Which cylinder base gasket?

[Zman]

Sorry to hear about your challenges. Does the new piston a dome top and does the original piston have a flat top? Is the new cylinder shorter than the old cylinder?

[Tukt]

Originally Posted by Zman

Sorry to hear about your challenges. Does the new piston a dome top and does the original piston have a flat top? Is the new cylinder shorter than the old cylinder?

That's correct mate! My new forged W?ssner got a dome top and the old piston got the flat surface on the top!

I sent the cylinder for a nikasil reparation (too lazy to check if I've already told you this.. xD) because there was a groove on the cylinder top/wall right where the inner o-ring is located so it was leaking in water.. I have no idea if this is the same cylinder but maybe they ''cut'' off all material above the groove on the cylinder top so it got flat again?

Or is the new piston longer because it got a dome top and that's the reason why it hits the cylinder head so easy?

[Zman]

It sounds like you need to get a flat top piston. There is a yz125 crossover. Do a search for the correct year.

[Tukt]

Originally Posted by Zman

It sounds like you need to get a flat top piston. There is a yz125 crossover. Do a search for the correct year.

After reading some stuff on this forum I came to the conclusion that the cylinder head is made for flat top pistons, right? It said that it would fit bikes from 2000-2013 but naah X(!

Edit: What do you mean by crossover btw? And which pistons got a flat top that fits my bike? :/

[Tukt]

I looked up the piston that was in the cylinder before and it says it's the same as I got now except that it got a flat top!

W?ssner 8079 (which I bought new) got a dome top, and W?ssner 8080 (the piston that sat there before) got a flat top. According to specifications they are the same and fit the same bikes, the only difference is the dome/flat top! Isn't it best if I order the 8080 piston so I'm sure it will fit because that's the piston which was mounted on the bike before! Can a dome piston top really make that big of a difference? :0

BTW, does the numbers below the model number have to match my current one or what are they there for? I'm talking about the ''13904-19'' number! PICTURE: http://imgur.com/zaC1dVR

[Zman]

Both pistons are options for the bike but the cylinder head needs to match the piston being used. There are pros and cons for both piston types. If you are looking for the easiest solution I would just get the same piston that was there before.

Since you need to order a new piston anyway you really should get the proper measurement device for setting the squish.

http://www.ebay.com/itm/Depth-Gauge-...AAAOSwFdtXzEfs

[Tukt]

Originally Posted by Zman

Both pistons are options for the bike but the cylinder head needs to match the piston being used. There are pros and cons for both piston types. If you are looking for the easiest solution I would just get the same piston that was there before.

Alright mate I think I'm just gonna go ahead and order the same piston that's been sitting in there before! But what about those numbers on the piston head? The upper text mentions the model of the piston, but what does the numbers below that mean? Pic: http://imgur.com/zaC1dVR

[Tukt]

Wtf, according to W?ssner the dome pistons are for the EC model and the flat for the MC model.. When I check the partlist manual it says that the cylinder head is the same on both models so?! Did they really make MC 125 bikes in 2010? Is there any difference between the EC and MC models in terms of engine parts and stuff like that?

[Zman]

Unless you have owned the bike since it was new it is hard to say what happened to it over its life. If you had the cylinder replated you need to get the finish bore measurement so you can order the correct diameter piston.

There are often several pistons for standard bore diameter. A,B,C and D. It looks like the B suffix indicates the diameter.

http://www.wossnerpistons.com/produc...ame=2+Off-road

The 1mm to 1.1mm squish I mentioned before is about the minimum for 93 octane fuel. Depending on the fuel you plan to run you may want to consider going to a larger squish. Regardless you need to pay attention to the sound of the engine and if you hear detonation under high load you need to either reduce compression or ignition timing or increase fuel octane or jet the bike richer.

[Tukt]

Originally Posted by Zman

Unless you have owned the bike since it was new it is hard to say what happened to it over its life. If you had the cylinder replated you need to get the finish bore measurement so you can order the correct diameter piston.

There are often several pistons for standard bore diameter. A,B,C and D. It looks like the B suffix indicates the diameter.

http://www.wossnerpistons.com/produc...ame=2+Off-road

The 1mm to 1.1mm squish I mentioned before is about the minimum for 93 octane fuel. Depending on the fuel you plan to run you may want to consider going to a larger squish. Regardless you need to pay attention to the sound of the engine and if you hear detonation under high load you need to either reduce compression or ignition timing or increase fuel octane or jet the bike richer.

I've been told to use size A when replating the cylinder and that's what it came with from the dudes who repaired it so I guess I'll go with size A!

I run 95 octane so how much squish would you recommend?