Should I worry about aligning an automatic to the block beyond a snug fit on the alignment dowels?

I have an engine that may make a considerable amount of horsepower and torque, a TCI 4L80E, a TCI machined Flex Plate and a TCI torque converter. With manual transmissions you want to align your bellhousing to the crank but I have never seen an automatic transmission installation do so, just install it on the dowels and tighten the bolts, presumably the torque converter and flexplate can account for any slight misalignment.

Open to suggestions. Thanks.

 

The biggest issue with ANY automatic trans install is making sure there is a gap between the flexplate and the mounting pads on the converter, BEFORE tightening the trans-to-block mounting bolts. If there is no gap, this often indicates the converter was not fully installed into the trans. A typical good gap is 1/8" +/- 1/16". The pilot on the converter will seat into the rear of the crankshaft to properly align the converter and input shaft of the trans.

Correction: Jake writes 1/8" - 3/16". See below.

 

Also for proper alignment you'll need to use a pilot hub adapter if your converter has a pilot that is not long enough for an LS application. The pilot hub adapter may have even come with your TCI flex plate. If not:

https://www.summitracing.com/parts/i...SABEgJHt_D_BwE

 

Oh, I have the hub spacer, and I know we need to have that bit of clearance between the flexplate and torque converter when assembled.

I am mostly concerned about concentric alignment, but that doesn't sound like something to be concerned about.

 

That is what the dowel pins are for... The concentric alignment is the snug fit of the dowel pins. Some MFG's that rebuild them for shops to install paint the dowel pin holes. This way they can see if there is a missing dowel pin. A 1/16" droop to one side can ruin the alignment. The bell-housing bolts fit loose in their respective holes to allow for a slight variation in machining processes from dowel pin to bolt holes.

 

Not 1/8" plus or minus.

1/8 minimum, + 1/16". In some cases (4L80E) they work better with more clearance, so closer to 3/16" is preferred.

 

Thank you for the correction Jake. I corrected my earlier post.

 

As both MRVEDIT and JAKE stated converter spacing is the primary concern with autos. However I have noted since starting over in my own bussiness that I am seeing more what I call with my southern self wollered out dowel pin holes in bells of late than I remember in past in cores I have torn down Of late along with many with the dowels still stuck in the bells which makes me question what they used when they replace the trans I am now using as a core.
So I would certainly make observation of the dowel pin holes in the bells.

 

GM only used the first half of the dowel pin holes in the bell housing. Clean the dowel pin holes, and then check to see if you can feel a ledge with your little finger.
If there is a ledge, it will be at the top of the hole. You will notice the the rear half of the dowel pin hole is still virgin. Install longer dowel pins that will use the unused back half of the hole. This will get the alignment back to where it should be. Make sure the bell housing (where it contacts the block surface) is flat (no high spots).
Most of the ones I have seen elongated over the years (TH400, TH350, 700R4) were 4WD versions. The extra weight of a 4WD transfer case could add to this problem. Oscillation (high frequency vibrations) can cause this to happen.

 

I have an issue with the 6.0 LS dowel pins being larger than the dowel holes in the 4L80e.

Block dowel pins are supposed to be 0.621 inches and the transmission holes are about 0.610 inches.

This makes for an interference fit and very difficult to pull apart.

First time I have had a bellhousing that did not just slip on dowels against the block and pull off without much effort.

 

3rd or 4th gen LS? Iron block? Just curious.

 

3rd Gen, iron block 6.0............think 2001 aluminum heads.

 

Measured up a bunch of old dowels. 1.15 inches long and 0.621 inch diameter.

Tried one in the 4L80e dowel hole and go in nice and meet resistance after .5 inches one side and 0.6 inches other side.

So looks like a non issue. Just a matter of cleaning the case holes and cleaning up the dowels still in the block.

Red quite a few posts about how hard they can be to get apart though.