1956 172 O-300A engine, can I use D case (not the accy case)

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1956 172 O-300A engine, can I use D case (not the accy case)

Postby an8pilot » Thu Mar 26, 2020 7:15 pm

Hello there.

This is for a 1956 C172, not the C172A but the straight original C172

I have a O-300A and have all the parts ready to reassemble. I'm an A&P IA.

I have a O-300D overhauled tagged case as well here. Just the case. Not the accessory case.

My only interest was I believe the D case, to be a better case than the A, with the way the cylinder studs were blind, and not threaded all the way through to the wet areas to stave off leaks there at the studs. Not the carry through bolt studs. Just the cylinder studs that don't go all the way through the case. I think it is a heavier stronger case.

So basically checking if there is anything to using a D case on an A engine.

That would be the original overhauled A counterweighted crank and rods, with the original overhauled cam, original A gears, original A accessory case and pump, no vacuum pump pad, and the B&C starter adapter for the A.

Is this a thing simply using what I think is a better case overall?

I called Continental and talked to a much older fella who didn't seem to think there was a problem with it, because you are keeping all the same parts as the A except the Case and not using a vaccuum pad and using the original accy case and gears, but didn't know off hand of any paperwork.


(The only other thing I wanted to do was make it into a Taildragger, but the kit/STC/modification, I haven't been able to find at a price I can afford. I have done that to a 1959 C-150 with the Jim Somerset/ACT Texas Taildragger conversion )

This is the old Post when I started this project.
viewtopic.php?f=24&t=11450
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Re: 1956 172 O-300A engine, can I use D case (not the accy c

Postby gahorn » Fri Mar 27, 2020 2:11 am

What you wish to accomplish is covered by TCM M75-6R1, SUBJECT: CONVERSION OF ENGINES FROM ONE MODEL TO ANOTHER

Short answer, Yes, it can be done, but the Maintenance Bulletin M75-6R1 must be followed.
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Re: 1956 172 O-300A engine, can I use D case (not the accy c

Postby an8pilot » Fri Mar 27, 2020 3:51 am

Thank you. I figured you (Gahorn) would say hi.

I can change the configuration but will it still be allowed under the 172 TCDS.
It will not be a D engine configuration. It would be an A configuration with an originally D case and A accessory case.

I. Model 172, 4 PCLM (Normal Category), approved November 4, 1955; 2 PCLM (Utility Category), approved December 14, 1956
Continental O-300-A or O-300-B

Going to re-read TCM M75-6R. I haven't read that in a long time.
-------//
Edit re-read TCM M75-6R. I remember my thoughts on that. TCM M75-6R is good for when you want to take one model of engine and put it on an aircraft that requires a different model, or you like the configuration of the different model and that different model is ok on the aircraft per the TCDS, or STC, or Field Approval.

So this would be the same configuration of A using a D case. All the other parts beside the case halves are A original and are the same p.n. as in thru bolts and A accessory case and gears and B&C starter STC on A configuration with A accessory case etc.
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Re: 1956 172 O-300A engine, can I use D case (not the accy c

Postby Bruce Fenstermacher » Fri Mar 27, 2020 10:14 am

But he is not changing the model of the engine. He wants to use what he thinks is aa later case design which he feels is better.

From the IPC:
Screen Shot 2020-03-27 at 5.46.25 AM.png


Notice there are no part numbers for case halves for any of the models of C-145 or 0-300. Every model uses the same cases. There is no difference. However there are 3 different Studding Assembly, Crankcases. One assembly for the C-125-2, C-145-2 and 0-300A. One for the C-145-2H and 0-300B. And the last for the 0-300C and D.

The difference between the -2/A model and the -2H/B model is the matching for the prop control lever. I can't think what the difference would be between the -2/A and the -C /-D assemblies. Likely less machining and or different plug sizes used at the oil galleys or something on that order. Besides the obvious differences in parts with the crank having the 6 bolt flange and the -D accessory change with related parts, I can't think of any other parts that would be different from the -2/A and the -C/-D engine.

Fact is Continental has a method in M75-6R1 of changing a -2/A engine assembly to a -C/-D so they must consider the case assemblies to be equivalent.

I'd agree with the guy at Continental, use the -C/-D studding assembly if you think it is better but Continental didn't think it made a difference or they wouldn't have allowed an old assembly to be changed to a later model. I think this a minor alteration blessed by Continental that might be documented in the build logs but you are not changing the model. A letter or email from the guy at Continental could be important years down the line when someone finds and questions this again like when you go to sell the plane or engine.

And a further thought. I've dealt with case half exchanges with companies who deal in case cleaning, repair and certification. My feeling is this. If you where to purchase outright, two case halves for replacement of your -A model cases, you'd likely get the -C/-D stud assemblies if that is what they had on hand, and they would not be identified other than what you wanted, for a -A. They may not even identify them differently. Most people would know no difference.
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Re: 1956 172 O-300A engine, can I use D case (not the accy c

Postby an8pilot » Fri Mar 27, 2020 7:28 pm

Can't wait to read this again carefully and go look at the parts book that is shown in the picture above and track the codes.

