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Engine rebuild advice - bottom end 23k miles

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Hi, im new to this forum. I recently got me an NX650(euro), but i didnt check the bike properly before buying it. Found some faults driving it home. Welded sprocket and noisy 4th gear. 23K miles stock. Might be wrong forum, but its the same engine as xr650r if im not mistaken?

This is my first rebuild, and it went somewhat bad. A couple of rounded allen bolts(rubber intake carb), bolt to head broke and rounded a allen when splitting the cases. 

Damages found so far - timing chain stretched, 4th gear broke, some scratches in cylinder, some scratches in oil pump, 4th gear broke. A lot of carbon build up in combustion chamber, guess oil have been burning. Cam and journal seems good. Rockers also seem good, hard to tell. Many pics, more upon request.


Now that its teared down, i need some help with purchase list. I dont know what is smart to change while im rebuilding it. Im building bike for reliability - mainly commuting. Power is always welcome, but rather reliability. 

List;

Quote

Complete used transmission from NX650(ebay) - only to change mainshaft and 4th gear(couple).
Mainshaft seal
Gaskets (OEM) and new bolts
Piston - wiseco 1mm oversize 9:1 compression
Timing chain and tensioner
Valve stem seals
New bolts for cylinder(?)

Poured some engine cleaner in combustion chamber and had it upside down over night. Valves didnt leak - guess they are OK? No need for re-seat? 
Is it necessary to change timing tensioner? 
Anymore seals or bearings i should change while im at it? 

Im guessing 4th gear breakdown is the reason for scratches in cylinder and oil pump. Found some metal parts. Why the exhaust valves have been running hot(white) is oil consumption due to scratches in cylinder? 

Teardown was "fun", looking forward to rebuild it and paint it. Ive done alot of research online, but feedback before rebuild is MUCH APPRECIATED. 

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Edited by MrMusic
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Do yourself a favor,,get the head done properly,,valves cut and seats ground,,worth every cent in longterm reliability and proper seal= power..

 

Cam and rockers look good from what I see..

 

B

Edited by brianhare
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Delivered cylinder to a machine-shop, they would have it back to me next week. In the meantime i washed the head and got ready for relapping. Guess what i found? The "usual" crack in head. Ouch. If im ever doing a rebuild again, ill clean all parts and inspect twice before throwing money at it. I should have bought a spare engine! 

About the crack - weldable? Prices on in the bay are steep. It doesnt seem to end at the plug yet. Missing socket to pull the plug. 

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I`D CHUCK IT IN THE TRASH...no way I`d bother playing with that,,,i`d always worry about seats dropping out after welding..they can weld the cracks,,but tension on the seats has been lost..they can remove the seats and weld and replace seats but the cost would not be worth the hassle..

I vote for tossing it over the fence and getting another,,your call..

 

B

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Yeah, you are right. Needed the right push. Part of me want to save money. Might be ok for some time, but upon failure the engine is trash. Even welding will cost as much as secondhand parts.

Got some leads on both complete engines and parts. Buying a complete engine is a risk(no idea on condition) and finding loose parts is hard. Breakers dont care for washing the parts which reveals damage... 

Anywho, upon rebuild - any seals or bearings worth changing? Gear shift seal perhaps?

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