The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: flying.finn on July 06, 2009, 04:03:57 AM

Title: Big bore R65
Post by: flying.finn on July 06, 2009, 04:03:57 AM

Has anyone out there swapped in a R90 or R100 motor to there R65  .. I'm toying with the idea for more power...

I also have a spare motor and iron lined cylinders but from what I have read boring these out would be a waste of time and money ..

Thoughts???

Title: Re: Big bore R65
Post by: Motu on July 06, 2009, 05:09:52 AM

I've heard it's not a good idea.But just reading Ian Falloon's The BMW Story....he mentions the 1979 ISDT GS80.This used 95mm pistons and the R65 61.5mm crankshaft...giving 872cc.So the factory have done it with success.

Better off with an R80 engine,that's been done enough times.

Title: Re: Big bore R65
Post by: flying.finn on July 06, 2009, 05:47:20 AM

Will the R80 exhaust fit on the R65 ??

Title: Re: Big bore R65
Post by: Motu on July 06, 2009, 06:01:26 AM

No.

Title: Re: Big bore R65
Post by: montmil on July 06, 2009, 06:03:58 AM

Quote

Will the R80 exhaust fit on the R65 ??

Another oddity of the R65. 38mm exhaust vs 40 mm for most other BMWs. It's the pipe-to-cylinder head issue.

Monte

Title: Re: Big bore R65
Post by: steve hawkins on July 06, 2009, 09:41:16 AM

You will need a R100 exhaust - which you will have to make fit

You will will need the R100 carbs.

You would probably be recomended in getting a more approriate Final drive - i.e. that of  R100.

Your R100 engine will have to be a similar age to your R65 - the old light/heavy flywheel and gearbox input shaft issue.

Some would have you believe that the 1/2 inch closer to the ground an R65 is compared to a R100, will mean that you will be scraping you R100 rockers on the deck.  I would contend that this will only be an issue if:

1.  You a riding on the track - i.e. racing
2.  Or you are indeed a riding god and ride every at 10/10nths - in which case you will be dead by the end of the summer anyway.
3.  You local roads have so much camber on them that you are already rubbing your rockers on a regular basis.

- there are plenty of ways around this issue  - including ignoring it.

R65 engines can be tuned but it costs, and you still won't be able to blow a R100 away.  R100 engine is the cheaper option :o

I have a spare R100 engine as well - but it is still in the R100...... ;D And I am loath to break it up.

Cheers

Steve

Title: Re: Big bore R65
Post by: Bob_Roller on July 06, 2009, 10:34:10 AM

Your spare engine, if it's an R65 engine, don't bother with boring it out to a larger displacement, as the engine life is greatly reduced, the lower end seems to not like it .

If you want a faster bike, buy one, unless you want to 'tinker' with your creation until it runs correctly .