C-85/O-200 Questions

[mike newall]

Nathan,

I wouldn't fly a 74" metal prop on the C-85.

When I did the change from A-65 to C-85 on my Champ, I wanted to use the same prop. The regulator in the UK ( PFA ) wouldn't allow it. I then visited Sun n Fun and spent 30 minutes on the McCauley stand explaining my problem.

He confirmed that the 74 is not suitable for the C-85 and it all has to do with vibration, harmonics and metal fatigue. Their prop/engine charts do not show this combination. He was really diligent, went on company CD's he had with him etc etc.

Chop the prop, it won't cost much and it is infinitely cheaper than throwing a blade in a couple hundred hours time.

[Nathan K. Hammond]

I need to talk to McCauly and get the full story. I had been told about the harmonics and vibration, the whole story but I wonder how much is honestly true.

This is an excert from the Type Certificate:

Propeller and Propeller Accessories
2. McCauley 1A90 with following limits:
...................
(c) (7DC only)
Static r.p.m. at maximum permissible throttle setting:
Not over 2465, not under 2300. No additional tolerance permitted.
Diameter: not over 71 in., not under 69.5 in.

(d) (S7DC only)
Static r.p.m. at maximum permissible throttle setting:
Not over 2440, not under 2290. No additional tolerance permitted.
Diameter: not over 74 in., not under 69.5 in.


So technically you can run the longer prop, but only if your on floats.

nkh

[Ron Babos]

Nathan: A quick look at the load charts on the 65-85 shows at 2300 rpm the 85 is putting out 4-5 hp less than the 65. You raise the point about the cam grind being different. Not having one to compare with, I would guess the duration and overlaps are longer in the 85 cam. The prop used on the 65 may not allow the 85 to rev up to the point where the cam will allow the engine to breathe in the higher rpms where it's designed to run. Once over the hump, all hell should break loose. Well not quite , but if you have ever monkeyed around will car engines and changed cams you may have noticed that at lower rpms the engine couldn't peel the skin off a banana ,and as the rpms come up it pins you in the seat. Same thing happening here with the two engines. The 85 may be better for racing, but the 65 will pull a plough better
Ron

[Guest]

run it as a c90 works great

[zero.one.victor]

Someone posted this link on the T Craft discussion forum. It's from the flybaby wevsite and has some good stuff about the small Continentals.

www.bowersflybaby.com/tech/fenton.htm

Eric

[zero.one.victor]

I was thinking about hodrod 4-bangers, here's an idea: C-85-8, with O-200 (stroker) crank, PLUS pistons and rods from an IO-240 in bored out cylinders (??) or using IO-240 cyl's modified for carberation instead of injection. The IO-240 puts out 125 horses, carberated it oughta be good for 120 or so. Should make for a nice light engine with the -8 case and no electrics. I don't have any idea which cam and prop would be best.
I don't know if this is even physically do-able-- I'm sure it isn't legal, except on an experimental. But it sure is fun to daydream!

Eric

[zero.one.victor]

Today a guy I know was telling me about his buddy who OH'd a C-85 and did the stroker crank mod. He said the guy "had" to put a C90 cam in it. Does the STC from Don's or from Aircraft Specialties allow and/or require a different cam, or is the C85 cam used? I've heard that the C90 cam is "the best one", but someone posted somewhere that the current part numbers for the C90 cam & the O200 cam are the same.
To further confuse the issue, the Fresno Airparts ad in the front of T-A-P lists 4 different cam p/n's in the C90/O200 section: 531076,530788,626608,& 643067. P/n 530788 is tagged "C90-12", and is the cheapest by a hundred bucks at $395. 531076 is tagged "24 degree overlap".
Also, in case someone's interested, there's an ad in the latest GA News for a disassembled C90-8F,inspected and ready to build, including Slicks & a Stromberg. Price is listed as $59,095-- I'm guessing that's a typo! If you're interested, contact Dave in Portland OR 503-284-4646

Eric

[Nathan K. Hammond]

"He said the guy "had" to put a C90 cam in it."

Don's STC makes no mention of cams in any manner, so that makes me think he "had" to put a 90 cam in to get best power (90's have more overlap). I'll see if I can scan the data pages of DDM's STC and post them.

There are several different cams made for different applications, hence the different p/n's. example:

530788 - steel (C90 - carburetor only - side fuel pump or none - replaced by 531076)
530977 - steel (C90 - carburetor or injector – replaced by 531146)
531076 - steel (C90 - carburetor only - replaces 530788)
531146 - steel (C90 - carburetor or injector – replaces 530977)

But the plot thickens, if you run a Steel C90 cam, then you have to use Cast Iron Lifter bodies from a C90, not Steel faced C85 lifters. So everything in these damn little engines are related, if you change one part, you have to change 4 more.

