LT80 rebuild

[surveywaters]

I put a new cylinder in last spring (50.5). I had the cylinder bored by a local machine shop. The quad ran like a top for about 30 hours (over a 1 year period), then it seemed to be overheating. Finally it stopped running and I disassembled to find lots of aluminum swapped from the piston to the cylinder.

Why would it be overheating and yet running fine?

Also, I have noticed a harmonic sort of noise when it was running ( real high pitch but not a squeal), is this normal?

Finally, if the cylinder had been bored too large, could it have caused this? The machinist said the service manual must be wrong and he gave more room for expansion due to heat.

[chunky0071]

Are you still using the oil injector? If you are and it is not putting out enough oil that could have caused your problem. On this small 2 strokes I all ways tell my customers to run high test fuel and good oil.

[surveywaters]

I appreciate the reponse.

I have never trusted injectors, especially on a unit this old ('87). I removed it many years ago and premix 40:1 with lucas oil and 93oct ethanol free petrol.

[LT80]

I can't see bore size doing it.
Was the gas in it old?

Just curious, how much clearance did the shop give it?

[surveywaters]

I can't remember the clearance and didn't think to write it down...wish I had. I really can't see this causing the problem either unless there was enough room for the piston to flop back and forth but I should have heard piston slap if that were the occuring. The gas was not that old.

The quad was drowned once in a creek, I immediately got the water out and had it running to evaporate all moisture. I guess this could have eventually lead to it's failure.

I am putting a new top end on it, should I replace the crank bearings? I haven't heard any moan or grrrr from them. I plan to replace the crank seals just to be certain there is no air leak there, does the case gasket need replaced? I would rather not split the case if I don't need to because I don't have the tools for this.

[LT80]

I've seen fans with fins broke.
Piston wasn't in backwards was it?
Wiseco piston?
The water shouldn't be the problem.
Air filter all good eh.
Pipe plugged??? This happens alot.

You don't have to replace the crank bearings.
By case gasket, I'll take it as you meant the clutch cover gasket, and I don't replace them.
There is no gasket to use when you split the cases. I use hondabond.

FYI: I use Suzuki or Pro-X pistons @ .0025 clearance.

[nastynotchback1]

i would put new crank bearings in it.You don't know what caused the problem and you don't know if any metal or other foreign matter has made it to the bottom.just my .02

[surveywaters]

It was a cheap ebay piston I had in there. I won't do that again. I was planning on using Wiseco piston kit. Could a crappy piston just fall to pieces?

Piston was in proper (arrow pointing to intake)
No broken fins.
Air filter is clean.

Pipe plugged? Which pipe? Exhaust is good.

[fearlessfred]

Originally posted by surveywaters
It was a cheap ebay piston I had in there. I won't do that again. I was planning on using Wiseco piston kit. Could a crappy piston just fall to pieces?

Piston was in proper (arrow pointing to intake)
No broken fins.
Air filter is clean.

Pipe plugged? Which pipe? Exhaust is good.
the arrow goes to the exhaust

[LT80]

And there you have it. :)
It sure seems to happen.
I don't use Wiseco pistons till the bore goes to 52mm.

"exhaust is good"
Just making sure there is air flow thru the pipe. A plugged up pipe is a common problem.

Nastynotchback:: I would have recommended the brg change but it seemed that the piston was scored not blew apart from detonation. That and he didn't want to split the cases. :)

[fearlessfred]

i think people get it turned around because they are used to the exhaust being at the front of the motor . for anybody who doent know the arrow indicates direction of flow

[surveywaters]

I used the manual to install the piston, I guess I spoke too quick, the arrow was pointed the way it's supposed to, towards the exhaust apparently.

Yes on the piston condition, not shattered, just heavily scored. No hole in the top, actually no grey ash look or carbon build up, fairly clean.

Could the cheap piston be the problem and is Pro-X a decent replacement? Why not Wiseco? I found a 51mm for $62 shipped.

[nastynotchback1]

Originally posted by LT80
And there you have it. :)
It sure seems to happen.
I don't use Wiseco pistons till the bore goes to 52mm.

"exhaust is good"
Just making sure there is air flow thru the pipe. A plugged up pipe is a common problem.

Nastynotchback:: I would have recommended the brg change but it seemed that the piston was scored not blew apart from detonation. That and he didn't want to split the cases. :)


That was not a shot at you.I had a bad day after replacing a piston and having it bored.It was just scared up but some how metal got in the crank bearings and then you know what happened.Just alittle funny these days about things.

[LT80]

I highly doubt that the ebay piston was the cause.

Yes, Pro-X is a fine piston. I've switched to Pro-X from the Suzuki pistons cuz they are a lil cheaper and come with the pin and clips.
I've been getting mine at:: Lytle racing
408-966-9595
Wiseco's demand more clearance when bored and a careful break-in.
Like stated , I only use them when the bore goes to 52mm.
They swell like my big ol belly on a beer night. :D :D

Nasty:: I took no offence. :)

[yophilly]

Originally posted by LT80
And there you have it. :)
It sure seems to happen.
I don't use Wiseco pistons till the bore goes to 52mm.

"exhaust is good"
Just making sure there is air flow thru the pipe. A plugged up pipe is a common problem.

