How far can the Cylinder base be shaved?

[thumper135]

This Rx135 2 stroker Piston I am currently dealing with is approximately 0.151" or 3.79mm below Cylinder deck height, since Cylinder base gasket is not an option here to increase the piston height, the next option that comes to mind would be to shave/mill the cylinder base to achieve optimal piston to cylinder deck height/clearance.

Possible?

 

[helio lucas]

yes, take care to cylinder not hit the crank and sometimes there´s a step to limit how far you can go without shaving the cases. or weaken the cylinder... 3,8mm is a lot...
but the question is why? that could change compression and port timing. what is the bike?
really, if you not sure about shave the cylinder you should left that job to a professional that fully understands it. you could easy damage it...

 

[whenfoxforks-ruled]

You would need the software program, virtual 2 stroke to be able to run your parameters in it and see. On a personal note, when I USED to listen to "guy, and track" talk, I took .015" off the bottom of a cr125, it ate a lot of pistons! What is an Rx135?

 

[plynn41]

Rx135 -- that's a prescription, isn't it?

 

[thumper135]

lol no its a Yamaha RXZ 135, 6 speed, single cylinder 2 stroke. apparently sold plenty to the euro and asian markets. :)

 

[plynn41]

Nice looking little bike!

 

[whenfoxforks-ruled]

6 speed straight, or high, low? Nice bike! What is the squish band now? From the edge of the piston to the lowest point of the head chamber?

 

[thumper135]

6 speed straight, or high, low? Nice bike! What is the squish band now? From the edge of the piston to the lowest point of the head chamber?

this is how it looks at top..

 

[whenfoxforks-ruled]

High compression piston, what, the stock one is flat? Got a pic of the head?

 

[thumper135]

High compression piston, what, the stock one is flat? Got a pic of the head?

how do i add pictures? my attachment quota's just 100kb which is used already and linking from places such as photobucket seems not to be allowed?

Stock piston is flat, yes.

 

[thumper135]

try these, just replace the alphabet x in "http" to t

hxtp://s175.photobucket.com/albums/w127/maan1502/?action=view&current=IMG0124A.jpg

hxtp://s175.photobucket.com/albums/w127/maan1502/?action=view&current=IMG0126A.jpg

here are the pistons (left is stock and right is the new one)

hxtp://s175.photobucket.com/albums/w127/maan1502/?action=view&current=IMG0127A.jpg

 

[whenfoxforks-ruled]

There is an optimal distance between the top of piston and the edge of the head, the squish band. I do not recall the amount. Your problem is going to be getting the port timing back to where it will run properly. I can not see the if the wrist pin location is the same, but the ring lands are not! You need a professional engine tuner is an understatement. May be that Rich knows a guy??????????

 

[thumper135]

There is an optimal distance between the top of piston and the edge of the head, the squish band. I do not recall the amount. Your problem is going to be getting the port timing back to where it will run properly. I can not see the if the wrist pin location is the same, but the ring lands are not! You need a professional engine tuner is an understatement. May be that Rich knows a guy??????????

the wrist pin location is the same, the ring land area is somewhat different, also the newer piston uses a thicker 2nd ring.

port timing is exactly whats keeping the build progress at the moment.

 

[SHSPVR]

the wrist pin location is the same, the ring land area is somewhat different, also the newer piston uses a thicker 2nd ring.

port timing is exactly whats keeping the build progress at the moment.

Is there any why you can't get the rigth OEM piston for it?.
Ok you said ring land area is somewhat different but dose both ring keep clear of the timimg ports?.

Base of what you said it look like you need shave and mill the cylinder base and case base at less 1.90mm that will bring your timing back in to stock spec.

Can you post a picture with 2 piston on the Wrist Pin or a picture with the old piston intall in the cylinder like other one.

 

[thumper135]

Is there any why you can't get the rigth OEM piston for it?.
Ok you said ring land area is somewhat different but dose both ring keep clear of the timimg ports?.

Base of what you said it look like you need shave and mill the cylinder base and case base at less 1.90mm that will bring your timing back in to stock spec.

Can you post a picture with 2 piston on the Wrist Pin or a picture with the old piston intall in the cylinder like other one.

the ring ends on the piston are exactly where the old piston has its.

this is how short the new piston is from deck.

 

[SHSPVR]

this is how short the new piston is from deck.

