Short stroke Nortons

Thanks Iain.
Good to hear that branch of evolution hasn't died...

Interesting sidelines in the autumn years of the OHC engine were Ray Petty's back to front cylinder head and Syd Mularney's four valve head, which once the bugs were sorted out was very successful on the racetrack.

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whistling Icon .



Was a Manx 4 valve head , to take std. camboxes , on Aus. ebay - not so long ago . or two . :?

Sid Mularney pictures are a bit hard to find . apparently if you have ' the Original ' its Classic Eligable . 8)

The ' supplied ' F-750 short strokes were said to be 80 H.P. , once blueprinted .
Supplied as a ' core unit ' , for fettling and finishing , rather than a ' as is ' unit .

The difference between a 4 valve Jawa Speedway engine and a two valve is a gain of about 10% more power. That doesn't necessarily apply to the 4 valve Triumph Weslake head compared with a 2 valve Triumph head. There is a serious question which should be asked and that is why the two valve 750 Commando engine is superior to the 750 Triumph two valve engine. My belief about the 4 valve Weslake head is that it allows higher revs to be used without a valve tangle. When the 4 valve manx was built they probably didn't have titanium valves available which might have given similar results. I remember a well built G50 fitted with titanium valves with 6mm stems, which beat every other 500 in Australian historic racing. If you get higher revs, the rest has to keep up and even with a stroke as short as 81mm in a big twin 10,000 RPM is a problem. You might get away with a 75mm stroke. A normal 650 Triumph twin will cop 8,000 RPM, however not continually. They are very rare in Australian historic racing these days, most have destroyed their bottom ends. That is why I persevered with the short stroke 500 Triton for all those years. In 12 years the only destruction occurred when I flipped the head off a valve at 11,000 RPM. It needed either the weslake head or Ti valves, and also a 6 speed box. In the end because of the race classes the exercise became pointless. And it was a bastard to ride anyway.
It would be interesting to do a controlled study comparing the Fullauto commando head with the weslake 4 valve head.

acotrel said:

There is a serious question which should be asked and that is why the two valve 750 Commando engine is superior to the 750 Triumph two valve engine.

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You are not serious, are you?

The angle between the valves on a Triumph is much greater than that of a Norton which nets a poor (steeper) combustion chamber; when increasing a Triumph piston dome height for compression, you get a poor performing combustion chamber. A poor combustion chamber shape requires greater ignition advance which always works against making good power. When I refer to combustion chamber here I am accounting for the piston at or near TDC.

Since the Norton valve geometery was rotated around the axis of the cylinder axis, Norton had (wanted to) to rotate the intake ports around the intake valve axis to achieve parallel ports. This yielded a much more favorable port to valve throat transition - a straighter shot into the valve throat. In simpler terms, the Norton intake has superior flow characteristics.

ntst8 said:

There was one racing in the just finished Manx Classic GP, but it was in the same class as the Paton twins.
Bruce Anstey came third overall (but i think first in class) on a McIntosh 1962 spec Manx, but considerably behind the 4 valve.

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Anstey came back this year with the intent of finishing and declared that he kept the revs down to do that.....saying '62 spec is misleading, for a bike last built by Norton to '61 spec...it is a brand new replica bike, better to ask 'what is the bore and stroke'

Molnar's 4 valver is short of development, mainly because he was banned from the UK short circuit race meetings he was trying to develop it in. (quite rightly in my own view). But he built if for the IoM to try and compete with the Patons. The IoM has adopted rules that allow a lot of modern parts on various machines. Molnar is clearly not there yet, and may never be, but logically, if he makes it work, 2 valve Manxes would become obsolete in these races.

However, there is rather more to finishing an IoM race than rpm or horsepower, ask John McGuinness....who otherwise might have won the race on a Paton.....or Michael Rutter, now the fastest ever round the IoM on a single cylinder bike, a 2 valve G50, which didn't finish either....

All of this BTW, is off topic, perhaps Jim should have called the thread 'Short Stroke Norton twins of 750 cc and over'

Chris said:

Have to say there are no 2 valve Triumphs running at the front in classic racing in the UK & they haven't for well over twenty years (the time I have been with the club)
Strangely all the Triumph twins running at the front have 8 valve top ends.
The front running twins are all weslakes the odd Norton BMW Ducati

But of course 4 valve heads are not any better than 2 valve Triumphs???????

