Building new short stroke engine

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comnoz said:
With modern materials it isn't hard to turn a long stroke over 9000 reliably. I have run one to 9500 with a reworked stock crank and Carrillo rods. It took me a while to figure out why the horsepower was on the downward spiral over 8200 no matter how it was cammed, carbed or flowed. Then I learned about piston friction and how it increases with piston speed and it all became clear. Jim
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Would the shorter piston like Jim's have made a difference?
 
It wouldn't make the friction loss any better. Pretty much stuck with that.
It would help with reciprocating weight and therefore the small loss from vibration.
 
swooshdave said:
comnoz said:
With modern materials it isn't hard to turn a long stroke over 9000 reliably. I have run one to 9500 with a reworked stock crank and Carrillo rods. It took me a while to figure out why the horsepower was on the downward spiral over 8200 no matter how it was cammed, carbed or flowed. Then I learned about piston friction and how it increases with piston speed and it all became clear. Jim
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Would the shorter piston like Jim's have made a difference?
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I think it will. With Jim`s pistons, your also need longer rods. Longer rods gives smaller force betveen piston and sylinder and less friction.
 
Kvinnhering said:
swooshdave said:
comnoz said:
With modern materials it isn't hard to turn a long stroke over 9000 reliably. I have run one to 9500 with a reworked stock crank and Carrillo rods. It took me a while to figure out why the horsepower was on the downward spiral over 8200 no matter how it was cammed, carbed or flowed. Then I learned about piston friction and how it increases with piston speed and it all became clear. Jim
Click to expand...

Would the shorter piston like Jim's have made a difference?
Click to expand...

I think it will. With Jim`s pistons, your also need longer rods. Longer rods gives smaller force betveen piston and sylinder and less friction.
Click to expand...

But no matter how hard the piston is thrust against the cylinder wall it is still riding on a film of oil. Rod length doesn't come into play. A good synthetic oil is about the best thing you can do but the actual benefit is small.
That wall you run into when increasing the piston speed has not been breached. That is why all modern performance engines are short stroke. Jim
 
Very educational, even if disappointing on our long toke Nortons rpm friction. Will be interesting to follow this build to see if a short stroke can be made as exciting as plain long stroke, seeing as how it ain't being rev'd to take advantage of its configuration. Also cost per usable performance too.
 
Kvinnhering said:
RennieK: The crank is 360 and I use the original height of the barrel. The rods are longer to compensate for smaller stroke. I have the original cylinder and bought +20 pistons from Jim.
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I thought Jim's Corrillo rods and piston set pretty much equalled a stock Norton rod and piston height at the top of the barrels. The rods are longer but the wrist pin to top deck height of the piston was shorter so the end result was equal compression more of less. With Jim's normal kit for the Norton in an 80.4 stroke crank would result in a 4mm lower piston deck with stock barrels. It sounds like you have even longer rods then or the piston wrist pin to top is longer.
 
RennieK said:
Kvinnhering said:
RennieK: The crank is 360 and I use the original height of the barrel. The rods are longer to compensate for smaller stroke. I have the original cylinder and bought +20 pistons from Jim.
Click to expand...
I thought Jim's Corrillo rods and piston set pretty much equalled a stock Norton rod and piston height at the top of the barrels. The rods are longer but the wrist pin to top deck height of the piston was shorter so the end result was equal compression more of less. With Jim's normal kit for the Norton in an 80.4 stroke crank would result in a 4mm lower piston deck with stock barrels. It sounds like you have even longer rods then or the piston wrist pin to top is longer.
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Yes, Jim does an even longer rod for the 80.4 crank, I have those, by waht he says 'Kvinnhering' does too.
 
comnoz said:
With modern materials it isn't hard to turn a long stroke over 9000 reliably. I have run one to 9500 with a reworked stock crank and Carrillo rods. It took me a while to figure out why the horsepower was on the downward spiral over 8200 no matter how it was cammed, carbed or flowed. Then I learned about piston friction and how it increases with piston speed and it all became clear.

Depending on gearing and the track it may be an advantage to rev it beyond the power peak but don't expect a power gain up there. A short stroke generally adds an extra 1000RPM. Jim
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I put a short stroke 750 from one of the factory flat track bikes (John Hateley's) into my PR and raced it for a few years. It wasn't nearly as extreme in buld as some of your long stroke monsters, Jim. It had a Sifton 460 cam and even larger than original valves in the full hemi head, but was not real high compression, just under 10:1. As I recall, it hit peak horsepower at about 7200 rpm, and was fairly flat up to 7700 rpm. In racing I used a 7500 rpm redline (more or less!) because of concerns about the crankshaft and crankcases. It got a lot of racing miles on it, but eventually broke one of the stock steel rods and chewed up everything except the head.

Ken
 
comnoz said:
The advantage is the ability to turn high RPMs without suffering from the power loss from piston friction.

