Tech Tip #196: Ford 300 Ring Gears Made Easy

The CSG649i is the industrial version of the Ford 300. This Ford industrial engine is used widely in such industrial applications as wood chippers, airport tugs, and other applications requiring a rugged six cylinder gas engine. While it is getting long in the tooth, it is still a very popular engine. The Ford 300 is a very heavy cast iron engine with all the usual components of a successful industrial engine including cast iron timing gears, severe duty crankshaft, etc. This Ford engine has good torque characteristics. So good in fact, that the six cylinder Ford 300 is a more powerful engine than some Ford V8s.

Nothing much goes wrong with these engines, except the ring gear! We tend to sell a ton of ring gears for this engine. Not because the OEM ring gear is weak and over stressed. But the ring gear fails because some people in an effort to save money (when the original industrial starter motor fails) often purchase a replacement starter motor at their local NAPA. This doesn’t work out very well. There is a mismatch between the automotive starter’s drive offset and the industrial engine ring gear. Rather than mesh smoothly, they grind together. As a result the OEM ring gear gets chewed up and needs replacing. Whenever our Dr. Diesel™ hears of this happening he mutters, “Yep, one more guy tried to “out-cheap it”.” While the CSG649i has used many different ring gears over the years, we have narrowed the number of commonly used ring gears down to three different part numbers.

How to Identify the Ford 300 Ring Gear You Need

Because the model and serial number of the engine doesn’t pin down which ring gear you have, we ask people to count the teeth of the ring gear they wish to replace. This is very important because the two most popular ring gears are almost exactly the same dimensions, differing only by ¼ of an inch in one dimension, the ID. We recommend that you count the teeth with paint and a paint brush and count them in 10 tooth intervals. It works best if you mark the teeth at each of the ten tooth intervals with your paint brush. We also ask them to measure the ring gear just to confirm that someone hasn’t retrofitted a DeSoto Firefly or Studebaker Hawk’s ring gear.

The chart below will be helpful when ordering a Ford CSG649i, Ford 300 ring gear.

Written by Dr. Diesel

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