Custom Clutch bar and Piston Skirt Trimming

[reg454]

By filing down the piston or raising the exhaust roof you increase exhaust duration. This in effect reduces the amount of time the expanding gasses push down on the pistion during the power stroke, hence less bottom end. And also a greater time from exhaust duration start and transfer start - ie blowdown time.

The problem is that if you run a fixed gear setup (ie no jack shaft kit) you dont want to go for "more HP" or more "power". All these mod tend to do is increase top end (obviously as expected). This is only good if you have gears because as you do these "HP" mods you move your bottom/mid range power and push it more up top. That is why you need gears for these mods - as you essentially narrow the useable power band you have to change teh gear ratio to keep the engine in the power band to use this newly aquired power.

If you dont have gears and you've done these mods your bike will suck up hill and will go great on the flats with a 36T sprocket. Like my first bike - 50km/h over slight hills in the country was good fun and no prob for the engine, as long as you never got to a real hill.

On the other hand, widen your intake and exhaust ports (no more than 33mm for the exhaust across the chord). This allows more flow with out affecting opening duration.

The intake mod is a bit like the exhaust mod (increase open duration) - tunes the enigne for top end at the loss of bottom end. However, my experiance tells me that I may lose like 5-10% bottom end and gain anything up to 20% gain in mid/top end. Which in my books is worth it where as an exhaust mod will more turn out to be a 15% loss in bottom end for a lousy 10% (at most!) gain in top end.

Just remember, your engine once dynoed produces a graph of the power output. The area under this graph is a set amount (some mods will vary this area) BUT what your exhaust duration mod does is shift this graph and skews it towards top end. Meaning you lose big time on bottom end. This is generally the case with many mods.

This is a huge deal because in a fixed gear setup you want to go for highest average torque throught out the RPM range - which allows you to cruse at a good pace on nearly any incline. Mods that do this are increase compression, high flow airfilter, opened (high flow) exhaust, larger carb (16mm bore is prefect for a fixed speed HT 66cc) and last but never yet done on a HT is to either use a larger piston or longer stroke crank.

Lastly, to change the area under the graph you would need to either fit a turbo/super charger or change the engines displacement. In addition, air filter mods and exhaust mods will increase this area slightly in a case where an engine has very restricted in and outputs (such as a HT).

And to who's wondering, the elusive squish band is only a means of increasing compression with out having detonation. Meaning, unless you run like a 7:1 (or more) CORRECTED compression ratio (around 5.75cc combustion chamber volume) , dont worry about it.

Also, a expansion chamber will work like a intake duration change. Slight loss in bottom end but a ok gain in topend (as a top end tuned pipe sacrifices low end for top end). However, many people experiance a HUGE gain in performance. This is not all due to the "expansion chamber" but to the fact that the new pipe has better flow, ie more torque, ie a greater reading on the seat of your pants dyno we all have.

PS - people who tune for "top end" and dont run a balanced crank are foolish as how will you ever get to the "top end" when your engine wouldnt see past 7K RPM?

Thanks for posting that.

 

[Bikedad1]

Thanks DIY for posting that. I have a single speed setup and want to only increase my torque for take offs and hill climbing. I live in North Western Washington and we have alot of steep hills.

 

[reg454]

Thanks DIY for posting that. I have a single speed setup and want to only increase my torque for take offs and hill climbing. I live in North Western Washington and we have alot of steep hills.

I put my bike back together today and went for a test ride and their is a noticeable power increase, before I was running to lean on the 3rd notch. Now I am running perfect, the motor is alot smother although their is more noise coming from the carb but it's ok the only thing I have to do now is take off the shim I put between the jug and the main body of the motor I just wanted to see the difference. I have to get my compression back to were it was before.

I also noticed after I did the piston trimming while riding their is alot less vibration coming from the engine hmm.


With the clutch arm I made I can go from a dead stop now (44tooth sprocket, 26" wheel) compared to the stock one. I just have to get an expansion chamber now.

I highly recommend the piston skirt trimming.

I also played around with the intake spacing betweem the motor and the carb. You get higher rpm's/ torque with the intake only 1" long (just enouph room to mount the carb). I went from a 2" spacing tested it and I was getting low rpm's but with the short intake a noticeable increase. If Creative Engineering (Manic Mechanic) made a 1" long intake I would buy it.

