Ok I need some more help: Earlier this season I had a port and polish job done on my sons 1989 LT80. The top end lasted a total of 10 hours aparently the pin circlip malfunctioned and put some pretty bad scares on the cylender. The piston kit was sent to Wiseco and discovered their circlip had malfunctioned. I had the cylender rebored and a new piston kit and was back in action (or at least I thought) the first day of riding it worked fine. First thing the next morning the top end went out again. I have not pulled the cylender off to see if it was circlip again. I spoke with the shop who did the port and polish and they notified me that it must be the rod bearing. Has anyone experenced this from a rod bearing? I need opinions before I start tearing the LT down to replace the lower rod bearings. I also heard that if the bore wasn't straight that it could cause this as well. I was warned by one machanic that if I did port and polish on this LT it might cause issues on the lower rod bearing.
Found some metal on the piston and scared the cylinder walls AGAIN. I have one bore left and the cylinder is scrap metal for a 100cc sleave. The machine shop has been very helpful in working with me on this issue, I wanted to hear what you guys had to say about this.

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I'm probably wrong, but I don't see how porting it should have any effect on the bore or on the rod and crank...unless.... the edges of the ports were not chamfered. (meaning they were left with s sharp edge) and the rings are catching this edge. Or the rod is bad (looses on the crank) In which case, I can see why it's not lasting to long. I don't see how the circlip could fail unless the groove in the piston was machined wrong. Heck, those things are a pain to get out!!! I would check the ports and make sure theres's no sharp edges. Check the rod and make sure thers no play in it. You didn't mention at what bore you are at, but you can bore the stock sleeve to fit a 105 bigbore piston with no problems. (You can actually go alittle beyond that if your carefull)

 

Do you think this could happen if I put the piston the wrong way, the arrow might be facing foward. I can't remember until i tear it down. IF I put the piston on wrong would it have ran as long as it did? And could this have caused circlip to come out of its groove.

 

I think the ring ends would be open to the ports if installed wrong. Which would be letting the rings catch as the go past the open port. Then its probably tring to knock the rings out or turn the piston, in which it probably is jarring it bad enough to knock stuff loose. (If thats the case, make double sure that the rod and crank are in good shape) It could be the cause of all your problems. If your going to bore it further, make sure you chamfer the port edges. Then install the new piston with the arrow to the back while making sure the rings are located at the right spot. (end gaps align with the pin in the piston)

As far as it running and then not..... I believe if you lubed everything up real good, it might have had enough grease and oil on everthing to let it slide for a while. Once it got hot and got all the extra goo off, then it started having problems. (remember, this is all just a geuss) I'd try tearing it down, paying extra close watch to the rings as you take the jug off, then check the piston onec you have it available, then check the rod and crank very closely. I'd bet that somewhere in all that you'll find something just not quite right and in that lies you answer. If not its probably something else!!!! (hahaha Relax, you got to laugh some or it will get the best of you)
Good luck and keep us posted on your findings!!

 

Well I am trying to laugh about all of it. But the lack of funds is starting to hurt my ear, sorry that's my wife I ment my wallet. In all realaty all is good. I just wanted some other opinions. like I said the shop that did the work on the top end has been very helpful. This advice is good and I will run with it and pay close attention to the piston and parts when I disasemble the top-end. Worse case is the lower-end but hey I have been wanting to tear it down to see whats all in there. I will keep you up to date as to what I find, if it is realy bad then I will post pictures of the distruction that occured. I still have my spare top-end that is port and polished but miled with the piston kit and gaskets. My intention was to get my son in the amiture racing but I have not had a successful trip on this LT since the top-end has been done.

 

Some pistons like Pro-X don't have an arrow so it's easy to install backward. I made this mistake but caught it before sliding the cylinder back on. You also have to make sure the circlip gaps are not open to the pin notch.

 

Ok, My opinion::
The rod bearings can go bad with alot of time on the motor.I don't suspect a problem there. See how much side to side play and if you can feel any up/down play.
Yes if the piston is in backwards asfas is correct.
The cir-clip ends are supposed to be at the 7 O'Clock position altho there is rarely a problem if they are double checked for correct positioning (meaning they are in the grove 100%). I push the piston pin both ways when I do it.

Last but not least,,, your recent failure:: I suspect it squeezed on you. Weisco's do that! I hate em. They need a minimum of .0035 clearance to start with. I rough up below the ring gaps to drag oil .You can also drill 3 holes below the ring gaps to try to help drag oil.

 

Ok looks like the lower rod bearings are bad the piston and cylinder are damaged and the scares look just like the pins in the bearing. There is allot of play on the crankshaft side to side about .250 of play. Looks like the case is going to have to be split. Piston circlips are still in place and there is no other missing metal parts. I am going to start disassembling the motor this weekend.
Thanks for the info.
And yes I did install the piston in the wrong way, the exhaust ports are chamfered and there are no marks or scares there. [img]i/expressions/face-icon-small-blush.gif[/img]

 

FYI: When you get to the crank:: my expieriences are:: by the time you buy the parts to re-build it, then pay labor, for a few bucks more you can get a new crank. That's what I recommend to all.
It's hard to re-build them and have them straight!
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how much side to side play is normal? I just ordered a new piston kit for Cody's Lt. He had some scars on the piston and cylinder I didn't like. It looks like the cylinder can be cleaned up without a bore job. Also what would cause one of the rings to stick and not compress freely?