checkster Posted November 5, 2003 Report Posted November 5, 2003 Hey guys couple Q's for you. Im getting ready to take my head off and get it milled. Right now on stock bore I am getting 110psi in both barrels at 500ft above see level. How much could I get milled off safely without worrying about to much compression? #2 does 110 at 500ft souns about right or sould I redo the top end while its apart? thanks checkster Quote
cheezehead Posted November 5, 2003 Report Posted November 5, 2003 I had about the same comp at 300ft and I took 30 thou off and was up to 145psi Later Quote
checkster Posted November 5, 2003 Author Report Posted November 5, 2003 thanks for the info, how does it run since you milled it? can you feel a difference? Quote
boonman Posted November 5, 2003 Report Posted November 5, 2003 I shave heads. I wouldn't go more than .035". That is about the maximum you can go without risking difficulty. PM me if you want pricing info on it, i provide same day service.... and 110 sounds like it is no problem. As long as you aren't below about 95-100, or have a difference of more than 5-10 PSI between the barrels... Quote
Banchetta Posted November 6, 2003 Report Posted November 6, 2003 110 sounds a bit low to me, and personally I'd freshen it up while its apart. You don't want to wait for a ring to snap and score your cylinders and get into the lower end bearings. Preventative maintenance.....I get 128psi at sea level w/ stock heads... As for the shaving head thing.....I don't recommend it. My friend tried that. He shaved .025 and kept putting holes through the top of the pistons. Put another stock head on and no problem. Not trying to stab anyone, but I just wouldn't like to see someone blow there motor ffrom someone else advice... A lot of people on here get away w/ it and it surprises me after seeing what my friend went through..... Quote
checkster Posted November 6, 2003 Author Report Posted November 6, 2003 Thanks for the info Banchetta, but im curious why his bike kept blowing up. Did he just have to much compression from milling to much, or was the engine temp way to high, or was the spark plug hitting the piston? id be interested to know why it kept blowing up just because the head was milled. i should be any different than say an aftermarket head with smaller domes...... got any more info? thanks checkster Quote
Banchetta Posted November 6, 2003 Report Posted November 6, 2003 Thanks for the info Banchetta, but im curious why his bike kept blowing up. Did he just have to much compression from milling to much, or was the engine temp way to high, or was the spark plug hitting the piston? id be interested to know why it kept blowing up just because the head was milled. i should be any different than say an aftermarket head with smaller domes...... got any more info? thanks checkster Detonation. He was running 93 octane w/ 145psi at rebuild. Motor didn't run long enough to fully break in. He went through 3 sets of pistons before he put the stock head back on....no problems after... The aftermarket heads are totoally different. The dome shape isn't the same. I have head mods and my domes aren't shaped anything close to stock. More of a cylinder shape and triangular at the top of the dome....Deeper cut too, but I get 165psi out of them..... Quote
BdBanshee Posted November 6, 2003 Report Posted November 6, 2003 There had to be something else wrong with that Banshee, or he had too much milled off, or not enough squish clearance. I have never seen anyone have problems related to a properly machined stock head. Another thing is compression testers vary greatly between types and brands. I only test with a Snap-On gauge anymore. I run over 175 psi on pump fuel, and this has been working great for about 14 years on my Banshee. Quote
boonman Posted November 6, 2003 Report Posted November 6, 2003 I am with BD here. Whoever cut that head did NOT cut just .025" off it. They must have cut more, and gave a wickedly small squish to make it detonate like that. Or, it was an improperly shaped dome if that was messed with. I have machined countless banshee heads, and snowmobile heads. Not one problem, or complaint. The MAX I will cut on a banshee head is .035", and that is cutting it close on the squish. .030", a TRUE .030" is a more comfortable number. 80% of the heads I machine are between .020" and .025". I don't know what was up with your buds bike, and I am not doubting that he did in fact blow a top end, but I would like to see the head to explore what made it happen. It wasn't from cutting it .025" though. It was cut more than that, or something else was not right.... Quote
BenBB Posted November 6, 2003 Report Posted November 6, 2003 I had mine shaved .020 and have been racing a year on it with zero problems, well worth doing in my opinion. Banchetta, by chance was he running Vito's or Magnum pistons that have a higher crown? Just a thought... Checkster, 110 is on the low side, I would go ahead and do a top end now if you can. Good luck. Quote
Banchetta Posted November 7, 2003 Report Posted November 7, 2003 He was using the pro-x pistons....I dont' know where the head is. He might still have it. I sold him my stock head and he changed them so I don't know what he did w/ the shaved one. I'll call him tonight and find out, maybe he still has it. If he does, then I'll send it to you Boony...maybe you can make some sense of his mess... Quote
boonman Posted November 7, 2003 Report Posted November 7, 2003 I would definitely like to check it out. Something doesn't sound right. My first thoughts lead me to believe that there is an improper squish, but speculation doesn't mean a damn thing..... keep me posted!!!!! Quote
fast87 Posted November 8, 2003 Report Posted November 8, 2003 allright i don;t want to takeover the post with my problems, but since you're all here, you said that 110 was low psi, i checked my comp. a few weeks ago, and it read 95psi!! i thought pretty low, plus they're about 7 years old says he guy i bought the bike from, he didn;t even know it was bored .50 over!!, i only ride top-end so i need something in writing that might help convince my dad to let me buy a piston kit...he seems to think it's like a car, 100,000 miles and should still be good..lol....i am not so easily convinced...what problems might come from 95psi?? too much pressure going into the bottom end?? but it starts first kick EVERY time...Thanks in acvance. ~Mark~ Quote
BenBB Posted November 8, 2003 Report Posted November 8, 2003 Fast87, there's a few things to consider; first of all, your elevation will make a difference on how much static compression you'll get (higher elevation, lower compression). Second, compression gauges vary, so you may want to try another gauge just in case. Third, you may have more compression if you test on a warm motor versus a cold one. As a general rule, under 100 psi or more than 10% difference between cylinders is a good indication that you need a new topend. Of course, if you're at 9000' you might only get 100 psi on a fresh topend. But alot depends on how well you maintain it and to a certain extent, luck. What happens to 2-stroke pistons is that with time & wear, the cylinders become tapered and out-of-round, and the piston skirts collapse. New pistons and making sure the bore is perfect are pretty much wear items on a 2-stroke (that's one reason to go oversize: the other reason is failure due to improper assembly or too much wear). To really know what condition they are in you need to tear it apart and check the clearances to see if they are within spec, compression is just a relatively easy way to tell how much wear they have (and the best way to do this is to take a reading with the same gauge when the topend is fresh and compare that to subsequent readings). If there's any doubt, do a fresh topend and break it in right. To answer your other question, what will happen if you keep running it when the pistons/cylinder are worn, is at best you'll break a piston ring and need a pair of pistons...at worst you'll shatter a piston and the flying debris can ruin the head, take out the crank, bust the cases, score the cylinders, etc. etc. all bad stuff. You still have alot of oversizes left now so I would do it as soon as you can... Quote
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