McChormick Deering 15-30 compression

We are coming right along with this restoration. Now its time to start her up. Would like to check compression first.

Does anyone have an idea what it should be on these old gals? I'm having a screw in adapter made and plan to turn it over with the belt pulley powered by another tractor.

Thanks ... Norm43

If you have OH'ed it (restored it?), a compression check won't be of much value 'til it's been started, run, worked, and "broken in".

On the 10-20s it is around 4-4.5 to one ratio. 15-30 may be close to that. I will also agree you won't get a good reading till it is broken in, but it might be neat to check it out now and then do it later and see how much difference you get.

Bob ... thanks. What I was really trying to find out it how many PSI of compression should I expect? The engine turns freely and has not been overhauled. I just want to be sure it is capable of running as I work with the Mag and Carb to try to get things all working correctly.

Is there a way to convert Compression ratio to PSI? Or does anyone know where I could look it up?

Thanks again in advance. ... Norm

The conversion is (Ratio * 14.7) - 14.7 = gage pressue

14.7 is standard atmosphere, so you're likely a bit less and this may be off farther if you have some really wild elevation - the reason the conversion required you to subtract it again is because the gage you're using likely starts at 0 gauge pressure (if it's an absolute gage, it will read 14.something sitting on the bench and then no subtraction needed).

The ratio noted above puts you around 50psi. For some reason I thought that was the minimum to expect rather than correct pressure, but to run low octane fuels these had lowwwww compressions so I wouldn't be surprised if I'm backward and 50 is the right number. Also, I'm more familiar with the 22-36 version, and not sure it the ratio [the stroke didn't, but depending upon the shape in the head] didn't increase slightly as well as the bore.

All confused now?! :lol:

Oh, if I may highjack this thread for a second: Hi everyone! I didn't fall off the face of the earth, but between a whole list of things my mother needed done to her house in town [and while I had tools there, didn't want to drag them back a month later] and my wife's honey-do list as well as helping her study for a test to qualify teaching more subjects: well not much time to work on tractors or log in here. However, the engine is back in that 22-36, but still decapitated. The clutch too, but haven't tuned it yet to the new facings. Still taking plenty of pictures, but haven't uploaded them either.

Good luck Norm! 8)

Thanks Spiffy1 ... this is all the info I need to go forward. And if I can remember where I noted the 14.7 number I can figure all the others I have as well. Good luck with your projects. ... Norm43

Most kerosene-distillate tractors were in the 4 to 1 ratio range. Any higher, and they knocked like crazy if burning those fuels. The specific ratio may be available somewhere, although I don't think I've ever run across it. One thing that occurs to me is that, even if you don't come up with an exact ratio, a fairly-uniform pressure across the four cylinders would suggest that things are ok. One thing that was sometimes done to these tractors was to put in higher-compression pistons (which were available, I believe, as "high-altitude" pistons). This would have been done to allow using gasoline exclusively. There is always the possibility that this has been done at some time in the life of this tractor.

(quoted from post at 09:58:13 03/04/09) if I can remember where I noted the 14.7 number I can figure all the others I have as well.

Click to expand...

Yes & no. Oh boy am I going to create confusion, but here it goes:

The formula I gave earlier doesn't take into account either pressure increases due to temperature introduced by the compression, pressure losses due to the inability to utilize the full stroke (valve timing, lower vacuum at the top of intake stroke, etc), nor probably a half dozen different things I can't think of! :lol:

However, cranking it slowly enough on these low-compression [which reduces the temp rise effects too; think diesel: high compression ratio producing high temp rise] engines: some of the temp rise is lost to the cylinder walls (OTOH, I think you were planning to belt it) and I have to think the intake losses are increased: all in all making the pressure equation somewhat mute likely giving half the potential pressure, yet potentially not bad of an estimate if the "mechanical" effects may be assumed to roughly equally counter the temp rise effects.

And I'm still probably missing half the idiosyncracies that would give an equation relating compression ratio the pressure tested immediately after break-in. :lol:

[b:038e45c714]All in all, Len's point is probably the easiest for your purposes here: if there is a descrepancy in one then something isn't doing it's job somewhere (rings, valves, head gasket) or everywhere but one or two.[/b:038e45c714]

Another thing I have done [though I'm rustier than some of the parts you're looking at!], easy, but mixed results if "loose" all over, or evenly but not perfectly "tight" - cross-talk in bad headgasket will really mess with your mind too. In-gear and blocked, give it about 50psi from your compressor in each hole about mid-compression stroke and follow the hiss or gurgle etc. An inline valve, timer (head count, stop watch, whatever), and shot of oil on the cyliner then second test : poor man's leak down test!

Norm43, ok, I must have misread, I thought you had just rebuilt it. I am not sure but the pressuer may be listed in the nebraska tests, but not sure on that. When I said 15-30s may be close to that the reason is some 15-30s have a 3rd tank sitting with the fuel and gas starting tanks that held water to use to help keep the engine from knocking. it was an early water injection system. Some of the IH stationary kero burning engines from 3 hp up had that as well. I am not sure why they did that unless the larger engines did have a slightly higher compression ratio or it may have had something to do with the larger cylinder size or possibly just to quench glowing carbon bits stuck to the head. There is no doubt a formula you could use, but I couldn't tell you what it is. It may take a dang good calculator or a slide rule to do it. I would just go ahead and give it a pull by hand and if it feels like it is giving 10-15 lbs or more pull on the crank handle, it should run if everything else is in order. If I had to take a wild guess I would say if you belted it up and had it turning at 500 rpm with throttle wide open you might get 60lbs on the gauge, but you could get more! You would have to test all cyls at the same RPM, Or if you want to make it real simple, just get it ready to start and see if it does fire up! I didn't see mention of the year but if it was made before 1929 it was made to run on kero only so it might miss out some when it warms up running on gas all the time. If it was made in 29 or later see if the 2 manifold baffles are set to Gasoline or Kerosene. I used to run my 10-20 on kero and it did ok, just have to use a curtain on the radiator till the lower elbow is nice and warm but not hot. and drain the oil down to the center petcock the morning after running it.