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Combat engine query

Classic Norton Commando Motorcycles.

Re: Combat engine query

Postby acotrel » Mon Sep 11, 2017 6:35 pm

I've never had an oil pressure gauge on my 850 motor. What pressure is normal in an 850 motor ? My experience has only been with Triumphs and I think 80 PSI is normal for those.
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Re: Combat engine query

Postby illf8ed » Mon Sep 11, 2017 7:43 pm

acotrel wrote:I'm interested in the comment about the Combat cam giving a power surge above 6000 RPM. I recently bought a 2S cam with a view to using it in my 850 motor. It appears to have too much lift. But when I race I usually keep the motor spinning between 5,500 RPM and 7,000 RPM by using the close ratio box judiciously. I have had trouble cutting the oil scroll into the cam, however your comment has made me think it might still be worth using it. What killed the Combat motors - was it revs or the lack of Superblend bearings ?


You need the compression for the combat cam to work, so on an 850 that will need to be worked out. I don't care for milling the head as Norton did. There were Hepolite Power Max Pistons (slight dome) in days past for 750. I have no idea if they were made for 850 or if you can find them.
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Re: Combat engine query

Postby rvich » Mon Sep 11, 2017 8:21 pm

If you really want to explore putting a combat cam into an 850 motor, you might want to start a thread specific to it. There is probably someone here who has done it. There are a lot of people here with more technical expertise than I. Below is a link to a previous discussion on this:

combat-cam-850-t13585.html

JS Motorsports has high compression pistons available:

http://www.jsmotorsport.com/products.asp

As to why the combat motors blew up, it is sort of a chicken and the egg thing. But it wasn't the fault of the cam unless you blame it for the fact that people ran them at high revs until they blew up.

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Re: Combat engine query

Postby acotrel » Tue Sep 12, 2017 3:01 pm

If the power surge occurs above 6000 RPM with the Combat cam, the usable rev range is probably too high for the rest of the motor. However a 2 into 1 exhaust might move it downwards ?
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Re: Combat engine query

Postby Fast Eddie » Tue Sep 12, 2017 5:51 pm

acotrel wrote:If the power surge occurs above 6000 RPM with the Combat cam, the usable rev range is probably too high for the rest of the motor. However a 2 into 1 exhaust might move it downwards ?


My understanding is that the 2S is strongest 5,000-7,500. A CR box would indeed work well with this.

The 2-1 Maney system definitely helps boost mid range. Whether or not yours does would have to be established through testing.

An 850 doesn't need domed pistons unless you want to go above 10.5:1. HC (ie raised crown) Flat pistons will give a nice squish effect and 10.5:1 if set up correctly.

The 2S cam and raised CR will definitely give more power if set up right. But whether the stock crank or crank cases will sustain repeated use of this power and revs seems to be the question.
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