Wossner arrow direction and Cylinder gasket Q's

[pscook]

The under side of the head appears dark, no exposed ally that I can see (engine is in the bike, getting ready to fire this week). The numbers that I can remember off the top of my head are as follows-

Top of piston to floor of exhaust port at BDC- 2.5mm
Squish- 2.2mm
Current Base gasket stack- 1.5mm
Old base gasket stack- 0.5mm
Old squish- Unknown

If I lower the cylinder to achieve 1.8mm of squish, the piston will be ~3mm above the exhaust port floor. If I raise the cylinder to get the top of piston flush with the port floor, I will have a base gasket stack of 4mm and a squish of 4.7mm. If I put the .5mm stack in like original, I will have 1.2mm squish, and the piston will be 3.5mm above the port floor.

The bike ran horribly before I tore it apart, so I can't say what was good or bad. I plan to ride it with the current set up and see how I like it. I just want to ride the bike and get it running properly, then I will attack the port tuning and squish numbers.

[(F5)]

ok that does sound queer. I put a wossner in last week & squish was the same as the std piston that came out of it. Sorry I didn't read the whole post, but are you sure you have the correct piston for your year. Perhaps the rod length changed or you have a KTM 72mm piston. I wouldn't lose sleep over the port at BDC, it won't have huge effect on power, but unlikely to be meant to be like that.

Port closing timing is super critical though. I never bothered to measure mine, as why would you if you liked the power. Could tell you for most of my other bikes as I've tuned them.

[pscook]

Originally Posted by (F5)

ok that does sound queer. I put a wossner in last week & squish was the same as the std piston that came out of it. Sorry I didn't read the whole post, but are you sure you have the correct piston for your year. Perhaps the rod length changed or you have a KTM 72mm piston. I wouldn't lose sleep over the port at BDC, it won't have huge effect on power, but unlikely to be meant to be like that.

Port closing timing is super critical though. I never bothered to measure mine, as why would you if you liked the power. Could tell you for most of my other bikes as I've tuned them.

I thought and thought and thought about piston/rod/etc dimensions, but even if the rod is a different length the stroke on the crank is the same. Same with piston and wrist pin location. All things being equal, the crank determines piston to port and head location, right? If it were a shorter rod, the piston would be lower than exhaust port at BDC and large squish at TDC. If it were a longer rod it would be above the port and tight squish.

I do know that the old piston is not a Wossner, that might determine the issues. If the old piston had a higher crown and lower edge/ring area (more severe dome shape) that would lower the edge of the piston and increase the squish on the old configuration. A flatter piston would do exactly what is going on here with me. Maybe I should pull the head and take a piston crown impression and compare it to the old piston. Lucky I don't have any water in it yet. Lucky me.

[(F5)]

Slide a old pin into the old piston & just into the side of the new one & that will compare pin to crown heights.

Sorry I can't tell you port timings, week before last it would have been a doddle. If someone had a barrel off they could at least measure the port to top of jug heights. that would tell you if any ports had been changed. Can you see any evidence of material removed from the base surface?

[pscook]

No evidence of material removed. Langcourt USA found a crack at the top of the exhaust port, it's fixed. Don't know a thing about porting on this cylinder, didn't look for any evidence. Cylinder is staying on for now, I'll check it out in 10 hours or so, assuming I get it running and jetted properly.

[pscook]

It's alive! Runs well, but it still has a bit of chatter when you get on the needle. Almost like it's four-stroking once the taper opens up. I have a 170 main and the Yamaha needle (N3EW?), top clip (leanest). I'll pore over the jetting threads and see if I can get any ideas. Don't want to go leaner yet because I'm breaking it in, but I would love to have it run right.

[Jakobi]

What are you conditions? Temp elevation etc. Fuel ratio. What size pilot jet? You're very lean already and I'd be hazardous about going leaner at this point.

What throttle opening is it 4 stroking?

[pscook]

Originally Posted by Jakobi

What are you conditions? Temp elevation etc. Fuel ratio. What size pilot jet? You're very lean already and I'd be hazardous about going leaner at this point.

What throttle opening is it 4 stroking?

Easy, cowboy. I need to get the bike properly warmed and seated before whacking it on, so I'll post more as I get there. But about 1/4 throttle it starts to gag. I actually have it a touch richer than it came, but that's not saying much.

Temp: 45 F (you do the math. I'm tired and have been drinking)
Humidity: raining
road: damp (see above)
elevation: 300' (again with the math)
40:1 Maxima 927, I think, summat?
Pilot: See first and fourth post

Going to give it a wringing soon, I'll put the camera on and let you all decide my fate. I'm slow, not stupid, but still slow. Any help is appreciated. If you will excuse me, I have some beverages to sleep off.

[Jakobi]

Hahah! I'm suffering the same effects of the alco, post night shift.. I feel about as sharp as a shovel..

I've run 40 N3EW#1 175 main. I could have probably afforded to move the main down to a 172. I'm not sure I'd try a 170.

This is at 95F, 1000ft, heaps of humidity (60-100%) and less oil (50:1). In saying that the bike is obviously letting you know what its asking for. Post the vid and wows us all

I now run 42 N3CJ#2 172 but it could probably go leaner on the clip. No burbles on the needle but not quite as responsive as the one above.