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Author Topic: Porting 1980 heads  (Read 177 times)

Offline tunnelrider

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Porting 1980 heads
« on: November 10, 2021, 05:20:46 AM »
I've just purchased an 860 upgrade and thinking to fit it to a spare 1980 R65 engine I have that's done less km's than my (205K) 1985 engine.  The compression on my 1985 heads is passable but not fantastic (i.e. it gets up and going ok but has no noticeable engine braking when hot) so I'm thinking of porting the 1980 heads to something suitable for the 860 kit - has anyone done this or know it's possible?  Could it be an exercise more costly than what it's worth?
For e.g., R80 heads have ports to fit 42mm intake valve/ 38mm exhaust valve, compared to 40mm/38mm valves for 1981 - 1996 R65 and 38mm/36mm valves for 1978-1980 R65. The R80 stems are 8mm compared to R65 7mm though.

Any advice or thoughts would be valued.

Thanks
« Last Edit: November 10, 2021, 05:31:29 AM by tunnelrider »
'85 Black R65 / '74 GT185 / '83 Pantah 500 / '90 Super Tenere 750  / '01 DRZ400 dirt only

Offline Tony Smith

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Re: Porting 1980 heads
« Reply #1 on: November 10, 2021, 11:41:44 PM »
The short answer is No. The cost to obtain any material advantage would simply not be worth it.

I say this for the following reasons.

Because of the small space in the R65 head the only way to increase valve size is to knock out the guides and seats, weld up the holes and move the centers, rebore the guides and rebore and fit new seats.

Next you will need the services of a person with a flow bench and the skills to use it.

As we are now approaching AU 3,000 dollars worth of work I would have to put to you the famous Carol Shelby question :- "speed costs money, how fast can you afford to go"?.

By chance I purchased some heads from Boxerman shortly before his untimely death that have all the above done to them.

Side by side with another R860 mine is slightly faster, but not by much. And mine is still a little slower than my wife's R65 that has an R80 engine with stock R100 pistons and barrels fitted.

If you really want warp factor 11 out of an R65 motor I would do the following.

Buy a set of 860 barrels only.
Fit with high compression R100 pistons and top with R100 40mm head. Then fit carbs and modify exhaust system. Whoops forgot a good Siebenrock cam.

Then you would have an R65 that would fly
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline dogshome

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Re: Porting 1980 heads
« Reply #2 on: November 11, 2021, 06:43:37 AM »
What he said  ;D

I looked at the ginormous squish-area band around the valves as an 860, then looked at the simple, open and 90 degree 'hemi' design. I saw no lumps, bumps, casting errors or misaligned flanges and quickly decided to leave alone. I've played about with various cars and bikes over the years - some have obvious flange misalignment or steps around the valve seats. The BMW doesn't have any of that. I didn't even need to grind the valves and there was no sign of oil or blowby.

I've fitted bigger pistons in engines before, but never this unfeasibly huge! The 450 to 860 is even more bonkers in terms of head and valve size vs bore and you can see on the power charts that it quickly runs out of steam when revved. The 650 holds on surprisingly well considering the big change in volume. All the BMW engines are oversquare, so it's not too surprising.

Now idiot here has got his ignition timing correct, my 1983 650 runs like a train as an 860. I guess technically, the earlier R65 won't respond as well, but unless you need new valves, seats and guides, I wouldn't bother.
肉(r?u)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
* Literally: To hit a dog with a meat-bun.:-O

Offline tunnelrider

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Re: Porting 1980 heads
« Reply #3 on: November 12, 2021, 06:45:11 AM »

As we are now approaching AU 3,000 dollars worth of work I would have to put to you the famous Carol Shelby question :- "speed costs money, how fast can you afford to go"?.

By chance I purchased some heads from Boxerman shortly before his untimely death that have all the above done to them.

Side by side with another R860 mine is slightly faster, but not by much. And mine is still a little slower than my wife's R65 that has an R80 engine with stock R100 pistons and barrels fitted.

Love it, Shelby's got some great quotes, was it also 'Ain't no substitute for cubes baby' as far as I recall?  He's more practiced in the art of speed than I am. 

