701 -can't figure out what went wrong

[SJ/XPBri]

When you measure the squish where are you putting the solder, it matters, there is a proper way to do it or your going to get messed up measurements. PSI compression readings is not what matters. Its the mechanical compression ratio that counts. Too many factors come into play when talking about psi readings, psi readings are indicate the condition of seal between the rings and the cylinder wall. Also did oil get into your guage? 40 thous squish is cutting it close with a stock crank and rods.

No oil in the gauge, I understand where the solder needs to be placed. The problem with the solder- the piston is kicking it just far enough away from the cylinder wall to get an accurate reading. I am going to be running the ski on powermist 111 race fuel, hopefully it'll give some added insurance. If this thing bends a rod, it'll be OK, I'll have some pics for the carnage section. I'll keep everyone posted on the results :biggrin:
Thanks,
Bri

 

[egbrig]

Try this; you will have to pull the head off, touque it down, then take it off again. Cut four equal length pieces of solder place them at 90 deg intervals, put grease on them, that should hold them in place and keep the piston from rocking when rolled over. I've never had a problem with measuring squish with this method, yam included.

 

[egbrig]

PS, get a book on two stroke theory. You can't listen to people who give advice then ask a question on the theory of the subject. Having a difference of opinion is one thing, but here your getting a bunch of misleading statements. Maybe Paul @ JR's will chime in and give you the right direction to work. BTW squish has a function thats not in direct relation with psi comp.

 

[SJ/XPBri]

Try this; you will have to pull the head off, touque it down, then take it off again. Cut four equal length pieces of solder place them at 90 deg intervals, put grease on them, that should hold them in place and keep the piston from rocking when rolled over. I've never had a problem with measuring squish with this method, yam included.

Going to give that a shot, I'll post the results in a little bit
Thanks,
Bri

 

[SJ/XPBri]

Here's the results (BTW, anyone know if Barnes & Nobles sells Blair's 2 Stroke Theory?)
Squish measured in this way gave me .061" on both pieces of the solder that ran parallel with the wrist pin. The other piece of solder running perpendicular to the wrist pin was .060" on the exhaust side, and .062" on the opposite side.
I hope you guys can make some sense of this, cuz I'm getting confused :ugh2:

The actual measurement of the parts that create the squish = .040"
The single piece of solder method to check squish = .072"
The 4 piece solder method = .061"
Which one do I go by, and will this ski run OK?
Thanks,
Bri

Before Crushing the Solder (sorry for the poor focus, I forgot to set the camera to macro)

After Crushing

Digital Mic Reading

Analog Caliper (Just took 2 measurements to make sure the caliper isn't out)

 

[egbrig]

The reason you got 72 was probably piston rock when crunching the solder. Yea, now I tell you. You want to use solder just a little thicker than the squish. I see you have some good measuring devices so you can do this. 61 thou could be tightened up for more performance but your ok. Don't forget the angle of the dome is greater than the piston dome angle so you’re not going to get the exact edge measurements. With a stock crank, rods, the tolerances are greater so don't go to tight. Yes, some engines will run right at 40 thou but that’s pushing it, and it better have at good set of parts. 61 could be tightened up to 55 and that’s a good safe margin. Now some people out there will run tighter and that’s fine they have probably checked everything, it really depends on the builders goals.

 

[SJ/XPBri]

Bringing this back from the dead. Just wanted to add, I bought an ADA girdled head from Paul with 35cc domes. Squish is now at .053" and the compression is at 185 lbs :biggrin:
Bri