What cylinder compression test result should I have for a 1973 850 ?

I am going down a rabbit hole of figuring out the cause of massive blowby and lots of milky oil
blown into the oil tank from engine despite oil changes...

If you can share with me what is very good compression I would be grateful.

Thanks

Dennis

DennisMo said:

I am going down a rabbit hole of figuring out the cause of massive blowby and lots of milky oil
blown into the oil tank from engine despite oil changes...

If you can share with me what is very good compression I would be grateful.

Thanks

Dennis

Click to expand...

Do you have an improved crankcase breather fitted?

The XS650 breather cured the mayonnaise production on my '74.

I do have a working one way breather.
My engine had no milk in oil for the first year of ownership, then I think I overheated it
in stopped traffic on a very hot summer day for a couple of hours...
So I am trying to get to the bottom of it
Very visible blowby out of oil tank vent at idle and lots of milky froth blown into
the little bottle I have out the oil tank vent into.
I keep oil in tank at the min level.
Dennis

Use the rubber hose method in intake & exhaust port while slowly rolling over to see if the valve seats are giving some hiss.


Then, use a tablespoon of oil in each cyl to see if readings improve.

I had 130PSI at last test, but gage calibration varies wildly.

Have you sent an oil sample to the lab?