Transfer Port Modification- Pictures and results here.

**Bikeguy Joe** · #1 02-05-2009, 02:15 PM

This is the place for posting your photos and results of the transfer port modification.
Do it with a hacksaw, dremel tool or a claw hammer (just kidding GEEZE!)

CAUTION TO INEXPERIENCED BIKE BUILDERS- This modification is for those that have a rudimentary knowledge of the two stroke engine, and is not suggested as a first timer's modification.

seca40 · #2 02-05-2009, 05:49 PM

I did this mod to my engine. I noticed a increase in top end power and a decrease in low end power. I may experiment with a longer intake runner to see if I can get some of the bottom end back. My engine also has been port matched, lowered intake, raised exhaust ports. I also did away with the head gasket and lapped the jug and head. I don't know how this mod would effect a stock engine. I used a good quality sawzall blade clamped in a pair of vice grips to do the cutting. Then I cleaned it up with a dremmel. It would be very easy to ruin a jug by gouging the cylinder wall while doing this mod. Be careful.

runslikeapenguin · #3 02-06-2009, 01:10 AM

Quote:

Originally Posted by seca40

I did this mod to my engine. I noticed a increase in top end power and a decrease in low end power. I may experiment with a longer intake runner to see if I can get some of the bottom end back. My engine also has been port matched, lowered intake, raised exhaust ports. I also did away with the head gasket and lapped the jug and head. I don't know how this mod would effect a stock engine. I used a good quality sawzall blade clamped in a pair of vice grips to do the cutting. Then I cleaned it up with a dremmel. It would be very easy to ruin a jug by gouging the cylinder wall while doing this mod. Be careful.

someone else was talking about this in another thread. i don't really see the advantage. the piston already stops before it hits the bottom of the transfer port, so the flow change would be virtually unmeasurable. i would think all this would do is reduce ring friction.

**Bikeguy Joe** · #4 02-06-2009, 10:10 AM

The other thread was removed...the reason being it was a dubious and questionable practice offered up by a new memeber....then he got mad when it was suggested that maybe it was a bunch of hoowie.

This is the place for adventurous tinkerers to post results if they try this mod.

It is an easy way to open up the transfer ports without grinding inside the jug, yes, it removes a lot of material, but I suspect it opens up the transfer ports, in a very "easy to do" hacksaw engineering, kind of way.

I think the first two posts covers the "DO IT AT YOUR OWN RISK" PORTION.

If you have done it, or want to try it, report your results (good or bad) here.

Now, you say the piston is done travelling downward before the port is totally uncovered, or thereabouts? Interesting....maybe any benefit is purely because the material removed allows the transfer port to be effectively enlarged?

Just a guess, I haven't done it.

**Bikeguy Joe** · #5 02-06-2009, 10:13 AM

A special thanks goes out to seca40 for trying this mod and posting results...anyone else?

Creative Engineering · #6 02-06-2009, 11:54 AM

Hey guys,

The guy who owns the shop next door builds F1 race boat 2 cycle engines. I've got an engine apart, and will get him to mark up the cylinder, case and piston for any modifications he deems appropriate.

I'll do it based on his recommendations and then show him the parts before reassembly to make sure I got it right.

I know quite a bit about 2 cycle tuning, which is about 1% of what Brendan power knows. If we're going to modify these engines we may as well do it right the first time.

Here's a link:

Brendan Power

Jim

jasonh · #7 02-06-2009, 12:01 PM

Sweet. It'd be nice to get a pro tuner's opinion on these little motors.

In addition, it might be beneficial to describe the common mods we do to these motors and see if he thinks any might be pointless, could be done differently, etc.

runslikeapenguin · #8 02-06-2009, 01:26 PM

i mentioned before that i was talking to a 2 stroke authority who used to race GP bikes back in the 60's. and i brought the transfer ports up to him and he told me for now i should leave them alone. but depending on the resulting flow characteristics he would probably recommend that we bevel the Piston top to have a smoother flow from the transfer port.

the exhaust is on the left and the transfer is the center port.
and as you can see this picture is of the piston at BDC. so by opening up the entire port i dont understand what is gained? the transfer port still stays the same size where it opens.

jasonh · #9 02-06-2009, 01:31 PM

That makes sense. But isn't the bottom portion of the transfer port severely restricted as is? I don't have a motor in front of me right now so I can't really check on which way the air flows.

runslikeapenguin · #10 02-06-2009, 01:54 PM

Quote:

Originally Posted by jasonh

That makes sense. But isn't the bottom portion of the transfer port severely restricted as is? I don't have a motor in front of me right now so I can't really check on which way the air flows.

i was told they were fine. but im sure they are another part that when changed will only change the power band, which makes sense. open= higher RPM power because of flow and when shut they create more Torque. but it seems like you could do enough porting to get them open without compromising the cylinder wall.