Xr600 Scoring In The Cylinder...


10 replies to this topic
  • BLSBRKR65

Posted February 04, 2007 - 07:22 PM

#1

Pulled out the engine to paint the frame and to see where the engine noise is coming from. The top end rockers, valves and cam with routine wear. Cam chain tight. Decided to look into the cylinder and noticed that there are some vertical scratches only on the intake side of the cylinder wall! It is deep enough that i can feel it with my finger. Is it time for a bore? How can i tell that it has been rebore. Will the piston have any marks indicating that it is oversized? What could have caused the scoring in the cylinder wall? Connecting rod issues? improper Lubrication? Lastly, could this be the cause of the engine noises? Thanks in advance!

  • cleonard

Posted February 04, 2007 - 10:41 PM

#2

Pulled out the engine to paint the frame and to see where the engine noise is coming from. The top end rockers, valves and cam with routine wear. Cam chain tight. Decided to look into the cylinder and noticed that there are some vertical scratches only on the intake side of the cylinder wall! It is deep enough that i can feel it with my finger. Is it time for a bore? How can i tell that it has been rebore. Will the piston have any marks indicating that it is oversized? What could have caused the scoring in the cylinder wall? Connecting rod issues? improper Lubrication? Lastly, could this be the cause of the engine noises? Thanks in advance!


It is unlikely that the scoring is making any noise. What kind of noise is it? Constant or intermittent? Knocking or ticking?

It's crud that made those grooves. It could have been almost anything, even carbon deposits from the combustion chamber. Take a close look at the choke plate on your carb. There is a little stainless steel flapper that breaks off and gets sucked through the engine. When I caught mine it was literally hanging by a thread. On mine the entire choke plate had a fatigue crack that was almost all the way through it.

If the groove is not too deep, it is possible that all you need is a hone job and a set of rings. You really need good measurement tools to decide if the cylinder and piston are ok or not. If you can't measure it yourself or get it done by a shop then go for a new piston and bore. You can check the rings. Carefully remove the top ring and put it in the bore. Use the piston to get is square in the bore about 1 inch down from the top. Measure the gap between the ends of the rings. I don't have my book handy, but the spec is like .020 or something. My bike was blowing oil out the breather and when I did this the ends were .125 or more. It was so big I didn't even measure it. However my bore and piston measured almost new. I honed and just got new rings.

  • creeky

Posted February 05, 2007 - 05:59 AM

#3

I would hone the bore until the scratches are gone then measure the bore. Measure at three locations, top middle and bottom at two intersecting axes. If the bore is out of spec for diameter, taper or out of round or any combination, you'll need to bore to the next oversize. The piston ring end gap for a new ring should be .008" to .016" for the top ring, .014" to .022" for the second ring. Wear limits are .020" and .026".

  • BLSBRKR65

Posted February 05, 2007 - 06:32 AM

#4

Engine noise is constant. Sounds like a grinding mill. It has fairly new cam chain and cam, probably less than 200 miles. I will take the cylinder to a machine shop for honing or probably a re-bore next size over. How much do you think the repair + bore would cost if i were to take it to the cleaners? Thanks!

  • Motosprtman

Posted February 05, 2007 - 07:20 AM

#5

try Dave at www.xlintperformance.com he does Xlint work! and reasonable too! I think a dirty air filter could of also been a contributor.

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  • BLSBRKR65

Posted February 05, 2007 - 03:04 PM

#6

Adjusted the valves... it was way out of adjustment on all 4 valves. I still suspect i might need to replace the cam chain. How would i know it's time to replace it? It's tight and the tensioner guides, shaft and cam chain tensioner itself have no unusual wear. Could the noise be coming from the misadjusted valves. How do you remove the carbon buildup in the exhaust ports and cylinder head dome? Do i need to remove the exhaust valves? Intake valves look clean and new...

  • cleonard

Posted February 05, 2007 - 08:04 PM

#7

If the valves were really loose then you found your noise. The RFVC head with the two part rocker arms is noisy even when adjusted correctly. They can make a real racket when loose.

My tensioner went out. It was fine while working on the engine. It kept the chain tight. Only when the engine was running and hot did it fail. The loose cam chain made some weird slapping noises at idle. It also caused some power loss as the valve timing changed. The only wear on the tensioner was some tiny blemishes where the ratchet rollers contact it. That was enough to make it not work right. I replaced it and it fixed those problems. I was far from sure at the time. I was worried that I was throwing money away replacing perfectly good parts.

I'm not too sure about how to decide if the cam chain is shot. I guess it the tensioner can't take the slack out then it's time. I replaced mine when I replaced the tensioner. I figured it was time.

I'd like to know a good way to clean everything. I've used mechanical methods like scraping or a wire wheel. Just be careful not to damage any gasket surfaces. I've heard of using oven cleaner, but I've never tried it.

  • oud31

Posted February 05, 2007 - 08:18 PM

#8

I had my cam chain replaced and the honda tech that did it told me that its tough to see wear untill you have it removed to compare length with a new one for wear. It's alot cheaper to pay for a cam chain than the aftermath of a broken one, so I think its cheap insurance if you have reason to believe there is wear.

  • BluezookS

Posted February 06, 2007 - 06:42 AM

#9

Are the Honda cylinders Nikasil plated?

  • cleonard

Posted February 06, 2007 - 07:49 AM

#10

Are the Honda cylinders Nikasil plated?


If I remember correctly only the 1988, 1989, and 1990 XR600 cylinders are Nikasil. All other XR600 and XR650L cylinders are steel sleeved. All XR650R's are Nikasil plated.

  • desert gorilla

Posted February 06, 2007 - 09:20 AM

#11

a good way to remove carbon is soaking parts in GM Top Engine cleaner, P/N-1050002. With the head on pull the carb and spark plug pour it in and let it soak over night. Kick it over slow with a rag to catch all the chunks and and goo that come out. Does a pretty good job. It will smoke like hell the first time you fire it up.





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