ESE's works engine tuner

[wobbly]

The only time I have ever seen base and or head nuts winding out is due to detonation - even if its not enough to create piston issues , constant background deto puts huge shock forces on the fixing studs/nuts.
Ive seen this in a big bore 1150 Seadoo that had the wrong fuel poured into it , and one of the early tests I did on a TM125MX kart where I tried 20:1 com on Methanol - it did 4 laps and the cylinder simply " fell off ".
The other one was a 250 KTM on Methanol where some idiot in a wheelchair measured the com at 16cc to the top of the plug , instead of 16cc + 2.2 of thread , it rattled like mad in the mid , and all the nuts unwound.
I would suspect that at 18:1 in an aircooled 250 the com is simply way too much.
My take would be 15:1 com would give a good combination of cylinder cooling Vs power production from the Methanol.


EDIT - and of course you know the easy way to check base timing is to set the piston at TDC and use a marker on the stator/rotor to put reference lines.
Set the timing in the Ignitech to zero , and spin it over on the dyno with the plug sitting on the head , and strobe the marks.
From memory it fires on the base timing up to 300 rpm , over that the programmed values.
If the lines dont line up past 300 rpm, then the base timing is wrong.

[pete376403]

.

Those cylinder base nuts have started loosening again.

It has become obvious that before I can ride this thing I will have to tear the engine down and change the balance factor.

Any advice here would be welcome.

Could you run long studs right up the side of the barrel and have nuts at the cylinder head? Or would transfers and so on get in the way?

[Frits Overmars]

the dynamic compression ratio with the cooling effect of methanol is much greater than with petrol.
Any advice here would be welcome.

Probably not the advice you were looking for, and call me pedantic if you like, but a compression ratio is volume A divided by volume B, and fueling won't change that.
I realize of course that you mean compression pressures, but using the correct terminology helps in forming a clear mental picture.

Having said all that, I don't think the cooling effect of methanol will have much influence on the cylinder pressure at exhaust port closure.

[Orengo98]

My 360 single was never balanced, not even after it had grown to over 370cc due to the occasional seizure. Wen it was idling, sitting down on it blurred my vision. But once I put it into gear and it had to work for a living, all vibrations disappeared. Too bad the seizures didn't.
You win some, you learn some. I learned a lot. Like avoiding shrunk-in cast-iron liners. And air cooling in general. And clutch cables that are thinner than brake cables. Pulling the clutch because of a seizure doesn't do much good if the cable snaps. I survived without a scratch but it left the longest tire skid mark I've ever seen.

Hi Frits!

If I remember right, your 360 was a Bultaco Bandido powered monocoque racer? Once you posted a picture of the combustion chamber, and I think to remember it had two plugs, so it would be a model 61. I know it is air-cooled and for "agricultural racing" but I'm building an engine like that for flat track use, is there any tip or suggestion in your experience, of where to start modifying this engine?

I believe a bigger carburetor would help, since the original is a 32mm, and the TSS that used the same engine used a 35.
Also, reshaping the cylinder head would be an easy mod I think. All the cylinder heads I have are full of detonation marks.

About the cylinder head, you wrote before that you prefer lower compression engines, as they produce hotter exhaust gases with more energy to use on the pipe. What compression ratio would you recommend? This type of engine would require a different pipe to make use of that extra energy, I suppose with a bigger belly? Would it be a good idea, or you think because the transfer design on this engine is not the best, the bigger diameter pipe is going to create more short-circuiting?

Thanks in advance!

[lohring]

i would think the addition of the acetone should helps keep the oil in suspension plus decreases the need for huge amounts of advance.as well as making it easier to start.
Grump wanted me to post this video on go kart engine balance factors.

The video gives me serious concerns about the EV future. What are we going to do?

