The Stovebolt Site Forums The Shop Area Engine Shop why did chevrolet have timing cover bolts on the inside

I just went thru the process of modifying my 261 chevrolet engine to have external timing cover bolts at the bottom.

The burning question I have, is why the heck would chevrolet design an engine to have the bottom two bolts on a 235 and 261 mount from the inside?
it seems crazy. But there has to be an original reason. Anybody have any guesses?

best regards

so you could adjust the bearing clearances without taking the whole engine apart. Or it was possibly to drive me insane. (or maybe I was already nuts)

They did it so guys like Jay Brown could ask that question.

Just kiddin' Jay. Now that would make sense. You
wouldn't have to pull the damper in order to adjust
the bearings.

Another reason that I believe they did it, was to
prevent oil leakage. The threads are easily sealed
with Permatex #2. When you drill the threads out for
bolt clearance it opens up the possibility of an oil
leak.
Never understood what the big deal was with installing the cover
the way it was intended, unless you forgot to install the cover
till after the pan was on. Once the timing cover is on there
shouldn't be any reason to remove it. And even if you did need
to access the timing gears that would indicate a problem severe
enough that dropping the pan would probably be in order also.

If the front seal was the target then the pan seals are most
likely leaking also and it wouldn't hurt to replace them also.
http://www.pbase.com/dennygraham/image/140809464
DG

so this was done because the engine had babbited bearings and these needed frequent adjustments?

what about after they switched to insert bearings? nor arguing just askin..

The later-model 216's had insert main bearings, but it was possible to fine-tune the clearance with shims. On the 235's and 261's it was just a holdover from the previous manufacturing procedures, since millions of similar engines had been made that way.
Jerry

i read that the later model engines with insert bearings also came with 2 .001 and 2 .002 shims.
i have no way to validate that statement.

thanks all for the history lesson. It makes a lot more sense to me now.

235's went from a shim-adjusted main bearing to a precision-clearance type somewhere in the mid-1950's. They also changed the anti-rotation system from a dowel pin in the back of the upper bearing to a tab at the parting line when they eliminated the shim adjustments. My Federal-Mogul master bearing catalog breaks down the exact change dates, but if your engine has anti-rotate tabs at the block/cap parting line it doesn't use shims.
Jerry

The 1960 Chevrolet Truck Shop Manual mentions the possible use of shims only when a main bearing cap is replaced.

I'd bet the last common use of shims with main bearing was in 1955-1st series (their use is described in the 1954 Truck Shop Manual - high pressure 235/261).