I think the racing results speak for themselves

Chris

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Exactamundo Chris.

I have been fortunate to race (and road ride) a number of different variations of Triumph and Nourish motors.

I raced a very highly developed and very fast Daytona in 500cc Historic racing, but it could not keep with NREs. I went over to a NRE 500, first a Rickman frame and then a Manx frame, and the difference in performance is not even comparable. I also raced 850cc bored / stroked / squished Triumphs in the unlimited class, but when I went NRE, I got 12bhp more peak and huge increases in the mid range, and that's comparing an un developed 8 valve with my best ever / pinnacle performance 4 valve!

I've no interest in going further with any academic discussion with this acotrel, 8 valve Triumph based motors kick 4 valve Triumph motors into the weeds. Period. There can be no (sensible) debate about this.

However, if you wish to start a debate in the other classics section about how an 8 valve can be improved further by bigger valves, steeper downdraught, lighter valves, etc, etc. then that's another matter !!

Matt Spencer said:

The shorter stroke of the Triumph is the main reason that Triumphs are competitive with Nortons, otherwise the Triumphs have an inferior Head design and they wouldn't have a chance except for their shorter stroke.

O'Rielly :shock: Held the World Speed Record for sixteen years , can'tve been to slow .

Be intresting to see a destoked 750 for 500 class ( Norton ) or a 88 ( 72.6 mm ) stroke 750 , or suchlike . Any Flow figures on the P. R. Heads :?:

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Can you tell us more about the O'Rielly Triumph?

short stroke vs stroker motorcycle entertainment
https://www.google.com/search?site=&sou ... ZGnuvujn-E

Matt Spencer said:

The ' supplied ' F-750 short strokes were said to be 80 H.P. , once blueprinted .
Supplied as a ' core unit ' , for fettling and finishing , rather than a ' as is ' unit .

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And Ron Wood got 84HP and a free trip to the Nort factory to prove it (they didn't believe it). The Norton ultra short 77mm stroke has a 90 HP potential but its not been built yet and may never be. But I'd like to see one race with a top rider. All the specs are waiting for someone to get serious (welded head with HD XR 750 ports plans are in my computer). As for reliability - its already been proven with the David Watson/Gordon Humphrey/Gary Thwaites 1000cc bike. No guarantee that it would beat Weslakes with their midrange power but only one way to find out.

O'Reilly . https://www.youtube.com/watch?v=zyuS8GcENfQ ( O Realy , Faulty towers . :wink: :shock:

Er . . .

Intresting the Triumph runs 38 b.t.d.c. ignition & the Norton 31 b.t.d.c. , but theyre Both 3/8 b.t.d.c.

Ive a old magazine here , early fifties , refering to a Taitanium Con Ron in a Jack Williams G - 50 ,
and a few on his ' head development ' , ive been meaning to post here , tecnology & cost permitting .

The Old Gold Star 500 was 85 x 88 , so 84.5 x 89 would get 999 c.c. , ifitd fit .

Digressing a trifle ; further . :x

T100 R , note the 136 mph . As its 80 mm stroke , that there matches the short stroke 750 stroke .
the JoMoCo Valves in mine , built / tuned pre 63 - when the ace snuffed it geared for 120 & 7000 ,
ran 7600 with the red mist , still going. Before outbrakeing the ' chap ' on the methanol 650 id repased
after buttoning off at 7000 ( Er 7200 , back to 7000 . WHAT not having this ! :shock: 8) ) later found the ' R '
redline was 8000 . :x like 30 years later . Was in a lightweight Triton on Av Gas , pretty useless on 98 pump gas.
Pulled from about 5000 . Did five meetings on it , in 1981 . :|

ANYWAY , the measured 7.25:1 C.R. matched the AMA Class ' C ' race regs of 7.5:1 max .Still needed Av Gas !
Can assure Acc a 650 will happily pull past 8.000 , or intently , at least . The TRIUMPH high dome pistons
were the cause of the Dual Plug and Central Plug crack the head nightmare . Putting oversize Valves 9 the 750
valves they all say are to big :lol: in the 40 over 40 inch , gets them out and proud ( just ) of the bowls .
Thus when theyre open theyre OPEN . Stock 61 T120 cams in the 61 T120 , with the lighter 68 / crank ,
and it GOES . with one or two exhaust mods . ( a stock 750 roadster not in the ballpark there, sorry chaps )

Next we'll mention it was EIGHT STUD , not the Unit head , And there were at least THREE ( stock T120 )
eight stud heads . A balnced combination rather than the Max Overkill approach , 17 yr old on a budget .
HALF of my monthly pay . 300 a month spent for about six months replaceing ALL suspect parts . Right What .



