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Old 03-31-2012, 07:17 AM   #16
Lornce
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Quote:
Originally Posted by woodgrain View Post
Wasn't '77 the only year with the big valve heads and the 40mm exhaust?

Woodgrain
Yes. But it was only part of the year. Lots of '77 RS's shipped with 38mm exhaust ports.

'77-'79 R100/7 used smaller intake valves.

By 1980, all 1000cc twins were using big valve (44mm intake) heads, though different in combustion shamber shape to the large valve '77/'78 S/RS heads. These heads were used until 1000cc production ceased in '84.

When 1000cc twin production was renewed in '87/'88 smaller intake valves and ports were utilised.

Clear as mud?

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Old 03-31-2012, 11:03 AM   #17
supershaft
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/7 R100 heads used smaller intake valves AND smaller ports. All the early eighties R100 heads had big valve heads and all big valve heads are big port heads. I don't think BMW ever put 44mm intakes in small port heads in any market? It's too bad because they work great in small port heads.

supershaft screwed with this post 03-31-2012 at 11:08 AM
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Old 04-01-2012, 07:08 AM   #18
bmwrench
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And they fit on the stock seats!
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Old 04-01-2012, 08:03 AM   #19
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Originally Posted by bmwrench View Post
And they fit on the stock seats!
Interesting. Never looked that closely at the stock seats in a small valve motor.

You're saying there's enough material to open them up to suit 44mm intake valves?

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Old 04-01-2012, 02:57 PM   #20
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The '87 on seats will take 44mm intake valves, the early small port seats will not.
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Old 04-01-2012, 04:14 PM   #21
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Oops!
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Old 04-01-2012, 06:59 PM   #22
Lornce
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Originally Posted by robtg View Post
The '87 on seats will take 44mm intake valves, the early small port seats will not.
Thanks, that's good information to know.

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