The International Cessna^® 170 Association

spiro wrote:

gahorn wrote:exactly what do you mean by insisting upon the use of a threadlocker on a non-threaded stud?

that's pretty silly. Where'd I give you that impression?

spiro wrote:huh? By definition a thru-stud doesn't have any threads in the case.

gahorn wrote:digging RTV out of a blind hole such as you mention has what to do with this discussion?

was my description that bad <g>? It's a through hole but the stud's already installed, "blinding" the hole. You're sealing the bottom of a blind threaded hole. - paul[/quote]

Well, if ever there was an example of bad terminology and bad form...THIS thread has to be one!

No fighting on MY topic!
I am pretty sure I fixed the problem today. If there is no more fighting for a week, I'll tell you what it was and how I fixed it. (And I'll put a few more hours on the airplane to be sure.)

I'm experiencing what seems to be the same problem. What was the fix?

I have about 7 hours now since the fix, and it is dry as a bone.
THe oil pump shaft is a bit too long. The shaft then keeps the generator from seating firmly against the case. The extra length is only enough to feel with a fingernail. Put a straight edge on it, and you can see some daylight between the edge and the case. The gasket shows a circular ring where the shaft has been spinning against it.
The fix was to use two gaskets. I cut out the first gasket to give room for the shaft. be careful to keep the cut area within the footprint of the generator. The thickness of the first gasket is plenty to accommodate the oil pump shaft. The second gasket goes on normally.
I suppost this is a temporary fix. I suppose that a proper fix might be to remove the accessory case, and grind down the end of the shaft.
Somewhere in its life, the accessory case has been overhauled, and the bushings put in for the oil pump gears. Maybe it has become too thin, or maybe the oil pump gear shaft is a bit too long.
A corrolary to Murphy's Law states: "All tolerances will accumulate unidirectionally leading to maximum difficulty of assembly."

N73087 wrote: Somewhere in its life, the accessory case has been overhauled, and the bushings put in for the oil pump gears. Maybe it has become too thin, or maybe the oil pump gear shaft is a bit too long.

Interesting; I did not realize that there was a fix to install bushings for the oil pump gears. It sounds like you've got a few thousands of wear on the inside face of the case where the gear runs, allowing the shaft to protrude slightly. I haven't been able to find my engine overhaul or parts books since my last move, so I can't say what the wear limit might be.

Also the extra gasket between the generator and the case changes the amount engagement of the generator gear with the camshaft gear. I'm not sure whether this is a problem, but worth thinking about.

Miles

Miles, a bit off topic, but I'm curious about your avatar. What's the significence of the route marked out on the US map?

Eric

zero.one.victor wrote:Miles, a bit off topic, but I'm curious about your avatar. What's the significence of the route marked out on the US map?

Eric

The left end is where I am. The right end is where I'll be on the morning of July 10. The points in between are fuel and friends.

Miles

And how did you create the map? What software?

N73087 wrote:And how did you create the map? What software?

Go to http://www.airnav.com, click on "Plan a flight with fuel stops" then fill in the blanks. It will either find a list of the shortest routes, or the cheapest routes based on reported fuel price. Select one from the list provided. The site will then give distances and bearings for all the legs, as well as the route map similar to the one in my avatar. Once you are on this page, you can generate any route you want by substituting the airport identifiers of your choice into the address at the top of the page. Be careful with the final results, as airnav DOES NOT take into account terrain or any special use airspace along the way.

My avatar is from the map generated by:

http://www.airnav.com/cgi-bin/fuelroute ... IS-2E8-ONZ.

I get this show on the road about 6am tomorrow. I don't yet have the technology to take the internet with me , so I'll be offline for a couple of weeks. Some of you I'll be seeing soon; for the rest, we'll let you know how it went when we return.

Miles

Thanks for the information about your fix. I’ve been chasing the same type leak and have tried all the same corrective actions you did all prior to reading this string. I’ll look into the shaft issue and post results.

