XR 600 Tear Down help I.D. Piston size

I am tearing into my 97 XR600,she started blowing oil a few months ago.I am the second owner,and the dude I bought it from says it was never bored or re ringed.Everything looks good,cylinder is not scored,cam and valve train look good.But how can I tell if the piston is stock sized and not bored over?I do not have a micrometer to measure the id of the jug.It looks fine,so i figure a new set of rings and a hone job ought to do it.The piston is marked MN1 on the top, and HF1 on the side near the wrist pin hole.Any help?

Where are the XR gearheads?

Take a micromeeter and mic the piston . then compare it to factory specs listed in your manual or call the honda shop to get them.

If no mic there might be numbers on top of the piston.(not sure ) but clean the top of the piston off real good and check.

You could also take the piston to a shop and they could tell you.

Most aftermarket pistons will have the size stamped on top of the piston..whether its std or oversize..

Most mach. shops will mike it for free,You'll just need the stock bore size and wear tolerances.. :thumbsup:

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.

Hope that helps. that is direcly out of a Hanes manual #2183

I had the same issue with my 93 XR600, blowing oil out the crankcase breather. The problem was the rings. I just finished this job a week ago. The piston and bore were fine. to check the rings carefully remove the top one. Put in the bore. Use the piston to get is square in the bore. Measure the end gap. The spec is less than .020. When I did it I didn't even measure it. It was like .150 or so.

As others have suggested, measure piston to figure out which size it is. Also measure the bore and calculate the clearance. In my case they were fine. New rings and a quick home job. The engine works way better than it did before. Way more low end torque.

You will need some kind of precision measurement device. The pistons come from Honda in .010 oversizes. Mine had the largest Honda oversize. I guess the previous owner wanted max displacement. The pistons in these bikes rarely wear much without dirt and sand getting in there from bad air filtration.

Now for the bad news. Get a flashlight and look at the gears carefully. Look for pitting on the driven faces. I had to replace 2sd and 3rd gears.

There are also several other problem areas to look out for. Usually, the valves and cam chain tensioner go before the rings. Check the choke plate on the carb. Then tend to get metal fatigue, break off, and get sucked into the engine. Mine was cracked and just about to go. I just pulled the choke completely out. I went for a ride yesterday, and I was able to start the bike in the morning when it was about 35F outside. I have to tip the bike over to "flood" it before it would start when so cold...

I asked several questions during my rebuild. Perhaps they will help you. Search for some of the threads that I started.

Thanks cleonard for the info.My piston end gap was probably .125 or more,so obviously worn that I did not measure it either.I will take a good look at the gears,but man,I sure don't want to split the case.I plan on lapping the valves and checking the springs,and if all looks good I'll button her up with new rings.The compression was definately lower on my last few rides,it was way too easy to kick.I can't wait to freshen her up and go for that first ride.I will look throuigh your posts too...Thanks, Tom :thumbsup:

If you're rebuilding your top-end, I would rebore the cylinder to the next oversize and buy a new oversize piston. Also replace the cam chain as it will be worn or close to it. Have the valves reset with new valve stem seals and you wont look back. It'll be a new top-end. Just replacing the rings is a quick fix and wont last anywhere near as long, but all the best with it they are great bikes!



If things measure good, why will in not last? After I honed my cylinder, out of round and taper were only .0008(.02mm), and the piston measured new. Resulting piston to bore clearance was well within spec as well. However, my rings were completely wasted. Given that I didn't get a new piston or have the cylinder bored. Is there another reason to get a new piston?

With any engine that is burning a lot of oil, it is right to point the finger at worn piston rings. However, 100% of the time, the bore is also worn. The extent of the wear depends on how much dirt the engine has eaten in its life and how many hours the engine has run. Replacing the rings wil "fix" the problem short term, but even though you have done this, the wear in the bore wether minor or major will defintely detract from the life of your re-ringed engine. Reboring to the next oversize and fitting a new piston and rings will effectively bring it back to brand new specs. So my advice is, to do the job properly (even though it will cost more) have the cylinder rebored and fit the next oversize piston and rings, have the valves re-ground and new valve stem seals fitted and fit a new cam chain. You wont look back.

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