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Bill_MN 
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Joined: 12 Sep 2009
Location: Sioux Falls, SD
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 Topic: WD compression
Posted: 31 Mar 2012 at 4:47pm |
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what was the compression ratio and psi of a bone stock WD engine when brand new? going to do some maintenance on mine and want to get a read on how worn it is. at what compression would you guys consider a rebuild? oil pressure is still very good
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1951 WD #78283, 1918 Case 28x50 Thresher #76738, Case Centennial B 2x16 Plow
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Longmeadow Farm
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Joined: 30 Jul 2011
Location: Eastern NY
Points: 321
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Posted: 31 Mar 2012 at 4:58pm |
WD specifications for gasoline version only 5.75 to 1 compression ratio 110 PSI
WD low octane fuel 4.5 to 1
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TedBuiskerN.IL.
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Joined: 11 Sep 2009
Location: Davis, IL.
Points: 1959
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Posted: 31 Mar 2012 at 8:40pm |
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I would be more interested in the balance between cylinders than compression pressure. If all cylinders are the same or close to the same, and oil burning is minimal, run it.
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Most problems can be solved with the proper application of high explosives.
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Brian G. NY
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Joined: 12 Sep 2009
Location: 12194
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Posted: 01 Apr 2012 at 10:35am |
I'm with Ted; Repair manuals rarely specify an exact compression pressure, but instead, (usually) indicate that there should be no more than a 10% difference between the readings on the highest and lowest cylinders.
Having said that, I have my WD-45 manual open before me and it states: Compression Pressure (Gas) 125# @ 500 RPM.
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DrAllis
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Joined: 12 Sep 2009
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Posted: 01 Apr 2012 at 1:51pm |
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I could care less what the number really is, as long as each cylinder is even and the engine doesn't use oil and oil pressure is acceptable. Remember, compression testers are like speedometers....no two may read exactly the same.
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Brian G. NY
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Posted: 01 Apr 2012 at 2:05pm |
Dr. Allis,
Then, even 10% difference is unacceptable to you?
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B26240
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Joined: 21 Nov 2009
Location: mn
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Posted: 01 Apr 2012 at 2:18pm |
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Im with the DR. on this the compression tester I have requires some skill to hold it in the hole while cranking and have found if I repeate the test I often will get a different reading. I also say that engine should have been running and warmed up befor testing.
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Glockhead SWMI
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Location: South West Mich
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Posted: 01 Apr 2012 at 3:47pm |
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my wc only has thirty PSI. granted, it doesn't start real well...
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Brian G. NY
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Posted: 01 Apr 2012 at 3:59pm |
B26240,
The good ones screw into the plug hole and do not leak.
Not to say they may not vary in accuracy!?
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wjohn
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Location: KS
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Posted: 01 Apr 2012 at 4:00pm |
 Glockhead SWMI wrote:
my wc only has thirty PSI. granted, it doesn't start real well... |
I bet it's easy to spin with the hand crank though haha! My WC is significantly tougher to hand crank than my B, so I think it has decent compression.
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1939 B, 1940 B, 1941 WC, 1951 WD, 1952 CA, 1956 WD-45
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Stan IL&TN
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Joined: 13 Sep 2009
Location: Elvis Land
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Posted: 01 Apr 2012 at 4:03pm |
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My compression tester has adapters that screw into the head with an o-ring seal and I find that they are very reproducable but I will agree that there would be some variance between guages.
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1957 WD45 dad's first AC
1968 one-seventy
1956 F40 Ferguson
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JimD
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Joined: 11 Sep 2009
Location: Mounds, OK
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Posted: 01 Apr 2012 at 4:14pm |
I guess I got lucky with mine. I seem to get very reproducable results. Maybe 5 or so psi different. But then testing the same hole over and over is still not going to get perfect results due to oiling, heat, and speed at which the starter spins. I usually recommend a rebuild around 90psi if the customer isn't happy with power. 125 seems to be a good target number, but I've had 125cu in engines go as high as 150, but I also didn't know what had been done prior to my work. JimD
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