As for the 24° cam:

Beginning with C90-8F, 8FJ, and 12FJ engine s/n 42205-9-12, and all C90-12F, the cam contour was changed to reduce valve overlap to 24°. The new camshaft number is 531076 for carburetor engines and 531146 for fuel injection engines. (#531146 may also be used in carburetor engines, but #531076 MAY NOT BE USED in fuel injection engines).

The biggest problem with these little engines is lack of knowledge. So many times I ask myself 'why the hell did they do that?' I guess the trick is to weed out the cow terds, I know I've left my share!

nkh

[Paul Agaliotis]

I would think you are going to find the camshaft specifications are the same. I have not charted any of these cams so I,m not certain of this. As Nathan pointed out there many applications for this cam so different part numbers would be needed.
Camhaft overlap, in a nut shell, moves the power to RPM ratio. Increase of overlap moves the power to a higher RPM. decrease the overlap to move the power to a lower RPM. I dont know if Continental increased or decreased the overlap to 24 degrees. But it doesnt matter as none of this can be changed without making a new cam. Sorry about all of the Mumbo-Jumbo.
Paul

[zero.one.victor]

I think I disagree about the cam specs all being the same and the different part numbers are just required due to different applications. I think if they were all the same cam, then Continental woulda just used the same number in whatever different parts lists and IPC's that profile cam was in. I think they're numbered different because they are different- whether it's the lift, the duration, the timing, the material, or whatever.
It woulda cost more to make 20 cams each stamped with 5 different p/n's, than 100 stamped the same- so I'm sure the bean-counters woulda done just that, it basic business sense.
Now, what we need is a table of cam specs (lift,duration,timing) for the various 4-cylinder cams to prove me wrong!

Eric

[Nathan K. Hammond]

Cam Timing in degrees
C-85 8-57-49-16 = intake duration 65’, exhaust duration 65’, with 24’ overlap
C-90 9-56-50-15 = intake duration 65’, exhaust duration 65’, with 24’ overlap
O-200 21-58-65-14 = intake duration 79’, exhaust duration 79’, with 35’ overlap

First Number Intake opens b.t.c.
Second Number Intake closes a.b.c.
Third Number Exhaust opens b.b.c.
Fourth Number Exhaust closes a.t.c.

The O-200 cam is the earlier model with 35’ overlap and not 24’. So there is a definite difference in the 2 O-200 cams, judging by overlap. I have tried to find the 24’ numbers but no luck yet, I may have to call a cam shop for the specs.

NOTE: These numbers were taken from the latest O/H manual dated 1984, but I am suspicious of the O-200 numbers. They indicate an early model 35' degree overlap, which was supposed to be scrapped for a 24' degree later model. The most likely scenario would be the O-200 numbers are the early model C-90/O-200 cams with 35'

Here's the diagram for the C85 cam.


nkh

[zero.one.victor]

Interesting that the C-85 and C-90 cam numbers are so close--within 1 degree. So I would say that a stroked 85 engine with the stock C-85 is pretty much eqivalent to a 90. Now I'm really curious what the numbers are for the 24 degree overlap O-200 cam.
Of course, there are other issues in picking out a suitable cam- for example,like Nathan pointed out, steel versus cast iron lifters.
Good job coming up with the scam specs, Nathan. Where did you dig those up?

Eric

[Nathan K. Hammond]

One other thing I forgot to mention;

Valve lift on the C75/C85 is .382
while the C90 and O-200 is .410

So the C90 cam is like the best of all worlds, you get the performance curve of the C85 with the taller lift of an O-200.

Eric, I went out and dissasembled my engine, pulled out the cam and measured the angles by hand. Or maybe I saw them in the Overhaul manual. The diagram was 10 minutes farting around with MS Paint.

nkh

[MikeB]

Nathan: What did you use for engine mount rubbers for your new engine installation? It seems I haven't been able to resolve the issue with Wag Aero yet (poor service life and cracking). The guy at Wag seemed to be trying to do something, but believe he also ran into a brick wall with their suppliers.

I guess I can try to follow up and see if any progress has been made. He did suggest trying the Continental mounts if I remember correctly, but it's too cold to work up here anyway. So it's easy to put it off. Actually, not enough snow for skis and too much for wheels .

Mike

[Nathan K. Hammond]

I used some from AC Spruce, which is most likely a Superiour product. We've used them in the past, and they last about a year, then begin to crack around the edges. So time will tell. Ironically the old rubbers I took off looked really good. One thing I did noticed is the new rubbers tried to bind when I installed them. It almost seemed like they went too deep into the case ... if that makes sence.

nkh