920 cc conversion?

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Hi, Iam considering using the 920 conversion kit ( as supplied by RGM motors)on my 850 rebuild.Can anyone tell me what other changes to the engine this neccesitates and what changes to reliability, fuel consumption, performance, vibration levels etc it may bring about . Thanks.
 
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teesrider wrote;
Can anyone tell me what other changes to the engine this neccesitates and what changes to reliability, fuel consumption, performance, vibration levels etc it may bring about

I have built two 920s, owning one and a friend owning the other. He bought mine from me fifteen or more years ago, and so he now owns two :D

On these two bikes there have been no reliability issues, although they were Norvil conversions and not RGM, and so had the conrods crack tested as part of the build process. I did have one blown head gasket, and you do have to as far as I know use copper gaskets as there aren't any eyeleted/composite to fit this size bore, but whether the blown head gasket was down to it being a 920, I'm not sure.

I can't remember about fuel consumption, but don't think there was any significant noticable change.

Regarding to performance, you get a lot more bottom end and mid range torque, but the top end remains similar. As far as I know, if you want the top end performance, you have to start having big valve heads and longer duration cams etc etc as the engine struggles to breath at the higher revs, but you do have more performance all around except for the top end. I managed my highest ever top speed on my Norton 920 in JPN guise (i.e. faired) which was 122mph on the clock 8)

For the engine you will need the crankcase mouths opening up a few mm so that the liners can be accomodated, but thats all. Regards vibration, I never had an increase on my bike.

I did speak to Roger at RGM earlier this year as I was considering 920ing my Norton, but he seemed to be trying to talk me out of it saying that a properly sorted 850 would be a better option. I found it a bit stange that he didn't try and sell me one, as he is selling them from his shop.

The one thing you do get though is better low down performance and I personally had no reliability issues.
 
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Some more anecdotal stuff!

Apparently some engineers (engine borers) get a bit freaked when fitting 920 liners to 850 barrels as they break through into daylight in some parts of the barrel when they are cutting the barrel to size prior to fitting the liner. The liner effectively becoming the outside of the barrel in these areas. According to Roger at RGM they see it as bad practice as they are potentially weakening the structure and aren't happy at doing it.

Obviously then the thing to do is to find somebody who is either aware of this and is happy to do it, or get somebody like Pete Lovell or Roger to do it for you. I spoke to a local engineering firm in Leeds who were happy to do it for me. I haven't taken them up on this offer yet, but may do when I decide what to do with my barrels which could do with a rebore.
 
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