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· Registered
1986 Honda NQ50 Spree
1,095 Posts
Hi BJ,
  • Your going to get a lot of opinions on this. So here's mine:
    • The cylinder head is junk. I believe it's junk because the circumference of one of the exhaust valve seats is straight. The other seat has just as deep gouges in it. The amount of cutting it would take to reseat a valve on these seats would exceed the small shim gap limit (too tight) after installing a new valve. A used head in good shape may come with valves installed that are in useable condition.
    • The cylinder would have to be measured to determine cut depth necessary to remove gouge and scoring. If the cut depth would exceed minimum wall thickness then you need a new cylinder. IF it could be cut then BOTH cylinders would require the same bore. Bigger bore requires different pistons and associated parts (x2) and head gaskets. A used cylinder likely won't need bored. A used cylinder could easily be honed and probably use an OEM zero over piston. Measurements will determine what is necessary.
    • The piston is holed. That piece of forged Aluminum is in the engine. Aluminum is soft but can still cause damage. Your engine has a removable oil screen at the bottom. Make sure you remove it and do a search for the aluminum chunk. If you don't see it there then you will be opening the cases.
    • You may consider looking for a good used engine. Machine work these days is VERY expensive. Good machine shops are charging over $100/hr. for the kind of work you would need.
    • Reusing a bent rod....Whether or not the rod is bent is something you need to discover. If it is, it should be replaced. And if it's bent then the top main bearing is probably flat. The main bearing is designed to fail BEFORE the rod. So it would be a good idea to examine them. It takes a lot to bend a rod. But when they do you need to examine everything to which it was connected.
    • Why did exhaust valves stay open too long in order for the piston to hit them is a question you will need to answer before reusing this valve train. Did the cam chain jump and retard the cam timing? If so, how or why? Since both valves look like they were equally damaged I would guess that the cam drove them into the piston. So that means the cam was late (retarded) in closing.
  • You have a project on your hands. The satisfaction of rebuilding an engine is almost immeasurable. The reason I still have my '01 GSXR600 is because of this feeling. I bought the bike with 28k on it for $475. Rebuilt the beat to crap engine with parts from ebay. Total parts under $400 which included a used crankshaft. It has 42k (41868) miles on it today.
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