ESE's works engine tuner

[wobbly]

You have to be very carefull with the switch point and the run time on the dyno.
The switch point is dead critical to 100rpm,so i always set it too high initially and make sure that the dyno is loading the acceleration rate to be as close to that on track as you can.
This gives the pipe time to heat up and affect the power over the top, as it would in reality.
On a RS250 dropping the switch point from 12800 ( std) to 12400 gives easily another 800 rpm of virtually no power drop past peak.
On the track,if the rider can feel the switch point ( it feels like hooking another gear)the jet is too big,when its right it should be seamless and just keep reving out.
Leaded fuel is the opposite to unleaded, in that as leaded likes to run lean - you can only use a small powerjet and thus only switch off a small amount.
A leaded engine works best with around 35 to 38 PJ, the unleaded fuel can switch a 60, in Keihin numbering, as the crap fuel makes best power at peak when quite rich..

[TZ350]

Thanks Wob and Bucket, now that I have some idea of how its supposed to work it has given me a bit of confidence to try the electronic power jet.......

[TZ350]

Taller gears will load slower & may produce different carburetion characteristics & posibly temp differences, but a 1 run won't have anywhere near as difference as an all gears run. Theoretically you should be able to overlay your (whatever gear) curve over an AG run & often this is true, but some bikes cough a bit between changes & load up (big inlet timed piston porters or rotary valves) & this can change how the next gear runs through. It will also show up fueling starvation in higher gears, or worsening heat build up in piston/pipe of advanced timing.

Its not one of our bikes but the only all gear run that we have recorded..........



It would be interesting to know what some of the features on the graph mean, like the little peaks at the begining of each run.

[F5 Dave]

That's pretty nice power. First gear is always crap , heaps of torque difference & 2nd doesn't always clear out fully. Seems a bit odd that the curve changes so much through the higher gears (6 speed), & top looks fine, maybe a rich bog whilst changing with lessening effect under more load?

I'd be wary of gear change technique creating variables. find what works best for that bike & be consistent.

Where are all these high power bikes coming from?

[Buckets4Me]

Where are all these high power bikes coming from?

back yard sheds or under the house
sometimes in the living room and or bedroom

[wobbly]

In the lower gears you have to back off more to get it to change, and thus the fueling on the needle affects the changes more.
This is because the rev drops are way bigger in the lower gears.
1st to 2nd you may well have 3000 rpm drop into the next gear, 5th to 6th may only be 600 rpm
I would say its rich on the pilot then goes lean as the needle is lifted.
The pipe is getting hotter with each change as well, this may or may not give more power, depending on how close to optimum the pipe is to start with, and how lean the main is - thus getting more heat as it revs out.

[TZ350]

Where are all these high power bikes coming from?

.....................Thomas and Bucket................

[TZ350]

You have to be very carefull with the switch point and the run time on the dyno.
The switch point is dead critical to 100rpm,so i always set it too high initially and make sure that the dyno is loading the acceleration rate to be as close to that on track as you can.
This gives the pipe time to heat up and affect the power over the top, as it would in reality.
On a RS250 dropping the switch point from 12800 ( std) to 12400 gives easily another 800 rpm of virtually no power drop past peak.
On the track,if the rider can feel the switch point ( it feels like hooking another gear)the jet is too big,when its right it should be seamless and just keep reving out.
Leaded fuel is the opposite to unleaded, in that as leaded likes to run lean - you can only use a small powerjet and thus only switch off a small amount.
A leaded engine works best with around 35 to 38 PJ, the unleaded fuel can switch a 60, in Keihin numbering, as the crap fuel makes best power at peak when quite rich..

Wob, thanks for the reply.

On the track, is it ok, to let the bike pull hard for an extended period on over rev in top gear like down the back straight of Puki or Taupo long track when the power jet is off (lean) and the ignition retarded?

Or should the power jet and ignition retard combo only be used in the lower gears?

TeeZee

[wobbly]

Thats the whole idea of retarding the spark and turning on ( fuel off) the powerjet.
This puts less heat into the piston, more into the pipe,to create overev power.
Its inherently "safe" as the bmep is low and the heat isnt going to sieze anything when you are over the top of the torque curve.

[TZ350]

Rebuilding the mallroy balanced crank.

Plenty of oil on the pin and in the pin hole.



Using a V block to start the pin straight.



A bit of time spent here aligning the flywheels saves a lot of time later.



Getting the rod side clearance right, 0.5-0.6mm



Checking that there is side clearance in the cases.



Balance Factor, the percentage of reciprocating mass counterbalanced by the flywheel.

