Proper compression on 1950 John Deere B

[CubBoy125]

I recently purchased a 1950 John Deere B. It has smoke coming from the clutch assembly and I was informed that there could be two things causing this. Either the vent pump on the fan shaft isn"t working or I have blow by from the pistons. I checked the compression and I get 60psi on each cylinder. From what I have read the "All Fuel" engines should be around 70psi and the regular gas models should be 110 psi. My tractor only has one fuel tank and nowhere does it say "All Fuel". Is it possible for the compression to only be half of what it should be if my tractor is not an All Fuel? It runs well with no smoke other than white smoke coming from the clutch pulley. I have the head off now and I will do rings if needed, but I don"t want to open a can of worms making repairs if I don"t have to. Any suggestions???
 

[F-I-T]

[thesmoothedeere]

Not to hijack you Fit ... But did you make it to China yet ? I would like to see some photos if you took any . I know you spoke of this trip just not sure when you were going . Thanks.
 

[F-I-T]

[craigco]

Did you check your compression with the choke open and at full throttle? 60psi seems like the throttle wasn't opened.
 

[CubBoy125]

I never did think to check it with a card before dissembling the tractor. I did notice that when I removed the oil filler cap when running the tractor the smoke stopped coming out of the clutch and came up through through the filler tube. I removed the pistons and they have quite a deep concave surface.

 

[CubBoy125]

You know that is a good question. I may have not had the throttle opened up all of the way. How much of an effect would that have on a compression test? Sorry, I am new to these tractors.
 

[F-I-T]

[buickanddeere]

Just install a set of model 50 LP pistons. Given the age,
hours and how cheap the machine work is. Have the cam and
followers reground. Measure the valve spring pressure, valve
stem to guide wear and exhaust seats.
Your B will feel like an A.
 

[CubBoy125]

From the information you provided me I was able to confirm the pistons in my tractor are indeed "gas" pistons. I also checked the position of the throttle lever on the column (which has not been moved since the compression check) and discovered it was at about half throttle. Makes since because it was slowly backed into the shop before being torn down. I am assuming because of this my compression reading is not quite accurate. I plan on installing new piston rings and removing the valves and checking the seats. If they appear to be in spec I will just lap them with grinding compound and put them back in. I see there are several brands of piston rings to choose from. Any suggested brands I should look for or avoid?
 

[buickanddeere]

The old suction cup on a stick with lapping
compound is a waste of time.
The valve sealing is very briefly improved.
It should not bankrupt an owner of a B to pay a
machine shop to grind the valves and seats. New
guides too if required.
 

[buickanddeere]

Know anybody around with a set of used standard bore 50
pistons? They will help make up for the extra blow by when
installing round rings and pistons in an egg shaped bore.
 

[CubBoy125]

I will toss a bore gauge on it this week. If it is out of round I will just go to over sized pistons and rings. Had work done at a local machine shop in town for other engines with great results. I may bring the head and valves over that way. No point in cutting corners this far in.