750 short stroke engine

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Evening all,

My 1972 Roadster has a short stroke engine which was fitted by Mick Hemmings many years ago.

It runs nicely but I would like to check the valve clearances. Am I right in assuming that they are 6 & 8 thou as per the 750? Also what plugs are recommended?

Would anyone be able to point me in the right direction for written spec for these engines and a source of spares should I need them?

Thanks…….Shaun.

Depends on the camshaft.…

Depends on the camshaft...

Some clearance figures for you here (bottom of page):
https://norton.norvil.net/tech03.htm

Plugs: N7Y should work fine.

Are you sure it's a short-stroke? They are rocking-horse poo rare.

Hi and thank you for your helpful comments.

The Head is stamped RH7.

The engine is stamped H1649 (lower left) and 235566.

The Black barrel has an 850 casting number.

I've been sifting through the pile of paperwork that came with my bike and have found out so far.....

Mick Hemmings has done a lot of work to this engine including fitting a PW3 camshaft, Wiseco pistons, MH (his own?) big valves, Nimonic 08 exhaust valves, 06.7820 cam followers and a raft of other engine work.

I also have a letter from the parts and service manager of Norton Triumph Europe dated 1976 offering to sell Mick 2 short stroke engines for £490 + vat for both!

There's other paperwork & info referring to a 750 short stroke engine.

I'm sure that these details alone are not enough to ascertain that this is indeed a short stroke engine but I'm intrigued now.

This bike is my third Commando and what I do know is that the engine characteristics are very different to my others. When you get to about 3500 rpm the thing just takes off and keeps revving!

Your thoughts (and valve clearances!) would be most appreciated.

Thanks............Shaun.

That's a special bike you…

That's a special bike you have. I've never seen a 750 short-stroke running, several "this is a conrod and piston out of a short-stroke", but never complete, in a bike and running.

Consensus here: https://www.accessnorton.com/NortonCommando/pw3-cam-timing.14255/
is that valve clearances are 0.011" inlet & exhaust. But you might check with Norman White, http://www.normanwhite.co.uk/p_w.htm , who will be able to give you chapter and verse on the short-stroke engine.

Yes, the short-stroke revs - that's how it makes power. Best check with Norman White but I'd suggest you'll need to rev it to 8,000 to get full power.

And, if you want to swap it for a more road suitable 750 Combat or 850 plus a bit of cash, drop me a line :)

235XXX confirms it as a…

235XXX confirms it as a short stroke 750 crankcase but there were some 850's stamped the same just to confuse matters but the short stroke cases could be used for either. Doubt they were really bothering matching numbers to engine type when the orders did not come in for the short stroke, regardless you have enough documentation to support it being a Factory 750 short stroke.