The International Cessna 170 Association

Excuse my ignorance but what exactly is the difference between a C-145 and a O-300?
Which one came first and which is better to have?
Are there mixes with parts of both?
Need to study up on airplane engine history.
Any wisdom is appreciated.

The C-145 came before the 0-300. The 0-300 was created when Continental changed the way they named their engines from horsepower (145) to cubic inches (300). For practically all intents they are the same engine with all parts being the same. There are differences in parts when you compare specific engine models. For example a C-145-2D uses the same crank as a 0-300-A. 0-300-C, D, and E models are the same as the 0-300-A but the crank has a six bolt flange instead of the 8 bolt found on the C-145-2, 2D, 2H and 0-300-A engines.

Is one better than the other. Not in my mind. In my mind they are all the same..

Now legality is another story. According to the Type Certificate Data Sheet, if you have a '48 170 you must have a C-145-2 or a 0-300-A. The C-145-2H is not approved. For the 170A and B you can have a C-145-2, C-145-2H, 0-300-A. The TIC170A has an STC that allows a 0-300-C, D or E on all models of the 170.

Bruce's description is essentially correct for most practical purposes, although there are numerous minor differences between C-145 and O-300 engines. Most of those differences are interchangeable, but nonetheless did occur. (An example which always comes to mind in this sort of comparison is the change from steel cam/cast-iron cam-followers to cast iron cam and steel lifter bodies, although such changes are capable of be applied to the earlier engines during rebuild.)
There are many other such minor changes which occured, but in general, it's largely a nomenclature change as Bruce correctly pointed out.

hey George, how long has it been since the older-style parts (cam and lifter bodies, etc) have been superceded by TCM? a while I bet, even though I imagine there are a many old dinosaurs out there with various older style parts, my 1969 factory 0-timed O300A among them.

when looking at any used engine it pays to look at when it was last overhauled and what parts were used, as supercedures occur regularly - due to technology changes, materials availability, costs, service record, etc. there is almost never a static point in an engine type's life where part designs are frozen, even old radials get newer tech parts as new manufacturers build for the spares market.

no point I guess, just an observation

Yes, some of the engines out in the field have original parts, and some were overhauled/rebuilt over 30 years ago, so their parts-list may be fairly dated. (The real problem with undocumented parts is that an owner is in the dark about subsequent AD's, SB's, etc. .... BTW, never use a steel cam with steel followers or iron cam with iron followers, as excessive wear will occur.)

While this subject is being discussed, wasn't there a difference in some models crankshafts having counter balances and others not or something along that line?

Yes.

Early C-145-2 engines by my research made I believe only in 1948, had undampened cranks. They didn't have the fifth order dampeners found on later cranks between the 5th and 6th rod bearing journals.

C-145-2 engines with a D suffix (C-145-2D) and all 0-300-A engines had dampened cranks if they have not been retrofitted with an older crank.

If memory serves me right, dampened cranks have an extra small hole in the prop flange that can be seen without disassembly but I'm not sure than is conclusive.

All C-145-2H and 0-300-B, C, D and E engines have dampened cranks. Cranks for these engines were never made undampened.

More on this here: http://cessna170.org/phpBB2/viewtopic.php?t=745

Thanks for all the info, Gentlemen.

Is there a cutaway diagram available for the O-300?
Still trying to understand how all that works...

If you want to pm me your email, i could send you some pages of diagrams out of the ohm.
Vic

Great,
PM send.
Thanks

While the two engines are extremely similar, they are not quite the same. For example, there are minor differences in the cases that mean you can't quite convert a C-145 into a O-300.
That being said, they use the same cylinders, (so does the O-200) and they make the same horsepower, but depending on the suffix, things like the Vac pump, starter types, (key start vs pull cable), etc., may not interchange.
But, this is something you you can find even between various O-300 engines of different letter suffix's

Just realized this thread is 16 years old!

If not already covered, I believe the accessory case and oil sump are different. C145 has three bolts accessory case to sump while the O-300 has 5. This was discussed recently in another thread specifically about the sump. Magnesium vs aluminum.

Rich,
I believe you're referring to this thread from last year. For what it's worth, according to the Continental Parts Interchangeabilty Catalog I referenced there, apparently there are some C-145 engines with the 5 bolt sump. It says, "Beginning with C125-2 engine #8205-9-2 and C145-2 engine #4384-D-9-2, a new type oil sump is used including five tapped holes for the sump-to-accessory case attaching cap screws, instead of three tapped holes for these attaching screws ... ."

Gary

Thanks, good to know. I have to check my S/N now! I have a spare sump with three bolts. I have to see what is in my airplane.

Rich