O-300D crank

[cnflys]

I am looking at purchasing a 170B that has an O-300D installed. The engine has an 8-bolt prop flange. It is my understanding that the O-300D normally has a 6-bolt prop. My question is, how can I ensure that the engine/crank combination is fully legal. The seller sent me the model # and serial # of the crank. Additionally, how can I find out if the prop on the plane (McCauley model 1A170/DM7650) is authorized for this engine/crank combination? Thanks.

[Bruce Fenstermacher]

There are four ways a 8 bolt crank can be legally used in a 0-300-D IF the engine is still in fact a D. The questions is what type of starter does it have, angle or straight. If straight then the 0-300-D could have been converted to an 0-300-A whether or not the paperwork is done is another story but this is one way. If it has an angle starter the engine still may have been converted to a A but then you have to wonder who the angle starter is being used.

The second way would be by STC and there is one for doing just this. And the owner of that STC has given anyone permission to use his STC. Whether or not the paper we have with his permission is enough for the FAA has not been tested as far as I know. But at least one engine has used the 8 bolt crank with the STC and that was the STC owners engine.

The third way would be that someone got a one time approval on a 337.

The fourth way would be that someone simple used the older 8 bolt crank as a repair thinking little of it and no additional paperwork was done.

Not surprising you will find at least 4 opinions was to which method is legal and which is not.

As for the prop, well, it depends. It all depends on how the engine is approved.

First a McCauley 1A170DM765X if the appropriate prop for the airplane with a C-145/0-300-A. So if the engine is considered to have been changed to an A then this is the prop. The STC doesn't call for this prop specifically but it does call for props that use the SAE 3 flange which happens to be those on the TCDS.

If you have a one time approval it would be up to what if anything was listed on that approval. If there is only a log entry for the installation of the crank I'll bet there is no mention of the prop.

So half of the methods of installing this crank also point to a prop choice. The others don't most likely because they considered the limitation to fall to the TCDS. Most reasonable people would agree but the FAA doesn't always think reasonably.

Now as to the pitch of that prop of 50 inches, that is a bit flat for a 170 and may allow a static RPM outside the TCDS limitations. A 51 inch prop is considered a climb prop with the 1A170DM and a 170.

BTW just as important as what this engine is is how has it been approved to be installed in a 170. This is a separate issue than putting the crank in the engine.

And there are three answers again depending on what the engine is considered to be. One, if the engine is considered an A model then it is allowed under the TCDS and no further approval is necessary. Second, if the engine is still a D model then you could have a one time approval for installation of that engine. Third, you have or buy the associations STC that allows installation of the 0-300-D. If you have a D and the associations STC then there may be a can of worms with the prop because the incorrect props are sited on our STC for that 8 bolt crank.

Got all that?

[jlwild]

cnflys,
I have a O-300 D engine in my 1955 170B, with the 8 bolt crankshaft P/N 530789. All the engine log books and engine rebuild paperwork is complete. The key points in my engine paperwork are the "D" engine was rebuilt by Bolduc Aviation, FAA Repair Sta. KM5R993M. During the rebuild they installed the 8 bolt crankshaft via TCM Engineering Variation Order NO. 4183. This paper work and the logbooks came with the engine when I bought the engine. I installed the engine in my plane using the 170 Association O-300 D STC paperwork. The prop I am running is a McCauley model MDM 7653, Design 1C172. Make sure the plane you are looking at has the correct engine paper work, the STC for Cessna 170 installation and 337 Forms. The STC will tell you which props can be used.

[Bruce Fenstermacher]

.... Make sure the plane you are looking at has the correct engine paper work, the STC for Cessna 170 installation and 337 Forms. The STC will tell you which props can be used.

Actually Jim, if you are referring to the Associations STC to tell someone which props (and spinners) can be used on a 0-300-D with a 8 bolt SAE 3 flange installed you are wrong. It will not. The Association STC only lists props (and spinners) that can be used on a stock 0-300-D with a 6 bolt ARP 502 Type I flange.

Now if your are referring to James W. Johnsons STC SE4725NM this STC only says the crank allows the use of props for an SAE 3 flange.

Most reasonable people with a 0-300-D with a 8 bolt SAE 3 flange crank would refer to the TCDS for the correct prop and spinner and Johnsons STC says props for an SAE 3 flange which are what is listed in the TCDS. But if you split hairs, which the FAA has been known to do, there is currently no direct listing of the correct prop (and spinner) by part number for this modified engine.

[GAHorn]

To further complicate this matter.... the STC developed/owned by a "Mr. Johnson"...and the handwritten/scribbled note attributed to him.... is not convincing. The hand scribbled note may have been written by anyone, anytime, anywhere, for any purpose. It is not authenticated, notarized, other otherwise shown to be his legal signature and no one has located or identified him. If I were an airworthiness inspector I would not accept that poor copy of that note as legitimate.

[cnflys]

Thanks for everyone's responses. The owner sent me a copy of the 337 for the engine replacement. It covers the engine change and prop (including P/N and S/N). The engine is an O-300D with the angle starter and vacuum pump which the 337 addresses. Do I need to be concerned with finding the documentation authorizing the 8-bolt crank installation in the engine? The crank was replaced in 1981 and the engine installation in the 170 occurred in 2005.

[Bruce Fenstermacher]

Do I need to be concerned with finding the documentation authorizing the 8-bolt crank installation in the engine? The crank was replaced in 1981 and the engine installation in the 170 occurred in 2005.

In a word, yes. Otherwise you don't have proper documentation for the crank to be in the engine to begin with.

[GAHorn]

Do I need to be concerned with finding the documentation authorizing the 8-bolt crank installation in the engine? The crank was replaced in 1981 and the engine installation in the 170 occurred in 2005.

In a word, yes. Otherwise you don't have proper documentation for the crank to be in the engine to begin with.

Unless the 337 for the engine installation has it's block 3 approved by FAA and specifically mentions that 8-bolt crank as being installed. (in which case the entire modification is "field approved". IF...big IF....such is the case....then it's a perfect example of how the field-approval process USED to work properly. IMO.)

[cnflys]

Today I heard back from the seller about the 8-bolt crank. He mentioned that in the Continental parts manual it states that for an 0300D-6-F, 8-bolt crank p/n 628124A2 is approved. It is the "-F" that makes the engine approved for the 8-bolt crank. Can anyone here confirm or deny the claim? Thanks.

[n2582d]

Only 12 years late in answering this but, according to SIL05-3A, the “F” is a shipping designation. B=Wood crate, F=Factory packaging.

SIL05-3A.pdf

(190.54 KiB) Downloaded 7 times

Note that this Service Information Letter says it is for “all current production engines” so it’s possible that the “F” meant something different 70 years ago.