Hi Martyn,
from the scans below of Product Bulletin Oct 21 1960 it tells us that indeed the 933 Pony is different to the normal D4-6 etc Pony.
To date I have not located any data on the "Modified Frame" mentioned in the article.
There were loads of mods. to these engines over the years.
Somewhere in the Parts Dept literature there should be a list of adaptability and conversions for these ponies--(hand grenades).
Hope this helps.
Cheers,
Eddie B.

The changes to starting engine, clutch/brake and pinion design on the 933 were many, and substantial, and cover a lengthy period of time.

Here is list of starting engine modifications for the 933, from the Master Index of Service Publications .. commencing from around early 1958 ..

SUBJECT ............................. MODEL ..... PUBLICATION ..... DATE ..... PAGE

Clutch/Pinion controls, adjustable ... 933 .......... SB ......... 2-13-58 ... 1

Clutch, nine disc ............................ 933 ........... SB ......... 3-19-58 ... 3

Pinion design ............................. All engines ..... SM ......... 6-20-58 ... 3

Exh pipe - longer curved sect ......... 933 .......... PB .......... 12-2-58 ... 2

Valve cover w/- welded-on Gov Spr Brkt .. 933 .. PB ........ 6-22-59 ... 4

Recoil Starter - New Cable Housing .. 933, D311H .. PB ...... 7-2-59 ... 4

Rocker arm strengthened .............. 933, D311H ... PB ..... 11-13-59 ... 4

Gov Cntrl Linkage, Imprvd Ball Joint .. 933, D311H .. PB ... 11-25-59 ... 4

Clutch brake - New, Lining bonded to Stationary Plate,
Rotating Plate welded to collar .......... 933, D311H .... PB .... 2-8-60 ... 1

Improvements - Cyl head, Valve location, Camshaft, One piece Ring Gear and Drive sprocket,
Recoil Starter, 12V starting motor, Over-running clutch, Cam-shaped pistons,
Clutch and Brake controls ...... 933F, D311H, D320A .. PB .. 10-21-60 .. 2

In addition, there are literally dozens and dozens of further improvements and re-designs done to this starting engine, from 1960 onwards. I am not surprised that no-one can recall the details of changes, they were constant and regular, and would fill a small book ..

Thanks everyone,its very interesting to see what improvements Caterpillar made to one model.The 933 seems to have had a lot of modifications over its production.Any mod info on the G series would be most welcome.
Thanks
Martyn

The biggest and most helpful change was removing the early start. engine common oil system with the diesel and putting a pan on so they had a separate oil system of their own and not using the old dirty oil from the diesel.I have changed lots of them old style engines to the separate system as Cat had a kit to do it and really helped the life of the engine.The best improvement was going to a direct start on them.

Hello SJ
Sometimes wish it had a direct start,but where is the fun when you got a sometimes tempremental starting emgine.
Martyn

Can't remember if I asked before......but what is the serial number of your unit???

Hello Old Magnet
42A 9034
Martyn

Martin 11A numbers were made in E. Peoria 42A made in aurora plant

That is a pretty late one as I show production ending at sr. # 9202 in 1968.
There is a parts book...Form # UEO36197 that covers from 42A5918 to 9202 that you may want to acquire (which I don't have).
I do have Form # 36197 for 42A5918-up but it doesn't cover to production end.

Even though they made lots of fiddly changes to that pony engine, the basic adjustments and operation is pretty much the same.

The best modification on the 933 was when they stopped making it.
AJ