tobster Posted November 22, 2014 Report Share Posted November 22, 2014 Hi. Can someone please tell me what the optimal squish is for my 1978 TY175 running on standard unleaded fuel? I plan on removing the head gasket as a starting point. I dread to ask but i will, what is the consensus on premix ratio using Castol A747 for trials riding??? Is Silkolene acceptable to Yamahas? That's it. Thanks Quote Link to comment Share on other sites More sharing options...
smelling123 Posted November 23, 2014 Report Share Posted November 23, 2014 Same bore and stroke as a TZ350 which run at 30 thou (0.75mm). Its good to get the squish right but you may need to drop the compression a little back to standard (although in my opinion TY175s benefit from a little higher compression - makes em a bit better low down and with such a big flywheel, theyre still soft enough). cheers 1 Quote Link to comment Share on other sites More sharing options...
bestrcpilot Posted November 27, 2014 Report Share Posted November 27, 2014 I find that a squish of .040 inches works well. Also reshaping the combustion chamber is a big improvement. A lot of videos on doing this on utube for a Yamaha Blaster. The stock head is cast and is not the best. When chucking the head in a Lathe and checking the run out you will see that most of the heads have a run out of as much as .180 inches. Quote Link to comment Share on other sites More sharing options...
crowley Posted November 28, 2014 Report Share Posted November 28, 2014 I've just built a Powervalve 350 for racing. I set the squish at 8 thou and it runs way better than stock. An added benefit is that it runs much cooler - which has saved a few bob on an oversize ally radiator Quote Link to comment Share on other sites More sharing options...
smelling123 Posted December 6, 2014 Report Share Posted December 6, 2014 8 thou is very tight, I'd suggest this will cause excessive combustion turbulence leading to detonation.... If you look at what modern race engines eg rs 125, and engines making more power from that period eg tz 350 they're running bigger squish gaps than that (at least the guys who are winning). Good luck with the racing, great fun bike to ride. Quote Link to comment Share on other sites More sharing options...
jse Posted December 6, 2014 Report Share Posted December 6, 2014 8 thou is very tight, I'd suggest this will cause excessive combustion turbulence leading to detonation.... If you look at what modern race engines eg rs 125, and engines making more power from that period eg tz 350 they're running bigger squish gaps than that (at least the guys who are winning). Good luck with the racing, great fun bike to ride. I totally agree. .008" is too tight, especially in an air-cooled engine. In TYs I usually set the squish at a little over 1mm, or .039". Jon Quote Link to comment Share on other sites More sharing options...
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