 

[Creative Engineering]

I put my bike back together today and went for a test ride and their is a noticeable power increase, before I was running to lean on the 3rd notch. Now I am running perfect, the motor is alot smother although their is more noise coming from the carb but it's ok the only thing I have to do now is take off the shim I put between the jug and the main body of the motor I just wanted to see the difference. I have to get my compression back to were it was before.


With the clutch arm I made I can go from a dead stop now (44tooth sprocket, 26" wheel) compared to the stock one. I just have to get an expansion chamber now.

I highly recommend the piston skirt trimming.

I also played around with the intake spacing betweem the motor and the carb. You get higher rpm's/ torque with the intake only 1" long (just enouph room to mount the carb). I went from a 2" spacing tested it and I was getting low rpm's but with the short intake a noticeable increase. If Creative Engineering (Manic Mechanic) made a 1" long intake I would buy it.

Reg,

Please post pics of the 2" spacing intake you made...and also the 1"

Jim

 

[reg454]

I just got back from another ride. lol's - I need to take a link or two out this is a different bike than I had before everything was fine earlier but not now chain fell off but thats an easy fix I am going to get rid of that crappy chain tensioner I have a rear derailer that I am going to modify to mount but if I can get away without one even better.

Plus the little pin that holds the clutch arm in fell out. What I did to fix it was, I found a screw a little bit bigger than the hole, drilled through the hole and screwed in the screw and it worked then I cut the remainder of the screw off becauce it was long (this is just a temp fix till I get a new clutch arm cover

 

[reg454]

Reg,

Please post pics of the 2" spacing intake you made...and also the 1"

Jim

This one is just a cut down version of the regular intake this is the one I get the crazy rpm range and the most HP.

Sorry not 2" more like 1 3/4". This pic the rpms are alot lower and their is bogging when you open up the throttle.

In the first pic I was doing some poking around and their is room for the carb the clutch cable will go behind the drain plug if their is just enouph room to mount the carb on the intake manifold.

Manic try it out just cut one of the custom ones down

after this weekend I have drill so I wont be here till sunday night I will make a short vid and post it on youtube showing the rpm ranges on the 2 intake lengths while riding

 

[reg454]

I should add this is a bikeberry motor.

 

[reg454]

I got home from drill today and went for a little ride, before that I took 1 link out of my chain so I could get rid of the chain idler. I only put a little more than a 1/8th of a tank of gas in and I was able to go 10 miles, then I ran out of gas. So i estimate if I ride like I did with a full tank I will get 80 miles, so that brings my motor to 160mpg.

One thing I had to do when I got home was tighten the clutch cable, it's a brand new cable and it stretched a little more than a 1/4in. It's good that I was still able to disengage the clutch or I would have to restart the motor every time I stopped, I was only a mile from my house when I noticed it.

 

[Creative Engineering]

Reg, I'm glad you're having fun with your engine...please don't recommend to other new guys; that they should do the same!!!

Jim

 

[reg454]

Reg, I'm glad you're having fun with your engine...please don't recommend to other new guys; that they should do the same!!!

Jim

no problem

 

[DanielMaia]

So..reg454, in the flange lenght, how much mm is from the intake (hope is the correct term) to the carb, for the best performance?

If you did't understood i put a picture

thanks

 

[Creative Engineering]

Reg,

If I remember right, the first intake I made was 1-3/4" total from the face that bolts to the cylinder to the carb mount.

The majority of the last production run was 1-1/2" total.

This production run, I made them 1-3/8". The nipple that the carb mounts on to is just under 1". The flange is 10mm.

I did shorten one up as far as it could go...1-1/4". I can't remember if the lengths made any difference, because it was weeks between having installed each one.

The one thing I did notice was a much better idle quality. I don't know if it's the straight run or the O-ring seal that has made the improvement.

Did you actually run yours with the carb at that angle? Was it O.K.?

I've been telling people not to buy an intake unless they can get their engine fairly level. Maybe it's not that critical. I can see 5, maybe 7 degress as being acceptable.

What is that between the cylinder and the intake?

Jim

 

[reg454]

Reg,

If I remember right, the first intake I made was 1-3/4" total from the face that bolts to the cylinder to the carb mount.

