Eye candy!

[Karl Snarl]

Interesting piece of info to note. I have a long time acquaintance who for the last thirty years does performance motorcycle work including engine maching rebuilds dyno etc. When I mentioned suggested squish clearance he felt that they were overly big. His ducati 250 twin that runs 10,000 rpm with big cast pistons sits at 0.6 mm. I did show him the cranks etc we run so he could see what we are dealing with as well. Food for thought.....

We arent running super awesomely engineered piece of machinery like a ol' Duc'. We are running pot metal engines and parts. Its why they are so wide.

 

[DieselTech]

Lol I didn't! I had .028", 032" & .052" head gaskets & of course needed a .040" to set it perfectly at .7mm. With a .028" head gasket & a head gasket made out of a aluminum beer bottle, I got it to .044" to allow for crush/seat in.

 

[mountain80]

We arent running super awesomely engineered piece of machinery like a ol' Duc'. We are running pot metal engines and parts. Its why they are so wide.

Yes he is aware of that as well. We also do not have the rod weight piston weight or piston speed that the duc has and it is part of the overall package in his giving me aproffesional opinion.

 

[Karl Snarl]

Yes he is aware of that as well. We also do not have the rod weight piston weight or piston speed that the duc has and it is part of the overall package in his giving me aproffesional opinion.

He does realize these things have huge clearances right? With that know it should be obvious why none of us set the squish too tight. Soon as ya warm up the engine,BOOM, the piston rams the head. Or when you get up to a high rpm, this weak pot metal starts stretching and that tight squish goes out the window and the piston into the head. Better to be safe on something manufactured to a rough tolerance than go all out like on a modern engine and watch it all explode from to tight a squish.

 

[mountain80]

My last oem engine runs 0.6 mm squish. Never a problem in 4000 miles. Im also a machinist and an ex motorcycle mechanic so some people might have different experience than you.

 

[Street Ryderz]

Interesting piece of info to note. I have a long time acquaintance who for the last thirty years does performance motorcycle work including engine maching rebuilds dyno etc. When I mentioned suggested squish clearance he felt that they were overly big. His ducati 250 twin that runs 10,000 rpm with big cast pistons sits at 0.6 mm. I did show him the cranks etc we run so he could see what we are dealing with as well. Food for thought.....

That makes no sense, the larger the bore the larger clearance to obtain the correct msv, most 250's have over 1mm of squish unless it's used solely for short run drag racing and rebuilt every run, even some of the 70cc Minarelli's the manufacture recommends 1-1.2 mm squish when used with stage 6 heads for circuit racing. This also has alot to do with compression and head chamber type also the piston top, many have used .6 in small displacement engines but has proved no real gains to be worth the risk with these poorly made China girls.

 

[Street Ryderz]

Here is my new head after I cut squish band to my 49mm bore. It cc'ed at 5.8cc after I cut it to my bore. Is that ok?View attachment 159501

Looks great, 5.8cc is fine but seems odd since most are 6 cc or more before being cut to suit our needs and this would raise the number not reduce it. The old stock heads used to be 10cc's and then the aftermarket ones came about reducing this to 6-8 cc's hence why they were listed as high comp but over time the stock heads went to 6cc's and then the aftermarket heads were no longer high comp compared to stock, just better chamber and more cooling area and also much harder to warp as the stock heads were bad for that when used to make some real power. This should work very well !

 

[DieselTech]

Thanks @Street Ryderz for all the good info, my measuring setup wasnt the best, i checked it 3-4 times just to be sure, but i could be off a little bit. Yeah I keep looking at mountain80's cylinder head & his chamber design looks a little bigger than that/ different design. His cylinder head is made by the same company. I was reading on another website & they were saying that each different head shape from CDH was a different cc amount, polygonal was 5.5cc, square was 6cc & the round head was 6.5-7cc.

 

[Karl Snarl]

My last oem engine runs 0.6 mm squish. Never a problem in 4000 miles. Im also a machinist and an ex motorcycle mechanic so some people might have different experience than you.

Im also a machinist, on my lunch break. Lol. You might get away with some, but most are to far out to go that tight with out hitting. I even have a home shop. To me not worth finding out of the rod is going to stretch or if it was a good cast. Lol

 

[DieselTech]

After my piston was just touching cylinder head, Lol could be over revved/rpms. Well I know from now on I'm going to check my squish 2 different directions, parallel to intake & exhaust & 90° from intake & exhaust. I think my stock head was milled unsquare in the combustion chamber is why it was just barely kissing one side of my old head. My squish was set at .73mm on that one. So I'd be leery of going to .6mm on squish.