Topic: Compression numbers - advice please

[Cevan]

I picked up a '76 C750F1 with 46,000 miles on it for $50.  It hadn't been on the road in 10 years.  I got it running and confirmed the bike shifts gears.  It seems to pull pretty good.  I finally got around  to doing a compression test.  The numbers in parathesis are after I added some oil.

#1-#4:  115 (150)   120 (145)   135 (170)   140 (185)


The spec per the shop manual is 150-180 psi.  So I'm thinking I need to hone and re-ring (assuming the pistons are within spec).  Given that I'll have the head off, what else should I replace?  Replacing the cam chain, tensioner and roller seems like good insurance. 

I've searched around the site here about what to do with the head.  Replacing the valve seals and having the valves refaced and then lapped also seems necessary, given the mileage.  What about the valve seats?  Camshaft?

[KingCustomCycles.com]

Those are not bad numbers for a barn find with little running time.  I would change the oil, ride it a 100 miles or so, and recheck.  The numbers will be up, or down, and you will know then what you have.  Other indications are justy as important as compression.  Things like blowby at the rocker cover, oil consumption, popping and valve seal issues.  I have seen similar numbers on bikes that I would ride anywhere.

[TwoTired]

I don't think it needs anything but some run time.  Check it after you have added 100 miles to the odometer.

The shop manual numbers are only relevant if you use the Honda shop specified compression test tool (which adds very little volume to the compression chamber, as opposed to the cheap ones sold by auto stores to check much larger engine and truck displacements).

And, if you added too much oil, you changed the compression ratio, which would explain the higher readings. (see the engine FAQ about compression testing.)