The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: led on April 13, 2018, 09:28:24 AM

Title: Bigger valves
Post by: led on April 13, 2018, 09:28:24 AM

Hi Everyone!

I have not been active here in such a long time I apologize  :-X

However since I have been gone I have built a landspeed racer and raced it (a little) last year.

I want to upgrade a few things and wanted to find out if anyone here has done a big valve conversion before?

I have a set of R80 valves and they are 2mm bigger (inled and exhaust) and wanted to know if anyone has done this successfully?

Bike background:
It is still stock 650cc
stock heads except dual plugged
336 BMW cam
38mm dellorto carbs

Superbike front end
R100 swingarm and diff (too long at this stage)
R65 rear wheel (might upgrade to R100 wheel in future)
No rear suspension

Title: Re: Bigger valves
Post by: Justin B. on April 13, 2018, 09:49:21 AM

I remember taking a rigid frame bike on a 1500 mile trip once - ouch...

Will the R80 heads bolt up or do you need to keep them r65 heads for some reason?

Title: Re: Bigger valves
Post by: Bob_Roller on April 13, 2018, 12:38:49 PM

When I had the heads from my '81 R65 worked on, due to valve recession, I had larger valves installed .
I think the intake went to 40mm and exhaust 38 mm, the valves had larger diameter valve stems as well .
I didn't notice any improvement in power output .

Title: Re: Bigger valves
Post by: Tony Smith on April 13, 2018, 03:53:28 PM

Mine also has the bigger valves - done by the previous owner of the heads, along with considerable porting/flow work.

I do not notice any stella level of performance, by my R65 will stroll away from the other R65 and R65LS that are in my local motorcycle restorer's club. given my size I suspect the difference might just be a little more exciting if a lighter rider were in charge.

What I am saying is that the difference is incremental.

Title: Re: Bigger valves
Post by: led on April 14, 2018, 12:14:52 AM

Thanks for all the replies.

I have thought about just fitting the R80 heads but then they need the second plug hole machined and a few other things as well (they are looking very ruf)

I suppose it is a sum of parts thing. I already have the cam fitted and I have the valves.

Maybe I should just fit the krauser heads from my R100  ;D

Any other go fast suggestions?

I'm going to up compression and have the heads ported as well.

Title: Re: Bigger valves
Post by: led on April 14, 2018, 12:16:22 AM

O yes suspension is not a problem on the racing surface and it is only 5 km so no problem