B-125 Cam Events

I did a mapping of the camshaft timing events on my well-worn Model B-125 Power Unit that came off my Allis-Chalmers Model 60 Combine. I purchased this combine from my neighbor about 40 years ago, and I saw it sitting in his barnyard for about 10 years prior to that. I did observe this combine running in their field combining oats about 50 years ago. I do not believe it has run since then, definitely not since I have owned it.

The engine was stuck when I pulled it from the combine this winter; I removed the head and got it un-stuck, it now rotates freely. The head shows evidence of a prior valve job of questionable quality as the valves are sitting at various depths. I suspect the exhaust valves were replaced as they do not appear to have been ground, but the intakes are all rather thin at the margins.

The main point being, this is NOT a pristine engine. The #1 Exhaust lobe measures about 0.013" less lift than the others. The valve events are all over the place as well. I ran the cam around at least twice on each lobe and got the same readings, therefore I believe them to be reliable. So be it. I intend to run it as-is anyway when I get the head back on.

One interesting observation is the fact that the 0.050" closing point on #1 and #4  Intake are identical at 28 Degrees ABDC and their Net duration is the same at 186 Degrees.

Likewise, the 0.050" #2 and #3 Intake closing points are the same at 23 Degrees ABDC and they both have Net Durations of 180 Degrees.

Is this just a bizarre coincidence, or did Allis-Chalmers actually go to the trouble of designing a camshaft with different patterns to compensate for the weird firing order of their engines which causes disruptions in the induction system due to the overlap events?

Allis-Chalmers Power Unit Model B-125
S/N 72128 B

#1 Exhaust
0.010“  Open @ 30 BBDC     0.237“ Lift
0.010“  Close @ 10 ATDC      Gross Duration 220

0.050“  Open @ 9   ABDC
0.050“  Close @ 11 BTDC     Net Duration 182


#1 Intake
0.010“  Open  @ 2  ATDC     0.250“ Lift
0.010“  Close  @ 26 ABDC    Gross Duration 204

0.050“  Open  @ 22 ATDC
0.050“  Close  @ 28 ABDC    Net Duration  186


#2 Intake
0.010“  Open @   4  ATDC     0.249“ Lift
0.010“  Close @  39 ABDC     Gross Duration 215

0.050“  Open @  23 ATDC
0.050“  Close @  23 ABDC     Net Duration 180

#2 Exhaust
0.010“  Open @ 37  BBDC     0.251“ Lift
0.010“  Close @ 13  ATDC      Gross Duration 230

0.050“  Open @ 17  BBDC
0.050“  Close @ 8    BTDC      Net Duration   189


#3 Exhaust
0.010“  Open @ 34  BBDC     0.249 Lift
0.010“  Close @ 9    ATDC     Gross Duration 223

0.050“  Open @ 15 BBDC
0.050“  Close @ 9   BTDC     Net Duration 186


#3 Intake
0.010“  Open @ 3  ATDC      0.250“ Lift
0.010“  Close @ 44 ABDC     Gross Duration 221

0.050“  Open @ 23 ATDC
0.050“  Close @ 23 ABDC     Net Duration 180

#4 Intake
0.010“  Open @  3  ATDC      0.249“ Lift
0.010“  Close @ 44 ABDC      Gross Duration 221

0.050“  Open @  22 ATDC
0.050“  Close @  28 ABDC     Net Duration  186


#4 Exhaust
0.010“  Open @ 32 BBDC      0.250“ Lift
0.010“  Close @ 8   ATDC       Gross Duration  220

0.050“  Open @ 10 BBDC
0.050“  Close @ 12 BTDC      Net Duration  178

Sugarmaker wrote: ... Do you have a plan for your engine?...

Yes, I plan to install it on a derelict Model C that a dear neighbor and old family friend once owned. This will be a LOW budget project, mostly a labor of love.

I was hoping that someone with more knowledge of these engines would chime in with some further insight on the apparent anomaly in the cam timing.

It is difficult for me to believe that this is not by design and merely an accident from wear.