Piston Not Fully Past Ports ?

[RYANHENRY]

i noticed when my piston is all the way down on the stroke its not fully past the side ports im pretty shure i have a stock stroke 85-86 crank and rod anyone else see this on theres? should i add a another base gasket ?

[Honda 250r 001]

How close is it to being even with the port? You might need a spacer plate, or a flat top CR piston or something like that.

[RYANHENRY]

hard to measure but i would say probably .040 .050 thousandths still into the ports

[Honda 250r 001]

You can buy base gaskets in thicknesses of .040 .030 .020 (stock) and .010 thicknesses and that may help you get rid of that gap. I found the gaskets in different thicknesses on ebay. It may just be the porting thats causing it to be off a bit. Or the cases have been decked... etc.

[RYANHENRY]

ok cool thanks ill see what i can find and do

[Honda 250r 001]

At top dead center is the edge of the piston even with the top of the cylinder? Or does it stick out a little more than the top of the cylinder?

http://www.ebay.com/itm/Honda-TRX-250R-Base-Gaskets-6-New-86-89-/300644707583?pt=Motors_ATV_Parts_Accessories&vxp=mtr&hash=item45ffd22cff

This is the guy I purchased the differnt thickness base gaskets from, It looks like he might not make the thickest ones anymore. You will have to email him. It was over a year ago when I bought the .040 thickness gaskets from him. I think he makes his own, maybe he would punch out a couple thicker ones for ya.

[Langbolt]

What Piston are you using ? Does it have a number on the top ?

Maybe it's not a 250R piston and the Pin Height is slightly off.

Just another thought

:devil:

[C-LEIGH RACING]

When your pistons at BDC & just a bit of the port still covered, about 98% of the crankcase charge has flowed into the cylinder already & only flow at that point, if any will be from the suction wave of the pipe, that is if the pipe matches up with the porting, so the piston stopping where it is, really not hurting performance any.

Is it doing the same in the exhaust port area ??.

What is more important, is where that piston is stopping at TDC, because you always what the piston crown edge to come up flat with the cylinder deck.
Neil

[wilkin250r]

Captain Johnny-come-lately. I was going to say the same thing as Neil, if the piston isn't dead-even with the bottom of the port, that's really not a big deal.

On a throttle, that's a big deal. You'd be surprised how much power is lost just in the turbulence around a small shelf still sticking into the air path. But that's because full throttle is maximum airflow.

On a port, however, maximum airflow is largely dependent upon maximum pressure. On the exhaust side, that occurs just after opening. On the intake side, I'm not 100% certain, but I would assume it occurs near the opening as well, because you're building pressure all the way on the piston downstroke before the ports open. After they open, the crankcase pressure is relieved into the cylinder. The VAST majority of the airflow of the intake charge occurs while the piston is still traveling downwards, so the intake charge almost never sees a 100% open port anyways.

Much more important is the deck height. I would never, never, never sacrifice or compromise my deck height specs with a thicker base gasket just to make the piston match the bottom of the ports at BDC.

[RYANHENRY]

no when the piston is at tdc it is very close to being at the deck height of the cylinder. the piston i had in it is a wossner 71.94 for the atc/trx250r 85-89 the piston says 33907-3 then 071.94 the piston fully down is past the exhaust port ummm i have no clue what kinda porting i have i bought the cylinder from ebay stock cylinder sleeved out to 300-310 what ever it is. on the side of the cylinder it is engraved TC racing or engines hard to tell but definitely says TC . i dont know if my pipe and porting match up im running the esr trx9 center mount when ist running it really rips it does have some really nice porting done anyone know who TC racing is and what kind of porting they do ? thanks guys

[machwon]

TC Racing stands for Tom Carlson. He was the engine builder for Digger when he won the nationals I think. He may still work for Supertrapp exhausts? At least they still sell an exhaust with TC as part of the name.

[RYANHENRY]

hummm ok so maybe he is the one who ported it and installed the sleeve thats cool it definitely looks good i wonder what kind of port job it is though now has me wondering lol