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88 Cam is out and boy is it ugly

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Got the cam, head and jug off yesterday. The piston had been full of water for quite some time and bugs living in the bore. I had to beat the cylinder out of the jug and it is now paperweight. The valves were covered with surface rust too. In spite of the rust the valves look good and should clean up easy enough. The engine has been apart before, about half of the flat washers under the head and jug bolts are missing. The cylinder is stamped 4.00mm , I assume it is oversized. I can tear something down and put it back together again but I need help when I get to the fine machine tolerances of a cylinder and jug

My plans are to:

1) Get a shop manual

2) Tear down the head and remove rust

3) Evaluate whether I can clean up jug and get new cylinder or use what I assume is a good jug and cylinder from the '85. I am leaning toward the 88 jug because I don't know how bad the '85 will be once I tear that down. I don't understand the 4.00MM stamp on the cylinder.

4) I'll need a new cam chain tensioner as the one in there was worn to the point where I couldn't grab the little nub to pull up and expose the hole to lock it in place.

If this is the wrong place to post my updates please let me know.

Mike

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If this is the wrong place to post my updates please let me know.
This is a very interesting topic, and will benefit anyone looking to restore older XRs, so keep posting. Maybe arrange to takes pics and make them available for viewing.

One minor point: the jug and cylinder are the same part. You must mean piston where you use cylinder. The 4.0MM stamped on the piston could refer to 4mm overbore, which is a lot, but not impossible as far as I know.

I have an '88 also, and swapped in a cam and head from a '90, so many XR engine parts interchange. Get a manual from eBay or Helminc.com. Helm publishes all of the Honda manuals. Stay away from Clymer. A parts catalog is useful for finding out which parts interchange. Helm has those also. The one I bought has '84 thru '91 all in one book.

Lastly, get the gasket kits instead of buying individual gaskets. You'll save bucks. As I recall, there are two: A and B. The parts catalog tells all.

Good luck,

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You can bore to 78mm on a stock cylinder sleeve, 73 is stock so thats 5mm over, tho I would have concerns about cylinder wall thickness at that size.

Sounds like someones bored it out to 277cc (77mm piston)

P.S keep posting here, Im sure there are many people who would be interested to hear of your experiances, myself included.

Cheers

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i just got an 88 xr250 also and i have been going through the same stuff you have. but mine actually is probably in worse shape! hahaha. the previous owner had overbored mine to a 78mm piston on the stock cylinder....trust me on this....it is not going to work that big!! i have a zip lock bag full of metal from the cylinder skirt exploding at the bottom to prove so and the piston is now an oval instead of being round. if you need to bore it out then you NEED to go ahead and resleave to a big bore sleave(75.5mm-78mm). this should save ya a lot of trouble later on. its what i am doing right now. i am making it a 277 (77mm piston) instead of a 284 like it was when it grenaded. this will give me one more safe overbore with the big bore sleeve. but even with all the metal that was in that engine and the previous owner driving it around with all that crap in the motor..it really didnt hurt it one bit...everything is still usuable.....except for the piston and sleeve of course. i have one bearing i have to replace but its not because if the metal its the inner bearing for the tranny output shaft and from what i understand they are the first to go out no matter what. i bought a manual for this bike but to be honest i havent even used it but once or twice to finger something out. i use the online microfiche parts places. they actually show great diagrams to help understand some things better. this is my first honda and i must say it seems like its going to be a great reliable bike when i get it back together... all my previous bikes/atvs have been yamaha.....well except for one arctic cat 4wheeler..... .....i really like my yammyhaws too.... even though i only have one of those left. but hondas up on my lists now as being great.

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