Do you have a 4 jaw independent chuck for your lathe?So... Just checked the three cylinders, doing the same every time with a drop of oil spread on the rings and a few spins to get the oil around, put the tester in and give it six firm pulls.
Stock Mahle Stihl - 165 psi
Stock Brazil Stihl - 164 psi
- 0.01" ish base cut Brazil Stihl - 181 psi
So, my thinking the compression may be up stock is wrong, the cylinder 'ceiling' is lower but the compression chamber must be a bit bigger.
I know that this test isn't perfect but I've read that a wet compression test is a good indication of what you'll get when the saw is run in? It looks like I've got a decent gain. I'd imagine that cutting the band and base by the same amount would give good gains. I'll have a think about a fixture to hold it.
I dont know about on those new cylinders you got there but on the old style cylinders after you cut the base/squish 98/118/77 works pretty wellHas anyone got any good timing numbers for an 026?
I'm going to have a go at one of these Brazil pots, got my depth gauge working and found that the outer ring is a bit higher by 0.25mm (less squish) but the roof is about 0.25mm lower and a close match to the piston crown. There is very little step compared to the Mahle.
I've cut the base to get the squish down, will fettle the ports and having sourced a right angle handpiece for a Foredom I fancy having a proper go at it......
Yep. You’ll make much better compression with a flat squish band and piston. It also gives you room to set a more agressive blowdown. I didn’t cut as much out of the band to keep intake higher.I’d have to check my notes. I believe I take .050-.055 out of the band, cut the dome flat, and cut the base to get .018” squish
My thoughts exactly. Lacking stuffers, the only option is more intake. Widen the hell out of the intake, and put an 044 carb on it. Keep the Intake relatively high. You have to feed that bigger volume but you want the intake closing early so the case will gain transfer pressure.The advantage of closed transfers is that the runner can be routed away from the piston to better direct flow when it exits. Open transfers can work fine, but nobody tries to rout them far from the piston. To just hog out the separator will greatly increase case compression and runner volume. You'll have a lazy engine that won't rev - you'll have low transfer velocity and poorer mixing & loop scavenging.
That sounds about right. My jug was 94 exhaust to start, so raising to 91 wouldn’t take much grindingI really didn't think I moved the exhaust up that much, width is a different story...
Band is cut, base is not, gasket delete only. Kind of wish I had of put the wheel on there before I started grinding now.