ESE's works engine tuner

[wobbly]

The KTM250 I built was based on a 300 bottom end that has the same stroke as the 250.
I dont know if your balance shaft engine is the same 72mm stroke ?
But with the same stroke, but bigger piston,the inertial loads will obviously be greater.
The small ends are bullet proof, the big ends dont seem to be affected as much by the piston weight as they
are affected by the cyclic loads due to rpm - though technically the two go hand in hand.
Main bearings will be loaded more by the extra out of balance forces of the balance shaft spec'd crank - but again these are
bullet proof, especially the roller main as used by KTM on one side.
My opinion would be that if you run the 300 to 10,000 then you are still within the loadings that the 250 see's regularly at 11,000 in roadracing.

[chrisc]

SP125 has a guide for running the front facing airbox on the RS125. Most of us run them and many of us have seen a noticeable effect on making sure they are properly sealed. I was reading the guide and don't quite understand the full effects of one of the recommendations. Can someone please elaborate on the effects of this slid hole:

4: CARBURETTOR VALVE SLIDE
Drill a small hole (Ø 1.0mm ~ 1.5mm) in the outside face of the carburettor slide, centrally, at adistance of 16.5mm from the top of the slide.

http://www.sp125racing.com/rs125-hon...tructions.html

[wobbly]

When running a sealed airbox you have residual pressure inside this volume after backing off into a corner.
With higher pressure on the intake side of the slide, and virtually no flow into the engine you will get an excess of
fuel being picked up by the idle circuit.
And when getting back on the gas the engine is then suddenly partially flooded with overun fuel.
The hole in the slide equalizes the pressure on both sides and prevents the airbox pressure from all running under the cutaway and
into the idle circuit.
Helps quite a bit in stopping those highsides that hurt like hell.

[chrisc]

When running a sealed airbox you have residual pressure inside this volume after backing off into a corner.
With higher pressure on the intake side of the slide, and virtually no flow into the engine you will get an excess of
fuel being picked up by the idle circuit.
And when getting back on the gas the engine is then suddenly partially flooded with overun fuel.
The hole in the slide equalizes the pressure on both sides and prevents the airbox pressure from all running under the cutaway and
into the idle circuit.
Helps quite a bit in stopping those highsides that hurt like hell.

Legend, thanks Wob, exactly what I wanted to know.
Step one is making sure all our airboxes are properly sealed. I'm not running the plastic divider which sits in front of the lower triple clamp that prevent air running up into the fairing so going to look into that first because I think there's some improvement to be made there. Not that I'm struggling for straight line performance. Have touched 204km/hr at Hampton and 206km/hr at Teretonga with my light weight.

Edit: This part, #1

[peewee]

what do they meen over expansion? are they refering to the exh gas or something

http://papers.sae.org/2016-01-1054/

[chrisc]

what do they meen over expansion? are they refering to the exh gas or something

http://papers.sae.org/2016-01-1054/

From the SAE paper preview:


Think they're referring to an asymmetrical power valve setup

[peewee]

ya chris i just seen that as i read further

[casal-fan]

The KTM250 I built was based on a 300 bottom end that has the same stroke as the 250.
I dont know if your balance shaft engine is the same 72mm stroke ?
But with the same stroke, but bigger piston,the inertial loads will obviously be greater.
The small ends are bullet proof, the big ends dont seem to be affected as much by the piston weight as they
are affected by the cyclic loads due to rpm - though technically the two go hand in hand.
Main bearings will be loaded more by the extra out of balance forces of the balance shaft spec'd crank - but again these are
bullet proof, especially the roller main as used by KTM on one side.
My opinion would be that if you run the 300 to 10,000 then you are still within the loadings that the 250 see's regularly at 11,000 in roadracing.

The Spanish 300cc quad engine is (to put it in simple terms) quite similar to the KTM engine.
It is a 72X72 configuration, with balance shaft, triple exhaust port, centrifugal force activated PV, 6 "decently" scaled gears with about 1200rpm loss 5-6th and 1250rpm loss 4-5th shifting at 10.000rpm with secondary gearing to go about 202 km/h. Not bad as a starting point for a track motorbike. Some mecanisms will come off, as the PV activation, perhaps even no PV...
The cranckshaft bearings are the same as KTM, roller on ignition side, ball on the other.
Conrod is 125,5mm but has to change as a quick WWW search showed 2 of these engines with snapped rod just below the little end, showing perhaps that cranckshaft inertia on the upstroke was trying to "spit" the piston through the exhaust, luckily 129mm KTM rod is a match.
Very greatful for the insight and opinion, it was exactly what I was hoping for. Many thanks.

This is the quad, the 300cc engine in question is mounted on:
https://www.youtube.com/watch?v=lnA6znRpU8A

[peewee]

casal-fan the 135mm 380ktm rod is a match as well. as is the 132mm rod from the same era i believe

[Peter1962]

The Spanish 300cc quad engine is (to put it in simple terms) quite similar to the KTM engine.
It is a 72X72 configuration, with balance shaft, triple exhaust port, centrifugal force activated PV, 6 "decently" scaled gears with about 1200rpm loss 5-6th and 1250rpm loss 4-5th shifting at 10.000rpm with secondary gearing to go about 202 km/h. Not bad as a starting point for a track motorbike. Some mecanisms will come off, as the PV activation, perhaps even no PV...
The cranckshaft bearings are the same as KTM, roller on ignition side, ball on the other.
Conrod is 125,5mm but has to change as a quick WWW search showed 2 of these engines with snapped rod just below the little end, showing perhaps that cranckshaft inertia on the upstroke was trying to "spit" the piston through the exhaust, luckily 129mm KTM rod is a match.
Very greatful for the insight and opinion, it was exactly what I was hoping for. Many thanks.