Two strokes forever. LOL

Lohring Miller

[wobbly]

When I first tried Methanol the engine was dead stock , and was simply rejetted with an fueling area ratio of 2.2 on all the jets.
I had read that doing this alone would increase power by 8% due to the calorific value of the fuel being ingested compared to petrol.
And so it proved , the thing all but exactly made 8% more power at a slightly lower rpm due to the lower egt.
I dont believe an increase in dynamic compression is part of the equation , this is only affected by an improvement in Trapping or Scavenging Efficiency or Delivery Ratio.

[TZ350]

- and of course you know the easy way to check base timing is to set the piston at TDC and use a marker on the stator/rotor to put reference lines.
Set the timing in the Ignitech to zero , and spin it over on the dyno with the plug sitting on the head , and strobe the marks. From memory it fires on the base timing up to 300 rpm , over that the programmed values. If the lines dont line up past 300 rpm, then the base timing is wrong.

Thanks, confirms we are basically on the right track. We used 15deg so we could actually run the motor and check things with a timing light. In the past we had issues with ghost triggering from the rotor magnets. This happened when the rpm got up a bit. Your method is much easier for getting started with. Thanks.

- compression ratio is volume A divided by volume B, and fueling won't change that. I realize of course that you mean compression pressures, but using the correct terminology helps in forming a clear mental picture.

Yes you are right, change in ultimate compression pressure paints a better picture.

[TZ350]

The only time I have ever seen base and or head nuts winding out is due to detonation - even if its not enough to create piston issues , constant background deto puts huge shock forces on the fixing studs/nuts. Ive seen this in a big bore 1150 Seadoo that had the wrong fuel poured into it , and one of the early tests I did on a TM125MX kart where I tried 20:1 com on Methanol - it did 4 laps and the cylinder simply " fell off ". The other one was a 250 KTM on Methanol where some idiot in a wheelchair measured the com at 16cc to the top of the plug , instead of 16cc + 2.2 of thread , it rattled like mad in the mid , and all the nuts unwound. I would suspect that at 18:1 in an aircooled 250 the com is simply way too much. My take would be 15:1 com would give a good combination of cylinder cooling Vs power production from the Methanol.

Ignition curve for the red line on the dyno graph. 18:1 com ratio, cylinder base bolts kept loosening off.

The 18:1 F81M vis standard 250 11:1 Head.

I have found a standard head so over the next night or two I will clean it up, "O" ring and counter bore it.

Then revert to less aggressive timing and run the std head up on the dyno.

[Frits Overmars]

Hi Frits! If I remember right, your 360 was a Bultaco Bandido powered monocoque racer? Once you posted a picture of the combustion chamber, and I think to remember it had two plugs, so it would be a model 61. I know it is air-cooled and for "agricultural racing" but I'm building an engine like that for flat track use, is there any tip or suggestion in your experience, of where to start modifying this engine?
I believe a bigger carburetor would help, since the original is a 32mm, and the TSS that used the same engine used a 35.
Also, reshaping the cylinder head would be an easy mod I think. All the cylinder heads I have are full of detonation marks.

Hi Orengo, my first reaction was: if you want to learn a lot, go ahead and do what I did. If you want to ride, don't.
My engine came with one central spark plug. I fitted a head with two plug holes after the original head had cracked, because that was all I could find. But I could only fit the forward plug; my monocoque frame got in the way of the rear plug.
It taught me the difference a plug position can make. Maximum power was not affected but with the forward plug the engine idled much nicer than with the central plug.

The 32 mm carb made way for a rotary valve inlet with a homebuilt 40 mm carb. Initially I used 0,4 mm thickness for the steel disc because that was what my friends were using in their 50cc machines. 0,4 mm might have been fine with their 24mm carbs, but not with my 40 mm one; crankcase pressure pushed the thin disc in the disc cover hole and the hexagon center of the disc perished (which taught me that a two-stroke will keep on running when the inlet stays open 24-7, as long as you can keep it in the power band).
A 0,8 mm disc solved the problem at the expence of some unbalance and vibration.

