Martinm210 Posted June 21, 2009 Report Share Posted June 21, 2009 I recently bought this 94. It had a hole in one piston, so I went through the motor. Found what looked like a partially siezed water pump bearing, and backward base gasket covering up the failed piston side. I ended up replacing the waterpump and bearing, installed all new bottom end seals, new crank, and and bought new Weisco Pro-Lite pistons. I think the last pistons were standard weisco pistons. Anyhow, a weekend later it gave up and would only run on one cylinder. Took it apart and found one piston had partially broke, but closer inspection it appears both were having squish/impact problems. Not sure if it was the gasket, the pro-lites, or the crank that was ever so slightly different. The old melt down didn't appear to have any problem with squish, just melted a hole which I think was due to the waterpump and/or that base gasket covering up half a transfer port. So on my round 2 rebuild, I'm sending the cylinders in to get bored out. I think the old bore was a bit worn which may have been part of the problem. Anyhow, here are some pics...too little squish is apparent. So...how much is right? I'm definately checking this next rebuild. The banshee is a 94 with a Hotrods standard crank, cylinders have been ported (will be going up to 45.00mm), the head is a chozen performance head (not sure which domes, but supposed to be the max for pump gas), FMF fatty pipes, K&N filters, +4 Ign. Adv. The bike ran awesome when it ran, but I definately want to check and set the squish properly this time.. So my question is: How much squish should I have with this setup? Do you think the dome in the picture is still ok? Should I polish it or anything? The marks left are very shallow and don't appear to be enough to cause a problem. I've got the case split right now to clean out all the little bits of aluminum and the cylinders are already off to get bored and matched to some standard weisco pistons. Quote Link to comment Share on other sites More sharing options...
blanco25 Posted June 21, 2009 Report Share Posted June 21, 2009 .045 thru .055 any lower than .045 less reliable. Ive heard of people running as low as .035. those people i guess can afford to tear down motors every couple weeks and replace parts Quote Link to comment Share on other sites More sharing options...
Martinm210 Posted June 21, 2009 Author Report Share Posted June 21, 2009 .045 thru .055 any lower than .045 less reliable. Ive heard of people running as low as .035. those people i guess can afford to tear down motors every couple weeks and replace parts Awesome, thanks! I'll be checking this very carefully this time... Quote Link to comment Share on other sites More sharing options...
Bansh-eman Posted June 21, 2009 Report Share Posted June 21, 2009 Different builders recommend different amounts. K&T says as close to .036 as you can get, my motor is sitting at .042 if I recall correctly. Quote Link to comment Share on other sites More sharing options...
Blewbyu Posted June 21, 2009 Report Share Posted June 21, 2009 Different builders recommend different amounts. K&T says as close to .036 as you can get, my motor is sitting at .042 if I recall correctly. I wouldn't run that tight of a squish on a little gas motor, I'd run upper 50's- low 60's. Quote Link to comment Share on other sites More sharing options...
shanYE west Posted June 21, 2009 Report Share Posted June 21, 2009 did the previous build use a stock head? I think .036 is way too tight.. I normally shoot for anything between .045 -.050 with the stockish motors. Quote Link to comment Share on other sites More sharing options...
armyvet Posted June 21, 2009 Report Share Posted June 21, 2009 you may have too much advance for your set up.. judgeing by the piston it also looks like too much clearance in the piston/cylinder causing excessive rocking Quote Link to comment Share on other sites More sharing options...
Onesickcrewcab Posted June 21, 2009 Report Share Posted June 21, 2009 Wow. Ive never seen that happen before. What thickness base gasket were you using? Someone correct me if I'm wrong, but I think you should pull that crank out and have it checked out. With the pistons smashing into the domes it could of knocked that crank out of true or off center. Especially if it wasnt welded. Was the crank you put in it a stock crank? Or a hot rods or some other brand? Almost looks like it may have been a long rod crank. Another possible reason is the guy who owned the bike before you might of had the bottom of the cylinders decked due to the cylinders being warped at some point. Then ran a thicker base gasket to make up for the deck. Good luck with it. Quote Link to comment Share on other sites More sharing options...
Martinm210 Posted June 21, 2009 Author Report Share Posted June 21, 2009 did the previous build use a stock head? I think .036 is way too tight.. I normally shoot for anything between .045 -.050 with the stockish motors. The previous build used the same Chozen Performance head, but it may have had a slightly thicker paper base gasket. The base gasket I used in this last build was one of those thinner metal Wiesco kit gaskets. I don't know what the squish was though, I never checked..obviously was too little. Quote Link to comment Share on other sites More sharing options...
Martinm210 Posted June 21, 2009 Author Report Share Posted June 21, 2009 you may have too much advance for your set up.. judgeing by the piston it also looks like too much clearance in the piston/cylinder causing excessive rocking I think there was too much clearance also, this is why I'm sending the cylinders off to get bored this time. Ring gaps was looser than what I wanted to see, but I threw it together anyhow figuring that it ran before, so it would be ok again. I guess this problem could have been a combination of the two, squish and too much clearance. When the piston is slightly rocked, it would extend further into the domes on the high side making squish a bigger problem. This time I think I'll check squish very carefully, do some break in heat up cool down cycles, and then pull the head to check. It's pretty obvious when there isn't enough by the rings that develop on the pistons. Quote Link to comment Share on other sites More sharing options...
