Recently I have got rather interested in Compression level testing on my 500 4 mainly down to trying to diagnose some running issues.
The Technical official Honda 500 Maintenance Manual indicates a "good level" of 170 PSI and anything under 140 indicating worn rings, poor valve seating etc
So off I went with my pressure tester and got 135 PSI on all 4 pots and started to panic, why are these levels so low compared to the Honda spec given that I rebuilt this engine only 2k miles ago with new pistons and rings and honed bores and all measured up to within official Honda sizes for a standard bore (56 mm) engine. Also the engine runs well with no smoke etc indicating worn rings or anything else wrong.
So why the large discrepancy.
I think there are a number of factors at play here
1) The compression tester I used was a fairly cheap unit but like many commonly available that has a long length of rubber hose. This significantly increases the volume of air being compressed and can drive down the readings on these small capacity cylinders as the additional volume of air is significant compared to the swept cylinder volume.
If you look at the Honda maintenance book picture the guy there is using a rigid metal small bore pipe connected to the gauge NOT a rubber hose. Also the Honda manual says nothing as to whether this is a dry or wet test but logic would assume dry as nothing says otherwise.
There is an excellent post on the USA forum about this that end up getting very technical but a really interesting read for the highly technical amongst us.
http://forums.sohc4.net/index.php?topic=39971.02) This was a dry test so I put some oil down the bores and the readings whacked up to 175 but I think I put way too much oil in there which was why such a jump. I thin I should have added just a few small drops !!
So now to my million $ question on these 4s what would be a sensible "good" level to get when using the type of gauge easily available and thet we all use.
My experience seems to lead me to around 135 psi on a dry test and that it does not rise dramatically on a wet test with a few drops of oil would indicate a pretty good condition engine. But that said I wonder what an acceptable lower level would be to indicate a top end problem.
Be very interested in others opinions here and how this thread develops.
A) Does anyone else have and readings from their bikes that may help?
B) Does anyone know what sort of increase is OK between a dry and a wet test?