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Old 01-13-2010, 09:54 PM   #1
Mr.P
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Piston replacement Q?

I got this project XR600. Needs a motor rebuild. I bought my first caliper gauge and it says the piston is 96.83 mm. I'm assuming this is a 97mm piston, and the rest is just gauge inaccuracy or piston wear.

The cylinder measures at 97.97mm. Does the difference seem in the range? 1.14mm in total means the piston to cylinder tolerance is .57mm. This seems big.

Neither the piston or cylinder show much in the way of wear, but I have to replace the rod and piston pin, so I figure might as well freshen it up.
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Old 01-13-2010, 10:01 PM   #2
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Do you have an owners manual? In the front section of the engine chapter there would be specs for the min/max for the bore/piston top and also piston skirt width.

also check the ring gaps/spacing to the piston shelfs.

What failed on the engine in the first place? rod bent? Was it a compression or leakage problem or simple rod bend/bearing problem?

Also on the block, I recommend using T-gauges and checking both axis up and down the bore to make sure its even/within specs.
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Old 01-13-2010, 10:02 PM   #3
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BTW the rings will clean up the remainder of the gap; it uses oil to seal also. Check the specs to know for sure.

Most manuals are available online if not free download from online forums for specific bikes after a certain number of posts etc.
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Old 01-13-2010, 10:21 PM   #4
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Quote:
Originally Posted by CaligoneTx View Post
Do you have an owners manual? In the front section of the engine chapter there would be specs for the min/max for the bore/piston top and also piston skirt width.

also check the ring gaps/spacing to the piston shelfs.

What failed on the engine in the first place? rod bent? Was it a compression or leakage problem or simple rod bend/bearing problem?

Also on the block, I recommend using T-gauges and checking both axis up and down the bore to make sure its even/within specs.
No manual yet. The motor stopped running cause the cams and lifters wore out. It ran until the very end, even clearing a couple of doubles at Needville, but the cams were maybe lifting only 40% of original, the lobes were sooo worn down.

I haven't taken it down any further, but there is up/down play piston to rod, and the crank can rock a bit side to side, so I'm going to do crank, rod, piston, lifters, cams.

Thanks for the help!
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Old 01-13-2010, 10:37 PM   #5
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if the crank itself is ok(spec it out) the thrust washer on the one crank bearing is what prevents the crank from walking. That will have to be checked and set anyways to ensure its within specs too after replacement.

Sounds like a project!!!!

How's the pump? no gunk in the oil? All that will have to be cleaned out cuz if it isnt, that stuff will go back through the system and starve oil to the bearings, premature wear/failure.
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Old 01-13-2010, 10:52 PM   #6
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Quote:
Originally Posted by CaligoneTx View Post
if the crank itself is ok(spec it out) the thrust washer on the one crank bearing is what prevents the crank from walking. That will have to be checked and set anyways to ensure its within specs too after replacement.

Sounds like a project!!!!

How's the pump? no gunk in the oil? All that will have to be cleaned out cuz if it isnt, that stuff will go back through the system and starve oil to the bearings, premature wear/failure.
I haven't gotten to the pump and strainer, the motor is still in the bike, but I will be tearing it down 100% and cleaning and reassembling from a bare case. Do you have any suggestions for someone to do the crank pressing and reasembly? I can only find a rod kit for this bike, not a complete crank.

Also, Google told me the following:

Piston should be (if standard) 3.8173 to 3.8284 inches. &

The wear limit is 3.813 at 0.40 above the bottom of the piston. &

pistons come from Honda in .010 oversizes

Mine is 3.83 at the top. So I guess I need to take a better measurement at the right point to be sure, right? Also, the stock bore is listed as 98mm, and mine is 97.97, so that says to me it's standard bore, so maybe the piston wasn't sized right last rebuild?
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Old 01-13-2010, 10:53 PM   #7
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Quote:
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Sounds like a project!!!!
My first of two. My DRZ needs the crank done as well. Best to practice on the crapper bike, right!
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