Gearing on the 24 T ( engine ) sprocket std. gets it coming on the pipes at 93 / 94 mph , running to 105 / 110
mph . In THIRD . a mathematically competant chap can thus derive top gear figures . ( Just a moment ) .
Though it'd run through to valve surge in top under favourable conditions . This was a ROAD BIKE , though ,
please note .
makes it 111 in top , though you only got this effect ' backed off a notch , hard out it'd come in around 5000 .
std ( not Close ) ratios . run through to 131 in top , mathematically - though thats the ' straigt to ' speed .
like anthing else unless overgeared , itd pick up another few mph once settled in up there , thus the valve surge.
Regret it never got the 25 t.
Didnt grenade till the second owner after on unit Primary gearing wit retards on a fresh engine build playing
in the mud . Apparently a mad caked motor doesnt cool well , so isnt a race proved option .Winkers !
( and thats NOT a ' i ' there . :wink: )
Right back to the plot , I figure you need a four inch bore for TWO sets of 750 valves , for a four valve .
And the 80 strokes fine , there . Current development is a 90 bore 4V , 35 in. & 31 ex. valves . 8 total .

Though if anyones got a spare low time Mk 5 750 spare , feel free to donate it to yours truely .

Back to CHAMBERS , the T120 ran 9.75 actual with 9.5 pistons , the Comando measuerd 8.7 , probly
why it was still streetable , higher C.r. I think wouldve made it entirely vicious , not just over 5000 .
intrestingly just throwing in a std. cam to replace the SS Combat got it enjoyable to ride , as in you
could relax , rather than maintain a eternal watch for ' obstacles ' , in town . also a good deal less critical
on throttle modulation under 2000 . Prviously you ALWAYS let a car get a letght ahead , if in traffic at
the lights , as ' walking pace ' wasnt a option , geared for 130 @ 7000 . Maybe the Air was a lot cleaner ,
more oxygen , less CO2 back then . :twisted:

SO , a supercharged short stroke 750 would go quite well . :twisted: :mrgreen:
Not trying to knock the Nortons here , but the Triumphs justify Defence . With No Exageraton . :|

The Simmons Said there 72 PR outaccelerated their imola Duke . though they were ring ding alingers .
and out top ended it too . Road Ridden back 77 or so , as useless ' Race ' Bikes . For yamahaha 350 kids , anyway.

Matt Spencer said:

Ive a old magazine here , early fifties , refering to a Taitanium Con Ron in a Jack Williams G - 50 ,
and a few on his ' head development ' , ive been meaning to post here , tecnology & cost permitting .
.

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Assuming thats just an odd way of speeling titanium - it has long been rumoured that some of the factory manxs had a titanium rod,
and some of the top tuners too. Thats how they got them so reliable.
It was also said that it was true exotica back then, and $$really expensive$$ - the rod was worth more than the bike was.
And houses were cheaper than new bikes... But we diverge.

To undiverge, where do we wire $$$ to for this 4 inch bore 8 valve beastie. ?
P.S. You can buy such things for HDs, but not sure they'd bolt on to Norton cases...

jseng1 said:

All the specs are waiting for someone to get serious (welded head with HD XR 750 ports plans are in my computer).

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What is it about the XR750 ports that appeals ?
Apart from all the love and attention and huge amounts of development that went into them,
not to mention the hp that comes out of them...

Jim showed us the HD ports have big oval shaped cross section. Brain Stark of Barbers told us Harley used ex-Norton Hopper's head design in Evo engines so essentially identical otherwise but don't know if so in XR heads.

Rohan said:

jseng1 said:

All the specs are waiting for someone to get serious (welded head with HD XR 750 ports plans are in my computer).

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What is it about the XR750 ports that appeals ?
Apart from all the love and attention and huge amounts of development that went into them,
not to mention the hp that comes out of them...

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Rohan - I think you just said it all in your paragraph above. To see the Harley ports and molds go to:

norton-intake-ports-compared-harley-750-t16544.html?hilit=harley

They are a radical departure form the round port norm. The development has already been done. It just needs to be applied to a Nort. It may have been done already by someone (there are rumors).