I think my MX-based engine made a bit more power than the factory-built TSS350. On top of that my bike was lighter. But the factory bike had five gears, one more than mine.
As it turned out, the most important difference was that the TSS had straight-cut primary gears. My engine did not, resulting in my crankshaft main bearings being pushed aside, breaking the retaining ring grooves out of the cases.
Next, the clutch was not up to the power. And when I had all of that sorted out, it rewarded me with breaking the gearbox shafts and destroying the cases in the process. That is when I gave up.

you wrote before that you prefer lower compression engines, as they produce hotter exhaust gases with more energy to use on the pipe. What compression ratio would you recommend? This type of engine would require a different pipe to make use of that extra energy, I suppose with a bigger belly? Would it be a good idea, or you think because the transfer design on this engine is not the best, the bigger diameter pipe is going to create more short-circuiting?

In my experience, low compression ratios make it easier to extract power from an engine. But for an air cooled big single with a shrunk-in cast-iron sleeve I would not go too low; relatively cool exhaust gases are more important than power. About 12:1 should be a good value.
The transfer design on my engine was rather different from the original MX-engine. I had enlarged the A-transfers and added a big third port where the piston-controlled inlet port used to be.
The pipe belly was considered huge at the time, but rather modest with 51 years of hindsight: 112 mm if I remember correctly.
I think nowadays that would be a good belly diameter for your more-or-less standard engine.

[wobbly]

Yea TeeZee , that's WAY too much timing with 18:1 - I would guarantee its detonating and its the shock thru the cylinder thats loosening off the nuts.
Running rich on Meth masks many evils , but deto creates havoc no matter what.

[husaberg]

Hi Frits!

If I remember right, your 360 was a Bultaco Bandido powered monocoque racer? Once you posted a picture of the combustion chamber, and I think to remember it had two plugs, so it would be a model 61. I know it is air-cooled and for "agricultural racing" but I'm building an engine like that for flat track use, is there any tip or suggestion in your experience, of where to start modifying this engine?

I believe a bigger carburetor would help, since the original is a 32mm, and the TSS that used the same engine used a 35.
Also, reshaping the cylinder head would be an easy mod I think. All the cylinder heads I have are full of detonation marks.

About the cylinder head, you wrote before that you prefer lower compression engines, as they produce hotter exhaust gases with more energy to use on the pipe. What compression ratio would you recommend? This type of engine would require a different pipe to make use of that extra energy, I suppose with a bigger belly? Would it be a good idea, or you think because the transfer design on this engine is not the best, the bigger diameter pipe is going to create more short-circuiting?

Thanks in advance!

Bert Flood prepped an el bandito for road racing in the late 60's or ealy 70's it was pretty successful
On two wheels detailed it.
i have a copy somewhere.

[TZ350]

F81M 18:1 Meth + Aggressive advance.



EngMod 2T's simulation of what it thinks Meth plus 18:1 at 32 deg advance would look like at the back wheel.
I graph in Kw when looking for RWHP as that is this lazy mans way of accounting for drive train losses.
I had previously entered 32 deg adv to get EngMod's opinion.

Yea TeeZee , that's WAY too much timing with 18:1 - I would guarantee its detonating and its the shock thru the cylinder thats loosening off the nuts.
Running rich on Meth masks many evils , but deto creates havoc no matter what.

TUmax graph in deg C. It is hitting 960. Would this be detonation territory? Maybe Ok for Av Gas but I have no idea what the limit is for Methanol. I understand Meth is prone to pre-ignition.

[TZ350]

.
All the other details of the 1971 Kawasaki F81M 250.

[Lef16]

If meth works at ~450* EGT as stated before,wouldnt this mean that you need an exhaust TL of about 950mm for 9500rpm and 200* exhaust port instead of 1000+?

[Frits Overmars]

https://www.youtube.com/watch?v=nkBabPAMIsc