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From: William R. Bayne [mailto:[EMAIL PROTECTED]
Sent: Thursday, June 09, 2005 3:41 PM
To: Ed Burkhead
Subject: WRB Re: [COUPERS-TECH] C-85 overheating
RLYTECH
Hi Jack,
Looks like "tis the season" for such problems. One "rule of thumb" is for "normal" temperature
in cruise to be ambient (per the OSA gauge) plus 100ºF.
Recent discussions on this subject have not mentioned one rather specific method of locating
bad baffle sealing, so I'll toss it (back) out. After dark, take a good flashligh (or better yet, a 120V
mechanic's "trouble, or shop light), place same in the cowling (alternately on each side of the
engine compartment down low, button things up and look for gaps. Anything over 1/8" requires attention.
Then open each side and peer down through the cylinders to verify the tightness of the seal around
the fins. Raise the light into the back area behind the starter and generator and peer backwards to verify
the tightness of the seal with the upper cowl. Gaps and holes are easily found this way that most owners
will not catch otherwise.
Gaps are common in the left front baffle in the area between the engine and said baffle, or around fuel
line baffle penetrations (which should be grommeted). Check for the presence of the tiny baffles on Fig. 17,
p. 22 of the Parts Manual, numbers 47 and 44. Don't worry if the gap exceeds 1/8" between the starter
and baffle no. 36. Excess air here helps cool the starter and the mags.
Our pistons have separate oil control rings and compression rings. With one or more broken oil control
rings but good compression you would have excessive oil consumption but no blowby problem.
With compression ring problems you get the crankcase pressurization which results in blowby. It is
normal for any cylinder to have poor compression on occasion. Rings are designed to rotate during service.
There are times when ring gaps become sufficiently in line as to adversely affect a compression reading.
This is why an occasional "bad" reading is not considered cause for concern unless it persists.
Most often rings wear more or less evenly in a given cylinder. If some clot installs new rings without fully
removing prior ring (wear) ridging, one or more broken rings will result when first run. The higher oil
temperature and consumption common during "break-in" will obscure any immediate symptoms.
I would strongly suggest after removal you send any suspect cylinder(s) to a cylinder shop for inspection
and repair. This is specialized work that requires equipment most A&Ps and IAs do not have. Grinding
and honing an air cooled engine cylinder is much more critical than fixing a liquid cooled auto engine.
There is no approved "carburetor with the automatic lean". Both the Stromberg (which you
probably have) and the Marvel have their mixture control manually operated by the pilot.
Both automatically enrich mixture at maximum throttle for extra (fuel) cooling in climb.
The Stromberg has an idle mixture circuit which is ground-adjustable. In-flight mixture is
controlled by the installed jet, and the jet choice is dictated by what is approved for the
carburetor fitted to your engine.
The Ercoupe had an automatic enrichment linkage on the Stromberg. This was activated
when the pilot reduced power, presumably for landing. This system is present and
operational on relatively few coupes today.
Some uninformed owners fly Ercoupes with their mixture control wired rich. Do not accept
without question any advice from these good people. I have yet to see FAA approval for such
disabling of any powerplant control on an engine when it was type certificated (so beware).
Regards,
William R. Bayne
<____|-(o)-|____>
(Copyright 2004)
--
On Jun 9, 2005, at 8:39 AM, Jack Catrett wrote:
Dear Coupers
I have had trouble with oil temperatures
in my 85hp coupe. The oil temp problems are more pronounced
in the Georgia summer time and when the coupe is loaded. The Coupe has
great oil pressure (30-35ibs hot and at idle); good oil analysis returns, an
oil filter that should help cooling and new baffles. The cylinders have
been replaced one at the time by the previous owner over about 100 hours
stretch of time before I bought the coupe. The replaced cylinders were a
mixture of new and serviceable.
I may have a blow by problem. I use
about a quart of oil for ever 3 to hours flown. I also had a cylinder
that was down on compression at the annual (ten hours or so ago). My
A&P and I soaked the cylinder with Marvel Mystery Oil (MMO) for two days by
pouring the MMO down the open top sparkplug hole. Two days later the cylinder
had great compression.
My questions for the tech line are:
1. How do you check to see if blow by is the problem?
2. Can I (My A&P and I) remove the cylinders, hone them out and replace the piston rings? Would
this help or do I have to send the cylinders to some shop to be checked? This seems like a simple task.
Piston rings are cheap. The cylinders have good compression ..
3. My coupe has the carburetor with the automatic lean. Is there a way to enrich the mixture?
4. (?) Any advice you have would be appreciated.
My A&P tells me to just fly the thing and not worry; however, the warm temps still concern me.
Warm in Georgia, Jack Catrett 99476
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