Short Stroke ~ High Compression

comnoz · Nov 23, 2014

X-file said:
Dances with Shrapnel said:

Why do you say 65% wet is the least stress on the crank. Are you considering peak load alone (which is really not that critical) or more important, the magnitude of the load reversal which has direct bearing on the crankshaft life?

Click to expand...

Yes, I'm considering peak inertia stress alone, because peak stress is what breaks things (in this case the crankshaft).
There will be enough cyclic applications of that peak stress until something finally breaks. If that stress was being constantly applied at the same magnitude and in the same direction there would be no metal fatigue, but it isn't.

You get close enough to full reversal of direction, if you consider the imbalance situation at TDC and again at around mid-stroke.

65% [actually 66%] is the point of least stress on the cases of a rigidly mounted engine. [like mounted in concrete]

When the engine is mounted in a frame -particularly a Commando - where the engine [and/or motorcycle] is able to move up and down more freely that it can move forward and back -then that figure will vary. Jim

Dances with Shrapnel · Nov 23, 2014

comnoz said:
With modern materials an 89mm stroke small bore engine can easily be spun to 10,000 rpm without breaking - but the friction vs piston speed wall would still be there and would still make turning the engine beyond about 7500 rpm pointless as far as building more horsepower. Jim

Jim, this begs the question: How does NASCAR and Formula 1 get away with mean piston speeds of 130% to 135% of our Norton twins?

I want what they have!

In all seriousness I read about the use of DLC for pistons and have raced with rocket scientists who have reduced ring force by back cutting the rings but........ Reducing piston thrust? Smaller skirts? Extra slippery oil? Where is the black magic?

Rohan · Nov 23, 2014

Dances with Shrapnel said:
In all seriousness I read about the use of DLC for pistons and have raced with rocket scientists who have reduced ring force by back cutting the rings but........ Reducing piston thrust? Smaller skirts? Extra slippery oil? Where is the black magic?

Quite some time back, it was mentioned that someone in F1 was applying 20+ different coatings to the pistons.
No other details supplied....

Oil jets supplying some serious cooling to the pistons has to be a part of it, or they'd simply melt ?

Can you make pistons out of titanium ?

Racing pistons have had only one piston ring for quite some years,
this was already common back in the 1950s.

Matt Spencer · Nov 23, 2014

Reducing piston thrust? Smaller skirts? Extra slippery oil?

Desaxe , Lighter Pistons , Differant rod length . Gudgeon location .

Shorter skirts usually leads to rocking . ( or is that V c V . )

matched component weights amougst other things , stops you having ' two singles .'

Thats why with your head up your Rs rohan . that theres only pansy twins made today .
puttem on 80 % nitro & theyd grenade . Though most of thatd be the turkey on the spanner . :mrgreen:

Rohan · Nov 23, 2014

Haven't had your meds yet Matt ?
It shows...

Can we have some nouns and verbs in your sentences please,
just to give some meaning, you understand.

Hobot · Nov 23, 2014

Alirighty then Jimmie and Jimmy, you 2 verify my understanding on this subject so thank you. i think Peel with the best stuff inside and built loosely with tapered bores + a hand full of treatments may be worth turning to 8 grand now and again, which may be about when the Drouin poops out so time to up shift to next wide gear ratio. If I hear much piston slap may suck em out to knurl em like past over rev'd Peel. Also can use the witness marks to hand file special shaped oil spreading recesses in piston load baring sides. Got a bit of practice on mower pistons with chain saw file leaving perfect feathered profile.

Rohan · Nov 23, 2014

Tapered bores died out in the 1920s, Steve ?
Things like J model Harleys had it, at some stage - and it was darned hard to get a good rebore job, by all accounts.

It was inclined to break piston rings at higher rpms ?
The factory race bikes didn't use it, for long ??

comnoz · Nov 23, 2014

Dances with Shrapnel said:
comnoz said:

With modern materials an 89mm stroke small bore engine can easily be spun to 10,000 rpm without breaking - but the friction vs piston speed wall would still be there and would still make turning the engine beyond about 7500 rpm pointless as far as building more horsepower. Jim

Click to expand...

