Clueless87JFrame Posted April 11, 2017 Report Share Posted April 11, 2017 Well let's start this off w some facts. I just joined this page, I don't know much about banshees besides what I've been through with my first (this one). It's an 87 Jframe, basically nothing stock besides the two block cases. Long story short - it's got all new seals, Pistons, rings, wrist bearings, and didn't show to have any air leaks after rebuild. Literally fired up on the first kick after rebuild. Motor idled and ran fine. 66.5 Wisecos - new porting and honing, the works. Clearances were correct - bored by a very reputable Yamaha shop as well as ported by a reputable fella/friend of mine in Pierre Parte. Well I did a few warm up cycles to get the pistons set right. Ran it around the yard for a few minutes. Got out on the road and made ashkrt burst then up and down w the RPMs just for extra break in. Turn around and head back - finally unleashed it and she popped the oring (Trinity Stage IV head w 21cc 160ish psi). So I popped th head off the next day - smoked the same right piston that was toast when I bought it and gummed up the cylinder (but didn't score it luckily). V Force 4 reeds (brand new) and billet intake (also brand new) all new gaskets. Basically spotless motor. Mikuni VM34 round slide carbs I went through and the jets were all open before hand w new bowl gaskets. So my question is - what am I overlooking ? I've read that those carbs are garbage - so I want to start off w brand new ones (whichever are the best because I hate rebuilding motors for myself spending money instead of the other way around). But what else could I be missing? I've rebuilt Hundreds of engines in my life, and not once had a major failure like this - def not in this short of time. I'm simply asking for help - not here to dig for specs or argue or anything like that so any responses would be appreciated !! Thanks in advance Quote Link to comment Share on other sites More sharing options...
hercalmighty Posted April 11, 2017 Report Share Posted April 11, 2017 Are the domes from trinity? Did you do a squish test? You said no air leaks. Did you do a leak down test? Sent from my VS990 using Tapatalk 1 Quote Link to comment Share on other sites More sharing options...
Clueless87JFrame Posted April 11, 2017 Author Report Share Posted April 11, 2017 Yeah it's got trinity domes - o-rings, studs, and nuts on the head. Idk how to post a picture of it but you could kind of see my dilemma Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted April 11, 2017 Report Share Posted April 11, 2017 #1-no proper leak test was done before start and before tear down (now we r just guessing) #2- no squish test done #3- you have 100 over pistons, most domes are only clearance to 80 over Over the yrs of being worked on most bores end up being slightly off center, couple that size of bore , size of domes it's a possibility the piston was lifting the head by nicking the dome Just some thoughts, did you take a compression reading 2 Quote Link to comment Share on other sites More sharing options...
Clueless87JFrame Posted April 11, 2017 Author Report Share Posted April 11, 2017 various reasons can be the cause. You need to actually check squish and perform a leak down test not (oh its running decent so it must not leak) a simple airleak would cause you to blow out a specific piston. Let me guess the side that blew out did it happen to be the PTO side? Trinity domes are a scary part to be installing on your motor. Well that's what was on it when I got it. I have not done a leak down test, nor squish test. I made sure everything was within spec, put all new seals and gaskets and torqued everything to spec and hoped for the best haha. I'm thinking the trinity head is going on the scrap pile along w that shiny new smoked piston, as well as the old round slide carbs. Going to remove both jugs and lap the decks while I'm at it. The clutch side jug is the one that popped Quote Link to comment Share on other sites More sharing options...
Clueless87JFrame Posted April 11, 2017 Author Report Share Posted April 11, 2017 (edited) #1-no proper leak test was done before start and before tear down (now we r just guessing) #2- no squish test done #3- you have 100 over pistons, most domes are only clearance to 80 over Over the yrs of being worked on most bores end up being slightly off center, couple that size of bore , size of domes it's a possibility the piston was lifting the head by nicking the dome Just some thoughts, did you take a compression reading Well I did at least remedy that problem in the lathe. These were 66mm 12deg 18cc domes to Start with - with around 185 psi comp. I knew it would be bored to 66.5 - so I cut the extra .020 clearance (.010 of each side) to keep that from happening. Tops of the pistons didn't have a single scratch or mark on them. Wasn't a point in doing a leak down test before. It had 185 psi on one cylinder and 40 on the other. Had to be rebuilt. So I replaced every seal in it like most folks would while they're at it I'd assume Edited April 11, 2017 by Clueless87JFrame Quote Link to comment Share on other sites More sharing options...
guns4children Posted April 11, 2017 Report Share Posted April 11, 2017 Leak down test? Put that up there with long travel suspension. Quote Link to comment Share on other sites More sharing options...
guns4children Posted April 11, 2017 Report Share Posted April 11, 2017 J bird we aren't talking about nuts gaybo Quote Link to comment Share on other sites More sharing options...
