Bell housing runout

[Kern Dog]

The topic of bell housing runout has gained a lot of attention the last few years with the rise in popularity of the aftermarket overdrive manual transmission kits.
Years ago, I never heard of it, never heard of anyone even talking of it. I'd hear guys talk of clutch chatter, the transmission popping out of gear, hard shifting, noise and stuff but did not ever hear that any of those issues being blamed on the runout.
For those that haven't heard, I'm referring to the relationship between the centerline of the crankshaft and the centerline of the transmission input shaft. When our engines and manual transmissions were first mated together, the story is that the factory put the bell on the engine and line bored the bell housing to the centerline of the crank. Any mis-alignment that may have existed was now corrected and would be eliminated....until you tried using a different bell housing.
I don't have a lot of experience with Mopar manual transmissions but the ones I've had didn't have any problems despite parts swapping without any regard for runout.
Now though, the companies offering these Tremec and other kits require proof of the measured runout to validate the warranty.
How close do you have to be?
Can you believe no more than .005" off center total.
Whuuut?
I'm a Carpenter.... All my life I dealt with framing houses and schools where if we were within 1/8 of an inch, we were good. (Kidding)
.005 now?? A human hair is wider than that, isn't it?
I know a guy that didn't measure his runout at all and his Tremec was fine. He beat on that car then sold it because he wanted to build a house and move out of the teepee he was in.

Yeah.....a teepee.



Back on point:
What is it about these new transmissions that the vendors require such precise alignment?
.005 is the limit for the SST kit. If you're at .006 they won't honor the warranty??

I did the dial indicator measuring of the runout twice in my car.... The first time WAS my first time ever. The second time was after I pulled and rebuilt the engine. It was a LOT easier with the engine out of the car.
Now I'm helping a FBBO member with his car and the initial number we got is over .080. That is.040 off center, more than a standard spark plug gap.
Correcting that could be difficult.
There are companies that make offset dowels to shift the bell housing around to align the bell to the crank but the available sizes are limited. Nobody makes a .040 dowel from what I've seen. SST suggests scraping any and all paint and crud from the mating surfaces of the engine block and bell. I'd be surprised to learn that it helps but it is a fast and no cost effort to try.
In the meantime....I'd be interested in opinions and comments on those that have dealt with unanswered transmission issues that may have been related to a misalignment.
Finally... how is it that automatics don't have this issue?
Maybe they do.
It could explain cracked flex plates or leaky input seals?

[Kern Dog]

My 440 block only needed .014 offset dowels to bring the bell into range.
The car I'm helping with now is over .040 off center. I wonder what the chances are of the bell itself being to blame. I wish I had another bell nearby to check. I'm going to put the word out to some local friends. I'd like to borrow one to do a test fit and measure.

[Kern Dog]

The vendor requires documentation of measuring the runout to no more than .005 or less to warranty the transmission. When you spend $7000 on one of these kits, you're inclined to do what it takes to get it right.
I have one friend that set aside a bellhousing for me to use. I wouldn't mind another though. If the other bells also have excessive runout in the same direction, it seems that would indicate an indexing issue with the crank not being centered or the mounting surface of the block being drilled out of spec.
Sometimes weird stuff happens and you have to find a way around it.
To the topic of automatic transmissions...
I noticed during my 5 speed swap when I pulled the flex plate off of my 440/493, it had 2 cracked ears.
I had a buddy that cracked the hubs on 2 different flexplates within a couple of months on a 64 Valiant with a mild 360.


What about you? Have you accidently found broken parts like this and didn't know what caused it?
What if all along it was excessive runout?

[Kern Dog]

Kern Dog said:
The topic of bell housing runout has gained a lot of attention the last few years with the rise in popularity of the aftermarket overdrive manual transmission kits.
What is it about these new transmissions that the vendors require such precise alignment?
.005 is the limit for the SST kit. If you're at .006 they won't honor the warranty??

Here is a screen shot of a YouTube video showing the tapered roller bearing used on the input shaft of the Tremec transmissions.



That explains why the runout has to be so small...The bearing can't tolerate much misalignment.

[Kern Dog]

The excessive runout of the SST aluminum bell had the owner of the Coronet disappointed.
We didn't know if the bell was drilled wrong or if his crank and block were out of spec. I was able to find 3 bell housings locally to do some additional trial fitting.
I also pulled a 1969 440 from my stash to do use as a test mule. I used my own dial indicator on this series of tests.
First was a bell from a truck, then a car. The truck bell was off by .020 or more, I don't recall exactly how much but it needed to move up and to the right to be centered.
The car bell was almost perfect. It fit within .004 and was one that would work without any offset dowels at all.
Next up was the SST aluminum bell. It was off by .0445 and needed to be shifted up and to the right to be spot on.
Now it was time to fit the SST bell back in the Coronet 440.
Using Rich's dial indicator, he came up with the exact same number.... .0445 with the runout being up and to the right. The .0445 is the TOTAL runout which means that you divide the number in half to get the number that you need to move to be centered. Tha number is .02225.
Today he bought a pair of .021 offset dowels.
The maximum tolerance is .005 off center for a total runout of .010.
The .021 dowels will allow us to get right inside the limit.