Farmall A Compression

jeb2 · Sep 13, 2018

What would be normal compression numbers for a healthy Farmall A? I have one that gets weekly mowing duty and has compression readings from 75-80 psi on all 4 cylinders. I suspect these compression numbers are low. Thanks for all replies.

old · Sep 13, 2018

Those number seem low to me also but with out going out and doing a compression reading on my BA I can only take an educate guess to that. I would think unless you have a distillate model the readings should be around 100-120 if not more. But if it runs good and does not use a ton of oil I would not worry about it

Charlie M · Sep 13, 2018

I would agree. If had a new valve job its probably low but otherwise it wouldn't be something I'd would worry about. I bought an A a few years ago where the guy had changed a sleeve and said he couldn't get it to run. Got it home and had between 0 and 10 psi on all cylinders. I can tell you that low doesn't run.LOL

old · Sep 13, 2018

So what did you find wrong with it?? An engine with those number I don't think you8 could start even if you pulled it at say 15MPH and had it in 3rd gear.

Red Dave · Sep 13, 2018

Flat top pistons or high compression?

If flat top, it is on the low end of normal. If it has high compression pistons, it is low, but they are nearly equal and consistent, so I wouldn't worry a lot about it.

Janicholson · Sep 13, 2018

Engines do run with loe compression, but not powerfully. They also smoke a lot. If it is a distillate tractor with a secont fuel tank, or the hole in the hood where it was located, it will be in that range. Also not all compression gauges read accurately. With the throttle open, all plugs out , a fully charged battery, and good wires to the starter, the compression will be as high as it can be. an accurate gauge is a must. Jim

fastfarmall · Sep 13, 2018

My B has a 170 lb's of compression,but i had to deck the block on it, about 10 years ago, but it handles the woods belly mower real good !

centash · Sep 13, 2018

Squirt a bit of oil in eaxh cylinder, then test the compression. If it is higher, then it indicates the rings are worn . If no higher, thats likely as good as it will be.
Ben

khouse6 · Sep 13, 2018

what does it mean to deck the block? never heard this

fastfarmall · Sep 13, 2018

Thats when you got to shave to top of the block off !

Charlie M · Sep 13, 2018

Valves were shot. Had the head rebuilt and it started up with no problems.

jeb2 · Sep 14, 2018

Thanks for all the replies and suggestions. This tractor is used by my 78 year old mother to mow 3 acres each week and an 8 acre field every 3 weeks. It seems to labor in 1st gear using a 59" woods mower with sharp blades. The tractor has been in our family for 40 years. I took compression readings with all plugs out, throttle open. I do not think it was a distillate tractor, it has the original engine, flat pistons and the only thing that has been done to it is head/valve work about 25 years ago. I tried searching the net for compression specs but i found very little data there. The tractor uses very little oil but it seems to have a good bit of blowby at the valve cover vent tube.

sald · Sep 15, 2018

I just tested my A a few weeks ago and got 120. In the morning, cold engine, removed all the plugs and neg battery ground. Cranked the engine for about 3-4 seconds on each cylinder averaged 120.

jeb2 · Sep 15, 2018

Thank you for posting your results, that's kind of the numbers I had in mind and was hoping to get. Looks like it might be time to freshen it up this winter.

Farmall A Compression

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