First off, I'm particularly asking this of anyone with a Tremec ( or T-5 ?) trans and a Bentsen bellhousing combo, but all opinions welcome. I'm assembling my driveline for hopefully the last time and I'm faced with a procedure I've never done before, I know its "the right thing to do" ..... just wondering how many have done this and found enough runout that required correction. What I'm blabbing about is setting up a dial indicator and magnetic base on the flywheel, rotating the crank and measuring the runout of the hole in the bellhousing that the trans mounts into. Most sources say .005" is max allowable, afterwhich offset dowel pins are needed to correct. My indicator is too big to set up in the 4 5/8 hole, so will need to buy/borrow one, and well...... I'm just asking of those who have done this, what did you find? Thanks
I've done the check on every bell housing I've ever installed for the last 45+ years. I've found that most of the stock housings are pretty close, while the ones needing the most adjustment and use of offset dowel pins were the aftermarket units, in particular, the lakewood units. I try to dial them all in within .003".
That pretty much sums it up. The OEM bellhousings are usually pretty close but the Lakewoods are all over the place. Two points I want to make. 1. If using a Lakewood, make sure that you tighten ALL of the bolts around the bellhousing before you take your measurements. The bellhousing slightly distorts as you tighten all of the bolts. 2. Check out the offset dowels from RobbMc PerformanceThey are well worth the price. http://www.robbmcperformance.com/products/dowels.html. Stan
Here is what I did.... I installed the flywheel so that I would have more surface area to attach and stabilize the magnetic base. Then I installed the bellhousing, torqued to spec. Last, I plagged the indicator base in as close to center as possible. The first thing I check is flatness of the mounting face, using a straight edge and feeler gauge. I didn't find more than .002" variation across the face. Next, I set up the dial indicator on the surface and rotated the crankshaft a full rotation, watching the runout on the dial. This tells you how square the surface is to the crankshaft. I think .008" is max you want to see from the high side to the low side. Last, and most important, I checked the concentric runout. It's not important that the mag base be centered here. You want the dial in the center, pointing straight out. Get it as close as possible. It doesn't need to be perfect, but if it is too far off to one side, it will tamper with your reading. I marked a starting place as .000", then rotated the crank about 20* at a time, marking the run out in each place. The total difference divided by 2 is your total indicated run out. +004 to -003 =007/2, so 0035 TIR. That's within the .005" allowed. +.008 and -.005 = .013/2, or .0065 TIR. You will need offset dowels to move the bell toward the + side, away from the - side. You can draw a line though the high and low points to understand the required orientation of the dowels. This line will not likely run through the center of the hole. The dowels should bias slightly away from the line, so as to correct it. Measure, adjust, repeat. Have fun.
Wow Scotty, Thank you for the pictorial/tutorial! I printed it out to use as a reference material. One question ..... obviously I'm not a machinist, don't you have to put some preload on the dial indicator, then reset to 0, in order to read the + as well as the - ? Thanks again- Shoebox
No reset necessary. At your starting point, adjust the gauge to read, for example, 0.020"; then a reading of 0.028" would be = to + 0.008" and a reading of 0.015"would = -0.005" (as in the example above). vic
I'll add one thought here, offset dowels absolutely must be installed in 'like' pairs. Also, offset dowels are available from dozens of sources and the prices vary wildly so shop around. Or, if you have a lathe with an independent jawed chuck, you can easily make your own. .
X2 on the robbmc dowels. If I understand it correctly, the other 'adjustable' dowels requires checking the runout every time the b.housing is removed. Not so with the Robbmc dowels. I got lucky(or at least I hope so) with our lakewood scattershield and found I was within .004" with stock dowels. With the tremec they say within .005" is acceptable, but like tagman said, .003" would be ideal.
Every dial indicator I've ever seen had an adjustable pointer that you use as your "zero". Just load the needle so that iy has plenty of travel in both directions, set your pointer and then note + or - on each side as you go around. Your welcome!
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