That's some interesting info there Tony, thanks for sharing that.  You've had some good comparisons come your way to test out, spiritly tested I bet and it's magic modified heads have moved within the circles of the most knowledgeable. 

It'll be a mission to even find a taller final drive, won't bother with the heads after hearing the advice from you and dogshome, cheers boys.  There is a little bit of a second hand airhead market in NZ, I'll see if the dream combo of R100 pistons and heads ever come by ;)
'85 Black R65 / '74 GT185 / '83 Pantah 500 / '90 Super Tenere 750  / '01 DRZ400 dirt only

Offline Tony Smith

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Re: Porting 1980 heads
« Reply #4 on: November 12, 2021, 06:45:42 PM »
Re final drives.

An R75 final drive works pretty well on an R65, but it is the duck's pyjamas on an R860.

I have tried an R100RS final drive because I have slicking around, but it was way too tall.

An R80 FD might be worth trying if I ever get my hands on one, but until then I will stick with the R75 one.
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline tunnelrider

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Re: Porting 1980 heads
« Reply #5 on: November 13, 2021, 05:59:16 AM »
Cheers Tony, I guess with every 860 kit being sold, R75 and 80 final drives are becoming more like finding hens teeth... Doesn't look like anyone does new ring and pinion gears from my quick search. So, a S/H final drive teeth count of 32/10 seems perhaps the best outcome, then 37/11 - what is the ratio of the R75 final drive you have Tony?  Snowbum mentions R65 came with 32/9 and 31/9 FD's - I think I recall seeing it stamped on the FD before, to find out what I've got?

You mentioned a Siebenrock cam - do they do a 'hotter' cam for the R65?  Just asking 'cause I'm kinda curious and amused about that, but it wouldn't be worth the trouble on my old engine either.  They should do new ring and pinion gear as well, make a killing!  Also while I'm at it, I'm quite impressed by yours and your wifes' combinations of motors in an R65, can an R80 engine fit straight in to the R65 frame and swing arm?

Thanks
'85 Black R65 / '74 GT185 / '83 Pantah 500 / '90 Super Tenere 750  / '01 DRZ400 dirt only

Offline Tony Smith

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Re: Porting 1980 heads
« Reply #6 on: November 15, 2021, 10:42:25 PM »
To dizpelt a myth that refuses to die. All R65s have exactly the same size mainframe as their bigger brethren, this is canon for the 1979 to 1984 models, the only thing that varies is the fork length and the swingarm length.

After 1985 (monoshock) the R65 runs the same cycle parts as the bigger engined models.
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline Tony Smith

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Re: Porting 1980 heads
« Reply #7 on: November 15, 2021, 10:53:06 PM »
I have the 32/10 final drive.
I think 37/11 is the GS ratio
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline Burt

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Re: Porting 1980 heads
« Reply #8 on: November 27, 2021, 08:48:19 PM »
Curious to your comment in #6 Tony regarding the frame size. 

Two things that come immediately to mind are the reasons:
1. For any aftermarket seats for 79-84 R65s are not the same for the R100, etc.  When looking at the "Gunfighter" style of single seats yonks ago, the websites always stated that all R series but not our R65s, or words to that effect.  I am sure that with a little engineering modification and patience that could be worked around. 

2. The handing issues associated with the "shorter" frame. The shorter length of the swingarm, yes and I assume different sized subframe which answers the above point. 

If the subframe was lengthened to fit the R100 seat then I would expect it to look ergonomically odd with the shorter wheelbase. 

I may have already answered my questions but will the post '85 subframe bolt onto the pre '85?  Or is the single shock mounting the issue? 
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Offline Barry

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Re: Porting 1980 heads
« Reply #9 on: November 28, 2021, 04:14:32 AM »
To dizpelt a myth that refuses to die. All R65s have exactly the same size mainframe as their bigger brethren, this is canon for the 1979 to 1984 models, the only thing that varies is the fork length and the swingarm length.


And the 78-80 R65 has a shorter wheelbase than the 81-84 R65 which may be down to a shorter swinging arm on the earlier model given they are different part nos ?
« Last Edit: November 28, 2021, 04:17:00 AM by Barry »
Barry Cheshire, England 79 R45