Wossner arrow direction and Cylinder gasket Q's

[pscook]

Wossner piston, arrow direction- To exhaust port?

Also, I am getting ready to set my cylinder on my rebuilt engine (300) but I can't get the top of the piston to the bottom of the exhaust port at BDC. I will need lots more gaskets to raise the cylinder enough to effectively lower the piston, are there any significant disadvantages to having the piston too high? I am at 1.5mm gasket stack, anything more and I will have to use old gaskets. Advice or suggestions?

[Jakobi]

Originally Posted by pscook

Wossner piston, arrow direction- To exhaust port?

Also, I am getting ready to set my cylinder on my rebuilt engine (300) but I can't get the top of the piston to the bottom of the exhaust port at BDC. I will need lots more gaskets to raise the cylinder enough to effectively lower the piston, are there any significant disadvantages to having the piston too high? I am at 1.5mm gasket stack, anything more and I will have to use old gaskets. Advice or suggestions?

Arrow towards exhaust port - check! Might want to double check which way the rings go on too. I can't remember if its the marked side up or down off the top of my memory. The ring gaps + pins face the intake side of the engine.

How far off is the exhaust timing? You could consider having a machinist make up a spacer if the gap is quite large. Then run a gasket each side of the spacer.

See this thread for some general info on how port timing, squish and porting modifications alter the power curve. http://www.gasgasrider.org/forum/showthread.php?t=10113

[Keg]

Rings face up with the letter or writing on it.

If the edge of the piston is slightly off, but it clears the rings, don't stress, and DONT use old gaskets.

[pscook]

Writing on rings up, check. Pins aft (intake), check. Arrow fwd (exhaust), check. Ring gap at 0.5mm 1" below cylinder deck, check. Piston edge at BDC is about 0.8mm (roughly) above exhaust port floor. Final gasket stack is ~1.4mm.

I read the link regarding gaskets the other, Jakobi, hence my questions (made me more confused, per the usual). Looking through it now, I do not see a reference to exhaust port/piston, just gasket stack. I just had the cylinder lined so I don't particularly want to start running a dremel around the ports, plus I wouldn't know where to start. I can drop the cylinder a bit, but I don't know if it's worth it.

Keg- What do you think regarding 1.4mm gasket stack? 2002 EC300, I don't know if the porting is stock or not. It was allegedly built by Eric Gorr many moons ago but there was no build sheet with the bike. I don't know the squish, I'll measure tomorrow.

[Fred1956]

You'll need to RAISE the cylinder, best power setup is piston edge even with exhaust port floor and THEN measure/adjust squish. You'd end up with 2.2mm gasket stack based on your numbers

[Jakobi]

Yeah as per the link.

"The Black line is the stock engine, in this case 2.5mm squish, 11.9:1 comp, 1.3mm base gasket stack, piston level with port floors at bdc"

From here they speak of dropping the cylinder (less gaskets).
0.7mm in this scenario boosts overall with a slight drop at top end, however going to 1.0mm results in a major sign off up top.

The figures will change depending on your bike, your compression ratios, squish etc, but basically regarding the port timing having the piston sit higher above the exhaust port results in exh duration drop, transfer duration drop. This increases bottom end at the expense of a good flowing top end. More back pressure, more grunt.

Increasing compression has the same effect on an engine. Adds to bottom end, but will be less willing to rev as high.

So by running less gaskets you end up increasing the compression and changing the ports to all focus on improvements in the bottom to mid. The top end is sacrificed.

If you time ports flush with piston at bdc you get a softer bottom end more inclined to rev out. Add some compression by changing your squish and you pick some up all over.

Make sense?