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LT-A50/KFX50 top end replacement difficulty?
So I picked up a 2006 KFX50, did the typical restrictor removal (exhaust, piggy back, intake, 67.5 main, air box). Still been somewhat difficult to start, and very little bottom end power, still sputters on the top end. But as I started it today, I could see smoke come out of the head gasket, and also some almost foam. I assume my head gasket is toast. I can have the head shaved down .045, I don’t really fear taking the head off, but if I’m going that far, should I go all the way and pull the cylinder off? I’ve got to say, the piston didn’t look the greatest when I had the flashlight in there doing the exhaust. Is this essentially a beginner job? Do I need to pull the whole engine? I believe I understand the basics, but the last time o touched a piston was small engines class in 98 and I was probably high. thanks for the advice |
Pulled the head this morning, cycled the cylinder, it seemed pretty smooth. Bit of carbon on the combustion chamber. Not sure anything stood out as excessive. |
1) please don't shave the head that much. I bet it'd hit the piston. I'd leave it stock for now.
2) get it together and do a compression test. 2 strokes top ends are easy. We'll help. :) |
To check if the head is warped, and also flatten it if it isn't too bad, I get an old sheet of glass, rub some coarse grinding pate on it and slide the head about on that. Where the paste is taking metal off, the surface takes on a dull grey/white appearance, if this shows a low spot, continue until it disappears. You will get fed up of doing this before you take too much metal off. You can do the same with the cylinder top surface if you think it is warped. Clean all traces of grinding paste off with solvent before re-assembly. If you do take the cylinder off, I would get it and the rings checked for wear. The rings may have a right way and wrong way up, and there will be a peg in each ring groove that the ring gap has to sit against, as two stroke rings must not move round on the piston.
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I can say, it’s incredible that this forum goes back to the years before during and after the LTA50. Lots of information stored in there. i got the .045 number from those archived posts. I’m under the belief at the moment that the head may have a slight warp. I could see the exhaust when cold, seemed to get better when warm. I’m going to take the head to a very experienced shop. I can probe and see what they think. www.billbune.com the goal is to have it back together and relatively functional in 2 weeks for the kids birthday, after that I can go deeper if needed. I have to draw the line somewhere I guess. I want the quad to have enough power to move on a limited throttle, and run good enough for the wife or grandma to start. |
https://youtu.be/MnQqOm3dz6M
As it got hot, it ran worse too. The wife wasn’t able to drive it back to the garage under it’s own power. I go 275 so it will be a bit different with the 35lb kid on it |
I wonder if the pipe is plugged.
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Originally Posted by LT80
(Post 3406128)
I wonder if the pipe is plugged.
When I bought the quad and brought it home to go through it good, the spark plug wasn't even tight. just black from soot. cant believe it started and ran. |
Take the pipe off and throw it in a fire (fire/charcoal/wood stove/etc) and get it red hot. Blow compressed air threw it. CAREFUL it'll blow flames. :D
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Originally Posted by LT80
(Post 3406131)
Take the pipe off and throw it in a fire (fire/charcoal/wood stove/etc) and get it red hot. Blow compressed air threw it. CAREFUL it'll blow flames. :D
Ok, I was going to say, I think I do have a plumbing snake that might work |
Zipped up to a guys shop and he took off .035. Not warped anymore!;) |
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If your plumbing snake can heat that pipe up cherry red, go for it. :D
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Got the head put on. Had to order a gasket kit for a JR50 as the “KFX “ was out of stock. Lol I cycled it around 2x to make sure the piston wasn’t going to touch the plug, then bam, first pull it lit right up. Blipped the throttle a couple times and it certainly seemed zippier. Even sounded better. Tomorrow I may have a chance to take a spin before I get the kid from daycare. Will take a look at the spark arrestor/exhaust insert in the muffler when I get a chance too. |
after the head work and removed the spark arrestor. Played around with which set up felt best with the silencer core/cap removed ect. Think it felt strongest with the guts out. Will try to burn out the pipe Friday |
little before and after. Pretty clear how quick it hits top rpm and higher revs too |
Cool
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Do you think over oiling from the injection system can cause tough starting cold? I’ve been running the quad a lot with the rear end in the air which lets the axle spin freely pumping oil like crazy where as if I had it on the ground, the oil mix would be greatly reduced. Quad runs great, easy to start warm, but after sitting a week, it’s brutal. i just filled the oil tank with Amsoil Dominator when I got it, I was hoping to make it through the tank before switching to premix. I guess no harm in transferring the tank oil back into the bottle |
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