Custom Clutch bar and Piston Skirt Trimming

[reg454]

Some Mods I did while I had the motor off today and for the next week.




The first Photo is where the piston skirt is normal on the top stroke.

The Second Photo is after I trimmed the Skirt.

The Third is the piston skirt after I trimmed.

the Forth photo is the custom Clutch Arm I made and some dampening of the clutch housing.

Can not wait till I get the motor back on the bike to feel the difference.

I also port matched the exhaust but no need for a photo their are enouph of those around to show you how to do it. If anyone needs help on making their own clutch arm let me know and i will let you know how I did it.(Cutoff wheel, a saw, drill press, a sander, and a tap set) use the old one as a form of template.

 

[reg454]

Edit I am making a better front mount so I removed the photo.

Custom clutch arm more photo's in page 2.

 

[Junster]

This is how I dampened my clutch cover. It's an old motorcycle tank badge. They are pretty easy to remove. Just saw it off the tank with some dental floss. They're pretty soft and easy to flatten.

 

[reg454]

nice looks cool too.

 

[Junster]

Thanks reg454, So I've been considering doing the piston skirt trim. I'm hesitant because of the carb blow back I'm already getting. (Oily Airfilter) I mean the blow back is probably coming from the downstroke on the piston anyway. Have you done this to other motors? What gains are you seeing? WOT or mid torque?

 

[reg454]

Thanks reg454, So I've been considering doing the piston skirt trim. I'm hesitant because of the carb blow back I'm already getting. (Oily Airfilter) I mean the blow back is probably coming from the downstroke on the piston anyway. Have you done this to other motors? What gains are you seeing? WOT or mid torque?

This is the only motor I have. From what I have read it gives makes the motor run smoother from allowing a full cycle of air and gas to get to the innards of it. I have read on this forum and another forum people that have done it have gotten good results I only had to trim a little bit off like a 1/16" of an inch but from the photo you see I did not get all of it off for a reason.

I have yet to put it back on the bike I am still doing other mods like building my own exhaust system.

 

[reg454]

Thanks reg454, So I've been considering doing the piston skirt trim. I'm hesitant because of the carb blow back I'm already getting. (Oily Airfilter) I mean the blow back is probably coming from the downstroke on the piston anyway. Have you done this to other motors? What gains are you seeing? WOT or mid torque?

What do you think of the custom clutch arm? I made it in like an hour.

 

[Creative Engineering]

Reg454,

Looks like you're having fun! That's what these bikes are all about.

Jim

 

[Junster]

It's nice.

 

[reg454]

I removed these photos because I'm making better ones.

 

[Goat Herder]

The intake and exhaust should be as big and breathable as you can get away with. The piston skirt mod is mandatory in my book . I recently started using the SBP tuned pipe I like it I put it at just a smidgen under 12 inch header whoa nice! These Chinas are fun LOL

 

[reg454]

I want to get a sbp expansion chambber but they are out of stock. I lost my head gasket the other day am going to spend all day looking for it lols. Butthe intake brackets i made, i expanded it a little more to fit the pipe i am using for it.that way I can weld up 2 points on it by the flange and around the pipeof corse a little grinding after words.

 

[reg454]

I found my head gasket lols, it was on the head all along just stuck their.

I took a few more pic's of the custom clutch arm in case people want to make one. In the pic's are the dimension's in mm. The blot i used was just a 1/4 20 x 1" long used a normal washer and lock washer. when you drill the main hole make it a little bit small so their is a snug fit.

You can use Aluminum or steel, but Aluminum is faster to make

In the second pic i left it long on top of the hole to allow a good area for the clutch cable to grip on.

I had to grind the area flat between the clutch arm and the plate that holds the arm because it was not flat you might have to do that too. I had to do it because when i had tightened the nut on top of the clutch arm it would bind so clearing that area stop it from binding and I could properly torq the arm in place.

 

[reg454]

I reground the piston skirt to make it better.

What you need to do is make the piston top dead center.

Use a black sharpie and mark the area that you need to grind away. (let dry for a minute)

Remove the jug and notice where the rings are at. Surround the head area below the piston with rags or paper make sure to cover any and all area that can get pieces in side the main body.


Using a grinding application of you chosen, i used some bits i had. Grind away the area with the black marker and after you want to hit the outside edge of the piston to get any burrs off of it.

Below I used the second bit with a 90 air tool.

If you have a compressor it helps.

Remove the paper or rags and use an air nozzle to get any and all dust out of the area.

I like to clean up the piston and jug with some brake cleaner on a rag to get all oil residue and gunk off of it to help put the piston back in. Make sure you clean the rings too. Remember I told you to remember where the rings are at when you put the jug back on you have to make sure the rings are at that area.

1st pic below is before grinding.

Pic below is after grinding.

Hope this post helps people out any questions let me know.

 

[reg454]

I've seen some people grind away at the top of the piston for the exhaust, I am not going to do this for the reason is that it is only 1mm of difference and that these motor are made in china, so you cannot know what type of aluminum it is if it was billet then it would be ok but we do not know. I am not going to compromise the integrity of the piston face unless someone makes a piston that is thicker and made out of billet aluminum. And has made that area preground for us.

But if you are going to use an expansion chamber then you will not need to that mod to the motor because you can blow your piston.

 

[DIYMark]

Haha...Haha

Im not feeling like putting up a big explanation as to why NOT to grind the piston/lift the exhaust port - but seeing as you've read the 2T tuners book you should rethink your decision of grinding the top of the piston and realise what it actually would do to the motors power output/performance (Hint - exhaust duration)

Should you go ahead and file the pistons exhaust side down; let me know what the bike feels like going up hills.

 

[reg454]

Haha...Haha

Im not feeling like putting up a big explanation as to why NOT to grind the piston/lift the exhaust port - but seeing as you've read the 2T tuners book you should rethink your decision of grinding the top of the piston and realise what it actually would do to the motors power output/performance (Hint - exhaust duration)

Should you go ahead and file the pistons exhaust side down; let me know what the bike feels like going up hills.

If you readthe post i am mot going to trim the top of the piston but please explain why not for everyone :-/

 

[mick29]

By trimming the bottom front edge of the piston how will it improve the power. Do higher performance 2 stroke motors have this already done? mick29

 

[reg454]

it allows the motor to get a full cycles of air and fuel not cutting it short when the piston is to long and covering the opening of the intake port. You will get a little more hp and your motor will breath better along with a more stable burn rate and smother operation.

 

[DIYMark]

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?