TF727, offset dowel pins...

TF727, offset dowel pins... - 11/27/12 05:33 PM

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

Posted By: John_Kunkel

Re: TF727, offset dowel pins... - 11/27/12 07:54 PM

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.

Posted By: Montclaire

Re: TF727, offset dowel pins... - 11/27/12 07:58 PM

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.

Posted By: Swedcharger67

Re: TF727, offset dowel pins... - 11/27/12 09:49 PM

Quote:

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...

Haha, good guess. The 1969 TF727 has been bolted to a 1971 383...and is now going to be bolted to a stroker based on a 1976 (if I remember correctly) 400-block...

Posted By: John_Kunkel

Re: TF727, offset dowel pins... - 11/28/12 12:04 AM

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.

Posted By: Swedcharger67

Re: TF727, offset dowel pins... - 11/28/12 11:03 AM

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!

Posted By: thehemikid

Re: TF727, offset dowel pins... - 11/29/12 08:34 AM

some neat dowels...

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

Posted By: Swedcharger67

Re: TF727, offset dowel pins... - 11/29/12 11:37 AM

Quote:

some neat dowels...

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

Yes, thanks, good info.
Here is a video that gives an idea about how to do it.
http://www.youtube.com/watch?v=3sTdTBq6-EI

Posted By: John_Kunkel

Re: TF727, offset dowel pins... - 11/29/12 07:38 PM

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.

Posted By: Swedcharger67

Re: TF727, offset dowel pins... - 11/29/12 08:03 PM

Quote:

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.

Not sure I understand you...I don't allow any misalignment..

Posted By: John_Kunkel

Re: TF727, offset dowel pins... - 11/30/12 12:35 AM

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

Posted By: Swedcharger67

Re: TF727, offset dowel pins... - 11/30/12 08:06 PM

Quote:

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

I will certainly do my best to, if possible, eliminate all misalignment. If I have done the best I can then that's ok with me.
With all internals and bearings/bushings new in engine and trans, and a "stiffer" flexplate to handle the significantly increased engine output, I think this issue has become important and I will do whatever it takes to get it right.

Posted By: John_Kunkel

Re: TF727, offset dowel pins... - 12/01/12 12:17 AM

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.

Posted By: Swedcharger67

Re: TF727, offset dowel pins... - 12/01/12 02:12 PM

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?

Posted By: John_Kunkel

Re: TF727, offset dowel pins... - 12/01/12 08:12 PM

#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.

Posted By: stumpy

Re: TF727, offset dowel pins... - 12/01/12 10:52 PM

Total waste of time and effort.

Posted By: fourgearsavoy

Re: TF727, offset dowel pins... - 12/02/12 12:37 AM

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

Gus