Two Stroke Motocross

Two Stroke Motocross Forum => Technical => Topic started by: helfrick15205 on March 26, 2012, 11:39:22 PM

Title: yz 125 piston
Post by: helfrick15205 on March 26, 2012, 11:39:22 PM: i started working on the 02 yz 125 project but i wasn't paying attention to the A,B,C,& D when i ordered the piston. I ordered the D and have a replated cylinder on the way. Will the D piston work with a new plated cylinder?
Title: yz 125 piston
Post by: SachsGS on March 27, 2012, 12:03:18 AM: You'll have to measure the piston and the cylinder to determine their compatibility.
Title: yz 125 piston
Post by: cnrcpla on March 27, 2012, 12:34:32 AM: Quote
You'll have to measure the piston and the cylinder to determine their compatibility. Grin
That, and check the piston ring gap to. If the gap is to small or to big (it should give you an acceptable measure in the manual) then it wont work. Just put the piston in with the rings on and take a feeler gauge and put it in the ring gap. Measure that and compare it, and measure the piston for compatibility like Sachs said and you should have your answer.
Title: yz 125 piston
Post by: TMKIWI on March 27, 2012, 07:22:09 AM: Quote from: cnrcpla on March 27, 2012, 07:34:32 AM
Just put the piston in with the rings on and take a feeler gauge and put it in the ring gap.

How can you fit a feeler gauge in the bore with the piston in.?
Put the ring down the bore about 20mm, pushing it square with the piston, then measure the gap.
Title: yz 125 piston
Post by: cnrcpla on March 27, 2012, 12:20:55 PM: Quote
How can you fit a feeler gauge in the bore with the piston in.?
True, sorry wasn't thinking about that. In that case just the ring will do. But make sure you check the gap...
Title: yz 125 piston
Post by: helfrick15205 on March 27, 2012, 02:40:19 PM: i did not know about the A,B,C,& D cylinders and the pistons that go with them when i got started. the bad thing about it is that i have the manual and didn't bother checking. the cylinders are marked on the intake side. i am going to have to measure the cylinder when it comes in and see what they replated it to. The difference is .004mm between the cylinders and about .004 with the pistons. kinda sucks i jumped right into buying parts and not checking

Cylinder A 54.000-54.002 Piston A 53.957-53.960
Cylinder B 54.004-54.006 Piston B 53.961-53.964
Cylinder C 54.008-54.010 Piston C 53.965-53.968
Cylinder D 54.012-54.014 Piston D 53.969- 53.972
Title: yz 125 piston
Post by: helfrick15205 on March 27, 2012, 02:46:05 PM: also could not find the marking so the only way for me to know is to measure. i am just worried about putting the bigger piston in the smallest cylinder.
Title: yz 125 piston
Post by: cnrcpla on March 27, 2012, 02:53:11 PM: Measure the cylinder bore? That's easy. Just get a pair of calipers (preferably metric) and measure the bore down to the nearest hundredth of a mm.
Title: yz 125 piston
Post by: MetalMike1982 on March 27, 2012, 06:01:44 PM: Quote from: helfrick15205 on March 27, 2012, 09:40:19 PM
i did not know about the A,B,C,& D cylinders and the pistons that go with them when i got started. the bad thing about it is that i have the manual and didn't bother checking. the cylinders are marked on the intake side. i am going to have to measure the cylinder when it comes in and see what they replated it to. The difference is .004mm between the cylinders and about .004 with the pistons. kinda sucks i jumped right into buying parts and not checking

Cylinder A 54.000-54.002 Piston A 53.957-53.960
Cylinder B 54.004-54.006 Piston B 53.961-53.964
Cylinder C 54.008-54.010 Piston C 53.965-53.968
Cylinder D 54.012-54.014 Piston D 53.969- 53.972

It happens dude you live and learn . Its always smart to get your cylinder done than measure it and order the correct piston
Title: yz 125 piston
Post by: Travis616 on March 27, 2012, 09:49:03 PM: Just like Vertex, it is nice to be able to match a piston to a specific cylinder, your manual will tell you piston to cyl. clearance and you can go from there. I think you mentioned it, but, every time you get a cylinder back from being replated/bored/etc. it should always be measured (just to be sure) and it will not necessarily match back to your original 'b' cylinder (or whatever it was)
Title: yz 125 piston
Post by: TMKIWI on March 28, 2012, 06:16:12 AM: Every motor I have had rebored I have sent the piston away with the cylinder.
All the engine shops here do it that way.
Then it can be bored to suit.
Title: yz 125 piston
Post by: MetalMike1982 on March 28, 2012, 01:36:56 PM: Quote from: TMKIWI on March 28, 2012, 01:16:12 PM
Every motor I have had rebored I have sent the piston away with the cylinder.
All the engine shops here do it that way.
Then it can be bored to suit.

I did that once and when the cylinder had to be bored more than the next size up I had to buy a different piston and wasted my money on the first one . The machine shop told me never to buy a piston unless the cylinder is done and you know exactly what your dealing with otherwise you waste money just as I did.