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XT600 Piston Slap & Cylinder Damage (PICS!!!)


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85 XT600 w/ 7k miles. I've had it for 8 months and put just over 1k on it. After one of my first hard off-road rides, the top end starting rattling and getting really loud up around the valve cover. I adjusted the valves and that helped some, but it was still pretty loud, but I have heard that this old singles sometimes sound like sewing machines on steroids. Anyway, over the last couple months it's developed quite a noticeable rattle and piston slap until it warms up. I changed the oil and it had lots of very fine metal specks in it. I was going to sell it so I took it to a local motorcycle mechanic to check it out, and he said the piston slap was way louder than it should be. Checked the oil and there was hardly any in there. I know I had filled it up properly according to the manual's instructions when I changed the oil a month ago, and it doesn't smoke or leak as far as I know.

It cranked fine, but would burp and fart occasionally around the carb until it got warmed up. (I've posted ab out that already)

I was going to have at bored out to 1 over and put a Wiseco in it, so I've started to tear into it. Here's what I've found. I've never erplaced a top end and am not an expert it diagnosing cylinder damage and its causes, so I'd love any input.

First, the plug:

Sorry to start with a sucky picture, but the camera I'm using takes terrible close-ups. The front half of the insulator, opposite the electrode, is whiteish, the back half is black. The electrode itself is grayish back to the bend and then black on down.

c11.jpg

Now to the cylinder head:

c5.jpg

It's got some carbon build-up, as you can see. But do you see the scraping on the right exhaust valve? sign of things to come . . .

The piston head:

c9.jpg

Carbon caked on there, and notice the silver scraping underneath it? Looks like someone took the end of a screw driver and carved lines across it. Weird. . . . :huh

Now on to the sides of the piston:

c4.jpg

Between the rings look pretty good on this side, but abrasion on the side.

c2.jpg

Some horizontal scratches on the right sidel and more color between the rings.

c3.jpg

Lots of color between the rings.

The cylinder wall:

c8.jpg

This one shows a concentrated wear spot:

c7.jpg

And at the bottom of the sleeve are some horizontal lines:

c6.jpg

The connecting rod has no vertical play that I can tell, and 1-2mm lateral play, so I assume the deeper bearings are sound. ??

The carbon build-up, the scratches on the piston head, the scarring of the cylinder wall. Should a new top end fix it or does some of this point to deeper issues? If it's just the cylinder wear and tear, I can go do the top-end for ~$250. If it's more than that, what is it and is it worth fixing or should i part it out and get what I can?

Thanks for your help.

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looks like normal wear and tear to me. aslong as those are surface scratches , which they appear to be your fine, put a ring in and check the end gap see if its in spec if it is hone the cylinder and put it back together. you can also mic the cylinder to see how loose it is. we have an 85 xr 500 that we dont do any maintanence on it sound like it going to blow up and it just runs and runs those older big 4t are bullet proof

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You need to check the bore wear [ in several places] with a micrometer against the service limits for you particular piston. A mate who's a pro car mechanic rebuilt one of these and thought the small amount of piston clearence was fine. I thought not as the pistons are very shallow. What seems to happen is that the piston rocks on it's axis at each end of the stroke. The noise is very noticeable.

Checking the wear with a ring tells you little if the ring itself is worn.

Anyway he didn't pay any attention to me, rebuilt it and the noise was still horrendous.

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