Motor Breakdown

[who_gives_a6]

Already did pour down the head and the valves do not leak amazingly. I may be kind of confusing to understand but basically what would happen is this when starting. The starter would act like it's fighting to turn it over and barely budge it. The guy would put the ratchet on the nut on the flywheel and turn it a slight bit to free it. Then you'd hit the starter and it would just turn over and over without issue until you let off the starter. Once it got turning it was fine. It was when I guess it hit TDC that it wouldn't budge at first. He didn't have to put much pressure in it though. Just connected the socket to it and a small push was it. Not alot of force to get it moving. This issue resolved when I took apart and redid timing as mentioned above though.

Engine has never idled and never gone faster than the starter can spin it. Never pull/push started either.
On a funnier note on getting bit on the purchase: the guy told me he knew the quads well and that it was just a weak battery not getting the power to crank over because of the compression. Battery was old and seemed weak so bought it under that thought. Figured $60 and it's running.

[cannondale27]

Maybe that motor wasnt run much but that piston was.It is junk.Absolutely.Positively.No question.

[who_gives_a6]

QUOTE (cannondale27 @ Dec 17 2010, 04:19 AM) <{POST_SNAPBACK}>

Maybe that motor wasnt run much but that piston was.It is junk.Absolutely.Positively.No question.

Being 97mm then what would a going rate for one be running?

[cannondale27]

I believe about $250.

[who_gives_a6]

I took off the piston and have checked it out. Piston was rocking obviously. It's hard to show and left camera at work but if you look at it the coating is worn on a few small edges on 4 different parts of the piston. The same places the little streaks in the sleeve were. You can also see a bit of rubbing on the head itself from it doing so. I did see one thing weird though. The piston on the bottom says CP MX96. So does this mean it's actually a 96mm or does that mean something else?

Planning on tearing it all down but late tonight and busy until Saturday. What is the crank's movement tolerance? I noticed the rod has some play left to right on the crank but virtually none top to bottom.

[claas900]

It is hard to know what to do with this motor, but the best advice I can give you and thats if you know how to work on a motor and have the manual. Is to tear this thing down %100. Only trust the ppl that you trust,dont trust a strangers word or work. If the cam timing got over looked I'd be willing to bet something else got over looked also.

[MX Quad Dad]

OK, I may be wrong here but, I am figuring that when the valves (I figure exhaust) came in contact with the piston it would rock the piston to the point that the skirt on the intake side made contact with the liner. At this point no harm done. When you crank it farther something has to give. Valve stems will flex a bit and so will the skirt. valves seem to be all right because they seal and the skirt could also flex with out stress damage. but, you are sliding an aluminum skit across a honed cylinder that was supposed to seat the rings. even though this was a very short distance it was under a pressure not intended for this skirt, how long would it take to shave off the equivalent of many hours of run time. now keep in mind we are not talking just one time. it sounds to me like it was manually turned past this point and then cranked with the starter and from the pics I am assuming quite a few times.

besides all of the possibilities that some parts may be good. this thing was not assembled properly. so every thing should be tore down and inspected. yes some or all parts may be ok, but I would want to know things like are the valve stems ok, strait and good grooves for the keepers, are the keepers installed and in good shape, is the port job ok, is the crank done right, is the counter balance timed correctly and who know what else.

Without some good measurements and knowledge of how far everything flexed the first time over and how much of this kind of abuse these parts can take, its pretty risky in my eyes.

My advice. is to completely disassemble, check everything twice, make sure you know if the crank is stock stroke. and unless you are an advanced rider put a new stock piston and liner in. assemble it correctly then ride. if the head is ported and boomer intake with a good exhaust I don't think you would notice the HP loss from the bigger piston. you could then shelf the piston and liner until you found some you could trust their opinion to inspect or what I think I would do is send it off to one of the dyno geeks here let them deside if its worth a risk for one of their experiments or use. they seem to have spare parts and use damaged cases and other parts when they think there might be a chance of failure. Most people here have gotten way more than the cost of a piston worth of help and information from these guys anyway and if you stick with the dales you will too. Heck one of them may even look over your crank an head to let you know if you should be concerned about it.

[wistech]

That sleeve looks like it has been rehoned. The honing marks go over the scratches. In that engines case I would for sure do a complete teardown including the crank. If they barred it over out of time or shaved head to much I will bet the case is cracked by the main bearing bore under the flywheel.
If it was done by blackwidow it should have all the parts on the reciept of what was done and installed.

[Canniboomer]

I really doubt that BW actually did that motor work. In looking back at the piston picture, the upper ring gap is directly above the top oil ring gap!?....and there is still ugly corrosion sitting on the coolant outlet elbow. That, along with the screwed-up timing is not the work of a paid builder with any experience....so yes, the entire assembly job is suspect.
I would guess that BW probably only supplied the parts.
I think you are down in SoCal?, so you might want to contact claas900 in Hanford CA.

[who_gives_a6]

Got the crank out and took to Thumper Racing. Got it checked over. Does have the Z400 bearing and said it was nicely balanced with correct amount of play. Previous owner gave me some extra bearings for the case on the crank flywheel side, so going to just replace that for the **** of it. Everything inside was nice and smooth, no gunk, and the bolts I checked were properly torqued/locticed to manual specs.

I did find one stripped bolt but a few minutes and it was out and no damage to threads. So a little extra cash I didn't want to spend but not a complete fool so listened and checked the crank. Feeling better atleast, haha. I'm going to reassemble the bottom end and then debate what to do for the top end. Thumper concluded that my speculation was correct as was some others here that the piston was rocking when the valves pressed down on it. They said no serious damage and personally would leave the piston as being the cost of it and low amount of damage (just some of the coating), but would replace valves just to be safe incase of a small unseen to the eye bend.

On that note: saw some valves on Ebay. Anyone here selling them or know if they're good ones? Like $45 for a set and sounds good to me for some extra assurance.