Jim, this begs the question: How does NASCAR and Formula 1 get away with mean piston speeds of 130% to 135% of our Norton twins?

I want what they have!

In all seriousness I read about the use of DLC for pistons and have raced with rocket scientists who have reduced ring force by back cutting the rings but........ Reducing piston thrust? Smaller skirts? Extra slippery oil? Where is the black magic?

The large bore means they can use large valves plus they have downdraft ports to make extra torque at higher speeds. They can overcome the friction to a higher piston speed.
Of course even then they are well into the downslope of torque/horsepower output at 9000 rpm. They only rev them that high so they have high enough speed and still be geared low enough for corner exits without shifting.

Rohan · Nov 23, 2014

comnoz said:
at 9000 rpm. They only rev them that high

I have seen somewhere that those pistons don't have a very long potential life at that speed.
They change and discard them fairly often ?

Matt Spencer · Nov 23, 2014

Sorry , we don't reveal classified secrets to Gulag Retardis Australlis .

though evident to any THINKING ' rational ' being , a Infernal Combustion Engine is a Ottocycle engine .

WW1 design era

notice the simalarities . Are you a POM or a Queenlander Rohan . or BOTH .

Matt Spencer · Nov 23, 2014

Sorry , we don't reveal classified secrets to Gulag Retardis Australlis .

though evident to any THINKING ' rational ' being , a Infernal Combustion Engine is a Ottocycle engine .

WW1 design era

notice the simalarities . Are you a POM or a Queenlander Rohan . or BOTH .

Hobot · Nov 23, 2014

Tappered bores were all the range in 1930's design aircooled engines and if questimated right by a machinist with long seasoned finesse the bores should become truer when going get fast and hot. Has anyone kept track of where in stroke the failed side occurred? Besides we know Nortons can run w/o failure with bores more worn out in worse area than Peel's taper.

Rohan · Nov 23, 2014

Are these just random dissassociated thoughts Matt, or is there some purpose to them.
You really are going to have to explain, or we are just left wondering wtf ?

Rohan · Nov 23, 2014

Where is your bore tapered Steve, and by how much ?

Sidevalve engines were sometimes bored with the cylinder hot and a torque plate fitted,
but tuners had to know what they were doing with this.
It saved extensive running in....

acotrel · Nov 23, 2014

What is this 'running in' thing ?

Rohan · Nov 23, 2014

Never owned a sidevalve Allan ?

Thats a trick that all the top tuners use.
Or perhaps used, past tense, since side valves are not terribly current in todays crop of superbikes....

comnoz · Nov 23, 2014

Rohan said:
comnoz said:

at 9000 rpm. They only rev them that high

Click to expand...

I have seen somewhere that those pistons don't have a very long potential life at that speed.
They change and discard them fairly often ?

They don't change them more than once per race.....

Rohan · Nov 24, 2014

comnoz said:
They don't change them more than once per race.....

!!!!!!!!!!!!!!!

Rohan · Nov 24, 2014

Somewhere it was mentioned that the cranks in the racing Tridents were changed quite frequently,
every 2 races was it ?

Manx Nortons changed the clutch between practice and the IoM race.
Along with the chains, tyres and valve springs, and ??

The price of racing reliability....

Hobot · Nov 24, 2014

One big reason for Peel's delay is making her about bullet proof with rpm factiods impressed beyond anyone limited views if only concerned with engine internals rpm tolerance. Peels targets don't have vintage limited anything so tire snapping frame twisting torque is only hope to make it to next turn first before their pile ups start and get down to business. Will be fun pitting torque against hp, skinny vs fat, soft center vs solid to the core, direct pilot control vs digit brain inferfaces, etc etc.

Someday a few folks will conspire to build isolastic frame that can take the new design wider cases for the over square big bore engine with the crank flex controled and optional planetary gear drive blower that don't stick out to foul leans over 55'. Then a comet strikes...

There's hp to free in here, just not for free, but what extra hp is?
https://www.google.com/?gws_rd=ssl#q=in ... gws_rd=ssl#q=internal+combustion+engine+friction+lossesfriction+losses

Short Stroke ~ High Compression

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