What about the old piston that what I wanted to see

Look at this screenshot below
Are you saying that the rings are in exactly same place as the old piston has its with the Wrist Pin install for side by side view if that the case then your timing port shouldn't change and don't need shave and mill the cylinder base and case base at all.
Is that old piston a flat top?.

 

[helio lucas]

what was the deck clearance with old piston?
simply shave the base to get the same amount and port timing will be the same and you´re done... this answer your question.

now the big question? why does the two pistons look different? old was high performance? not the same model?
are you not able to get one like the old? because later you might need one like the old one.

 

[whenfoxforks-ruled]

No professionals yet. My guy figuring says shave the bottom also, the same amount as the difference. Then check the head. The width of the ring lands are the problem though, you can get 1 side to match port timing, but, how to make the other stroke match? Vintage Bob

 

[thumper135]

What about the old piston that what I wanted to see

Look at this screenshot below
Are you saying that the rings are in exactly same place as the old piston has its with the Wrist Pin install for side by side view if that the case then your timing port shouldn't change and don't need shave and mill the cylinder base and case base at all.
Is that old piston a flat top?.

yes the old piston is flat. the old piston is no longer available to compare, it was a 56mm while the new piston is 62mm.

the ring end locks on the new piston are exactly how they were on the old piston, apart from the diameter of the new piston which is bigger than the stock, there are not many differences apart from the thicker 2nd ring on the new piston.

the old piston was 26mm in height from pin center to piston top lip, the new piston on the other hand is 2mm shorter than the old piston height (24mm)

 

[thumper135]

what was the deck clearance with old piston?
simply shave the base to get the same amount and port timing will be the same and you´re done... this answer your question.

now the big question? why does the two pistons look different? old was high performance? not the same model?
are you not able to get one like the old? because later you might need one like the old one.

the deck clearance, the new piston was 2mm shorter in height from the deck.

the cylinder base has been shaved 2mm with precision being the utmost priority.

Old was the stock rxz135 55K piston, the newer piston is from a 780cc 4 cylinder.

 

[thumper135]

No professionals yet. My guy figuring says shave the bottom also, the same amount as the difference. Then check the head. The width of the ring lands are the problem though, you can get 1 side to match port timing, but, how to make the other stroke match? Vintage Bob

shaved it has been, 2mm in total has been taken out from the base of the cylinder. that's how short the new piston was from the old.

ring land area, 2nd ring might be a problem? since it uses a thicker ring?

 

[SHSPVR]

ring land area, 2nd ring might be a problem?

What he ref to is where ring gap is going when it going up and down in the cylinder bore is should contacting the cylinder wall at all time not near any port passages see below screenshot becuase sometime you have pull old pin out and move it in new place by re-drilling a new hole that holds the ring in place.
Also it necessary to chamfer the port edges. Rounding of the sharp edge prevents premature wear on the piston and ring assembly. Using a rotary burr to make the initial chamfer, and finishing it out with a sandroll, is a good way to get the proper angle and finish.
Take look here
http://atvconnection.com/Departments/ATV_Tech/Cylinder-Boring.cfm

since it uses a thicker ring?

This will not hurt at all in fact it should give you better fresh fuel/air mix transfer

 

[thumper135]

What he ref to is where ring gap is going when it going up and down in the cylinder bore is should contacting the cylinder wall at all time not near any port passages see below screenshot becuase sometime you have pull old pin out and move it in new place by re-drilling a new hole that holds the ring in place.
Also it necessary to chamfer the port edges. Rounding of the sharp edge prevents premature wear on the piston and ring assembly. Using a rotary burr to make the initial chamfer, and finishing it out with a sandroll, is a good way to get the proper angle and finish.
Take look here
http://atvconnection.com/Departments/ATV_Tech/Cylinder-Boring.cfm


This will not hurt at all in fact it should give you better fresh fuel/air mix transfer

okay i just went out to make sure where the ring end gap pins line exactly in the cylinder.

Over here both the ring gap pins are inside the wall, no problem I assume?

Now over here if you take a look at the top port passage you will see 1st ring pin crossing in the port. what next? :|

 

[SHSPVR]

Now over here if you take a look at the top port passage you will see 1st ring pin crossing in the port. what next?

You need pull that pin and move it and re-drilling a new hole in new place with out it crossing into any port.

 

[thumper135]

You need pull that pin and move by re-drilling a new hole in new place with out it crossing into any port

and leaving it as it is will cause problems? worth a risk?

the new hole can be drilled anywhere?

what about the old hole, will it have to be refilled/closed or just let it be there?