Clueless87JFrame Posted April 11, 2017 Author Report Share Posted April 11, 2017 well.. without checking squish nor performing a leak down test those are 2 huge steps to skip when building a motor. even just swapping out seals... I have no experience in domes but there's a lot of design and "Step angles" that go into them, I would be shocked if they are another reason the motor didnt last. If you carbs are clean, and properly adjusted to spec I wouldn't be jumping the gun and blame the carbs, though I will say 34 PJ's are brutal carbs compared to the standard PWK's. Well like I've already said - this is my first rodeo with the banshee engine. I've had some gudaince from some seasoned gents and the boring was done by a very reputable motor shop. Went by the manual on it - didn't really know what else needed to be done. My background is in outboard two strokes so this is a different animal on some aspects but in all reality not too much. Quote Link to comment Share on other sites More sharing options...
Clueless87JFrame Posted April 11, 2017 Author Report Share Posted April 11, 2017 J bird we aren't talking about nuts gaybo Oh you should have seen the flywheel key they had in this dude before hand Quote Link to comment Share on other sites More sharing options...
Clueless87JFrame Posted April 11, 2017 Author Report Share Posted April 11, 2017 (edited) It took me forever to collect the parts for parts of this rig. Has a RAD Manufacturing axle carrier that I had to dig around to get specs on, aftermarket j/a arms and swing arm. But I just went ahead and bought all new electronics, Denso cdi box, dynatec coil, and wiring harness since this one was a chopped up nightmare. New ball joints, tie rod ends, brakes, rotors, bearings, seals, etc etc etc hell even new fenders sandblasted the frame and slapped some burnt orange urethane on it........ then I got 15 minutes of fun ! Haha Edited April 11, 2017 by Clueless87JFrame Quote Link to comment Share on other sites More sharing options...
Clueless87JFrame Posted April 11, 2017 Author Report Share Posted April 11, 2017 Yessir stator, flywheel are stock. Only thing not stock on the stator is the billet adjustable timing plate. Are the pro design cool heads the best or which direction would I need to go? I applied the yamabond to the key ways and everywhere else the videos I've watched showed, wiped all surfaces with acetone before to make sure the surface was ready, and all new seals. So if it is leaking somewhere - it would have to be the head I would think. But I may be wrong that's why I'm asking haha Quote Link to comment Share on other sites More sharing options...
Clueless87JFrame Posted April 11, 2017 Author Report Share Posted April 11, 2017 Would pics help? I noticed when the rig was idling it was only smoking out of one pipe until you gave it some throttle. Almost like that carb wasn't fueling - but then it would come in just as soon as you touched the throttle and stay that way until you let off. And it ran like a scalded ass ape for the short time it ran. But my plan is to remove the engine - and both cylinders - maybe find something. Never tried a leak down test on the outboards - they were so simple and easy to work on we never had any problems and they're all still running to my knowledge Quote Link to comment Share on other sites More sharing options...
Clueless87JFrame Posted April 11, 2017 Author Report Share Posted April 11, 2017 (edited) Banshees seem to be EXTREMELY picky when it comes to a tune and air leaks. Another bad spot for leaks that are often over looked is the intake, most aftermarket intakes will leak pretty badly if you didnt seal them with some sealer. 1 cyl not firing on idle can point to a few issues, Air leak Carbs not properly synced or adjusted Electrical issue Well it just throws me off that both sides have the same new intake and boots, as well as brand new vforce reeds, gaskets, etc. But one question I haven't been able to find an answer to - are the actual domes themselves suppose to be flush w the rest of the head - or protruding a few thousandths ? Just hard to believe that little oring can handle that burn. When the oring popped is when I imagine the piston fried. But I may be wrong. The intakes are CNC billet aluminum pretty nice ones I just got and some nice boots to go with them. Hell when I got this thing it had the stock ones w a dang piece of radiator hose for the carb boots hahaha. Also all brand new electronics and all OHMd out to spec and both plugs throwing a hell of an arc. Seems like it's that shitty head and carbs to me. What about the terry braided throttle cables ? It's got those but they seems loose on the caps Edited April 11, 2017 by Clueless87JFrame Quote Link to comment Share on other sites More sharing options...
Clueless87JFrame Posted April 11, 2017 Author Report Share Posted April 11, 2017 Yea see those aftermarket intakes are known to leak even with the gaskets. I apply case sealant to all the gaskets and seats and matting surfaces through out the intake track inlcuding the gaskets on the reeds.... I can make that happen. I've got a large lapping block I will run them over as well while I'm doing to top of the cylinders before I slap on a new head. So what's the general consensus on the best new billet head? Quote Link to comment Share on other sites More sharing options...
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