Nastynotchback:: I would have recommended the brg change but it seemed that the piston was scored not blew apart from detonation. That and he didn't want to split the cases. :)


Hey LT80,

I'm curious about your method to test flow through an LT80 exhaust pipe. I have two of these bikes that run well but I'm always interested in gaining knowledge from others.

[LT80]

It's a 2 step process......
1) blow thru pipe.
2) wipe black stuff off lips. :devil:


I did that once anyways..:D :D

I have no way to gauge the flow.
Some get so gummed up they have no flow.
I generally use the air compressor these days and if it blows thru it's fine enough I guess.
Any question on flow and I just heat them up and then blow the carbon out of it.

[LT80]

I gotta say, considering that the LT80 is a red headed step child these days, it's nice to see others chime in. :)

[yophilly]

Yeah, I know the LT80 isn't the latest, greatest thing out there; but they're affordable,easy to ride,my kids love them, and I can still rip around on them when I want!

Thanks for your info.........I thought you may have some kind of 'voodoo-trick' that I might want to try.

Happy New Year...cheers...

[surveywaters]

Okay, to sumarize...
1: No known cause or even speculations on the cause
2: Replace top end with Pro-X piston and new gasket set
3: Replace seals after flushing crank with diesel or kerosene
4: No need to replace the mains if the crank turns smoothly

Anything I missed here? I really want to avoid spending $200 twice.

Is 40:1 a decent mix ratio?

With Pro-X piston, is the service manuals clearance okay?

It was said that the Wiseco piston expands, if the ebay piston did this, would it have caused the seizure?

[fearlessfred]

Originally posted by surveywaters
Okay, to sumarize...
1: No known cause or even speculations on the cause
2: Replace top end with Pro-X piston and new gasket set
3: Replace seals after flushing crank with diesel or kerosene
4: No need to replace the mains if the crank turns smoothly

Anything I missed here? I really want to avoid spending $200 twice.

Is 40:1 a decent mix ratio?

With Pro-X piston, is the service manuals clearance okay?

It was said that the Wiseco piston expands, if the ebay piston did this, would it have caused the seizure?
a pic of the piston would be worth a thousand words

[LT80]

I do not know when pro-X started making the LT80 pistons. I just started seeing them a few months ago.
That being said, a year ago I only saw wiseco pistons on ebay.
I think you got yourself a wiseco piston.
They require not only a good break in but a good warming up too.
I think once all is checked out and reassembled, it'll be just fine.
.0025 clearance on Suzuki or Pro-X pistons.

I agree on the pic. :)

[chunky0071]

LT80 I still believe in these bikes I don't know how many I see in the shop mostly clean the carb or a new battery and send them back out to ride. I will have one for sale in a week or so and I know it won't last long.

[surveywaters]

Okay, here are some pics of the piston. The scaring is not uniform. It's heaviest on one side where you can see the rings are ground too. The other side has wider rubbage but not as deep. I hope the pics help to identify the cause. Stamped inside the forged piston is "ARI".

http://s799.photobucket.com/albums/yy279/surveywaters/LT80/

[LT80]

Your correct, a forged piston.
IMO there is nothing wrong with the piston brand.
There are like only 2 company's that make all the pistons.

[yophilly]

I'm calling that damage DIRT. I think you said the bike got swamped. I would have to say that some dirt got in there and it took a while to kill the piston.

I would chalk it up to a bad day, split the case; really clean EVERYTHING inside and out. New crank bearings , seals, piston, re-bore (again...I know it sucks but ya gotta do it).

Ebay has motion pro case splitters for about $60.00

It seems lika a big job but once you get into it, the task goes quickly.

BTW..Does it have a oem air cleaner assembly? Is the intake boot (funnel looking thingy) nice and soft and the clamps are good?...just checking...

Good luck...

[surveywaters]

Thanks for the run down; I'll get the bearings too. Yes I have the OEM air box, our trail system has some shallow creek crossings so I can't use a pod filter. I ordered a new intake boot today because, as you are aware, they get hard. The one on there is the original '87 and is probably gonna crack next time I pull it off.

Do I need to worry about the bottom rod bearing? I can flush it thouroughly while the case is split. If I need a new crank also, I think this quad may be parted out unfortunately. I have to draw a dollar line somewhere.

[yophilly]

That's a good question. I would clean it really well and check it to see if there is any binding or up-and-down play in the bearing.
If it feels smooth, I would load it up with moly paste (assembly lube)and run it.

Do you agree LT80?

[LT80]

To sum the problem up, I agree with Yo. I'm with dirt being some/all of the problem.

I agree with checking the lower rod bearing for up/down.
The lower rod only has a slit for the lube so I'm unsure of the moly thing. I usually use 2 stroke oil on the upper bearing, I'd prolly shoot some of the 2 stroke oil on the lower brg.

I think the gentelman should NOT attempt doing the bottom end himself.
This is best left to someone that's done this before...And likes doing it.
Comming apart isn't the issue, it's getting it back together with a >straight< crank is.
After doing it quite a few times now, I'm starting to get the hang of it. LOL
I've had to cut the bearings off the crank before. They stick on hard.
Like I mentioned, 3 hours on average is what I get into it.
A customer came up. Thought this was a 20 minute job. He got home late. :D