The majority of the last production run was 1-1/2" total.

This production run, I made them 1-3/8". The nipple that the carb mounts on to is just under 1". The flange is 10mm.

I did shorten one up as far as it could go...1-1/4". I can't remember if the lengths made any difference, because it was weeks between having installed each one.

The one thing I did notice was a much better idle quality. I don't know if it's the straight run or the O-ring seal that has made the improvement.

Did you actually run yours with the carb at that angle? Was it O.K.?

I've been telling people not to buy an intake unless they can get their engine fairly level. Maybe it's not that critical. I can see 5, maybe 7 degress as being acceptable.

What is that between the cylinder and the intake?

Jim

Jim yes the motor runs really well except when I run WOT for a while I can feel the carb bubbling or overflowing from the vibration but that was to be excepted from that angle, if I run at a normal speed it does not matter. Those things you saw were spacers that I made to test the difference of the spacing they are both the same diameter i clamped them together before drilling them and the main hole diameter is like 1/16" larger than the stock carb. the 1 1/4" one you made is very close to the spacing I have, mine is 20mm for the intake length and the flange thickness is like 7mm. My idle is perfect, how much would it cost to get an intake 1 1/4" made up, would it be the same price because my motor is setup to run the intake level if it is straight. I am thinking I will get better performance when I do switch to a level intake.

Did you read the post I made about my motor running lean then I did the piston skirt trimming and then it was running perfect.

 

[reg454]

So..reg454, in the flange lenght, how much mm is from the intake (hope is the correct term) to the carb, for the best performance?

If you did't understood i put a picture

thanks

20mm for the intake and the stock flange thickness is like 7mm so 27mm total. But if you read the post above this you will read about one of the symptoms I have with that carb angle that I am running right now. But if I can get a straight intake then that will solve it.

 

[DanielMaia]

So..the best performance setup is the flange leveled, with no angle, right?

The distance between the intake and the carb, should be the closest possible?

What is "WOT"?

Thanks reg

 

[reg454]

So..the best performance setup is the flange leveled, with no angle, right?

The distance between the intake and the carb, should be the closest possible?

What is "WOT"?

Thanks reg

The leveler you are the better I just cut down the stock intake to test the difference. On your second question that is what I have seen, and your third question WOT is wide open throttle.

 

[Forbisher]

Hi Jim
This pic was taken at El Dorado park meet by rockvoice
but I have lots more pics taken at my shop

Raullys red Husqvarna Felt # 71 bike uses your straight intake manifold
It was 2" long overall and just cleared the float bowl behind the clutch bolt

Check out the angle of the Grubee 66 cc Starfire which also has your clutch kit on it
I rode the bike and it ran great, in fact it was the nicest motored bike I have ridden

Was a new motor so I rode it easy, but idled great and very smooth

The yellow Yamaha Felt belongs to John aka HBLocal

Both bikes run the chain direct without a tensioner which eliminates a lot of noise
and vibration from the chain line
They use King 44 tooth sprockets but are changing to my 35 tooth 3 way sprocket
and the rag joint

Reg,

If I remember right, the first intake I made was 1-3/4" total from the face that bolts to the cylinder to the carb mount.

The majority of the last production run was 1-1/2" total.

This production run, I made them 1-3/8". The nipple that the carb mounts on to is just under 1". The flange is 10mm.

I did shorten one up as far as it could go...1-1/4". I can't remember if the lengths made any difference, because it was weeks between having installed each one.

The one thing I did notice was a much better idle quality. I don't know if it's the straight run or the O-ring seal that has made the improvement.

I've been telling people not to buy an intake unless they can get their engine fairly level. Maybe it's not that critical. I can see 5, maybe 7 degress as being acceptable.

Jim

 

[DanielMaia]

Forbisher, that was the pretiest bike i have ever seen!

Guys, the stock gigleur is #70 ? i bought a #95 gigleur, and at full throttle she stops completely. #95 is too much

#80 is the better gigleurs with full stock engine and parts?

 

[reg454]

I'm glad I made that custom throttle cable adjuster because today I noticed that my throttle cable had stretched some more. I tightened it and all was well

 

[heyscuba]

what does dampening the clutch cover do for ya,...?
and cutting the skirt of the piston,,,?