I just rebuilt the engine for my 88 LT250R, new crank, rod, piston etc. I just put the cylinder on and tourqed it down to spec and when the piston is at TDC it comes out of the cylinder a little bit, just enough to notice. I dont have my feeler gauge to measure how much it comes out. I was wondering if this is normal for the LT's? My friend who did the boring forgot the head at school so i cant look to see if it would hit it or not. It doesn't seem right to me but i could be wrong. Let me know




mahnster

 

The domed portion should be above the top of the cylinder, however at the edges of the piston shouldn't be. The top of the cylinder may have been milled down at some point to clean/square it up. Depending on how much it is sticking out, the head gasket may be thick enough to compensate. Usaully a head gasket is ~.030" thick when compressed.

You may want to check the clearence using the old head gasket, (or buy another new one) put some modeling clay on top the piston and install the head. Turn the engine over a couple times, remove the head, cut a section out of the clay and measure the thickness. I can't say what a good clearence is exactly, but I think .015" should be enough to allow for heat expansion. If you don't have at least this much the fix is to run two cylinder base gaskets to raise the jug up a little.

 

I knew the dome would go above the cylinder but this is the edge of the piston. Would it be safe to run two base gaskets? I have always heard not to run two gaskets together. Thanks for the reply.

 

Running two base gaskets increases the chance of an air leak. I've heard not to do it as well, but then again when I raced TRX250R's I knew people who did it without any problems. Short of buying another jug or trying to turn down the top of the piston it is your only choice. Just torque it down evenly and when it's running spray some carb cleaner around the base and listen for a change in rpm/pitch.

 

dont go using two stock base gaskets,you are asking for trouble big time,i went through this *exact* same deal and it was from someone cutting down the top of the cylinder to flatten it out. TRINITY racing sells extra thick base gaskets. a stock base gasket is about 15-20 thousandths thick,and trinity sells them up to like 60 thousandths thick,wich would be three times over sized. i bought a .040 thousandths base gasket when my engine was like this and it solved the problem just fine,and it ran fine. these machines are notorious for base gasket leaks,so i would think putting two base gaskets on when you can buy one extra thick one is not a good idea,and by the way they only cost like 12 bucks

 

I wasn't aware anyone sold thicker base gaskets, in that case that is what I would do if it's needed.

 

Yeah the gaskets are sold in diferent thicknesses to allow you to change port timing without portwork. the thicker of a base gasket that you use the more it pushes your power the top end of the rpm range. When i used the 40 thousandths thick gasket,i could not really even notice a diference though,although that quad was friggin fast fast! But if all you need to do is raise the cylinder a tad,i would think thats definitely your best bet

 

Thanks superevil I will have to check that out.

 

What is the stock thickness for the base gasket?