Martinm210 Posted June 21, 2009 Author Report Share Posted June 21, 2009 Wow. Ive never seen that happen before. What thickness base gasket were you using? Someone correct me if I'm wrong, but I think you should pull that crank out and have it checked out. With the pistons smashing into the domes it could of knocked that crank out of true or off center. Especially if it wasnt welded. Was the crank you put in it a stock crank? Or a hot rods or some other brand? Almost looks like it may have been a long rod crank. Another possible reason is the guy who owned the bike before you might of had the bottom of the cylinders decked due to the cylinders being warped at some point. Then ran a thicker base gasket to make up for the deck. Good luck with it. The crank was a new hotrods crank that was supposed to be stock. I got it as part of the package. Not sure on the cylinders, I know the guy I bought it from didn't do anything with the cylinders. Most of the work that had be done was by the previous owner before him and I have no idea what was done there. When I took it apart, the crank was a stock welded crank, but the outer bearing were pretty rough. The HotRods crank came with the package, so I put it in. This banshee is actually intended for my wife, so reliability is more important than every ounce of HP. I'll make sure it has plenty of squish this time around, that'll make sure I have enough regardless of any minor crank differences. The crank seems to be fine from what I can tell. It was brand new except for this one weekend excursion. The piston failure didn't occur suddenly or with any sort of sudden seizure, so I'm hoping these stresses and failures were all smaller impacts that wouldn't have been enough to damage the crank. The bike actually would start with these pistons like this, but it was only really firing on the right side cylinder that still had decent compression. Anyhow...all new to me. I did know better about squish. I've checked it before when rebuilding some chainsaws recently, but I didn't know what the banshee should be and was in a hurry to get it running before our dunes trip. Oh well. Education is never free...at least we had pretty much a full weekend on this first failed build and I'll be meticulous about squish bands in the future... Quote Link to comment Share on other sites More sharing options...
mopar1rules Posted June 21, 2009 Report Share Posted June 21, 2009 i'm thinking the previous owner had either the deck of the cylinders, or the bases of them cut 1mm (.040"). the step cut in your domes, i would be willing to bet is like .035". you're like missing .040" of clearance. measure up your cylinders....from the deck to the base w/a caliper. you should get 4.036" or 102.5mm. if your measurement is less, you know the cylinders have been cut for sure. to find out which side has been cut....base or top, measure from the cylinder deck to the top of the exhaust port. you should get 30.5mm for the measurement to the OEM exhaust port. if that measurement is less, the cylinder deck was cut......assuming your porting is OEM. also, if you're more than 30.5mm from the deck to port roof, that would be because you're bored out some and as you bore out your cylinder, the exhaust port will get lower, cause it leaves the cylinder wall at a downward angle. hope this helps. get back to us on the measurements. Quote Link to comment Share on other sites More sharing options...
shanYE west Posted June 21, 2009 Report Share Posted June 21, 2009 i'm thinking the previous owner had either the deck of the cylinders, or the bases of them cut 1mm (.040"). the step cut in your domes, i would be willing to bet is like .035". you're like missing .040" of clearance. measure up your cylinders....from the deck to the base w/a caliper. you should get 4.036" or 102.5mm. if your measurement is less, you know the cylinders have been cut for sure. to find out which side has been cut....base or top, measure from the cylinder deck to the top of the exhaust port. you should get 30.5mm for the measurement to the OEM exhaust port. if that measurement is less, the cylinder deck was cut......assuming your porting is OEM. also, if you're more than 30.5mm from the deck to port roof, that would be because you're bored out some and as you bore out your cylinder, the exhaust port will get lower, cause it leaves the cylinder wall at a downward angle. hope this helps. get back to us on the measurements. Thats why I asked if the last build had a stock head.. I was thinking the same thing. I figured the stock head was rechambered for the decking.. I just assumed it was a stock head on the last build. Quote Link to comment Share on other sites More sharing options...
mopar1rules Posted June 22, 2009 Report Share Posted June 22, 2009 i forgot to mention, that if you have a .035" step cut in the dome and the cylinder deck/bases where uncut, and you were using a base gasket from cometic/wiseco or like moose, your squish clearance should be .050". you clearly don't have that, so i'm willing to bet the farm that the cylinders have been cut. Quote Link to comment Share on other sites More sharing options...
Martinm210 Posted June 22, 2009 Author Report Share Posted June 22, 2009 i forgot to mention, that if you have a .035" step cut in the dome and the cylinder deck/bases where uncut, and you were using a base gasket from cometic/wiseco or like moose, your squish clearance should be .050". you clearly don't have that, so i'm willing to bet the farm that the cylinders have been cut. Thanks I'll look that over also when the bored cylinders come back. The weird thing is, the previous build that used a stock crank and standard wiesco pistons didn't have any squish issues like this. So I've been leaning toward either the new HotRods crank, the Pro-lites, or the different base gasket. The previous build did have a thicker paper type base gasket, so it may also have simply been the thinner metal base gasket that pushed it over the edge. That or there is a tiny difference between the stock crank and this hotRods crank. The banshee ran like this for probably 15 or more running hours which makes me think the impact was only happening when running it WOT and for extended periods. This time I'll check squish and adjust the base gasket unil I get to .045-.055. Then I'll check the domes again shortly after running it for some warm up cool down break in cycles. Quote Link to comment Share on other sites More sharing options...
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