Piston modifications?
- Thread starter MadMaxed
- Start date
Are you talking about ramping at the transfer and exhaust ports?
If so, this is really easy but can still be messed up if you take off too much or taper in too little or too far.
just cut the ramps so they're about 1mm below the top of the piston so you leave enough metal to support the top ring, then taper smoothly about 10mm toward the center, Once this is done you can use some emery cloth at the edge of the rampped sections and slightly round off the abrupt edge and it'll improve flow even more without having to cut too deep.
For the transfers, you cut the same 1mm deep but aim the ramps slightly toward the intake port so it'll begin to direct the intake charge away from the exhaust port, it doesn't seem like it does much but it can help, basically this angle should look like you're pointing the ramp out from the center of the piston crown to the front side of the transfer port, then make the line parallel for the back side of the ramp. Like I said, it isn't much, but it's enough to make a difference.
The ramping it's self adds more transfer and exhaust duration which mimicks raising the roofs of these ports, you can ramp down a piston to find where your engine performs best, then measure how much you cut out, then cut out the same amount off the roof of the exhaust port and replace the rampped piston with a new uncut piston, you can do the same for the transfers, but it's a little more tricky raising a transfer roof while keeping that angle the same as before so you can also raise the exhaust roof once you find the sweet spot for the exhaust, then ramp the transfers only on a new piston for a more complete squish band and slightly better compression... Or you can just ramp the piston and not mess with the ports at all and still pick up a slight gain at higher rpm.
If so, this is really easy but can still be messed up if you take off too much or taper in too little or too far.
just cut the ramps so they're about 1mm below the top of the piston so you leave enough metal to support the top ring, then taper smoothly about 10mm toward the center, Once this is done you can use some emery cloth at the edge of the rampped sections and slightly round off the abrupt edge and it'll improve flow even more without having to cut too deep.
For the transfers, you cut the same 1mm deep but aim the ramps slightly toward the intake port so it'll begin to direct the intake charge away from the exhaust port, it doesn't seem like it does much but it can help, basically this angle should look like you're pointing the ramp out from the center of the piston crown to the front side of the transfer port, then make the line parallel for the back side of the ramp. Like I said, it isn't much, but it's enough to make a difference.
The ramping it's self adds more transfer and exhaust duration which mimicks raising the roofs of these ports, you can ramp down a piston to find where your engine performs best, then measure how much you cut out, then cut out the same amount off the roof of the exhaust port and replace the rampped piston with a new uncut piston, you can do the same for the transfers, but it's a little more tricky raising a transfer roof while keeping that angle the same as before so you can also raise the exhaust roof once you find the sweet spot for the exhaust, then ramp the transfers only on a new piston for a more complete squish band and slightly better compression... Or you can just ramp the piston and not mess with the ports at all and still pick up a slight gain at higher rpm.
yup... you cut down 1mm off the piston at the transfer and exhaust openings so you have these little ramps to help the fresh charge come in and the exhaust to exit. This is done because it's easier to cut the piston than the cylinder, and because pistons are more expendable... the whole $10 vs $25 thing if you mess up... I guess I should add that you should have at least one spare piston on hand when doing the ramping so you can stay on the road if you do mess one up.
I am running this piston in my current motor
Running nicely with great low end and midrange power. It also four strokes much less than most chinadoll motors which I think is due to better transfer flow and less mixture contamination after the ramping mod.
Running nicely with great low end and midrange power. It also four strokes much less than most chinadoll motors which I think is due to better transfer flow and less mixture contamination after the ramping mod.
Not to run away with the conversation...
maniac- Does the smoothness of those cut outs matter much? Your getting good performance now, would there be a difference you think- or not worth the time?
maniac- Does the smoothness of those cut outs matter much? Your getting good performance now, would there be a difference you think- or not worth the time?
^^ Exatcly what he's showing... Also notice the angle on the transfer ramp on the bottom picture, it's just that little bit on the piston that makes a big improvement to prevent your fresh air/fuel charge from "short circuiting" and blowing right out the exhaust port unused. That little trick does amke a noticeable power difference from just off idle all the way to the top.
Smoother is better, but even like his are cut you'll see improvement.. I used a dremel and an air powered file to do mine up, but a nice hand operated file will help with smoothness. Carbide burrs on the dremel are great for cutting to size and shape fast, then switching to a sanding drum will do the finishing touches and smooth everything out.
^^What he said. I left it like this due to the simple fact I only have two bits for my dremel. Lol!
But it makes very little difference as long as it's not so rough it creates hotspots and causes pre-ignition.
I'm working with ZERO budget. I have to sell a bike to build a bike to sell a bike, etc.
Being unable to afford makes me good at making do. But I don't have to like it.
edit: One thing I would point out, is that it LOOKS far worse than it actually IS. The pics show all the tool marks. It's much smoother to the touch than it looks.
