engine models

Post by **Bruce Fenstermacher** » Tue Aug 19, 2003 1:57 am

... So I asked them how much they'd charge to overhaul my O-300C engine to new limits.....and they wouldn't quote it stating they didn't know what a C engine was. (The ONLY difference between a C and an A is that the C uses the same crankshaft as the D which has only 6 prop bolts.)

So George, you have a 300C? I've looked in the parts manual and it does seem that you can use the D crank with the A case. So are what you saying is that if I replace the crank in my c-145-2 with a D model crank (which is dampened) and of course the prop, I'd have a 0300C and I could then use a 35 amp generator and a fancy Aeromatic Prop? What model prop do you have George, and what makes it legal on our planes?
This is all very interesting cause I need to upgrade my generator, I would love to find an Aeromatic prop, I have a friend with two Aeromatic prop hubs (6 bolt) and an extra crank and my engine is currently disassembled in his garage. My brain is churning

Post by **GAHorn** » Tue Aug 19, 2003 6:26 pm

Well, Bruce, this is slightly more complicated/convoluted that you might at first suppose.
I have a McCauley EM7355, which is the 6-bolt version of the MDM7655 (which was the standard prop for the 170, 170A, 170B airplanes.) The only difference is the 6 bolt rather than the 8 bolt attachment.
While the C/D crank will physically fit an A engine, it is not the correct pn, and will require some sort of approval basis. Ordinarily it would be used to convert an A to a C or D engine, which gets it's approval by TCM Service Bulletin (M75-6R1).
So, I'm not sure that a D crank is actually an approved subtitute part for an A engine. (But it would be for an A engine being modified to a D or C engine.) It's a technical diffrence, but also a legal one.
In my airplane's case, both the engine and prop installations were approved directly by FAA inspection and original issuance of an airworthiness certificate. As far as I know, it's the only such case. Ordinarily it would only be done by field approval.

Post by **Bruce Fenstermacher** » Wed Aug 20, 2003 1:38 am

While the C/D crank will physically fit an A engine, it is not the correct pn, and will require some sort of approval basis. Ordinarily it would be used to convert an A to a C or D engine, which gets it's approval by TCM Service Bulletin (M75-6R1).
So, I'm not sure that a D crank is actually an approved subtitute part for an A engine. (But it would be for an A engine being modified to a D or C engine.) It's a technical diffrence, but also a legal one.

So George what you are saying is that if I put a D crank in my engine and call my engine an A then I would need approval to do that but not to reinstall the engine in the 170 and I'd also have to have approval for the prop on the engine /plane .
Or
I could put the same D crank in the A case, call the engine a 0300C then get approval to put it on the plane along with approval for the prop which is what happened in your case.

...Now lets see maybe I can through a hot Corvair cam in there and get that approved while I'm at it. Just kidding but it would be fun to see the reaction by the feds to that request.

I've not been able to read M75-6R1 which you refer to to see if it helps either situation.

This has gotten just a bit more serious as I've just found out my crank needs to be cut .010 under.

BTW George, do the judges now your plane has a modified engine and prop?

Post by **GAHorn** » Wed Aug 20, 2003 4:33 pm

Yep. They know. It's only one item demerit, which still keeps it out of the "custom" category. (But hey,...it's painted the correct color!)

Dave Clark · Post by **Dave Clark** » Thu Aug 21, 2003 2:13 pm

Bruce

Why would you worry about a crank with a fresh grind to -.010? I'd rather have that with a new limits fit than a worn to service limits fit at standard size.

Post by **Bruce Fenstermacher** » Thu Aug 21, 2003 4:16 pm

Dave I'm not worried about a .010 under crank but it does cost money. I'm looking at other options I might have to "improve" my plane so I can take advantage of other things that interest me such as the 35 amp Generator and the Aeromatic Prop, neither of which I could use on my C-145-2 with a standard or under ground crank. I should mention my current crank is not dampend which stops me from using those items and finding a good correct PN dampened crank could be difficult and costly. My friend already has the D model crank ready to go.

Dave Clark · Post by **Dave Clark** » Fri Aug 22, 2003 1:22 pm

Oh I get it now!