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Old cam for New cam

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bobdcamp
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Joined: Tue Sep 06, 2011 8:30 pm

Old cam for New cam

Post by bobdcamp »

Hello, I'm starting working on a 72 R60/5, My idea is to use a nice R80 jugs and pistons and heads, 1986 vintage. I know the jugs will not fit without opening up the block. I have a extra 336? cam from a 75 R90s can I use it. What pitfalls am I
letting myself in for.
Thanks Bob D
Bob Distelcamp

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schrader7032
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Re: Old cam for New cam

Post by schrader7032 »

For one that I can think of is that the /5 engine case opening for the cylinder is 97mm. The R80 jug is designed to fit in a 99mm engine case.

If you get that far, I've not heard good things about the 336 cam. If I remember correctly, this cam was never designed for street use. It was designed for a racing program in Europe in the 1970s. In order for BMW to use it, they had to make enough of the part so that it qualified as an "everyday" part...the term for this is homologation. There are lot of other things that have to be changed to get this to work. The 336 cam resulted in very peaky power over 5000 RPM and the tuning aspects of the bike must be spot on.

Snowbum discusses cams in this site:

https://bmwmotorcycletech.info/cams.htm
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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srankin
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Re: Old cam for New cam

Post by srankin »

As Kurt has written the 336 cam moves the power band up the RPM ladder.

With the 336 you will loose low end torque mostly in the range of street riding. Not a problem if you wind the engine over 5K RPM or higher to pass a car or leave a stop light.


Other than that, I guess I would be concerned about physical installation of the new cam. Personally, I would stick to the stock cam. St.
Owner of a 84, R80RT and 78, R100RS

Bmwwrench
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Re: Old cam for New cam

Post by Bmwwrench »

It's easier to have the R80 cylinder spigot turned to fit the early case than to bore the case.

The "Sport" cam works well, with the engine pulling harder from 5500 vs. 4500 RPM of the 308. It should be noted the the R50 and R60 cam has less lift and duration than the cam used in the R75 and larger engines. The Sport cams midrange can be improved by advancing it's timing.

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srankin
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Re: Old cam for New cam

Post by srankin »

Interesting information, thanks for sharing. St.
Owner of a 84, R80RT and 78, R100RS

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