C85-8 compared to C85-12..?

[pftcraft]

I have a chance to trade my O200 for a C85-12. I am looking for a C85-8. Does anyone know if the 12 can be used in place of the 8 for installation in the BC12D for the Option 1 of the Harer STC.

[Robert Lees]

Re: C85-8 compared to C85-12..?

From an engineering perspective: not without the long engine mount.

The C85-12 can be converted to a -8 , using an A65 accessory case modified with additional holes to mount to the -12 case halves (that's what I've just done, with the stroker mods). A change of mags and crank gears is also required from the -12 to -8.

Probably not worth it...wait for a -8 to become available.

Rob

[Dan Michaels]

Re: C85-8 compared to C85-12..?

I have a chance to trade my O200 for a C85-12. I am looking for a C85-8. Does anyone know if the 12 can be used in place of the 8 for installation in the BC12D for the Option 1 of the Harer STC.

Don's Dream machines can convert your 12 to an 8.

Dan

[Dan Michaels]

Re: C85-8 compared to C85-12..?

From an engineering perspective: not without the long engine mount.

The C85-12 can be converted to a -8 , using an A65 accessory case modified with additional holes to mount to the -12 case halves (that's what I've just done, with the stroker mods). A change of mags and crank gears is also required from the -12 to -8.

Probably not worth it...wait for a -8 to become available.

Rob

I asked Don's dream Machines if the conversion could be done with just the acc case. They said that there were mods that had to be done to the case also. I believe it has to do with the oil passages and the starter.

Dan

[Robert Lees]

Re: C85-8 compared to C85-12..?

There is no starter on the -8 (as you know) so no mods required there (they may be referring to the gear mods.) The crank is the same.

As to the oil passages, I don't know...I just paid the bill and got the engine! This is the second engine so modified by our engine shop, and they appear used to doing these mods in the UK.

[Dan Michaels]

Re: C85-8 compared to C85-12..?

There is no starter on the -8 (as you know) so no mods required there (they may be referring to the gear mods.) The crank is the same.

As to the oil passages, I don't know...I just paid the bill and got the engine! This is the second engine so modified by our engine shop, and they appear used to doing these mods in the UK.

Going from a -12 to a -8 the -12 has a starter and alt that has to be removed and a mod done to the case to make it a -8. This mod has to do with an oil passage for the starter drive I believe.

Dan

[Ragwing nut]

Re: C85-8 compared to C85-12..?

The top ears have to come off the -12 and 2 studs have to be moved and all studs replaced with shorter ones. Crank gear, camgear, mag gears all have to change. Magnetos have to be changed as well. -8 is right hand rotation mag, -12 is left hand rotation.

[VictorBravo]

Re: C85-8 compared to C85-12..?

I have a chance to trade my O200 for a C85-12. I am looking for a C85-8. Does anyone know if the 12 can be used in place of the 8 for installation in the BC12D for the Option 1 of the Harer STC.

You guys all missed his question I think. All he wants to know is if he can use a -12 engine without the starter and generator on the short mount for the STC. The answer is YES, with a little additional difficulty.

Removing the starter and generator and installing the proper covers ("blanking plates" to some) makes your -12 engine into the FUNCTIONAL EQUIVALENT of a -8 and has been used many many times in the "option 1" Harer STC. My recent conversion used a -12 with cover plates. The difficulty was that I had Eisemann magnetos which have no clearance from the firewall on the short mount. The C-85-8 has a THINNER accessory case which moves the mags further away from the firewall and you have a little more clearance.

So the answer is yes you can use a -12 engine if you have one available, install the cover plates (Continental made them for just this purpose) and use the smallest magnetos you can find. We had to pound a slight dimple into the firewall to clear the Eisemanns which is a pain in the ass.

If you have an engine shop that will convert your -12 to a -8 at a reasonable cost, that's an option... HOWEVER, more than one person is now working on STC's to install the newfangled small starters and alternators on the short mount, so you might want to leave that option open.

Your logbook entry and 337 form should read something like "... installed C-85-12 engine with starter/generator removed and cover plates installed, yielding the equivalent of a C-85-8 engine, per STC SA-1-210..."

[Robert Lees]

Re: C85-8 compared to C85-12..?

The top ears have to come off the -12

What ears?

You guys all missed his question

Your point noted, Bill, but I don't see the Harer specifically allowing a -12 on the short mount (blanking plates or no, it's still legally a -12 if the data plate so states).