I'm the same way right now... gotta make do with what I got but luckily I got lots of tooling.
I got a full set of carbide rotray files off ebay that fit the dremel last year for under $20 and they help a lot and I got a few sets of the diamond ones from harbor freight for pretty cheap, the diamond ones are best for finishing and smoothing or when precision is more important than a fast cut, the diamond tips work best with a little lube and just let the tool rpm do the work... a very light touch is all you want to do with these or they'll wear out fast.... basically the diamond coating strips off if you try to really push into the work.
the sanding drums work very well on aluminum too but a little lube is also needed to prevent loading up. A light coat of grease works great but if you can get some boelube, that stuff works wonders on the diamond tips but also prevents loading up the carbide or high speed steel ones, the stuff is cheap and you can get it on ebay or at aircraft tool supply places. The white solid or the blue paste works best as its very versatile for drilling cutting or using on rotary files of all types.
I got a full set of carbide rotray files off ebay that fit the dremel last year for under $20 and they help a lot and I got a few sets of the diamond ones from harbor freight for pretty cheap, the diamond ones are best for finishing and smoothing or when precision is more important than a fast cut, the diamond tips work best with a little lube and just let the tool rpm do the work... a very light touch is all you want to do with these or they'll wear out fast.... basically the diamond coating strips off if you try to really push into the work.
the sanding drums work very well on aluminum too but a little lube is also needed to prevent loading up. A light coat of grease works great but if you can get some boelube, that stuff works wonders on the diamond tips but also prevents loading up the carbide or high speed steel ones, the stuff is cheap and you can get it on ebay or at aircraft tool supply places. The white solid or the blue paste works best as its very versatile for drilling cutting or using on rotary files of all types.
Most of the information has been covered here I just thought I'd add some more pictures of my piston ramps and what they look like in addition to Dave's
This was before I shaved the top of the jug off
And lastly after it had been shaved and ran for about 25 miles
This was before I shaved the top of the jug off
And lastly after it had been shaved and ran for about 25 miles
Also differences in weight after ramps were added makes a smoother engine. Here is pictures of weight reduction
This piston is already drilled and skirts cut
After ramps added
This piston is already drilled and skirts cut
After ramps added
That piston looks good too... if you polish the crown starting with 1000 grit paper to smooth everything out and remove most scratches and roughness, then finish the job with some aluminum polish on a paper towel it'll prevent that buildup you're getting on the piston crown.
You can even start with 400 grit paper then go up to 1000, then finish with 2000 and finally buff with the aluminum polish it will polish quicker if you gotta do it by hand. I did mine in a lathe and started with 1000 grit then straight to the aluminum polish to get the crown as smooth as possible but not take off much at all as I can still see the original machining grooves in the crown when done.
the end result is a very smooth top and not much can stick to it, just a bit of browning on the top is all mine shows. I did the same to the combustion chamber but only used the aluminum polish since the Fred heads are already really smooth in the combustion area.
Its not something that has to be done but it helps keep it nice and clean...
The last piston I ramped last week was the best one so far, I used a carbide burr to do most the cutting then switched to flat filing it the last little bit by hand and all 3 ramps came out very smooth and uniform. I only ramped it down about 1/2 mm tho because I need this engine to make more low end torque than I usually set mine up for, this one was set up for a heavy bike with a heavy rider so I set it up a little different.
You can even start with 400 grit paper then go up to 1000, then finish with 2000 and finally buff with the aluminum polish it will polish quicker if you gotta do it by hand. I did mine in a lathe and started with 1000 grit then straight to the aluminum polish to get the crown as smooth as possible but not take off much at all as I can still see the original machining grooves in the crown when done.
the end result is a very smooth top and not much can stick to it, just a bit of browning on the top is all mine shows. I did the same to the combustion chamber but only used the aluminum polish since the Fred heads are already really smooth in the combustion area.
Its not something that has to be done but it helps keep it nice and clean...
The last piston I ramped last week was the best one so far, I used a carbide burr to do most the cutting then switched to flat filing it the last little bit by hand and all 3 ramps came out very smooth and uniform. I only ramped it down about 1/2 mm tho because I need this engine to make more low end torque than I usually set mine up for, this one was set up for a heavy bike with a heavy rider so I set it up a little different.
Not buy'n it , this here's BOY GO FAST. Look ma no brakes remember ?, Like I said to to the basics ain't to become like this here OK ? Now you take one more guess. If you are building a mouse trap then fine. Otherwise,you will need to remove the studs on the intake and exhaust ports and double up the width on each without interfering with the height of them so's not to disturb the timing.Once completed you now must weld in the replacements and grind off the weld or pool a weld large enough to grind flat and drill and trap the studs back in place your choice OK ? I'm serious some of you kids have mice.
