SandBastard Posted December 10, 2003 Report Share Posted December 10, 2003 Thanks HQ. for all the killer info.I recently installed a Chozen performance head and am a little worried about the tight clearance.The porting is stock and the domes are 21cc. Does anyone think I should do something about it? Quote Link to comment Share on other sites More sharing options...
frocashmoney24 Posted December 10, 2003 Report Share Posted December 10, 2003 no sounds ok to me, but im not a cylinder expert Quote Link to comment Share on other sites More sharing options...
fixitrod Posted December 10, 2003 Report Share Posted December 10, 2003 .029 might be okay. I've seen a lot of builder go between .030 up to .039. Hopefully dlnoss will chime in on this one. Quote Link to comment Share on other sites More sharing options...
D34 Posted December 10, 2003 Report Share Posted December 10, 2003 u should b ok... what brand of base gasket do u run??? L8r d34 Quote Link to comment Share on other sites More sharing options...
dlnoss Posted December 10, 2003 Report Share Posted December 10, 2003 That's pretty tight. How did you check it? Quote Link to comment Share on other sites More sharing options...
fixitrod Posted December 10, 2003 Report Share Posted December 10, 2003 That's pretty tight. How did you check it? Excellent point. You can check it by putting a piece of solder in the cylinder at 4 to 8 different positions. Push it into the spark plug hole and make sure it goes all the way to the cylinder wall. Crank it over with the kick starter, pull the solder out and measure it with a caliper. That's the most accurate. Even though it's a zero deck motor, there my be a little variation. Quote Link to comment Share on other sites More sharing options...
itsaripper Posted December 10, 2003 Report Share Posted December 10, 2003 The information I have gathered says you should be .030 to .035 on the piston to head clearance, at the squish band. Check the clearance in four places like 12 o'clock and 3,6,9, etc. I think for one thousants your measure could be off. Have you talked to Chris Paxton at CPRacing yet? He workes with these heads all the time. Quote Link to comment Share on other sites More sharing options...
boonman Posted December 10, 2003 Report Share Posted December 10, 2003 IMHO you should be alright with that clearance, provided you watch out for pinging. Your motor may detonate, depending on other factors. It could be a recipe for death, and it may be alright. I would prefer you to be at a slightly more on the squish at arounf .035", as it can make a world of difference. I too am curious as to the measuring method used. SOlder is one of the most accurate ways.... Quote Link to comment Share on other sites More sharing options...
SandBastard Posted December 17, 2003 Author Report Share Posted December 17, 2003 Wow thanks for all of the replies. I checked the clearance with solder four times in various positions. I used a factory Yamaha base gasket. You guys seem to be somewhat devided on the clearance issue, if I were to increase the clearance what would be the best way to do it , thicker base gasket, or is there some other better way to do it? Quote Link to comment Share on other sites More sharing options...
SandBastard Posted December 17, 2003 Author Report Share Posted December 17, 2003 Sorry for the double post. I talked to Chris and he said no problem.I also talked to luke (forgot last name) at cycle quest and he said he thought it would be ok as long as I dont let a bunch of carbon build up in the combustion chamber. I just dont want to take any chances. Boonman, the rest of my motor is fairly tame the timing is only advanced three deg. but when I ride I hold full throttle for extended periods of time in top gear at the dunes, and Ive heard high RPM motors need more clearance any thoughts? sorry for the long reply. Thanks again. Quote Link to comment Share on other sites More sharing options...
fixitrod Posted December 18, 2003 Report Share Posted December 18, 2003 some cut and pastes I found The Squish Band or "Quench" is defined as that area between the flat of the piston and the flat of the cylinder head at top dead center (TDC). On the compression stroke, as the piston approaches TDC, the compressed mixture of fuel and air is "squished" to the remaining space of the combustion chamber where the spark plug and valves reside. The "squeezing" of the mixture creates turbulence and is expected to promote a better and more complete combustion. Typical figures for this measurement are in the range of .040" to.045" which allows for rod stretch, carbon build-up and other variables. RB Racing's Harley Big Twin ORCA motors are designed with .035" squish to accelerate the turbulence and to further concentrate the mixture in the remaining combustion chamber while leaving a small margin for carbon build-up. Pure race engines with short duration applications may reduce this figure to .025" as some builders aren't happy till the pistons "kiss" the cylinder head. The sites I found them at http://www.rbracing-rsr.com/squishcalc1.html Quote Link to comment Share on other sites More sharing options...
fixitrod Posted December 18, 2003 Report Share Posted December 18, 2003 So, from what I've been reading on a lot of sites, Everyone is correct. It is a tight tolerance, but should work fine as long as your bearing stay tight and no carbon gets built up. Just listen to your motor. If you want to be on the safer side, get a gasket that's .020 instead of .010. This will take away performance though. If I were you, I'd run it the way it is and have fun. I've seen the tolerance as tight as .020 in some of these motors online but they rebuild them after every race. I think your at a good number for performance. Just keep an eye on it. Quote Link to comment Share on other sites More sharing options...
brock_fuzzy_69 Posted December 19, 2003 Report Share Posted December 19, 2003 i guess soem guys take a cheapy feeler guage and cut up a few blades into 3 pieces you can tack a 30 thou feeler guage to the piston top in a few places with a dab of grease then slowly turn the motor over with the head on and the USED head gasket in place yeah he suggested about 30 thou as a min number for clearance Quote Link to comment Share on other sites More sharing options...
SandBastard Posted December 20, 2003 Author Report Share Posted December 20, 2003 That sounds like a terribly inaccurate way to check anything. Quote Link to comment Share on other sites More sharing options...
SandBastard Posted December 20, 2003 Author Report Share Posted December 20, 2003 Thanks fixitrod. I'll have to check out that website. Wife says I'm becoming a banshee info junky. Maybe. A great book I have referred to many times lists: minimum clearance for a 175cc cylinder as .8mm. The book basically states the reason for the squish band is, at the very outer limits of the combustion chamber exists the "end gases" that self ignite and cause detonation. These end gases are heated by the surrounding metal of the piston crown and combustion chamber and also by the heat radiating from the advancing spark ignited flame. if the spark flame reaches the outer edges of the combustion chamber quickly enough, these end gases will not have time to heat up sufficiently to self-ignite and precipitate detonation. Herein lies the key to prevent detonation - keep the end gases cool and reduce the time rquired for the combustion flame to reach the end gases. therefore they suggest making the combustion chamber as small as possible. sorry for the novel. The books title is "Two Stroke Performance Tuning" by A. Graham Bell. Werd! Awesome book!!!!! Wife typed that thanks babe. Quote Link to comment Share on other sites More sharing options...
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