This is the quad, the 300cc engine in question is mounted on:
https://www.youtube.com/watch?v=lnA6znRpU8A

No PV ? What could you possibly gain by doing that ? Would it not be better to mount a servo tot the PV so that is can function the way it should have been done by the manufacturer ?

[JanBros]

No PV ? What could you possibly gain by doing that ?

on a track, you are not supposed to drop out the powerband, so it doesn't matter much how little power there is outside the powerband ?
and it' s more in line with the KISS principle ?

I'm planning on doing the same when (been planning this for 2 years and have the bits already for over a year ) I'm gonna built a 400cc track bike based on a YPVS 350.

[wobbly]

Using the MX based motors means by default that there are huge rpm drops between gears.
In the KTM250 I built there is 1400 rpm drop hitting 5th gear from 10500.
This is only " just " enough to stay close to peak torque on the upshift and many roadracing karters have real trouble getting
a good compromise between top speed and actually being able to accelerate hard in 5th gear.
Gear it tall enough to be as fast as the aero will allow, and it simple wont have enough power to accelerate at all from 9000 rpm.
Having a servo PV that isnt usually fully open till around 1000 rpm before peak, means that this acceleration issue simply goes away.
But i reiterate, it must be a servo drive, as the mechanical types open over an ever narrowing rpm range as the preload spring is wound up
to lift the full open rpm.
I have seen a TM125 that opened from fully closed to fully open over only 800 rpm when the adjustment was set for full up at 11,000.
Sure you can get different springs wound to help this problem, but why fuck about when we have simple and cheap servo drives and the ECU
to open them in any way the dyno says is best.

[casal-fan]

This project has been on the drawing for years, and several engines were studied to try and make a good picture of what would be easyer to adapt to road motorcycle track.
The KTM sinned (for me) in 2 aspects. The scalling of the only 5speed gearbox, and how difficult it would be to implement an effective second gearing without having to use too much money on custom built sprockets.
This of course is irrelevant for karts, even the CR250 engine is popular and highly sucessful in kart, even if for motorbike road racing, it would be very hard work (and money) to get the gearing suitable. No doubt a Wobbly KTM for superkart will be one to watch for.
Many thanks for the comment on the PV, subject. PV it is then...
The thoughts of not using PV came from the study wich this picture results from, as well as this would of course be an element taken from the equation, it would not weigh anything, cost anything, and it would never break... simple

Also the engine on this video, purpose superkart build 68X68, "based" on the gasgas EC engine (wich I´ll be using as well) seems to have a very similar gear scalling as the pic. above... shame there is no data to see, apart from what the engine sound. It has no PV... doesn´t seem to be missing it either...
https://www.youtube.com/watch?v=4z7KJNVCvtg

peewee, apart from the reassuring comment from Wobbly wich helped me a lot, piston inertia forces calculations on this 300 engine, at the rpms that I think could be viable, and with the 3,5mm longer 129mm KTM rod, are already quite similar-even higher then what the top 66,4X72 superkart engines are showing. Going longer on the rod would make this even worst...
Thought here being to achive the best balance possible - reliability but still have some power gained from rpm.

[twotempi]

Attachment 323073Attachment 323074

I think Yamaha used Piano wire in their TZ pistons. Where the pin is inserted down from the top and secured by bending the end over inside the small blind relief hole drilled into the side.

I use a 1.5mm dia needle roller from a little end bearing . Material is tough and also polished so there is no fretting on the ends of the ring. Drill down from the top of the piston allowing for some interference fit (say .05mm ) so the end of the pin is 1 - 1.5mm below top of piston, then weld over the hole to prevent the pin from coming out. You may get a slight swelling of the piston diameter at the position of the pin. Dress this off carefully with a mill-cut file. With a two ring piston you will have the ring gap in the same spot for both rings but this is fine.

[peewee]

I use a 1.5mm dia needle roller from a little end bearing . Material is tough and also polished so there is no fretting on the ends of the ring. Drill down from the top of the piston allowing for some interference fit (say .05mm ) so the end of the pin is 1 - 1.5mm below top of piston, then weld over the hole to prevent the pin from coming out. You may get a slight swelling of the piston diameter at the position of the pin. Dress this off carefully with a mill-cut file. With a two ring piston you will have the ring gap in the same spot for both rings but this is fine.

great suggestion I wonder why I didn't think of a needle bearing . surely theres some laying around the garage. I plan to do more practicing on old pistons this weekend and ill report back how it goes. still im leaning towards the welding idea as the final method but I may see if the peening idea could work also. with simple calipers from last weekends welding I didn't notice any dimensional distortion of the piston skirts but I will be more precise this time with a micrometer . im not even sure the ring grooves distorted but really I didn't pay attention to that. the first thing I realized is its easy to melt off the top corner of the piston