The counterbalance is 121g and the reciprocating mass is 232g so (121/232)*100=52% balance factor, lets see how that goes, last time the balance at 38% was so far out it frothed the fuel up and out of the tank when the bike was being dynoed, 46% was better but still frightening. I was aiming for 50 but 52% will do.

Original BF was 72% and vibrated as the rpm got up, with the balance holes plugged and the bigger pin and rod the BF became 38%, after drilling some holes in the big end area the BF moved to 46% now with the Mallory plugs and no drilled holes around the big end area its 52%.

I will keep changing it a bit at a time untill I find the sweet spot and it runs smooth in the rpm range where the power is, 9-13K rpm.

[wobbly]

Just a couple of points - I would consider 0.6mm as the very minimum of big end clearance for a race engine.
I shoot for 0.8 with 0.2 in the case.
Do you float the crank on the side not locked by the drive gear/nut, some cranks are not locked and can float the 0.2mm by polishing both main jounals - it does make a difference.
The other thing I just learned from Overmars, Aprilia ( Jan Thiel) found that anything under 1mm clearance anywhere on the crank lost alot of power, due he said to increased fluid shear of the A/F mixture.

[F5 Dave]

Hey Wobbly, at what point do you think clearance gets dangerous? Too much clearance is sited as causing rod breakages & I've seen a recently rebuilt crank break the rod of my MB at not much more than 12000rpm (20 years ago) but sadly didn't measure the clearance after the event (I assumed it was a cheapo Long brand Rod issue, the bearing still rotated fine) & I gave the crank back to the rebuilder but never saw it again.

[TZ350]

I would consider 0.6mm as the very minimum of big end clearance for a race engine. I shoot for 0.8.

My source was Bells book, thanks for the heads up and the more up to date thoughts on rod side clearance.

If the 0.8 is with the traditional large side-locating washers, would it be the same with my crank.

My crank uses the original RGV rod set up that’s located in the piston by thrust washers and the big end is much more open with small steel rings centralising the big end brg.



Does this kind of big end setup need 0.8mm side clearance too?

Do you float the crank on the side not locked by the drive gear/nut, some cranks are not locked and can float the 0.2mm by polishing both main jounals - it does make a difference.

No, my crank is a light press fit in the ignition side brg, should it be a slip fit?

How does it make a difference to have the shaft a slip fit?

Wont the shaft spin in the brg if it was polished to 0.2mm clearance?

I just learned from Overmars, Aprilia ( Jan Thiel) found that anything under 1mm clearance anywhere on the crank lost a lot of power, due he said to increased fluid shear of the A/F mixture.

Does Frits mean there should be at least 1mm clearance between the side of the flywheel and the crankcase wall and also the flywheel rim and the case.

I can see my crank coming apart again for some modification.........

[kel]

Does Frits mean there should be at least 1mm clearance between the side of the flywheel and the crankcase wall and also the flywheel rim and the case.

I can see my crank coming apart again for some modification.........

Frits Overmars
Sujet: Re: [GP125] Caractéristiques Aprilia RSA Mer 8 Déc - 13:36
In theory enclosed cranks are good. Jan Thiel did some experiments at Aprilia with a kart engine that had its reed valve at the front: the incoming mixture had to move against the direction of crank rotation. And although the crankcase stretched over the crank webs, reversing the direction of rotation brought another HP. So the crankshaft does have an influence.
But in practice, if you reduce the distances between crankshaft and crankcase walls to less than 1 mm, the viscous friction of the mixture between the surfaces really costs power at high rpm. And if you make the clearances so tight that lubricating oil can no longer reach the big-end and crankshaft bearings, it will also cost engines
Another negative aspect: any volume with a narrow 'entrance' between the crankshaft and crankcase surfaces acts as an hydraulic damper on the Helmholtz-resonance in the crankcase.
Aprilia has avoided this by making the space between the crank webs as wide as the big-end bearing. As a result the crankcase volume of the 125 cc RSA engine at TDC is about 650 cc, so the exhaust pipe really has some volume to breathe from.
So much for the fairy tale of high crankcase compression

[wobbly]

The 0.8mm clearance is for the "normal" big washer setup, so I cant say what would be the go with the open type - except to say that the whole idea of the 0.8 was to get more oil into the bearing and the open type wont have this issue at all.
The 0.2mm is side clearance, I just polish the journal such that the bearing inner race will "just" slide on by hand.
The floating crank allows the crank to move on the bearing as the case heats up and takes up all the side clearance in the main bearing.With it just floating the bearing will always centralise, thus reducing friction.
I would machine the case to get the 1mm clearance everywhere.