Commonly mismatched parts...

[carasdad]

One thing I have not seen anyone post about here are commonly mismatched parts.. The number one most common one I see on folks Scoots are replacement pistons that are not correct for the cylinder. I have though seen posts and incidents in person where someone orders a new piston and performance degrades from even worse than the worn original piston and rings. It seems we fail to remember that the piston ports must match the cylinder they are going in. Below are a few pics of different style pistons. Take note of how large and how small the piston ports are..how high up or low down they are from the piston skirt. If they don't match the cylinders porting..performance degradation will occur. The last pic shown here is of a new Athena Aluminum 2 ring cylinder kit I have. Note not only how small the cylinder port is in comparison to most kits..but look at the piston port. It is only a notch at the bottom of the piston and not 2 elongated holes in the piston like many kits. I myself have simply bought new piston kits..tossed them in..then wondered why it was hard to tune and performance stunk.. Now I match the old piston to the replacement one before ordering and have found the performance was back to its original power output. Just some food for thought..something to ponder..and a chance for you 2T gurus here that build some of these monster machines we see on this site..to possibly explain and enlighten us regarding this vast array of piston designs we see..and how each affects us. So please input as much as possible. I think this has been an overlooked and never discussed issue with our Scoots.. Thanks, Glenn

Lastly..this is the bizarre looking Athena kit..again note the tiny cylinder port..and notched piston port..blew my mind and makes me wonder if this thing will even run.

[carasdad]

Slow down on all the replies..I can't keep up..lol all these views but not any input..so maybe I worded it wrong? Or possibly it is common knowledge and I am just a late bloomer?..

[Gimpdog]

I've never thought of that before. Definitely makes sense. So how does the backyard mechanic, hopping his/her scoot, make sure everything fits the 1st time ordering a piston and parts, w/o the pain of finding out the parts don't fit???

[carasdad]

Originally Posted by Gimpdog

I've never thought of that before. Definitely makes sense. So how does the backyard mechanic, hopping his/her scoot, make sure everything fits the 1st time ordering a piston and parts, w/o the pain of finding out the parts don't fit???

Exactly! The new piston kits do fit..BUT with even slightly piston porting differences..many on here have an engine that runs worse that it ever did before..so they blame the carb..CDI..plug..ignition coil etc..and never really get it to run properly..
Does this mean this site is only for things like.. "Scoot died won't start".."My battery won't charge".."Will a 34mm carb work on my stock 50 and give better performance".."How do I make a 50cc GY6 go 60 mph?"..and repeated things of that nature.. I was hoping somebody could explain the port differences and what they do..since we know that installing the wrong piston kit has Ill effects on the engine..

[thumper650]

I haven't had to rebuild my engine, yet. But I'll keep this in mind if/when I have to.

[Firehawk989]

I'd say that as long as the piston you get in your kit is designed to work with the cylinder you have, it should be all good. Buy your piston separately from your cylinder and all bets are off.

From my limited knowledge of 2-strokes, the width and height of the ports can have a large effect on how the engine runs. Different manufacturers might lay out their ports a little differently to go after more torque vs hp, or the other way around.

[carasdad]

Originally Posted by Firehawk989

I'd say that as long as the piston you get in your kit is designed to work with the cylinder you have, it should be all good. Buy your piston separately from your cylinder and all bets are off.

From my limited knowledge of 2-strokes, the width and height of the ports can have a large effect on how the engine runs. Different manufacturers might lay out their ports a little differently to go after more torque vs hp, or the other way around.

Exactly..and why I brought this up. Many folks here have run into issues when replacing a piston/ring set in their cylinder. Suddenly it runs like crap. I have 7 new piston/ring sets in my parts bins. Some bought from the same vendors with same part numbers..and all 7 are different! So the chance of just buying a new 47mm piston/ring kit..installing it and having it run right..or even run at all came be a gamble. So when I rebuild a customers 2T engine I keep the old piston and match it to the new one. BUT!! you CANNOT rely on a vendors website pics..as MANY use a generic pic and not a pic of the actual product. They NEED to use real pics AND have the measurements with the pic. Such as wrist pin to to crown height...and piston over all height. Again the 'REAL' pic should also have a good view of the ports in the piston. But oddly..just as most of my posts here..I get very few replies or feedback...while a post about "What size belt does my GY6 50cc short case need" will get 20-30 replies. Maybe my findings are common knowledge and I am the only one that did not know about or notice this.. Or maybe to many.. a piston is a piston..and a big port..small port..high or low port on the piston shouldn't matter?.. I suppose if port timing is not important..we shouldn't bother lining up the cams on our 4T Scoots either?..

[Firehawk989]

Originally Posted by carasdad

Exactly..and why I brought this up. Many folks here have run into issues when replacing a piston/ring set in their cylinder. Suddenly it runs like crap. I have 7 new piston/ring sets in my parts bins. Some bought from the same vendors with same part numbers..and all 7 are different! So the chance of just buying a new 47mm piston/ring kit..installing it and having it run right..or even run at all came be a gamble. So when I rebuild a customers 2T engine I keep the old piston and match it to the new one. BUT!! you CANNOT rely on a vendors website pics..as MANY use a generic pic and not a pic of the actual product. They NEED to use real pics AND have the measurements with the pic. Such as wrist pin to to crown height...and piston over all height. Again the 'REAL' pic should also have a good view of the ports in the piston. But oddly..just as most of my posts here..I get very few replies or feedback...while a post about "What size belt does my GY6 50cc short case need" will get 20-30 replies. Maybe my findings are common knowledge and I am the only one that did not know about or notice this.. Or maybe to many.. a piston is a piston..and a big port..small port..high or low port on the piston shouldn't matter?.. I suppose if port timing is not important..we shouldn't bother lining up the cams on our 4T Scoots either?..

I think the issue is just that most people will buy a whole new cylinder and piston together when it's time to replace either one because it's not much more expensive than buying a piston and rings on their own. When you buy both together in a kit, it's usually safe to assume that they'll work properly together.

But yes, I agree that the sellers should be more vigilant about putting up real pics of things like a piston that needs to meet very tight tolerances to work properly.