ESE's works engine tuner

[TZ350]

Eric Offenstadt NSR 500V https://www.mcnews.com.au/honda-nsr5...ic-offenstadt/

That is a very interesting bike. I particularly like the chain idler pulley. AS well as neutralizing some of the chain pull effects on suspension geometry. It looks a great way to stop the chain dragging on the swing-arm. I am going to copy the idea for my bike as the chain is slowly cutting its way through the swing-arm pivot on my beast.

https://www.mcnews.com.au/honda-nsr5...ic-offenstadt/

[husaberg]

That is a very interesting bike. I particularly like the chain idler pulley. AS well as neutralizing some of the chain pull effects on suspension geometry. It looks a great way to stop the chain dragging on the swing-arm. I am going to copy the idea for my bike as the chain is slowly cutting its way through the swing-arm pivot on my beast.

https://www.mcnews.com.au/honda-nsr5...ic-offenstadt/

ATK used to do it with two small sprockets one top one bottom.
https://motocrossactionmag.com/the-r...horst-leitner/

[Michael Moore]

The large idler wheel will give a lower RPM at the bearing than the small wheels/sprockets, but it is more difficult to fit in an often crowded space. An idler that locates the bottom run of the chain can adjust the reaction to the lower forces on the over-run.

[F5 Dave]

My understanding is that will absorb a decent amount of power, if it gets warm you'll know, but try it on the dyno.

[JanBros]

I particularly like the chain idler pulley. AS well as neutralizing some of the chain pull effects on suspension geometry.

you also lose the benefits of the chain-effect. there is a reason not a single racing motorcycle uses this ;-)

[Michael Moore]

You can also have too much chain effect which is one reason why so many powerful race bikes have adjustable swing arm pivots. In addition, it may be that they are not so much trying to increase/reduce the chain effects, but to reduce the amount of variation in them in the working area of the rear suspension so the suspension can work smoothly based on contact patch loads and not the chain jerking things around.

Chris Cosentino has used dual idlers to control chain forces on his Rotacular singles and had them as a design feature on his Moto2 project (thanks for killing that FIM with the "no prototypes" rule):

http://www.eurospares.com/graphics/c...singleiso2.jpg

[Pursang]

Countershaft sprocket is nice and close to swingarm pivot.

C/S is inline with S/A pivot or slightly above.
This can cause chain to contact the bottom of the Swing arm, during suspension compression.

C/S sprocket is about as small (13T) as would generally be recommended.
A larger sprocket would provide more S/A clearance, but require correspondingly larger rear sprocket to maintain ratio.
(More chain length, more mass, more inertia and more unsprung weight.)
Idler, as positioned, keeps chain further away from S/A than it would be without one.

Idler is significantly behind S/A pivot, and located on the frame, not on S/A, so does not really try to eliminate chain length variation through the suspension travel.
Hence, spring loaded chain tensioner, fitted on bottom of S/A.

Idler is 'sort of' in line with lower pivot point of suspension unit and might also be intended to direct squat/anti-squat chain forces to the line of action of the rear suspension.
Is this a good thing? Too many unknowns and variables for me to know.

But I give 1 point to the builder, for trying something outside the box.

Cheers, Daryl

[TZ350]

But I give 1 point to the builder, for trying something outside the box.

Totally agree, ....... for trying something outside the box.

[pete376403]

BMW G450X had the countershaft sprocket centre in line with the swingarm pivot, so chain tension remained constant and to reduce chain effect on the rear suspension

[diesel pig]

BMW G450X had the countershaft sprocket centre in line with the swingarm pivot, so chain tension remained constant and to reduce chain effect on the rear suspension

Which is the gimmick Bimota used in the 1970's but had forgot about by the 1990's.

[andreas]

Old gold Blair. He says 23* spark advance is optimum. How would a kart 250 single spark graph look, like 19* at peak torque?

[OopsClunkThud]

Have a scavenging balance question. Is there a recommended target or range for the 'radial scavenging direction resultant'?
Clearly it's bad if it's greater than 90°, but is 90° the target or is it better to keep the resultant leaning away from the exhaust to keep it attached to the back wall?

Cylinder I'm starting with has a resultant of 73°

I understand this method is only a guidance and starting point, but that's where I'm at with this cylinder.

[Frits Overmars]

Have a scavenging balance question. Is there a recommended target or range for the 'radial scavenging direction resultant'? Clearly it's bad if it's greater than 90°, but is 90° the target or is it better to keep the resultant leaning away from the exhaust to keep it attached to the back wall? Cylinder I'm starting with has a resultant of 73°.
I understand this method is only a guidance and starting point, but that's where I'm at with this cylinder.

With a radial scavenging direction resultant of 73° the scavenging column is leaning away from the exhaust, which in itself is a good thing: no losses.
But if you wish to maximize the transfer area, you'll also need ports more or less opposite the exhaust port, which will make the scavenging column lean towards the exhaust. A little leaning can be tolerated as a compromise (more area and more losses), but do not go too far past 100°.

[Frits Overmars]

Old gold Blair. He says 23* spark advance is optimum.

Blair wrote that this value was for a designed BMEP of 105 psi, or 7,24 bar in real money. That was some time ago, in 1971.
The Aprilia RSA, a somewhat younger engine (2005), has a BMEP of more than double that, at 16° spark advance. Take your pick.

[wobbly]

Blairs 500 single was hamstrung by super conservative design elements.
A square Exhaust port - parallel header - 120mm skinny pipe etc.
This then results in very low dynamic compression, and with the low bmep generated , peak combustion efficiency was only gained with a ton of advance.
Modern race engines generate double the bmep , and all end up needing around 15* advance at peak power.