| Author | Message | ||
     Greg_e |
So I'm finally getting some work finished on my little race bike. When I ran it with the stock piston last year, I had to remove the base gasket to get the squish close. Finishing up a new cam and a 13:1 piston today and only got to the point where I put clay on the piston to check squish... got about 0.015 to 0.010 inch thickness in the clay for the squish. Specs: 54mm bore 54mm stroke piston rises slightly about cylinder and head gasket 10k redline I haven't checked to see what the valve clearance is going to be, need to do that next, but wanted to check with people that know more than I do about optimal racing spec. squish clearance. | ||
| 651lance |
I ran .027 head gaskets with shaved cylinders to give me .027 piston to head clearance on my S2. It was vary picky on what fuel I used and the engine needed to be fully warmed up before you can pound on the motor. I also ran the jetting on the rich side to keep the engine cooled down. | ||
| Greg_e |
I'll be running 108 race fuel unless Shell gets their $hit together and makes their 110 more widely available. | ||
| Tootal |
A square motor. Cool! All I can say is I'd like to see a little more clearance on an engine running 10,000 rpm! That rod is going to heat up and grow and if you get any bearing wear it might explode. Check your valve clearance and let's hear what that is. We run a minimum of .030" clearance but prefer .040". | ||
| Greg_e |
Yeah, I think I'm going to check again with solder so I can get a more accurate read, and probably increase up to around 0.025-0.030 (add the base gasket). If I need a larger gap, then I'm going to have to find thicker gaskets for this thing or double stack a gasket. Everything I've been buying is a metal MLS type gasket for base and head and they squish down to about 0.010. I'll have to look specifically for thicker base or head gaskets and I think I'd really like to take up the space in the base gasket. Maybe I could cut a rubber gasket for the base, think I bought some 0.015 now that I think about it a little. Have to check my stock tonight and see what I bought last summer. Shouldn't be a lot of stretch, this piston weighs nothing and the con-rod is pretty close to the same nothingness. The con-rod is either cast or sintered metal forged (guessing cast but those Chinese companies can be pretty advanced with their clones), never measured the amount of change when it is hot. The stock squish was larger than the 0.064 solder I tried to use to measure it and had a big thick base gasket. | ||
| Teeps |
Curious: Engine make & model?? What was the stock squish measurement? | ||
| Greg_e |
It is a Taiwanese clone of a Yamaha TT-R125 dirtbike engine that they use in a bunch of their road and ATV vehicles. So far every Yamaha part that I've needed has fit. No idea what the stock squish is supposed to be, they had it at more than 0.064 inch. Many of the TTR125 guys are running between 0.025-0.030 inch so I assume that is safe. At least safe until you go the wrong way on the shifter and over-rev. too far, then it is float a valve into pretty much whatever your spacing happens to be. The fix is TTR valves and springs. (Message edited by Greg_E on April 24, 2017) | ||
| Fast1075 |
I'm with Tootal on this. .030 to .040 is safe, and a lot better than .065+. | ||
| Greg_e |
Here is some interesting reading and a calculator https://www.rbracing-rsr.com/squishcalc1.html Still kind of thinking that as the components decrease in size that the squish could be tightened up, but I have nothing to back that up. | ||
| Tootal |
I have no doubt you could get away with the decreased dimensions but it's been my experience that a faster engine that doesn't last the whole race is useless. Err to the side of longevity!  | ||
| Greg_e |
Got the solder in there tonight, measured 0.025 across the pin. The base gaskets are 0.020 so look like I'll probably be around 0.045, at least until I can track down a thinner gasket. | ||
| Sagehawk |
I have a road king evo, that I used solid .005" copper gaskets under cylinders. After all the checking , with those gaskets and .045" s&s head gaskets , I had .037 and .039 squish. You might see if you can find solid copper gaskets for base of cylinder or have some made. I sprayed galvanize cold spray on them to help with sealing. 30000+ miles with no oil leaks. Heads were milled .040" and for more mileage on road bike I'm going to go a bit larger on squish. Had to go to a later closing intake valve with this setup as static compression was a bit high. | ||
| Greg_e |
Yeah, I do have some soft copper in 0.005 that I bought for this, and might cut a gasket from it. Still deciding what to do and inexperience is the real problem here. I guess it may come down to gotta do something to know how bad things could be. Because how good they could be never really matters until something pops. Haven't even looked at static compression yet. With the new cam and the 13:1 I hope I can still kick it. Not going to get to work on it until Saturday or Sunday. But gotta get movin' because the first practice is May 12 and that's not far away. | ||
| Greg_e |
Got some time to work on this again, going to run it as it is now. About 0.040 squish, something more than 0.062 on intake valve, about 0.061 on exhaust valve. The exhaust just barely left a trace of solder on the valve, solder is 0.062. The stock static compression used to get to 180psi, this is getting up to about 240psi with a few kicks on rings that haven't been seated yet. Got the carb on but need to rig up the start enrichment cable and take up some slack in the throttle cable. If it wasn't for those things I'd have gas in it and probably started. Another day. Hope it doesn't blow up! | ||
| Tootal |
Compression release? | ||
| Greg_e |
It's kicking over fine right now, have to see when I get some time running it and see what happens. |
