more turbulence on the intake side. On the exhaust side it won't matter. Better not to commit by cutting metal there. To put it back takes some welding. You need one hell of a nice port and polish job with plenty of flow bench time to get advantages out of port work.

I recently had my heads done, the guides stick into the ports the same amount the original ones did. Ask Ted Porter where he gets them. I like long guides (reason I didn't cut them back to the port surface) because they offer better support and last longer (more metal taking the wear).
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