The International Cessna^® 170 Association

Currently, my project has a a C-145. I can get an O-300A for it. However, I was told that if I was to convert, I should put in an O-300D.

Can anyone enlighten me on this. Also, what are the advantages/pitfalls of changing engines?

As far as I know, the C-145-2 & O-300A are identical except for the numbers stamped on the data plate. The O-300D is a slightly different beast-- 6 bolt prop (instead of 8 bolt), button start (instead of pull-start), right-angle starter. You'll need to buy some new stuff (prop & starter) unless the D engine you buy comes with it, as well as rework other stuff (wire in starter button). You'll also need a field approval via 337.
The O-300A will go right on with same accessories, no reworking necesary, no field approval required as it's listed on the type certificate. depending on who you talk to, you will need to file a 337 (NOT a field approval) or just make a logbook entry. See other topics for more on this issue.
The only advantage to a D engine is a factory-standard engine-driven vacuum pump. Personally, I prefer the venturi's, or no vacuum system at all for VFR flying, so I don't feel the D engine is worth the hassle unless you can get a hell of a deal on a low-time one. The only disadvantage to a C-145 or O-300A is that the crankshafts are getting pretty scarce if you should ever need a replacement.

Eric

Eric is right on about the differences from the A to the D model. I'll add that a TIC170A member has a STC to install a C or D model engine so the paper work involved is no big deal. He even sells the STC at a very very attractive price and donates the proceeds to the TIC170A I've heard.

The O-300-D STC was donated to the assn TIC170A by Ron Massicot. Check with headquarters@cessna170.org for current pricing (presently about the same as annual membership.) Cheap.

What? The Association owns an STC

Nope. I erred. The deal is Ron Massicot owns it. It will cost non-members $150. It will cost members $75 which which turns into a donation to TIC170A. (Ron's a good guy who slept thru economics class.)