RGM 920 kit

Has anyone here installed one of these or another version and put some miles on? Jim Comstock mentioned that the 920s generally don't live too long. I've got one of these kits and now a spare 850 engine is available locally at a good price. This spare 850 needs rebuilding and it is tempting to do it as a 920. It would likely also get an RH 10 modified by Jim for flow (big valve conversion) and a bit of a cam.
Does the standard trans hold up to the extra power?
Over the years I have noticed quite a number of people on this site have done 920 conversions, just wondering how far down the road these engines went before problems arrived?

I realize this question has been asked before, however the last info on 920s is from a couple of years back. An update from those running these engines would be most helpful.

Glen

No problems with either of my 920's of which one is sold to a friend. My first conversion was from Norvil in the late 1980's where they bored out the small end to fit the (Ford?) piston, and my present conversion are Steve Maney's bespoke 920 Barrels and pistons. I can't comment on RGMs version.
The only issue for me if you can call it one, is that there aren't any composite head gaskets for the 920, and so I use copper but always seem to have a slight weep from the push rod area, which I didn't have with the composite type and the engine was 850.
No problems with the transmission either......not yet anyway.

I got quite a few "special products" parts from RGM some years ago when I was building up a café style fastback. Unless their parts quality has improved, I wouldn't go with their stuff. Just my experience.
JUG

no way no how would I do a 920 on a standard 850 cylinder. also the head gasket bore is IMHO WAY to close to the cylinder through bolts for a good seal. when you can see the sleeve through the casting you have taken WAY to much materiel from it to have ANY integrity much less to keep a round cylinder wall. IMHO an 880 is as big as I would think of building in the 850 cases and head bolt pattern.

I think Fullauto is working on new cylinders that I suspect will have some extra meat where it's needed.

A friend of mine did a 920 conversion a few years ago,but it would never stop blowing blue smoke due to oil burning and leaking/ weaping head gasket. I followed him to a Norton Rally one time 1,200 kms round trip,blew smoke the whole time.
I helped him out one weekend to remove the head and could see why it was burning oil.There is so little material of head gasket to seal the area between the push rod holes and the cylinder bore that no wonder it was leaking.
I had thought about doing the conversion at one point to my own 850 ,but having seen the issues that the conversion causes I think you have to be mad to do it.
Why not fit a Fullauto head,decent carbs,ignition,some port work etc and just stay with the std 850 bore,much easier and proven too.
Brett

I sent the following comments on my own experience with 920 conversions to Glen by PM, but didn't post them here because they mostly had to do with race bikes. But I'm copying them here now, because there seems to be some interest in the subject.

"I was thinking about posting to your thread, but didn't because most of my 920 experience is with race engines. I did run a 920 in a MK3 street bike for a while, but never put a lot of miles on it. It was a bike I had built so I could have an electric start race bike. I raced it a couple or times, then turned it back into a street bike. It was OK on the track, but enough heavier that I didn't like it as well as my 750 PR. It was a fun street bike, with no issues, but I didn't keep it long enough to put more than a couple thousand miles on it. I eventually put a 920 in the PR, which made a great race bike. I raced both it and a monoshock Norton with a 920 with good results. The only reliability issues I had were at Daytona, where I managed to break two 920 crankcases in one meet, but that was from really extreme abuse. I ran the last 920 engine for several years in the PR, and later fit it into a streamliner and ran several times at Bonneville with no engine issues, until last year, when I added a nitrous system and cracked the cases. I think a 920 is plenty reliable for street use, but don't know how well it will hold up in terms of bore wear for high mileage street use. The liner is a bit thin, and if not bored and honed properly with torque plates, will lose ring seal. When done properly, it has held up well on the race bikes, but I don't know about street use endurance. I should mention that almost all of my 920 experience has been with sleeved iron cylinders. I've built one 920 with Steve Maney's alloy cylinders, but it hasn't been run yet, so I have no experience with it.

The only 920 I've run with a stock 4-speed was the MK3 I mentioned above. I did manage to break the transmission case in its first race by downshifting into a lower gear at too high a speed. I was used to close ratio 5-speeds, and misjudged the shift. I put a new gearbox in and never had another problem with it. I think the 4-speed should be fine, as long as you don't get in the habit of doing burnouts at every start. I had pretty good luck with the Quaife gearboxes with the 920 in the other race bikes, but did have to occasionally replace a gear or shaft when they showed cracks or gear pitting."

Ken

worntorn said:

Has anyone here installed one of these or another version and put some miles on? Jim Comstock mentioned that the 920s generally don't live too long. I've got one of these kits and now a spare 850 engine is available locally at a good price. This spare 850 needs rebuilding and it is tempting to do it as a 920. It would likely also get an RH 10 modified by Jim for flow (big valve conversion) and a bit of a cam.
Does the standard trans hold up to the extra power?
Over the years I have noticed quite a number of people on this site have done 920 conversions, just wondering how far down the road these engines went before problems arrived?

I realize this question has been asked before, however the last info on 920s is from a couple of years back. An update from those running these engines would be most helpful.

Glen

Click to expand...

My advise if you want a big cc engine is don't go over about a 79.5mm bore.
Increase the stroke to go bigger. You will get larger returns on a street app from a stroke increase. Jim

One thing I forgot to add, but was reminded of by Rosey's post. I found early on that the only way I could keep a good seal around the bores was by cutting a groove around the top of the bores and fitting a copper o-ring. That, in combination with a copper head gasket and Pliobond adhesive as a gasket cement, has worked well for me. I also lay a ring of either thread or very thin copper wire in the Pliobond as a barrier around the pushrod holes. I've run that combo extensively with CR of 10.5 and higher with no leakage. The other point of possible oil leakage is at the front of the cylinder where the sleeve is exposed by boring through the cylinder wall. I use Loctite penetrating sealant for that, and have no leaks. Once again, this is all for sleeved iron cylinders. With the Maney alloy cylinders, I'd still use Pliobond, and the thread/wire around the pushrod tunnels, but not the copper o-ring. Steve leaves the top of the liner slightly proud to accomplish the same effect.

Although the 920 has worked very well in the race bikes, I really don't know how well it would hold up in a high mileage street bike. I'm currently finishing a MK3 street bike build for myself and my grandson, and settled on a 79.5 mm overbore for an 883 cc engine instead.

Ken

The pistons in the RGM kit measure 80.25 mm and weigh 370 grams with the pin but without rings. This is supposed to be the same or very close to the same weight as stock 850 pistons. Roger had them made up to that weight so that rebalancing of the crank would not be necessary.
The kit is labelled "920 kit", however at 80.25 mm the displacement figures to 900 cc., not 920.

To add- a bit of searching here and on the JS site shows stock 850 hepolites at 317 grams, bare piston. LCR Ken mentions in another thread that stock 850 pins are 78.8 grams, so that is 395.8 grams for stock 850 piston with pin.

Glen

worntorn said:

The pistons in the RGM kit measure 80.25 mm and weigh 370 grams with the pin but without rings. This is supposed to be the same or very close to the same weight as stock 850 pistons. Roger had them made up to that weight so that rebalancing of the crank would not be necessary.
The kit is labelled "920 kit", however at 80.25 mm the displacement figures to 900 cc., not 920.

To add- a bit of searching here and on the JS site shows stock 850 hepolites at 317 grams, bare piston. LCR Ken mentions in another thread that stock 850 pins are 78.8 grams, so that is 395.8 grams for stock 850 piston with pin.

Glen

Click to expand...

With the 920 kit you will need to open the throats of the crankcase to take the larger liner and machine head to suit. Not just a bolt on kit, some serious machining needed.

Cheers