Friction loss goes up on a very sharp curve when the piston speed gets above the recommended maximum speeds. Friction loss becomes a serious player on a longstroke at around 6000 RPM. Somewhere around 8000 rpm with a longstroke motor, it becomes impossible to make additional horsepower gains from RPM. Any possible gain will be eaten up by friction loss. Jim
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Did you ever look at using just one compression ring and low tension oil rings? Probably not a very clever idea for a street bike but it may help for a race engine. The ring profile and ring-ring groove clearance could have a significant influence here as well with the formation of the hydrodynamic film between the ring and liner. I have got some measured plots of lubricated piston ring liner friction forces somewhere although I never did work out the power loss from different parts of the stroke, I was also only really looking at ring wear so I didnt take much notice of the mid stroke speed as it usually has not metal to metal contact.
 
In my racebikes I normally used the 1mm compression rings and a 2 mm low tension oil ring. Jim
 
SteveA said:
RennieK said:
Kvinnhering said:
RennieK: The crank is 360 and I use the original height of the barrel. The rods are longer to compensate for smaller stroke. I have the original cylinder and bought +20 pistons from Jim.
Click to expand...
I thought Jim's Corrillo rods and piston set pretty much equalled a stock Norton rod and piston height at the top of the barrels. The rods are longer but the wrist pin to top deck height of the piston was shorter so the end result was equal compression more of less. With Jim's normal kit for the Norton in an 80.4 stroke crank would result in a 4mm lower piston deck with stock barrels. It sounds like you have even longer rods then or the piston wrist pin to top is longer.
Click to expand...


Yes, Jim does an even longer rod for the 80.4 crank, I have those, by waht he says 'Kvinnhering' does too.
Click to expand...
Thanks for clarifying Steve. What bore size are you using? How does the engine perform with your configuration or is it a work in progress?
 
The project goes slowly forward. New crankcase from Maney been purchased and is located on my bench. Fine piece of work, but 1.43 kg heavier an original.
I have adjusted the axial clearance to the crankshaft to 0014 "(0.35 mm). Camshaft has a clearance (0.021") 0.54 mm so this must also be adjusted. But the question is, where can I buy shims that I can place the behind the sprocket? Or should I make shims by myself?

Kvinnhering
 
On a standard motor the cam end-float is 'managed' by the bevelled shim adjacent to the worm gear on the cam behind the timing-side case.

I've never measured it myself, but I'd assume (dangerous,I know!) that the intermediate gear and cam pinion are the same width with respect to the sprocket distance from the crankcase?

I'm intensely jealous of what you're doing, and you could make this far worse by posting photos ;)
 
Fine piece of work, but 1.43 kg heavier an original.

Kvinnhering[/quote]


This provides greater dimensional stability ( STRONGER ) Kent blocks ( Ford 1600 ) are neaer twice the Wt in the late high output series , 10 yrs development .

He recomends the tirteen thou Crank end float ?? 6 or 7 thou ordinarilly ? Probably the greater dimensional stability requires the larger setting . 8)

7.500 is fairly conservative , should give good service life . But maybe at or below peak output rpms . 8.000 was the resason D'tair (however you pronounce it )
of the short stroke .
Reading all the drivle , it comes to Williams useing 7.500 on the std. works 750s , and Maybe Dunstall . For RACEING .I.E. regular overhaul & Inspection .
 
Kvinnhering said:
The project goes slowly forward. New crankcase from Maney been purchased and is located on my bench. Fine piece of work, but 1.43 kg heavier an original.
I have adjusted the axial clearance to the crankshaft to 0014 "(0.35 mm). Camshaft has a clearance (0.021") 0.54 mm so this must also be adjusted. But the question is, where can I buy shims that I can place the behind the sprocket? Or should I make shims by myself?

Kvinnhering
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The camshaft end float is not very important. There were no factory shims, with yours at 021" its OK. Remember this is chain drive, the drive sprocket is going to pull the cam sprocket to where it wants it to be.

Mick
 
1.43 kg = 3.15 lb. Most of that in the inch thick DS face to take the crank shaft fling and torque loads at hi rpm. Helps lower CoG and only uses up 1/2 hp in extra mass, which is supposed to be worth it for the extra power it tolerates.

Tach drive is what sucks the cam to RH limit of its cone spacer and flat thrust washer. If no tack drive, chain not likely to hold full to RH so back to shims to limit LH drift.
I think Maney blocks are configured to take factory innards so no special RH spacers needed.
 
Maybe not camshaft end float is not Very Important, but NOC Tech Digest says that ideal endfloat for all Norton twins is 005 "(0.127 mm). Crank endfloat is rated at 010" - 024 "(0.25 to 0.61 mm) .
I will try to adjust the clearances to these recommendations. So, does anyone know where I can buy shims for the cam :?:

If it turns out that the power curve is over 7500, I will follow up to 8000 PPM. Remember that I only have Stage 1 camshaft from Jim. :)

And yes, I will post pictures soon. I just take a business trip to Poland first :wink:
 
Following this thread with extreme interest as Bike #2 project engine will be rebuilt along the same lines.
What balance factor are you aiming for?
Any chance of some pics?
Regards Mike
 
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