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Old 06-17-2010, 05:37 AM   #1
igormortis OP
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Airhead Heads

Specifically GS heads onwards. What are the differences?

I seem to recall that the US and Euro spec heads are different, pulse air stuff notwithstanding.

What can you tell me?
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Old 06-17-2010, 06:15 AM   #2
Rucksta
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Not what you asked for

http://moragafalconers.org/BMW_Pistons/

I found this link usefull for matching pistons to heads.
It may make interesting reading until someone comes along to answer your question.
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Old 06-17-2010, 06:51 AM   #3
tatters
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My german import R100GSPD was fitted with the air pulse pipework, can casue head warpage at high tempatures and looks awful on the bike so l removed mine, pluged the holes up on the heads and at the airbox.
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Old 06-17-2010, 07:23 AM   #4
AntonLargiader
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Quote:
Originally Posted by igormortis
Specifically GS heads onwards. What are the differences.
AFAIK all 1988-on (reintroduction of R100, introduction of GS) R100 heads are the same. R80s were still made and they were different.
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Old 06-17-2010, 03:37 PM   #5
Rob Farmer
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They all look the same to me. Apart from the larger exhaust port on my 78 RS heads the valves are the same size as my 93 GS ones. I think it was just the yanks who confused things.

Rob Farmer screwed with this post 06-17-2010 at 05:07 PM
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Old 06-17-2010, 04:40 PM   #6
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Thanks for the replies - I'm getting there I think.

So the difference with the R80 heads is the size of the combustion chamber? I assuming this is what gives room to create a squish band with certain R100 pistons?

Rucksta - does your link above show all the R100 piston variations?
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Old 06-17-2010, 05:15 PM   #7
Rob Farmer
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I wouldn't get hung up over the squish bands. Apart from the USA the later non squish band engines (81-84) produced the highest outputs at 70 BHP compared to the 77-78 engines 67. If you want a quick engine put it to the UK 83-84 RS or RT engine spec.
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Old 06-17-2010, 05:44 PM   #8
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I have a US spec '89 R100GS. I presume that it has the 8.5:1 pistons?

My goal is a tractable, reliable engine for overland use. 2up and loaded over varied terrain. Able to cope with low octane fuel.

You could argue that I've just described the standard engine. And I'd be pretty happy if I left it at that. But there's a good chance that I'd overhaul the engine before The Big Trip so if I can build a better one with OEM parts that will better suit my needs, then that's a good opportunity.

I'm interested to see what people have done with the R80 heads, since I already have a pair in the shed.
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Old 06-17-2010, 06:18 PM   #9
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Quote:
Originally Posted by igormortis
Thanks for the replies - I'm getting there I think.

So the difference with the R80 heads is the size of the combustion chamber? I assuming this is what gives room to create a squish band with certain R100 pistons?

Rucksta - does your link above show all the R100 piston variations?
I think it does show all the R100 variations but there are a number of aftermarket variations.

One of the popular ones is the Siebenrock powerup kit which uses a 100 piston designed for use with the unmodified 80 head with no squishband / pinging problems.
Some say this produces more usable midrange than a 100 head at the same capacity.

The 80 head has much in common with the 65 heads.
I found it easier achieve a high reving engine with the R80 G/S head and valve train than I have with the 78 R100s heads. (I was looking for top end before I knew about higher 5th gears kits)

I like my '78 'S' heads & pistons on my '81 block & barrels. It seems to outperform '84 RS & RTs and R100GS but then the bike is 100lbs lighter with lower gearing.

Squish bands still confuse me but when I went from a full dome 9.5:1 piston back to a '78 squish type 9.5:1. I got a cleaner burn though I did lose some performance.
Milling the head to get the squish band thickness to 0.30 gave me back the (excecssive) compression I was geting with the dome piston and a slight performance improvement probably due to ease of tuning. Pinging was less of a problem and a tendancy to build carbon around the edge of the piston was eliminated.

Good luck on your mission whatever it may be.
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