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Author Topic: Bigger valves  (Read 1397 times)

Offline led

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  • More than two cylinders is not a bike...
Bigger valves
« 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

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1978 BMW R45 (vin nr 57)
1983 BMW R65
198.. BMW R65 Landspeed racer called Leftover
1976 BMW R100s 4valve Krauser heads

Offline Justin B.

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Re: Bigger valves
« Reply #1 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?
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Justin B.

2004 BMW R1150RT
1981 R100RT - Summer bike, NEKKID!!!

Offline Bob_Roller

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Re: Bigger valves
« Reply #2 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 .
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'81 R65
'82 R65 LS
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!

Offline Tony Smith

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Re: Bigger valves
« Reply #3 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.


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1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline led

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Re: Bigger valves
« Reply #4 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.
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1978 BMW R45 (vin nr 57)
1983 BMW R65
198.. BMW R65 Landspeed racer called Leftover
1976 BMW R100s 4valve Krauser heads

Offline led

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  • Posts: 11
  • More than two cylinders is not a bike...
Re: Bigger valves
« Reply #5 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
Logged
1978 BMW R45 (vin nr 57)
1983 BMW R65
198.. BMW R65 Landspeed racer called Leftover
1976 BMW R100s 4valve Krauser heads
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