BC12-D A65 to A75 Conversion

[Ragwing nut]

Re: BC12-D A65 to A75 Conversion

Richard,
I'm working with out a net here, but if my feeble memory serves it has the stellite faced valves, waffled underside of the piston and lube holes in the intake rockers for oil cooling the springs. If someone has the parts manual handy they should be able to compare part numbers.
EO

Also drilled connecting rods for A75. I still do not know what changes are made to make one a -14.

[Edwin Otha]

Re: BC12-D A65 to A75 Conversion

Richard,
I'm working with out a net here, but if my feeble memory serves it has the stellite faced valves, waffled underside of the piston and lube holes in the intake rockers for oil cooling the springs. If someone has the parts manual handy they should be able to compare part numbers.
EO

[Pearson]

Re: BC12-D A65 to A75 Conversion

I went to the FAA website above and downloaded a copy of the Type Certificate Data Sheet (TCDS) for the Continental A65 engine. Very interesting reading, especially "note 7" referenced above. It reads, "NOTE 7. Model A-65-14 differs from A-65-8 only in that it incorporates special pistons, rocker arms and exhaust valves, seats and guides.".

So now I am wondering, since there appears to be a way to get 75 hp out of an A65 without having to jump through the hoops associated with converting to an A75, what kind of pistons, rocker arms, and exhaust valves are used to convert an A65 to a -14 with 75 HP?

[Edwin Otha]

Re: BC12-D A65 to A75 Conversion

Charles,
Looks like you figured it out. The SB I listed pretty much lets you convert any engine of the same model to a different modification level, or "dash number". Provided you use the correct parts for the change.
Make the correct log entry and let's go flying.
EO

[flybikefarm]

Re: BC12-D A65 to A75 Conversion

Go here check note 7.




http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/f67f14de69fae5c38525670e00450a67/$FILE/E-205.pdf

[Ragwing nut]

Re: BC12-D A65 to A75 Conversion

New information....

I missed a crucial piece of info. Apparently the fellow who did the engine overhaul installed the "75HP" mods to convert the engine to an A65-14, NOT an A75-8.

According to the Continental Type Cert:
"Model A-65-14 differs from A-65-8 only in that it incorporates special pistons, rocker arms and exhaust valves, seats and guides."

Unfortunately I can find nothing in the Continental Conversion SB about details for this conversion. Anybody know anything about it?

what is a -14? i know what a c90-14 is, but never heard of an a65-14.

[CStence]

Re: BC12-D A65 to A75 Conversion

New information....

I missed a crucial piece of info. Apparently the fellow who did the engine overhaul installed the "75HP" mods to convert the engine to an A65-14, NOT an A75-8.

According to the Continental Type Cert:
"Model A-65-14 differs from A-65-8 only in that it incorporates special pistons, rocker arms and exhaust valves, seats and guides."

Unfortunately I can find nothing in the Continental Conversion SB about details for this conversion. Anybody know anything about it?

[CStence]

Re: BC12-D A65 to A75 Conversion

I definitely see your point about slowing down with an A75. However, it isn't me who wants to do the upgrade, it is the owner. Keeping it an A65 would be much easier from a paperwork point of view....
I'm still waiting to hear back from the FAA.

[Edwin Otha]

Re: BC12-D A65 to A75 Conversion

I'm not so sure you want to put the A75 on. By the time you get a prop to spin up to rated RPM you don't have enough prop to pull the plane. And your fuel burn goes way up.
You can check out TCM Service Bulletin M75-6r1. It has some information on conversion of engines, not much, but some.
EO

[barnstmr]

Re: BC12-D A65 to A75 Conversion

I have done approvals or been involved in certifying various ways...

1. Engine with A65 data plate but rebuilt with A75 parts. Then stamp the data tag with "-C-A75" after the "A65" model number.
2. Airplane conversion removing an A65 and installing an A75 (or A65-C-A75). This can be done two different ways.... either with 75 hp rating or de-rated with 65 hp rating.

• The 75 hp rating for a Tcraft means that a different propeller is required as mentioned.... one that would allow the engine to turn faster RPM (statically and at takeoff). To certify this way, quite a few CAR 4 regulations come in to question by the FAA such as structural adequacy of the frame, engine cooling, etc. While the answers to these questions may be simple, some FAA inspectors don't see it this way. So its easier sometimes to certify with 65hp. Then there's not much in question because its the same. I used to do these approvals until about 2004, when the FAA changed the rules. Now STC is required almost exclusively across the FAA. You still might find some FAA inspectors who see this as straightforward and allow it to go through as a 337 with a DER approval or a 337 with "field approval".
• The 65hp (de-rating) means the engine is still an A75, but you use a prop that matches up to the A65 static and takeoff rpm. This would then limit the A75 engine to 65 horsepower by limiting the RPM (In other words - keep the original prop). This is the simplest way for some FAA inspectors to understand that it is OK to install an A75 in place of an A65. I have done several DER approvals this way in support of 337s. The FAA allows this without STC.

Whichever route you go, it needs to be clear to the pilot with the instrument markings properly matching the power rating as certified.

[Edwin Otha]

Re: BC12-D A65 to A75 Conversion

I guess a STC would be required for the A75 installation. But an A65 with some A75 internal parts should still be an A65. If the data plate was A65 or A65 CONV it would still be an A65.
EO

[Hank Jarrett]

Re: BC12-D A65 to A75 Conversion

I thought the jetting change was for the 85 HP engine, but I AM NOT an engine guy!
Hank

[flybikefarm]

Re: BC12-D A65 to A75 Conversion

From my hotrod years I learned an engine is like a big airpump. The three major ways to get more power are more cubic inches, super chager - turbo charger, or turn the engine faster. And yes I know there are other ways such as valve lift and valve timing, changing the flow of the cylinder heads, intake and exhaust work ect. ect. ect.. George

[CStence]

Re: BC12-D A65 to A75 Conversion

Since we're on the topic, I've found something else that many seem to be confused about - how to convert an A65 to an A75. I work on these little guys all the time and always assumed everyone used Continental SB M47-16 to convert. This service bulletin, put out by Continental, basically specifies waffle pistons and oil squirt holes in the rods. The only way you actually get the extra HP is by changing the prop - the engine changes are merely for cooling to handle the extra RPM and power. In several places on this forum I've seen folks talk about a "jet change" for the carb. No where in the Type Certificate or the Service Bulletin does it call for this - I even asked a carb shop about it and they said the A65 and A75 carb are identical. I've attached the Continental SB. Does anyone know if maybe there is an alternative approved method (STC etc) to get the extra 10 HP? Just curious.

[CStence]

Re: BC12-D A65 to A75 Conversion

Thanks for the replies folks. I should have what I need now to get a field approval from my FSDO. I'll be sure to post a copy of the 337, should it go thru, so others will have the paperwork readily available.

The only trick now is trying to come up with a suitable "case" for a static RPM range on the field approval, as opposed to a single prop. If the owner wants to repitch in the future, he would technically have to get another field approval. :grumpy: Fortunately, Palm Beach Prop has been a great help and provided some prop application info which should look "official" enough for the FAA.