U1 Power Unit RPM

Sun Mar 20, 2005 10:39 am

I'm curious. I was looking through some IH brochures and found one that covered Engines and Power Units (Form # A-490-MM. 6-17) that list the U1 (Cub) power unit as having 16 horsepower "at rated governed engine speed of 2500 r.p.m.". I don't know the date of the brochure, that's why I listed the form number.

Since that is a higher rpm than the early Cubs, and higher than the 2300 rpm listed (GSS-1408, Rev. No. 2) as the rated load engine rpm (governed) for the 184 and 185 Cub Lo-Boy, what is different about the U1 that allows it to operate at a higher rpm than the tractor engines????? :? Or maybe I am miss-reading something. :oops:

Sun Mar 20, 2005 11:34 am

It was common for the power units to run faster than the "same" engine in a tractor. I have never dug through the parts books to see what is different. Of course, just seeing a different part number won't tell you how they are different. I have heard that crankshafts may have been better balanced, even had counterbalance weights, but haven't verified it. There may have even been a durability tradeoff, where they wanted to make sure tractors held together when well worn.

The higher revs themselves were typically done with governor (or even just governor spring) changes.

Your brochure is from 1949 (MM code).

Sun Mar 20, 2005 12:28 pm

Who will volunteer to set their governer at 2500 RPM on a fresh rebuilt engine and let us know how it does. I think GW should try it and report back. It's only 700 RPM more. Rick Prentice you would be a good one to try it.

Sun Mar 20, 2005 12:35 pm

Over speed a fresh rebuild by 40%, that wouldn't be on my short list of things to do! But if anyone does - put it on a dyno and publish the data.

Sun Mar 20, 2005 12:37 pm

Thanks Jim. I assumed the brochure was an early one just from the pictures of the units. I was just curious about the engine speed being faster than even the late Cub engines, on a power unit that could supposedly run several hours at a time, basically unattended, although that may apply more to the higher hp units that the U1.

Is there a listing posted somewhere of the date codes on IH brochures? Some of the brochures have single alpha codes, some have alpha numeric codes, some have double alpha codes. I suppose that was just to confuse people that look at them 40-50 years or more after they were printed, and wonder "when the @&*% was this printed". :) :roll:

Sun Mar 20, 2005 12:48 pm

The power units on bailers and threshers also are 2500 RPM full load and 2800 no load. I have books on the # 64 harvester thresher an d the U! and they both say the same thing.


Sun Mar 20, 2005 12:54 pm

On my tag it says Power Unit-T, There is no mention of (U-1). Is that the same as a the U1 that you Guys are talking about?.

Sun Mar 20, 2005 1:16 pm

Is that an engine serial number or a chasis serial number? On the 64 harvester thresher combine the chasis serial number is on the transmission housing on the same side as the oil dip stick. It starts 64HTC- ___________ Just above the oil dip stick there is a engine serial number just to the right of the carb. It will read IMCUBM________________. If Rudi has gotten a chance to get this on the server it is illustrated on page 2.


Sun Mar 20, 2005 2:01 pm

To those of us who are used to the cubs with a top rpm of 1600 to 1800, the 2500 seems fast and makes you wonder aobut longevity. However when you stop to think about it, the engine on a combine or thresher, while when it started ran steady for several hours at a time, the number of hours per year it ran was probably only a fraction of those run by a tractor which was used year round.

Sun Mar 20, 2005 2:07 pm

No Bill, That is on a tag on the side of the power-unit head on the same side as dip-stick and the serial# reads, 30B...6400.

The serial# on the engine above the dip-stick is [FcubM..103502] That last 0 could possibly be an [8].

Sun Mar 20, 2005 2:45 pm

I found the other power unit book of mine. The UC60. It is a 60 CU IN engine also. The Power unit Serial is UC-60____________ and the engine serial is UCUBM___________. You can see that on page 3 of the unit. I sent Rudi a copy of that also. I sent him these around the time he was sick so I don't know if he has them on the server yet. His health business and family come first, not necessarily in that order.
There are also power units using the Super A engine. These have overhead valves and replaceable cylinder liners. It caused me some confusion till I got the books because in the trouble shooting section for the harvester there is talk of worn liners and replacing them. It first led me to believe the cub engines for threshers had liners. Upon closer examination it turns out it is the Super A engines in the more powerful versions of the same thresher. Sort of like getting a V6 or V8 in your pickup.


Sun Mar 20, 2005 2:59 pm

OK Bill, The difference between the engine serial#s of the one you mentioned and mine is that your number is UCUBM and mine is FCUBM.

Sun Mar 20, 2005 3:17 pm

Model numbers on the power units can get more confusing than the tractor models, which can be bad enough. Basic Cub-based power unit was U-1, built from '49 - '57. In '57 the model designations changed to be displacement based. The new Cub-based unit was the UC-60, built from '57 to '71. Dont know if it was discontinued in '71 or if my list is from '71. (At least I finally have a list!!) Additional complication is that many power units were built to special specs. Those engines often had a specific model designation or serial number prefix, and sometimes their own sequence numbers.

That is a switch, a tractor engine in a power unit. It usually seems to happen the other way around.

I have a list of year codes for brochures, but I am not sure it is complete or totally accurate. They don't apply to all types of documents either. Basic scheme:

A = 1911 through Z = 1936
AA = 1937 through NN =1950
A = 1951 through P = 1964
R = 1965 through W =1970
X, Y and Z 1971 (maybe X wasn't used)
A = 72 through H = 79.

If there is a digit after the letter, it indicates a revision of the original brochure. Probably still within the same year.

Sun Mar 20, 2005 4:39 pm

For info purposes, along with the other power units talked about above, the Operators manual for " Engine, (2-5/8 x 2-3/4"), for McCORMICK Nos. 55-T and 55-W Balers" say the power unit S/N is on a tag attached to the flywheel housing, and the S/N is preceded by the number and letter 55B-, and the engine S/N is preceded by the letters "IMCUBM".

The 50 series balers, 50-T & 50-AW, were equipped with a 4 cylinder 16 hp, "International Harvester tractor-type power unit", which I understand is a Continental that is about the size of a Cub engine.

Thanks Jim
So would this form number on the back of a Cub Cadet brochure, AD-3994-U 10-13-T , mean that the brochure was for 1968, but printed in Oct 67? The brochure is for the model 72-104-105-124-125 Cub Cadet built from 11/67 t0 8/69

Sun Mar 20, 2005 8:43 pm

I would guess the 10-13-T was something like a release/approval date for the brochure. The main ID indicates department source, sequential numbering of some sort and a year.