Here's a photo for reference of a short stroke 750 that was on a production racer at the Quail show in Carmel, Ca last May. engine number is 235713.

I do like the position of that relocated crank breather.

pvisseriii wrote:I do like the position of that relocated crank breather.

Got the same breather mod on my '72 combat.

nortonspeed wrote:Just to show you how good the RH7 heads were: in the seventies me and a friend built two 850 longstroke Commando racing engines, mine with (expensive) RH7 head plus Omega pistons and my friend used his own RH10 head tuned by Mick Hemmings (big valve conversion at half the price of a RH7 head) with flat pistons. Apart from the heads same engine specifications (including compression ratio). The "RH7 Commando" could keep up with a 1000 MG LeMans (big bore 850) not in the least due to weight advantage but the "Hemmings big valve conversion Commando" wasn't up to the same performance.

Gooday nortonspeed,

Pleased to hear the omega pistons worked with RH7 heads. I have heard a few negatives. The motor is to be the core of a period correct road/track bike that best reflects the 750 short stroke era. There are not many original motors left and I felt compelled to save this one. I am now looking for omega pistons.

Cheers

illf8ed wrote:

pvisseriii wrote:I do like the position of that relocated crank breather.

Got the same breather mod on my '72 combat.

Yeah, but it's in the wrong place.

I've got both breathers on my '72 Combat--the conventional one plumbed to the oil tank and an 850-style timing-case breather exhausting to atmosphere through a mini-pod filter--it is truly astounding how much air moves through both at idle


Tim Kraakevik
kraakevik@voyager.net
'72 Combat, '74 RH10 850

Nortiboy wrote:

nortonspeed wrote:Just to show you how good the RH7 heads were: in the seventies me and a friend built two 850 longstroke Commando racing engines, mine with (expensive) RH7 head plus Omega pistons and my friend used his own RH10 head tuned by Mick Hemmings (big valve conversion at half the price of a RH7 head) with flat pistons. Apart from the heads same engine specifications (including compression ratio). The "RH7 Commando" could keep up with a 1000 MG LeMans (big bore 850) not in the least due to weight advantage but the "Hemmings big valve conversion Commando" wasn't up to the same performance.

Gooday nortonspeed,

Pleased to hear the omega pistons worked with RH7 heads. I have heard a few negatives. The motor is to be the core of a period correct road/track bike that best reflects the 750 short stroke era. There are not many original motors left and I felt compelled to save this one. I AM NOW LOOKING FOR OMEGA PISTONS.

Cheers

Here you are Nortiboy, good luck:

by ZFD » Sat Oct 15, 2011 7:39 am

If anybody needs short-stroke pistons- I have about two dozen pairs, STD and +.020"...... not useable in a standard engine without mods because the gudgeon pin diameter is bigger. Apart from that nice high-comp pistons! And a set of those bloody heavy steel conrods- would not use them if I could help it. Which I could, using standard production ones and shortening the barrel.

Joe S.

David ,
off topic , but whatever goop you used to seal the cases , you used way too much of it .
If it bulges out like this on the outside , it will do the same on the inside :
And you don't have a mesh filter plug ..

Interesting to hear about Nortonspeeds 850 'short stroke'. I also built one, but courtesy of a former Norton employee! So it was not so expensive, but Mick Hemmings did become familiar with parts of it. Empirically, yes the Omega piston and the full hemishere worked, it was faster than the 750 and 850 Nortons I raced against.

The Omega pistons I had were machined with the smaller gudgeon (piston) pin hole from the blank, so were fitted with standard alloy rods on a MkIII crank in MKIII cases, cam was marked TX so was similar to 4S, but maybe more like PW3 in reality.

The motor as originally built ran 150mph, 6,700rpm approaching Knickerbrook at Outlon, with no chicanes.....and out dragged John Caffreys 840, 180 crank Weslake, which pissed him off just a little....pissed him off more that when he asked 'whats in there', I just said, 'standard Norton mate'....didn't fool him much because the head fins and exhaust ports were machined away to let the motor fit into a monococque frame.....

(He told me he had trouble push starting the 180 crank motor, and had been passing a couple of bikes each corner until he came up behind me through Island....he expected to get by on the power like he had with everyone else, and I just powered away....and di that well enough to keep him there till the flag even if he was a quicker rider...)

Norton themselves built a couple of motors to this spec when the rules allowed 850cc, F750 did not and they did race the short stroke, contrary to a suggestion above. Don't forget that if you want to build one today then you can get extra long rods from Jim Schmitt, for use with his pistons and especially for short strokes, I have a pair.

Then one day I hung on at the end of a straight fighting with a TZ350 and I let it run to 7,200 running low gearing and the motor dropped a valve......so I had to take the head to Mick Hemmings to recover it, but the barrels needed +40, and the pistons were unobtanium, so we had 40 though off the head face 60 though off the barrels to get similar 10.25 compression with flat top pistons from Hemmings, though I had to have a champher put on the top edge of the pistons to get a working clearance with the hemishpere.....in this spec it was not quite as quick, still made strong power and normally then only revved to just over 6,200 but would still pull high gearing, probably by then I was braking later as well

The Rickman cost me about £1200 to build, winter of '75/76 using a new chassis, but Norton were trying to sell their 750 Short Stroke Clubman racer in the UK for over £1450, no it was not popular, and taller and heavier than the Rickman. Most open class Norton racers of the day were then Seeley or Rickman framed, and that year Yamaha did a special on TZ350s for £1200 including a few spares....70hp lightweigh two stroke with international potential!