LT80 fresh rebuild noise/lack of power
#1
LT80 fresh rebuild noise/lack of power
I noticed another thread with a similar issue while searching for an answer to my problem, but I was afraid of hijacking, so I started a new thread.
I built LT80 for my sons, I did a few mods while it was apart (Boyeson reeds & ported reed cage, .030" head cut, 190 gram rear shoes, 4 rollers in front clutch, widened exhaust sleeve to match jug casting about .060", raised to match sleeve to port about .015") When I first put it together it had no power and a real weird knocking under low speed high load/high throttle which I thought for sure was piston noise. I took the head off, and it was fine, no head contact or excessive piston movement noticeable. Then I took the front clutch off and went from 4 to 6 rollers. When I put it back together, it ran great with no noise! For about 20 minutes. Now the noise and lack of power is back, and I've had the clutch apart 3 times with no change. I did notice that the front clutch had side to side play while at rest. Also, the rubber on the movable plate that retains the rollers allows a little bit of "rattle". It has bout 1/8" side to side and about 1/8" or so of rotational play at the outer face of the clutch. I suspect this is the noise.
Compression is somewhere in the 140's cold. I didn't write it down and my memory is crap. It took several cranks to get there. I'm used to 4 stroke car engines being done it 3-4 cranks. It took about 10 or so if I remember correctly.
I'm starting to look like a chump in front of my boys! I usually can get things fixed in short order, but this one is about to drive me up the wall.
Does anyone have any suggestions to try?
Thanks
Lynn
I built LT80 for my sons, I did a few mods while it was apart (Boyeson reeds & ported reed cage, .030" head cut, 190 gram rear shoes, 4 rollers in front clutch, widened exhaust sleeve to match jug casting about .060", raised to match sleeve to port about .015") When I first put it together it had no power and a real weird knocking under low speed high load/high throttle which I thought for sure was piston noise. I took the head off, and it was fine, no head contact or excessive piston movement noticeable. Then I took the front clutch off and went from 4 to 6 rollers. When I put it back together, it ran great with no noise! For about 20 minutes. Now the noise and lack of power is back, and I've had the clutch apart 3 times with no change. I did notice that the front clutch had side to side play while at rest. Also, the rubber on the movable plate that retains the rollers allows a little bit of "rattle". It has bout 1/8" side to side and about 1/8" or so of rotational play at the outer face of the clutch. I suspect this is the noise.
Compression is somewhere in the 140's cold. I didn't write it down and my memory is crap. It took several cranks to get there. I'm used to 4 stroke car engines being done it 3-4 cranks. It took about 10 or so if I remember correctly.
I'm starting to look like a chump in front of my boys! I usually can get things fixed in short order, but this one is about to drive me up the wall.
Does anyone have any suggestions to try?
Thanks
Lynn
#3
#4
I'd double check the front clutch installation. It sounds like the roller plate notch may have gotten off the key (this happens).You can turn the key around for a good edge.
FYI: when you remove the clutch, the rollers will flip. No way to tell that aspect.
Check the splines on the crankshaft and fixxed face.
FYI: when you remove the clutch, the rollers will flip. No way to tell that aspect.
Check the splines on the crankshaft and fixxed face.
#5
Thats one thing I was really worried about is the key going into the clutch. The one that came on the bike didn't engage well into the clutch, so I ordered a new one, and it is just as bad. It is engaged as good as I can get it. I think the rotational free play is due to the looseness of the 3 rubber isolators in the roller plate. What I am not sure of is how loose it should be.
I have another running LT80 here that I may start swapping parts from until I get it figured out.
Thanks
Lynn
I have another running LT80 here that I may start swapping parts from until I get it figured out.
Thanks
Lynn
#7
I used one of the $50 kits. I also rebuild the crank using a bronco connecting rod kit so I had the whole shebang apart. Weirdest thing is, I took the head off to inspect for head to piston contact, and nothing looked bad. So, while it was in the shop I took the clutch apart and fooled with it. Immediately after that tear down it ran great for a little bit. I haven't fooled with it for a couple weeks. I need a break to cool my head. I am probably going to work on it tonight.
Lynn
Lynn
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#8
The noise wound up being the head gasket leaking. The gasket that came with the rebuild kit was a thin stainless gasket. I cleaned up the aluminum gasket that was on the bike when I bought it, and it seems to be sealing up now.
Now the dang thing is ringing from the top end. I just can't catch a break on this one.
Now the dang thing is ringing from the top end. I just can't catch a break on this one.
#9
Just an update on the problems I was having. Every single problem had to do with the head. I initially had a head gasket leak. Once I fixed that, it started ringing in the top end. Turns out the milled head was getting hit by the piston. I don't know if it had been milled before I bought the bike or not. I do know after taking .030" off of it, there was no longer a margin on the inside of that chamber.
I replaced the head with an untouched stock head and it is running good now. We went to a local riding area, and my son rode it for three hours straight with no issues!
Thanks for your help and suggestions.
Lynn
I replaced the head with an untouched stock head and it is running good now. We went to a local riding area, and my son rode it for three hours straight with no issues!
Thanks for your help and suggestions.
Lynn
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