cb450 almost starting

C

Crunchybeard

Active Member
I have a cb450 1972 honda and the compression on both cylinders are 110 psi. Im wondering what I can do to increase compression. The timing on everything is good, but do i have to get it bored out? I tried lapping the valves by myself, but when i test the leakage with brake fluid, a drop always comes out of the sides of the valve head. Im thinking about taking it to a machinist to clean it and bore it. its popping when i try to start it, but it never happens. any advice would be appreciated.
 
Normal compression is 180 PSI. 150 is recommended to repair.

Low compression causes?

Compression rings worn or broken
Cylinder walls scored.
Valves bent
Valves worn
Valves leaking
Valve seat bad
Valves over tightened (adjustment)
leaking head gasket

I might of missed one or two....

Low compression can have one or all the problems above....Need to check things.

Start with valve adjustment...if not that, then further testing/surgery will be required
 
Crunchybeard said:
when i test the leakage with brake fluid, a drop always comes out of the sides of the valve head
Click to expand...

The amount of permissible leakage is none. Also, try using something even thinner, like gasoline or acetone.

Valve seats will probably need to be recut and it won't hurt having the valves inspected.
 
Once you start cutting new seats you're going to have to shorten the valves to accommodate.
 
Helve said:
Once you start cutting new seats you're going to have to shorten the valves to accommodate.
Click to expand...

Or just properly adjust tappets, right? I'm no expert on engine work, but it would seem to me that that would be unnecessary
 
The cam type adjusters have limited range. If you cut the seats, assemble the head, and find you can't get the valves adjusted, it all comes apart again. If you measure the stem height before, then after, it pays to reduce the height to the stock height, so adjustment has the range you need and you won't have to remove the head and replace the head gasket a second time.

Or learn the other way....
 
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