78 Special - Top End

Duck749

XS650 Enthusiast
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Since doing the tracker build a couple years ago, I have been keeping up with maintenance on the motor (over 20k miles), its original and I don’t believe ever apart. It has been having oil blow by which my side covers have spray, drip of oil on the plug wires, etc. I have replaced the cam orings which hasn’t resolved the issue. In addition, one of my oil changes I had the tell tale signs of the chain guide wear/age with plastic pieces in the filter. I am thinking of just a top end and pending other signs or issues do a full rebuild if needed.

When removing exhaust pipes I noticed a film that was sitting at the bottom of the exhaust port, is this a sign of valve sealing issue? I have not located a specific leak around the external of the head leading to the blow by issue and wondering if this is problem. When riding it then blows back all over covers and plug wires?

I have read some on replacing the cam chain if there is excessive wear, can this be done with just a top end or does it require full rebuild? I am envisioning connecting new/old chain to pull around crank for install but not sure if it’s as easy as I am thinking…
 
If I recall correctly, I did it (cam chain) just that way on a Honda CB450. Surely that method will work on an XS engine.
Those with XS rebuild experience can say for sure.
 
Yes, you can attach the new chain to the old and just pull it through without tearing the bottom end apart.
There's a top end buildup in Tech. It'll help you familiarize yourself with what's involved.

https://www.xs650.com/threads/xs650-top-end-buildup.52041/

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Excellent write up and detail Jim!

I ordered the factory manual and have Hans Pahl book (the Yamaha S 650 Engine) for additional reference. Snowy day in NY today so was able to get started.
 

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You'll need to buy a seal kit also. Look for ARS seals. ARS made the OEM seals. They sometimes come as TourMax branded.
 
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