250r piston question

[blakerman]

Hey guys I just bought an 87 250r and I am in the process of installing a new top end. I am just trying to determine what caused the piston to score previously so that it doesnt happen again. Today I discovered that the previous builder did not drill the 3 holes on the exhaust side of the piston that wiesco reccomends. My question is: do you guys think that not having the drill holes could cause the topend to fail.

Oh and by the way it has a fresh crank and the engine is bored .40 over.

[clutch22]

one important thing would be to make sure you're not running lean. Make sure it is on the rich side when you break it in (see the break in process "stickie note") and after it is broke-in, check your spark plug and adjust the jets until the plug is a chocolate color.

[wilkin250r]

Nothing wrong with a Wiseco piston, but I always preferred a cast piston (wiseco is forged).

The forging process changes the grain structure of the piston, which in turn changes the thermal expansion characteristics. It's a trade-off. It makes the piston stronger, but it makes a seizure more likely, and requires greater clearances.

My method of thinking is this: A forged piston is great in a 400EX or otherwise very reliable engine that needs almost no maintenance. The added strength of the piston will make it last just that much longer.

But a 2-stroke revs faster, and gets much more frequent rebuilds. I don't need great strength in my pistons, I'll change them before they are in danger of breaking anyways. I'll trade that strength for tighter clearances, and less danger of seizing.


I'm not trying to scare you or change your mind, or imply that Wiseco pistons are bad in any way. There are a lot of people that have run Wiseco pistons successfully. These are just my own personal choices and reasons behind them.

[C-LEIGH RACING]

Can you post pics of the messed up piston.

A lot of times, what you see in cases like this is the piston will seize in the area of the exhaust bridge first, then if allowed to run anymore, seize up in other areas because of the tightness created by the first seizure in the bridge area.

Most automotive bore shops, after the finish honing is completed in the cylinder thats all they know to do not realizing the exhaust bridge needs clearancing or that the port window edges need champhering.
I'm just guessing because I havnt seen anything yet but this is what happens lots of times.

One, of the most important things after rebuilding a two stroke engine is to do a presure check on the crankcase & cylinder to see if theres any air leaks anywhere. Air leaks anywhere in the case can destory the engine in a very short time of running.
Neil

[peeping TOM]

[QUOTE]Originally posted by C-LEIGH RACING


Most automotive bore shops, after the finish honing is completed in the cylinder thats all they know to do not realizing the exhaust bridge needs clearancing or that the port window edges need champhering.

totallly agree, had first hand experience ,theres loads of machine shops don,t know about {relieving) the exhaust bridge...