Desmobob,

In 1983, Fox made .29s, .36s, and.40s, all in the same basic configuration. These were the Series 5 engines. The 36s had NO markings. The 29s were stamped "29" on the top of the left mounting lug. The 40s were stamped "40" on top of the left mounting lug.

As you suspected, only the bores were different. They were 29-.730", 36-.800", 40-.840".

Fox called these BB engines, but in fact, they only had a REAR ball bearing, the front end was bushed.

Later on in 1987, Fox came out with a twin BB engine.

The pictures show the 1983 engine and the 1987 engines. You can clearly see the large front BB housing on the 1987 engine. The engines came in both RC and control line (no throttle) styles.

Sometimes, the 1983 36 control line versions are called the Mark V Combat Special, but they really weren't very racy!

Incidentally, the 1983 Fox 29s were the last 29s Fox made.