N73087 wrote:I have about 7 hours now since the fix, and it is dry as a bone.
THe oil pump shaft is a bit too long. The shaft then keeps the generator from seating firmly against the case. The extra length is only enough to feel with a fingernail. Put a straight edge on it, and you can see some daylight between the edge and the case. The gasket shows a circular ring where the shaft has been spinning against it.
The fix was to use two gaskets. I cut out the first gasket to give room for the shaft. be careful to keep the cut area within the footprint of the generator. The thickness of the first gasket is plenty to accommodate the oil pump shaft. The second gasket goes on normally.
I suppost this is a temporary fix. I suppose that a proper fix might be to remove the accessory case, and grind down the end of the shaft.
Somewhere in its life, the accessory case has been overhauled, and the bushings put in for the oil pump gears. Maybe it has become too thin, or maybe the oil pump gear shaft is a bit too long.
A corrolary to Murphy's Law states: "All tolerances will accumulate unidirectionally leading to maximum difficulty of assembly."

I wonder if your case or accy case has been milled/re-faced to "true" the surface and perhaps was taken down too far. This has been done occasionally by unknowledgeable automotive shops and caused loss of the case.

I am experiencing the same problems with a leak. I am in the process of pulling the Gen on my 52 B. I have quite a bad leak and was sure it was coming from the Gen seal but now I'm not sure.
I couldn't get the gen to come loose today. Is there a trick to it? This gen was overhauled in 03 when the engine was done. The leak has gotten consistently worse. Yesterday i blew the 30 amp fuse which has temporarliy grounded me but I don't think they are related .

While you have the gen off, be sure to replace the tach seal, and the gen seal. Also replace the gen drive rubbers to start the 500 hour clock on the AD.
By changing two seals and the gasket, you will stay awake at night wondering which one fixed the problem.

N73087 wrote:While you have the gen off, be sure to replace the tach seal, and the gen seal. Also replace the gen drive rubbers to start the 500 hour clock on the AD.
By changing two seals and the gasket, you will stay awake at night wondering which one fixed the problem.

Which AD were you speaking of?

01 January 1949 49-50-01


Subject: TCM ENGINE - GENERATOR DRIVE COULPLING RUBBER DISC


CONTINENTAL: Applies to All Continental C-75, C-85, C-90, C-125 and
C-145 Engines Equipped With Generators, Except Those Engines Listed
Below. (A-65 Series Engines Are No Longer Subjected to Compliance
With This Note.)

To be accomplished prior to May 2, 1949, and upon each 100 hours of
operation after inspection has been accomplished, or at major
overhaul, as indicated.

To preclude possible engine failure as a result of disintegration of
the generator drive coupling rubber disc, inspect and/or replace the
disc as follows:

I. Old Type - Without Metal Retainer Cup.
(1) Inspect rubber disc, P/N 22348 prior to May 2, 1949, and at
100-hour intervals after this inspection, and replace if
deterioration or cracks are noted. Special attention should
be given corners of slot to detect beginning of cracks or
tears.
(2) Above periodic inspection may be discontinued by installing
the improved type of coupling incorporating metal retainer
cup P/N 352030.

II. Improved Type - With Metal Retainer Cup.
(1) Rubber disc P/N 25120 must be replaced at major overhaul.
NOTE: Engines with the following serial numbers are excluded from
the inspection requirements of this directive. However, if
rubber disc P/N 25120 is incorporated, it must be replaced at
major overhaul.
C-75: Serial No. 5257-7-12 and all higher numbers.
C-85: Serial No. 30568-8-12 and all higher numbers.
C-90: Serial No. 41132-8-12 and all higher numbers and
including Nos. 41122 and 41124 through 41127.
C-125: Serial No. 8108-8-2 and all higher numbers.
C-145: Serial No. 3470-8-2 and all higher numbers.
All "C" model engines reworked at Continental Motors Corp.
since September 1, 1948.
(Description of generator drive couplings is contained in
Continental Motors Corp. Service Bulletin Number M49-4.)

This supersedes AD 49-47-1.