Piston problems

[Xboxbum]

That's weird because when you use your peddles the pressure is tightning the threads so it shouldn't do that at all,does it tighten clockwise ? If you put the wrong piston in the total height from deck(top of cylinder)to the top of the dome(highest piont of piston)would be twice that roughly so closer to half an inch and really look wrong!the top ring would be close to or even at your deck height if pic is not an option then messure it really well as described and these guy's can help you chose where to add a gasket!

Yeah that was just a estimate top ring is close top deck hight. Will take pics soon as i figure out how to post them on here.

 

[gary55]

Yeah that was just a estimate top ring is close top deck hight. Will take pics soon as i figure out how to post them on here.

Their may be another way, but the only way it lets me add photos is to add media to my album then insert them to the post with the camera icon.

 

[Purple Haze]

Has anyone tried putting one of these pistons in a lathe and cut the dome down to get a true "0" deck height? I think that a flat-top piston would work better than a dome as far as flame travel and squish are concerned. Don't know if there is enough "meat" on the piston to do this.

 

[gary55]

Has anyone tried putting one of these pistons in a lathe and cut the dome down to get a true "0" deck height? I think that a flat-top piston would work better than a dome as far as flame travel and squish are concerned. Don't know if there is enough "meat" on the piston to do this.

1. Not enough metal. 2. flame travel is what you are correcting with the squish to stop detonation while having high compression. 3. compression would be lowered way to much, so a different head design would be needed to keep comparable power. The older designs used flat tops. The change to a domed piston was a performance boost.

 

[MotorBicycleRacing]

If you put the wrong piston in the total height from deck(top of cylinder)to the top of the dome(highest piont of piston)would be twice that roughly so closer to half an inch and really look wrong!the top ring would be close to or even at your deck height if pic is not an option then messure it really well as described and these guy's can help you chose where to add a gasket!

Putting a low wrist pin piston into a high wrist pin engine makes the piston pop out of the cylinder by the space above the top ring which is about 1/8" and to the top of the crown is under 1/4"

 

[Street Ryderz]

Has anyone tried putting one of these pistons in a lathe and cut the dome down to get a true "0" deck height? I think that a flat-top piston would work better than a dome as far as flame travel and squish are concerned. Don't know if there is enough "meat" on the piston to do this.

getting your piston crown to come flush to the deck is not hard to achive! and best to do with rod length because if you just lower the jug it ends up reducing the the transfer and exhaust durations! My little 50cc listed in other post has -.5mm the crown actualy comes above the deck by half a mm and with the dome volume leaves my chamber at just under 5cc's!

 

[Street Ryderz]

Putting a low wrist pin piston into a high wrist pin engine makes the piston pop out of the cylinder by the space above the top ring which is about 1/8" and to the top of the crown is under 1/4"

Dude do you actually work on these engines? if you put a low wrist pin piston on a high pin engine that has a 38mm stroke it's only the difference of 3mm!from the crown to top of dome is around a 1/4" itself!

 

[MotorBicycleRacing]

Dude do you actually work on these engines? if you put a low wrist pin piston on a high pin engine that has a 38mm stroke it's only the difference of 3mm!from the crown to top of dome is around a 1/4" itself!

I have the pic of what it looks like because a customer did just that.
Your garbled reply makes absolutely no sense, dude.

 

[gary55]

getting your piston crown to come flush to the deck is not hard to achive! and best to do with rod length because if you just lower the jug it ends up reducing the the transfer and exhaust durations! My little 50cc listed in other post has -.5mm the crown actualy comes above the deck by half a mm and with the dome volume leaves my chamber at just under 5cc's!

I'll disagree on the rod length being the best way to get the edge of piston flush with the top of jug. If your lowering at the base you would shorten port durations. If you deck the top there is no chance in ports.
There are a lot of variables on these engines so there is no standard. I have found decking 1mm on most will get you very close, and any more risks bouncing the piston when using a stock slant plug head, again no standard I have had them bounce at 1mm removed. Some of the stock heads enter the chamber as much as 2.5mm before curving up so the gasket thickness is not enough for clearance unless you mod. the head or go after market.
I'm guessing the head on your 50 dosen't enter the chamber before rising. The OP says the new and original pistons are the same, so even if they shipped him the 69.5 mm jug it shouldn't stick up as much as he is saying if at all. Maybe he will post some pics. and clear up this mystery. The only way I see it poss. is a type piston in b type engine.

 

[Street Ryderz]

I'll disagree on the rod length being the best way to get the edge of piston flush with the top of jug. If your lowering at the base you would shorten port durations. If you deck the top there is no chance in ports.
There are a lot of variables on these engines so there is no standard. I have found decking 1mm on most will get you very close, and any more risks bouncing the piston when using a stock slant plug head, again no standard I have had them bounce at 1mm removed. Some of the stock heads enter the chamber as much as 2.5mm before curving up so the gasket thickness is not enough for clearance unless you mod. the head or go after market.
I'm guessing the head on your 50 dosen't enter the chamber before rising. The OP says the new and original pistons are the same, so even if they shipped him the 69.5 mm jug it shouldn't stick up as much as he is saying if at all. Maybe he will post some pics. and clear up this mystery. The only way I see it poss. is a type piston in b type engine.

Your right! alot easier to deck it but adding rod length and a little lifting of the jug gives more displacement and slight advance of timing and I'm all ways looking for more lol!