Hi all,
I'm doing a complete overhaul of both engine and the 727. The 727 is totally worn out in all bushings and the thrust washer between input and output shafts is in a really bad condition.
I see that offset dowel pins, for accurately lining up the engine with the auto, are available from several wellknown sources.
How can I predict what offset I need, and can I measure it somehow??
Cheers,
Martin

The only way to know for sure is to bolt the actual (empty) case that you're going to use to the block and dial it like you would a standard bellhousing using the pump housing bore.

Case alignment would affect some of the bushings but if all the bushings are bad I wouldn't suspect case alignment....probably lack of lube.

It has to be done with an empty case and a dial indicator. I think it is worth doing if you have noticed odd wear or if you are using like a 66 trans with a 76 block. I have a set of three pairs of dowels that I do not need and would sell at a reasonable price, along with a copy of an article on how to measure. PM me if you are interested.

The year of the case is irrelevant, all 727 cases are (supposed to be) machined to the same center relative to the dowels.

Gross misalignment is due to accumulated tolerances, i.e. dowel holes to the extreme tolerance in one direction and the the crank bore to the extreme tolerance in the opposite direction. Doesn't happen that often and usually results in cracked flex plates.

Yes, I don't expect a big problem here.
But I'm spending a lot of money on both engine and trans, it would be a pity not to make sure that they mate together perfectly. A perfect aligment will probably be good for longevity, smooth running, and it would make me feel good!

some neat dowels...

http://www.robbmcperformance.com/products/dowels.html

If you intend to dial in an auto trans case the question becomes what do you use for a tolerance for runout. Auto trans will forgive more misalignment than a standard trans due to the auto trans' flexplate.

So if it's .002" out you're gonna correct it?

So, your goal is zero misalignment?

Let's take a practical look at that; suppose you dial the case dead nuts center but the center hole in the pump housing is off center to the right the maximum allowable tolerance and the input shaft support is off center the maximum allowable tolerance also to the right. Then suppose your case was offset to the right but you corrected it to center....what you have done is taken a set of tolerances that resulted in perfection and made them imperfect.

My point? Mass production doesn't make for perfect parts, they have a deviation tolerance and those tolerances can work for you or against you. Bottom line, leave it alone...you're overthinking it.

I see it this way:
Everything has manufacturing tolerance + or -.
In this case we have:
1. the position of the crank in the block
2. the position of the dowel pins in the block
3. the position of the dowel pins in the bellhousing
4. the position of the pump bore in the bellhousing
5. the position of the center in the pump housing.

If I line up the crank with the bellhousing pump bore, with little or no misaligment, I have cancelled out all the manufacturing tolerances 1-4, no matter what they are.
What I have left is number 5, the position of the center in the pump housing.
Since I guess the outer perimeter of the pump housing is getting finished in a lathe with the center hole as the reference, and I must assume this is pretty accurate and centered.

I cannot see any other conclusion than that the alignment efforts are well worth doing?

#5 assumption is iffy and you forgot #6 the center of the reaction shaft support.

Worth doing? An exercise in futility IMHO but have at it.

Total waste of time and effort.

I always looked at it this way,if the converter moves easily with tranny bolted in place then it's probably aligned OK
Gus