Practically from an engineering standpoint, you may be correct, but unless exp, the engine is still a -12.

I stand to be corrected, of course.

[Ragwing nut]

Re: C85-8 compared to C85-12..?

What ears?

The top of the case where the top two bolts goes through the starter. THat area does not exist on a -8.

[Ragwing nut]

Re: C85-8 compared to C85-12..?

In short no, STC does not allow a -12 on a short mount as you can't use the correct exhaust system

[pftcraft]

Re: C85-8 compared to C85-12..?

After going through the paper work again I discovered on Engineering Order 100, "To Identify power plant on Dwg G161" Revision A, For the BC12D85 conversion use Continental C85-8, For the Model 19 conversion use the C85-12 engine.. What if you used slick mags.. would the wires still interfere with the firewall using the short mount..? Has anyone completed the Harer STC Option "1" using the C85-12 converting the BC12D into a BC12D-85..?

[VictorBravo]

Re: C85-8 compared to C85-12..?

After going through the paper work again I discovered on Engineering Order 100, "To Identify power plant on Dwg G161" Revision A, For the BC12D85 conversion use Continental C85-8, For the Model 19 conversion use the C85-12 engine.. What if you used slick mags.. would the wires still interfere with the firewall using the short mount..? Has anyone completed the Harer STC Option "1" using the C85-12 converting the BC12D into a BC12D-85..?

This is yet another one of those areas where the Gilberti/Harer STC is too vague or does not address things correctly. The STC should read "for BC-12D-85 install C-85-8 or C-85-12 with starter and generator removed..."

By removing the starter and generator you are in essence converting the -12 back to a -8. This of course does not change the data plate or official engine designation, as Rob points out. However, it is (thankfully) still well understood and accepted by the FAA that it is the functional equivalent and meets the intentions of the STC. This also CLEARLY falls within the discretion of an IA as a "minor alteration".

Your IA can simply state that a C-85-12 was installed instead of the not readily available C-85-8, and that the C-85-12 with the starter and generator removed is in fact a functionally equivalent alternative, and that the size, power, weight and systems are virtually identical, and that substituting the hand start -12 is a minor alteration well within the IA's authority both in the scope and the intent of the FAR's covering minor alterations.

I have personally and recently installed a C-85-12, with starter and generator removed and Continental cover plates installed, on a BC-65 under STC SA-1-210. There have not been any issues with either the installing mechanic or the FAA. There is little or no clearance for the original Eisemann mags, which makes the installation more difficult. Smaller magnetos such as Slicks will still be close to the firewall, often with the wires touching. This is simply one of the overwhelming joys of Taylorcraft ownership, and there's little that can be done about it.

Unfortunately, a simple one inch spacer to move the engine forward from the firewall will make the engine cowling not fit, because back in 1938 good old CG and the boys designed the closed cowl way too !($#^% tight on the engine! The Continental engines have very little distance between the #4 cylinger and the prop flange. The shape and location of the air inlets is in the wrong position.... causing the #4 front cylinder baffles to have to be squashed into a too-small space... leaving not even a half-inch room to move the engine forward in the nose cowl... to get the !($^%@# mags away from the firewall.

The C-85-8 is therefore easier to install, because the accessory case is thinner. BUT... I understand there are some magnetos that will go right on the thin case, but some magnetos need big spacers (which give you the same problem as the -12 engine!!)

Bottom line: If you have easy access to a -12 engine then you can do it. If you are buying an engine, buy a -8 if you can, but you will never be able to add one of the new small starters and generators when they finally get approved..

[Ragwing nut]

Re: C85-8 compared to C85-12..?

The C-85-8 is therefore easier to install, because the accessory case is thinner. BUT... I understand there are some magnetos that will go right on the thin case, but some magnetos need big spacers (which give you the same problem as the -12 engine!!)

Slick kits have one impluse for the left side and use a Lycoming spacer to give clearance for the gear forcing the mag back.

If you can find right hand rotation Eismann LA-4 impulse mags for a -12, the mag wires come out the top so no problems with wires against the firewall.

The issue missing is the STC does not give an alternate exhaust system to use with a -12 on a short mount as the stock -8 system will not work, and the F-19 exhaust will not clear the firewall.

[VictorBravo]

Re: C85-8 compared to C85-12..?

Mike's correct, the exhaust from my A-65 had to be cut, spread apart 3/8", and welded back together.