1971 R60/5 compression readings

I want to check the compression readings on my /5. What kind of numbers should I see for a healthy motor.? What kind of numbers should I see that would indicate engine work is needed?
The motor is running fine at the present time. I'm just curious to know the state of health of my /5/

Thank you,
Airhead Bob

The listed compression ratio is 9.2:1. The rule of thumb I've used is to add 1.0 to that and multiply by 14.7. I get something around 150. I don't know how low it would have to go to suggest an overhaul. I have heard that the compression should be within 10% of each other to be considered OK. Certainly, if you're burning oil, have poor performance, those would indicate problems.

Another check would be to do a leakdown test. If leakdown rate is too high (greater than say 10%), then that would be an issue. You can listen to find out where the problem is. If you hear air hissing out of the oil fill hole, then it's rings. Air from the carbs means intake valve, air from the mufflers means exhaust valves.

Compression test numbers

According to Clymer, 110 is on the low side, 130 on the high side, and 120 is the expected number. Apparently, that's good for all models. If you have CV carbs, you may have to remove them to make sure you get the benefit of the full throat area.
The value itself will be affected by how well the gauge plug seals, temperature, cylinder lubrication, valve settings, etc. Because of this, the difference between the cylinders is the first thing to check.
If the value is within 6 psi, which should be around 5%, and around 120 psi indicated, you're probably fine. Even 110 is probably acceptable.
As a reference, when I measured my R100RT after resealing the top end, I got 121 and 122 psi after a short engine warmup.

Marc

Forced me to look at my Haynes! For bikes that are basically 1985-on, they say that a good pressure is 131 psi. For "all other models", it says that good is 145 psi and normal is 123-145 psi. I scratch my head as to how an R75/5 and an R90S would have the same compression. The /5 is 9:0.1 while the R90S is 9:5.1. Seems like there should be specific numbers for each compression ratio.