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Discussion Starter #1
Hello.

I've been trying to save this bike for a few weeks now and your help is greatly appreciated.

Torn off the head when it was clear the valves were bent, and glad I did. They were down-right curly.

New cam chain, tensioner, roller and arm (the old ones were trashed) and good, refurbed valves.

In the process of rebuild I lost TDC, so before I buttoned it up I reset the piston at the top, making sure it was set to 'LT' on the compression stroke, lined up with the cam gear and the cam pin at 12 o'clock. However, something still isn't right as I can only get 60psi on either cylinder.

1 - It appears to me that when setting TDC, the cam pin should be at the 6 o'clock position at TDC and not the 12 o'clock position as is stated in the literature. At 6 o'clock the lobes for the left cylinder are down (valves closed) as the piston hits TDC. Is that correct?

2 - Also, when rolling the engine, the compression stroke never lines up with the cam gear / cam pin. If I do it by the book, I only get the compression stroke when the cam pin is at 6 o'clock. Is that correct?

In the photo, you see the cam pin at almost 12 o'clock and the lobes are up.

Thanks in advance.
 

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For cam timig you don't need to be concerned with compression stroke.
Line up the cam pin at 12 o clock and the horizontal line on the cam sprocket, and Confirm LT is left piston tdc
 

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Once you connect the chain you can roll the crank ahead one turn to LT again and the pin will be at the 12 o'clock position.
 

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In the photo, you see the cam pin at almost 12 o'clock and the lobes are up.

.
You CAN NOT see the cam pin in that picture.....
That is a hole in the cam's bearing surface, and is not for the cam pin...
(The pin "keys" the advance unit on the thinnest part of the left end of the shaft)
 

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Discussion Starter #5
Thanks for the replies. I think I've got the idea now.

I'm still seeing terrible compression. Setting the cam tension and the valve clearance using the common-motor.com vids as a guide, I'm seeing 60 to 70 psi on each cylinder. Head bolts tightened to 13-15 ft/lbs. I've got a cb350 parts engine that registers at 130 to 140 .

Where else would you look?
 

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Are you holding the throttle wide open while you turn the engine over? ...ask me how I know.
Best way to tell where all your compression is going is to do a leak down test. Hook up a compressor to #1 spark plug hole, rotate engine to TDC on the compression stroke for #1. Let the compressor pump up and hold the crank at TDC (it should try to move) Listen for escaping air. Depending on where it's coming from, you could have leaky valves or rings. Repeat the procedure for #2.
 

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Discussion Starter #7
The engine is off the bike. When I replaced the valves I greased the stems and spun them in the guide so I know they have clearance and movement but I didn't inspect the guides more than that...live and learn. If I could ask, when a valve is bent does it necessarily mess up the valve guide?
 

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The engine is off the bike. When I replaced the valves I greased the stems and spun them in the guide so I know they have clearance and movement but I didn't inspect the guides more than that...live and learn. If I could ask, when a valve is bent does it necessarily mess up the valve guide?
that depends on how bad it was bent! did you do the leak down test?


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