I was checking the runout on my bellhousing today, in preperation for the Tremec. I started at "0" at the top. I had ".024" for the bottom reading. My question is...do I take the reading of .024 and divide by 2 to get .012 offset dowel pins?
On a side note, I got a reading of "0" at the 11 O'clock position, and a reading of ".026" (my highest reading) at the 5 O'clock position. Will I actually need a .013 and offset them a little off of the 12 O'clock position?

Here's a pic of the reading....




My mounting surface is also way off. I have "0" at the top and ".030" at the bottom, so I guess I'll have to have this surfaced as well. And yes I made sure the mating surfaces of the block and bellhousing were clean and free of paint and burrs.

Pics of the surface check

 

Don't have an answer but thanks for the pictures. I always wondered how this was done. Now it makes sense.
Brian

 

On a positve note, at least the car had an 11" Centerforce clutch

 

The runout of .024 is way.....way to much for a stock bellhousing. Something else must be wrong! Take the bellhousing back off and make sure that you don't have a large burr, dirt or grunt mark that would give you the .030 parallel runout. Carefully check the dowel pin holes for a fine crack to the outside. Also check the inside dowel holes diameter to see if someone has been in there with a large file. Put it back on and with loose bolts see if you can move it with a jack and get a large dial indicator movement. Up and down the bellhousing is .012 low + it has to head toward the 10 o'clock range. If it is really that bad you need the .014 offset dowels (use Moresco not Lakewood). You better also check the bore in that bellhousing as it appears to be junk!
John

 

I checked mine for burrs etc. as well, but when I slid it on it would rock just a little. So I ran a .0015" feeler guage around the entire mating surface while it was bolted up.

When I took it back off I found some small dents and chips that I could swear were not there when I cleaned it all up.

I played with it until it would lay flat with out rocking, then did my checks as you did. I got .002" on the bell centering, and .0015" on the parallel measurement.

 

Thanks guys, I'll double check again.
It fit tight on the dowels. I had to tap it on with my hand. I even removed it, and reinstalled it and got the same measurement.
I'll check the bore too. What is the bore supposed to be?

 

65vette, I am doing a Tremec into my 57 Chevy, same drive train as a 57 Corvette. (More or less!) My bone stock AACA Senior National winner, all matching numbers, history known since new, has a bellhousing misalignment of .024 TIR exactly like yours! Don't let people tell you this is uncommon. On these cars up to .040 or more TIR has been seen!
Use your finger on the indicator needle to visualize if the .026 reading is going in the plus or minus direction. That way you will know if the bellhousing is too high up, or too low down. Once you know that, then proceed. I am assuming that your reading says the bell housing is too high up.
I am using the lakewood Adjustable offset dowel set, the .014 size. I have them in the block now, they are easy to install because of the adjustable feature. Pricey at $50 a set or so, but worth it! You don't have to drive them out to re-adjust like the Moroso's. I also have a set of Moroso's to compare, and they are nice, but on my car driving the dowels in and out is not that easy!
In your situation you need to move your bellhousing almost straight down .012. So get the .014 dowels (which are the closest match) and install them so the "high point" of the dowels is positioned at 6 O'clock. But..... since your misalignment is a little offset to the drivers side, put your "high point" at 5 O'clock, to make up for that. Basically you put your dowel's "high offset point" right at your highest indicator reading. Then bolt the bell houing up tight and recheck. If necessary, rotate the adjustable dowels in the appropriate direction.
Hope this helps on the concentricity situation. But on your parallelism situation, you will have to have your bellhouing machined at a shop to correct that. Like others have said, run a small flat file over both surfaces, use your hands like a surgeon's to feel small bumps and remove them. Good luck!

 

Is the indicator tip moving outward or inward (+ or -)as you sweep through the 6 o'clock position?

 

Ok....I tore everything back off. This time I removed the flywheel as well. I removed some paint from the flywheel mating surfaces off the crank and flywheel itself. I took a flat file to both block, and bellhousing mating surfaces, as well as removed a little paint from the alignment pins themselves.

My new measurement are shown in the pic (the circled numbers) Much better now. Only .013 at it's worst point, and still in the same 10/11ish and 4 5ish o'clock positions. My trans mating surface is also much improved...only .007 total runout.
Guess I'll get a .006 offset dowel and call it good.

John...It's moving to the + position at 6 o'clock, indicating the bottom is high.

Thanks for all the help everyone.

 

good thread

 

What happened to the days when you just bolted the bell up, slung the tranny in palce and everything worked out fine? I don't recall ever hearing about alignment and runout problems,and I doubt GM took the time to dial indicate and recitify every engine/tranny assembly off the production line.

Look at the slop in the input shaft of any transmission, they wobble all over the place, and can certainly handle .020" or better off axis/off center alignment betwixt crank and tranny case. Hell, check the way your bronze pilot bushing is hogged out on a motor taha has a few miles on it, and you will often find ten thou or more slop there.

Doug

 

with the older transmissions, but I think these new Tremecs, have a tighter tolerance to them. I'm sure with modern computerized machining the newer stuff has much tighter tolerances than we "old school" guys are used too.