McCormick Deering W4 Correct Engine Compression

[Jake96]

Hello All,

I am just asking to find out what the Correct Engine Compression is for each Cylinder on the Petrol Engine.

As my current tractor is easy to crank over and feels quite Low on Compression.

May be because the tractor has been sitting for 5 years or could be tired engine from its early working life. As it is a 1948 Model McCormick Deering W4.

Hope someone can Help in this enquiry.
Regards,
Jake96

 

[Janicholson]

If the tractor was to operate on Distillate, or Kerosene, the compression ratio was low to accommodate poor knock resistance of the fuel. compression pressure
can be expected to be between 80 and 90 psi. If gasoline only, the compression was higher resulting in pressures of 120 to 135 or so. Uniform pressure between
cylinders is important + - 5 pounds is good. Compression is checked with throttle open, and spark plugs out. Hand cranking will not produce good compression
numbers. at least 6 compression strokes are needed to achieve a good reading. X1 suffix in the serial number often indicates gasoline only. Jim

 

[Jake96]

Thank You,

The tractor has Twin Tanks the Starting Tank at 3 gal and then the Main Tank. My Serial Number at the end is W6.

So what would be the Compression PSI Rate on this type of W4 Tractor.
Plus what is the Correct Compression Pressure on this tractor with twin tanks.
Regards
Jake96

 

[Janicholson]

That would be the low compression engine. A small Gasoline starting tank, and a distillate (or) Kero operating tank. (there are differences between the two, but
not important. Yours was most likely specifically for Distillate tractor fuel. Because compression tester gauges, procedure, and engine wear, a specific
pressure is not important. A factory manual will tell you what it was intended to be, but as noted below the range is OK. do not assume a non running engine
compression pressures are real. If it has been sitting, compression may be way off, but the engine just needs to have the metaphorical cobwebs blown out. Jim

 

[John M]

Suffix W6 in the serial number is for low speed gears, so it wouldnt have any bearing on the engine. Jims numbers would be close,
but who knows whats been done to it over the years.

 

[mccormicksw4]

(quoted from post at 07:30:19 07/19/19) Suffix W6 in the serial number is for low speed gears, so it wouldnt have any bearing on the engine. Jims numbers would be close,
but who knows whats been done to it over the years.

That's 100% bang on. when someone asks what the compression should be on a Letter Series or what hp theres no right answer IMHO
A simple upgrade of cylinder heads the first time it needed a valve job and its a new reading. or domed pistons when it got rebuilt
Does it have domed pistons or a gas head?

 

[mccormicksw4]

(quoted from post at 03:41:14 07/19/19) Hello All,

I am just asking to find out what the Correct Engine Compression is for each Cylinder on the Petrol Engine.

As my current tractor is easy to crank over and feels quite Low on Compression.

May be because the tractor has been sitting for 5 years or could be tired engine from its early working life. As it is a 1948 Model McCormick Deering W4.

Hope someone can Help in this enquiry.
Regards,
Jake96

btw Jake if the tractor has sat 5 years I would make sure the valves are opening and closing and I would put a good dose of Marvel Mystery Oil in each cylinder and let it sit a week
I seldom see anyone recommend a Cylinder Leakdown tester rather than a compression test. I feel they are more conclusive and in your case it does not matter if the engine has been modified sometime in its life. I for one would not spend 10 cents on a distillate head if it needed a valve job
heres a good video
https://youtu.be/hGv70RyiGGc

 

[BarnyardEngineering]

75PSI on a standard compression test is about as low as you can get and have the tractor still start with the battery starter. Much below that and you will have to tow it in a low gear and really spin the snot out of the engine to build up enough pressure to get it to fire.

Leakdown test will tell you where the problem is but frankly is not a replacement for the compression test. Together they give you a clear picture of the health of the engine.

In the leakdown test, if air is hissing out the intake, it's the intake valve. Air hissing from the exhaust indicates an exhaust valve leak. Air hissing from the crankcase indicates rings.