Side note: there is, on the D, needing to tap and pipe plug the oil gallery going to the original starter location when configured as an A model.

I would like to try to find the latest parts IPC and overhaul manual on PDF as I am just getting back into putting this together.
Mine are out in the shop somewhere and I'm organizing today and trying to find them.

I am overhauling everything to make it meet specs. But not going to call it overhauled. Cylinders already overhauled and done, as well as both sets of cases, rods, later cam p.n., crank and C/W overhaul, crank was placed in the oven in the fixture to relax it at Aircraft Specialties as well as balanced and rods weighed to match same weight across from each other, and lifter bodies done. Just haven't bit the bullet on new carry thru bolts since not calling it overhauled. They are truly expensive.
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Re: 1956 172 O-300A engine, can I use D case (not the accy c

Postby gahorn » Fri Mar 27, 2020 7:54 pm

an8pilot wrote:Thank you. I figured you (Gahorn) would say hi.

I can change the configuration but will it still be allowed under the 172 TCDS.
It will not be a D engine configuration. It would be an A configuration with an originally D case and A accessory case.

I. Model 172, 4 PCLM (Normal Category), approved November 4, 1955; 2 PCLM (Utility Category), approved December 14, 1956
Continental O-300-A or O-300-B

Going to re-read TCM M75-6R. I haven't read that in a long time.
-------//
Edit re-read TCM M75-6R. I remember my thoughts on that. TCM M75-6R is good for when you want to take one model of engine and put it on an aircraft that requires a different model, or you like the configuration of the different model and that different model is ok on the aircraft per the TCDS, or STC, or Field Approval.

So this would be the same configuration of A using a D case. All the other parts beside the case halves are A original and are the same p.n. as in thru bolts and A accessory case and gears and B&C starter STC on A configuration with A accessory case etc.


If you convert a D engine to A configuration under the M75-6R1... then you will be installing an A engine in the 172, which is approved byTCDS.
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Re: 1956 172 O-300A engine, can I use D case (not the accy c

Postby an8pilot » Sun May 03, 2020 3:46 am

The case used in D configuration, if that D case used in A configuration, must have the oil gallery that was drilled for starter gear oiling, tapped and plugged.

The back side of the later cases cylinder hold down stud holes, the ones that do not accept thru bolts, those stud holes are blind on the later cases. Where on the cases used on the earlier A case those stud holes were drilled all the way through into the wet area letting oil leak through the stud threads. But oil stops corrosion doesn't it. (Again, not talking about the through bolt holes)

I haven't built this engine yet. I've been waiting and debating on sending my through bolts in for magnaflux inspection. I am not calling it overhauled. Just repair because I was only replacing the cam, and replacing cylinders.

Those through bolts are costly.
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Re: 1956 172 O-300A engine, can I use D case (not the accy c

Postby n2582d » Sun May 03, 2020 6:42 am

an8pilot wrote:... Where on the cases used on the earlier A case those stud holes were drilled all the way through into the wet area letting oil leak through the stud threads. But oil stops corrosion doesn't it. ...

Section 11, paragraph 3 of the overhaul manual says, “Coat the new studs coarse thread with Alco Thread Lube if the hole is blind or with National Oil Seal Compound if it is a through hole that is subject to oil spray.”

SIL99-2C specifies Loctite 592 Teflon PS/T Pipe Sealant on “All threaded fasteners installed in a through hole to an oil source.”

What have you guys that have overhauled C-145/O-300’s used?
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Re: 1956 172 O-300A engine, can I use D case (not the accy c

Postby cessna170bdriver » Sun May 03, 2020 11:58 am

n2582d wrote:
an8pilot wrote:... Where on the cases used on the earlier A case those stud holes were drilled all the way through into the wet area letting oil leak through the stud threads. But oil stops corrosion doesn't it. ...

Section 11, paragraph 3 of the overhaul manual says, “Coat the new studs coarse thread with Alco Thread Lube if the hole is blind or with National Oil Seal Compound if it is a through hole that is subject to oil spray.”

SIL99-2C specifies Loctite 592 Teflon PS/T Pipe Sealant on “All threaded fasteners installed in a through hole to an oil source.”

What have you guys that have overhauled C-145/O-300’s used?


Call Mena Aircraft Engines in Arkansas. Other than the breather tube, my engine hasn’t leaked a drop of oil in 268 hours over the course of three years.
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Re: 1956 172 O-300A engine, can I use D case (not the accy c

Postby gahorn » Sun May 03, 2020 10:30 pm

cessna170bdriver wrote:...

Call Mena Aircraft Engines in Arkansas. Other than the breather tube, my engine hasn’t leaked a drop of oil in 268 hours over the course of three years.


OMG! Something’s WRONG! :lol:
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Re: 1956 172 O-300A engine, can I use D case (not the accy c

Postby an8pilot » Mon May 04, 2020 3:08 am

:D
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