Horsepower International Big Bore Motor (2015)

Good Morning,

I have a 920 Commando motor with a Horsepower International 920 (940?) kit in it. I’m about to pull it apart and hope to rebuild it.

Now that George and HPI are gone does anyone know who, if anyone, has the HPI rights and technical data? Is there anyone out there with “The Knowledge” about these motors? If so, I’d be pleased to hear who it is.

I will contact Arias, but this may be ancient history for them and of no interest any more. As I remember, the rings supplied with the pistons were for an Harley Davidson(!), but that was a long time ago and I no longer have the details.

Any information will help reduce the detective work.

Thanks and Cheers,

Lance

You need a new head to bring out the best. I know this guy......

If you run into trouble sourcing rings, you might give Wiseco a call. They have been very helpful to me in sourcing odd rings, such as for a short-stroke Norton.

Skip

Lance,
if he doesn't notice this post you could pm icrken on this forum, he had the full specs for an HPI supplied cam that used to be fitted to my bike so may know where to find more info.
cheers
iain.

I used to visit George pretty regularly, so I'll offer what I can recall. George did do some 940s, but mostly built them at 920 with an 81 mm bore. He had the stock iron 850 cylinders bored and sleeved by Q&E Engineering in Anaheim. They are still in business, but haven't done any Norton cylinders for decades, and didn't supply the pistons and rings, just the sleeves. I talked to them a while back, and they were up to the third generation of owners from the original family. Only the old man recalled any of the details of the Norton cylinders, but they were wiling to do them again if asked. The didn't have any of the liners left, but could source new liners from LA Sleeve, who originally supplied them. RGM also supplies 920 liners, as well as a complete 920 conversion kit, but you would have to have someone bore the stock cylinders and insert the liners. I believe Jim Comstock will also do big bore liner conversions. If you should need new cylinders, you might consider the 920 alloy (with iron liners) cylinders from Steve Maney.

If you need pistons, RGM still supplies GPM cast pistons in 81 mm and 81 mm +.020". If you need forged pistons in 81 mm, you can get the JE high compression racing pistons from me or from Steve Maney. Norvil may also still supply their cast pistons, but I don't deal with them much, so I don't know the details of what they have available. But I'm pretty sure they do still supply the 920 and 940 pistons. Forgedture, Venolia, and Arias all made forged 920 pistons for Nortons back in the late '70s and early '80s, and might still be willing to make them on special order. If all you need are new rings, I'm sure you can find replacements once you know the bore size and the ring widths.

Copper head gaskets for the 920 are readily available for several sources, including Jim Schmidt, Steve Maney, RGM, and probably Norvil.

George built quite a few 920 engines for customers. He had several cam grinds he used, but most were flat tappet grinds. He did do some fairly radical grinds using the radiused BSA lifter conversion. You really won't know the details of what you have until you tear it apart.

You shouldn't have any real problems in rebuilding the engine, if needed. The only really critical requirement is that if you bore and/or hone the original cylinders, you need to use torque plates. If not, I can guarantee that you will not have good ring seal at the top of the bore adjacent to the counterbores for the through bolts.

Hope that helps some.

Ken

Ken, above, mentions torque plates for properly stressing cylinder prior to boring or honing.

Anyone know if these plates are being manufactured or are we on our own?

Skip

The only ones I've seen have been made by individuals. I previously posted these pictures of the ones I made:


They are not all that difficult to make, if you have access to a mill, or lathe and drill press.

Ken

Thanks for the invaluable help, chaps.

I'm hoping to get away with only new rings (and the new head), but will see what it looks and measures up like, when I open it up. It's great to know where to go, if I need to go further than that. Will keep you advised.

Out of interest, are there many (any?) of George's motors still running out there?

Thanks again and all the very best,

Lance

I recall George Gjonovich of HPI. I only remember the 940 kits (he called them the "Z1 eater", a reference to the Kawasaki 900) and the nitrous kits. The head cylinders had a gap in the center and the sleeves were touching each other on the inside. The sleeves were needed due to temperature expansion (same or similar alloy as the pistons). I recall that HPI's early location was next door to the White Brothers when they first started up, who made performance parts for dirt bikes, but I don't recall if this was in Garden Grove or another city. Later HPI moved, and this was in Garden Grove.

I bought a used 1973 Norton 850 Commando Roadster (Blue) from a private seller in 1975, and later went to HPI for maintenance on the Norton. I had the bike until 1982 when I bought a Suzuki GS1100e. Around that time, George became ill and was rarely at HPI anymore. I think one of his relatives was running the shop. I don't know when HPI shut down. There was some British bike place in or near San Juan Capistrano, that sold and maintained Nortons (and other British bikes), but they too shut down.

Lance, how did the 920 work out for you?
Did you get many miles from it before the need to rebuild?

Glen

Lance was last seen a year and a half ago. You may need to ping him with a PM.

Right, missed the date!
Hopefully he got the 920 sorted.

I'm always hopeful that someone will say
" Yes I rode it hard for 70,000 miles and it was ever so reliable"
Havent seen any 920 reports like that to date.
It's generally more like " I rode it for part of the summer but now its blowing oil and won't go more than 55 mph!"

I just had a coffee with Lance a few weeks ago. He has one of my heads on a pretty standard 850 which he has owned for a long time. I believe he still spends time in his workshop playing with his Norton stuff. He has been slowed up a bit with health issues, but I will get a message to him so that he can fill in the details.

Glen, Reggie and Matchless put decent road miles on their 920s I believe...

I was out on the 920 (my favourite bike) a week ago. Only did 140 miles as it was rather chilly & wet, but every one of them was a joy. Due to having lots of other bikes I have only managed about 7000 miles on the 920 motor, but it really is a lovely thing & coupled to the 5 speed 'box it's my perfect Brit bike. It is also oil tight, easy to start, & uses very little oil. It's so good in fact, they should be available on the National Health!

I've never ridden Martyn's (Matchless) 920, but I can vouch it's a lovely thing, in fact it's the best road going Norton I've ever seen and yes it should be available on the NHS.
sam

Martyn, how about posting a few pics of your bike ?

Martyn, which brand of 920 components are in your engine?
I have a very dusty RGM kit here.

Glen

Maney Barrels + JS pistons n rods + Martyn’s Engineering and mechanical flair !

Glen,
The parts are Maney cases, crank & barrels, Comstock modified Fullauto head, JS rods & pistons, PW3 camshaft, reed valve breather & Trispark ignition. In fact the only Norton parts left in the engine are the rockers, timing gears/sprockets & oil pump. This all makes for a very nice reliable road going engine, & worth every penny.
Sam, as you know I am rather clueless with computers, but Jim at JS Motorsports did post some pics of the bike when I first built it. I don't know if they are still on the site somewhere.

Lance has been given the message, but he could be in hospital at the moment for some surgery. I'm sure he will post when able.