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Old 12-20-2012, 01:02 PM   #1
prichmon OP
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Joined: Feb 2009
Location: Huntington, wv
Oddometer: 121
1981 Yamaha YZ60 Xmas for my 13 yr old

I have been working diligently for ~2 months rebuilding a 1981 Yamaha YZ60 for my 13 yr old son. I found the bike for $50 90% complete in pieces. We reassembled to find it had 15psi compression. I also found the seals were dried out in the bottom end.

The brgs seem good so we moved to replacing the top end and sealing the bottom. It was already at 3rd OS so I decided to use a KX60 piston kit based on info from another forum. The KX60 piston required the window to be cut to match the YZ60. I got a little carried away with my dremel and made the height of the port a little more than 13/16" rather than 3/4". As far as I can tell the added height should have no effect on the engine compression. After reassembly the bike made 15psi compression with new bore, piston, rings and gaskets.

I returned the bike to the shop who did the work. I was informed the piston was down in the bore compared to the oem YZ piston. The shop milled the jug to bring the compression up. We verified the compression was up to 65psi with 6 kicks but wouldn't start due to flooding from the leaky fuel petcock and poorly routed overflow line.

I can't tell if the rings have seated nor if everything is OK since it flooded over night and I have not seen it stay running yet. The only things left to complete are: the clutch cable seems to be sticking, the kicker is not "catching" but ~50%, the fuel petcock needs rebuilt since it leaks a little. I have a used kicker assembly, idler, rear brake shoes, air box and the chain.

Can anyone explain to me if the height of the intake window would significantly affect compression? Has anyone done this type of conversion or rebuild? What is the best method to loosen up the clutch cable? How many turns on the clutch pivot shaft should be in place?

If anyone has a line on the original heat shield and side panels I would appreciate anyone contacting me.

We'll try to start the bike tomorrow if all goes well... If anyone can help please give me a yell.

Thanks for any help;

Rich
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Old 12-20-2012, 01:50 PM   #2
kellymac530
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Joined: Feb 2010
Location: so. cal.
Oddometer: 1,052
The clutch issue is usually simple. I assume that while you had it apart for the crank seals you checked and cleaned the clutch disc and inspected them...? Not sure on that yz60, but most have a small ball bearing on the end of the clutch acutator push rod, if that got left out, EASY TO MISS, then the feel will be wrong and cause VERY rapid wear on the clutch basket and push rod. If it even works at all.

If those issues are good, then the other issues could be a worn actuator shaft {not the push rod, but the arm the clutch cable pills on} making for a notchy feel in the lever.

Most likely though, the problem is just in the cable. To replace it is easy and probably $15-20. You will likely have to try to match it up to some newer model like a KX60/65 or maybe a KTM 65.

First though I would try and clean and lube the cable that is there. This is simple, get a bucket, like a 5gal andcoil the cable into the bottom. Pour some solvent in the bucket deep enough to completely cover the cable, I like Mineral Spirits personally because it is a bit oily feeling so it aids in not only cleaning but also lubing and braking the grime loose.

I let it soak over night and then start pushing and pulling to full extension for a few minutes, let it soak a bit more and work it back and forth every few minutes until it slide completely freely. If there are any kinks in the housing or cable, or any fraying of the inner cable wires it will usually never free up.

If the cable is now free and works smoothly, dry it off really well, and then I usually soak it for a bit in ATF, this penetrates well, lubes well, and seems to attract less dirt than motor oil soaking. There are actual cable lube sprays but I find a good soak works the best. You can spray it off with some carb or brake spray on the outside of the housing to clean it off, I usually hang the cables vertically to let the excess oil drain out then wipe it off and install.

The last place to service is the actual clutch lever on the handlebars. Take off the lever and inspect the lever and the pivot bolt for any wear or grooves and that the bolt is the propper shank type bolt and not some temporary fix with a regular bolt that is grooving up the lever. After cleaning and inspecting well then a bit of light grease on the pivot bolt and reassemble.

Smooth as butter and easily pull should be evident or there may be one of the other issues I mentioned.

Lastly, if your son likes riding, start saving for a 125cc bike, that 60 is WAY to small for a 13 yr old unless he is really small for his age. Fine to learn on, but way undersuspended and small.
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Old 12-23-2012, 10:17 AM   #3
prichmon OP
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Joined: Feb 2009
Location: Huntington, wv
Oddometer: 121
Thanks

I appreciate the comments. I do not recall a ball on the end of the pushrod so I will start there since I have to replace the kicker shaft assm. We'll drop the cable in a pan of oil later today.

We plan on passing the YZ on in the next 6-12 months. My boy takes after mommy thank the lord. He's barely 105# and 5' tall and turns 14 next week. I figure he will gain another 2-4" and 50# by summer. I am hoping to find a decent older dual sport which can transition to a license like a KE100, dr125se, NX125 or similar. I've got a line on a 2000 KE100 for $500 and hope to see it today or tomorrow.

Rich
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Old 01-12-2013, 11:42 AM   #4
prichmon OP
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Joined: Feb 2009
Location: Huntington, wv
Oddometer: 121
Got it running

Thanks for the help. I really appreciate the help.

After returning the bike to the machine shop they went through what I had performed. It seems the KX60 sits slightly lower in the bore than the YZ piston. The shop decked the cylinder to raise the compression further.

I did find out the ball was missing between the 2 pushrods. A couple of days in tranny fluid loosened up the cable to a functional level.

We replaced the brake shoes and found the lever arm was in the wrong position.

The PO had used a large nut and lock washer for a spacer. We installed a proper spacer and installed the chain.

The kicker was jumping due to severely worn gears. I bought a used set off ebay to correct the issue.

The only issues remaining are the following:

Hard starting on the kicker. Seems to start fine if push started. Makes it a 1/2-1 tire revolution and bangs over fine. Even when warm it doesn't want to start on the kicker.

Once running it seems to idle up and down. Reminds me a an old civic I had with worn throttle shafts. It acts like it has a intermittent air leak???

Lastly the rear wheel wobbles. Is there any easy way to align the wheel? I've never adjusted spokes before.

Thanks,

Rich
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Old 05-29-2013, 07:58 PM   #5
prichmon OP
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Joined: Feb 2009
Location: Huntington, wv
Oddometer: 121
Too LEAN

I ran the bike too lean and destroyed the engine... We're looking at a complete rebuild.

Anyone need a project for cheap????

Rich
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