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Discussion Starter · #1 ·
Hi all. Thank you for reading

~2 years ago I had the top rebuilt. It ran perfectly since then until now. I was riding her hard and before I knew it the engine was sounding weak and I had almost no compression. She did keep turning over no problem but I shut her off immediately.
I pulled off the valve cover today and checked the valve clearance. All are perfect except for the right exhaust which has no clearance.

https://imgur.com/gallery/okbQ8

looks like the top of the valve has been smashed.
 

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Hi all. Thank you for reading

~2 years ago I had the top rebuilt. It ran perfectly since then until now. I was riding her hard and before I knew it the engine was sounding weak and I had almost no compression. She did keep turning over no problem but I shut her off immediately.
I pulled off the valve cover today and checked the valve clearance. All are perfect except for the right exhaust which has no clearance.

https://imgur.com/gallery/okbQ8

looks like the top of the valve has been smashed.
That photo is not a DOHC 450..........wrong Forum,
 

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I suspect that is a seized valve from your rather grainy photo; looks like the valve collets are pulled out the valve seat and mashed up. If the valve has seized it stretches before the valve head pops off into the combustion chamber and your piston and head become toast. You have got a problem that needs inspection. Pull the plugs and look in the chamber first if you haven't all ready....
Nigel
 

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Gixxer-18 is right and I would tear it down and see what other things are wrong.

Bill.

" Dont let yesterday take up to much of today. " Will Rogers
 

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Moved to SOHC Engine section
Head definitely has to come off for inspection. I'm going to guess that the machine shop that did the head ground the valves. These valves cannot be ground, the hard face is only @.002" thick and grinding destroy it.
 

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Discussion Starter · #6 ·
My bad not checking the right forum. Yeah, they ground the valves and the seats.

This is what I went through: HONDA CB450 CB500T CYLINDER HEAD REBUILD SERVICE VALVE JOB | eBay

This listing is for a complete cylinder head rebuild including a full set of new bronze valve guides and viton valve seals for the CB450/500 twins. This service involves disassembly, cleaning and inspection of all components. Ports and chambers bead blasted. Installation of our exclusive bronze valve guide conversion kit that uses a modern positive type viton valve seal (available separately in my other items). 3 angle valve seat machining in Serdi equipment. Valve faces and tips ground and stems polished. All valve seats vacuum tested to ensure a good seal. Final assembly of valve train components and torsion bars (does not include assembly of cams or rockers). Performance upgrades available!
Is this thing toast?
 

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The head should be fine. However you will need all new valves. Per section 6, page 12 of the FSM
Here's a source for aftermarket valves, part numbers, Intake YH0700A and Exhaust YH1700A. I'm using these exact valves in the road bike.
Motorcycle Restorations
59161 Nelson Avenue
Yucca Valley, CA 92284
+1 626 429 4464
E-Mail:[email protected]
 
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