Accessory case and oil sump installation

[blueldr]

If the oil sump is bolted up tight first, it will be difficult to get the best seal between the accessory case and the oil sump. That particular parting surface is probably more prone to leakage since it is continuously flooded with oil rather than the upper sump/crankcase surface which is above the static oil level.

[cessna170bdriver]

When you refer to the "service manual" are you referring to the engine overhaul manual or the "Pre-1962" 100-series Cessna Service Manual? The engine overhaul manual details the procedure for installing the sump and accessory case. I don't recall exactly, and I don't have my manual with me, but per my memory of doing this almost 6 years ago, there is a particular order of torquing the accessory case to the crank case, the sump to the crank case, and the accessory case to the sump. That may or may not be the actual order (there are 6 possibilities) so consult the engine overhaul manual to be sure.

EDIT:

After posting I remembered the article I wrote on doing my overhaul. The following excerpt appears in the 3rd Quarter 2006 170 News, page 9:

Installation of Oil Sump and Crankcase Cover
The overhaul manual specifies a specific order in
torquing these two parts. This is necessary to make sure
both parts fit properly to the case and to each other,
making a tight joint at all three interfaces. The crankcase
cover gasket covers both the rear of the crankcase and
the rear of the oil sump. The sump gasket ends at the
rear of the crankcase. Both gaskets are prepared with
sealants, and both parts are put in place on the engine.
The cover is torqued to the crankcase first. Then the 14
nuts holding the sump to the bottom of the crankcase
are then tightened by hand only, just enough to snug the
sump to the case. The 5 screws holding the bottom of
crankcase cover to the sump are then tightened to ensure
that the sump is pulled snug to the cover. The sump-to-
case nuts are then tightened working from the front to
the rear (bottom to top in this picture). Before the rear set
of nuts are tightened, the 5 cover-to-sump screws are
loosened to make sure the rear of the sump tightens properly
to the rear of the crankcase. After all of the sump
nuts are properly torqued, the 5 screws are then retorqued.

[LBPilot82]

Does anyone happen to know if you can successfully replace just the accessory case gasket without having to remove the sump?

[cessna170bdriver]

Yes Richard you can; I've done it several times. I believe the purpose of the above procedure is to properly locate the sump in the right fore/aft position so that the aft face ends up in exactly the same plane as the aft face of the case. If you don't loosen the sump, that relative location doesn't chantge.