Chopped fins

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Victor500T
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Chopped fins

Postby Victor500T » Wed Sep 13, 2017 11:24 am

Is there any reason why so many B50s have their cooling fins chopped? I mean, does this practice provide any actual benefit, mechanically? Do the standard fins over-cool the engine or something, or is it just a fashion thing?

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Re: Chopped fins

Postby minetymenace » Wed Sep 13, 2017 11:41 am

Moto-crossers do it so the mud is less likely to clog the fins, it looks cool, that's about it. :cool:
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Re: Chopped fins

Postby Victor500T » Wed Sep 13, 2017 9:59 pm

Aha! (as Alan Partridge might say). Just as I suspected. It does look cool though, but unless everyone who does it has access to a vertical milling machine, I wonder how they do it?

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Re: Chopped fins

Postby twinshocker » Wed Sep 13, 2017 10:53 pm

On CCMs they simply cut the fins with a hacksaw into segments and broke the fins, no milling

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Re: Chopped fins

Postby BSA_WM20 » Thu Sep 14, 2017 8:11 am

It also makes the engine quieter by preventing the find becoming tuning forks.
On a lot of modern air cooled singles you will see the fins cut into segments or being joined together or with dampers between them.
Most old engines grossly over cooled the barrels.
Therimonics came in around the late 70's and for the first time engineers got accurate real time heat dispersal information
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Re: Chopped fins

Postby ampshire-og » Thu Sep 14, 2017 12:32 pm

What most road going riders only ever consider engines from their point of view, the reason why moto crossers remove fins is because their running on dope (methanol) which runs much cooler (and kinder) to the engine. Thus less finning helps keep the temperature up. :thumb
there is the added benefit of mud clearance on mucky days, but that's a bi-product of the above.

And yes I find the best way of doing it is a vertical milling m/c and hand finishing to get a better effect. I've done several head and barrels and got it down to approx 8 hours of solid work.

so a hacksaw and the use of a pair of long nose pilers is an option, just looks crap!
Last edited by ampshire-og on Thu Sep 14, 2017 3:35 pm, edited 1 time in total.

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Re: Chopped fins

Postby Victor500T » Thu Sep 14, 2017 3:33 pm

If running on methanol is commonplace on moto-x bikes, that really would explain it. Presumably there are (or were) higher compression pistons for methanol?

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Re: Chopped fins

Postby ampshire-og » Thu Sep 14, 2017 3:38 pm

yes there were/are, however appropriate machining of the head, barrel and piston can achieve the required results i.e. like 12:1


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