The Stovebolt Site Forums The Shop Area Engine Shop Bellhousing Alignment

I installed my cast iron bellhousing on my 292 block the other night and checked the alignment of the transmission hole to the crank shaft. The alignment is off by 0.015".

Novak Conversions (which is a great place to go for general knowledge) states that anything over 0.007 or 0.010 is too much and alignment should be fixed using offset dowels.
http://www.novak-adapt.com/knowledge/clutches_etc.htm

Is 0.015" really to much mis-allignment? How hard is it to install offset dowels? Note that this is not going to be a race engine, but will be stronger than stock. Thanks!

are you sure that you do not have a bur or piece of crap betwen the b/h and block
ron

Recheck dialing in the housing again. If you still have too much runout, remove the housing and inspect things as mentioned above. Is the runout in the hole or on the flat surface. If its on the flat surface, it until its within specs. If the hole is off, remove the dowels, center it, tighten up the bolts and drill and install oversize dowels. This has been a common practice for many years and is described in the Cummins service manual. It was in the book for the 855 cu inch Cummins that was built until 2003 and this engine could be rated up to 600 HP and 1850 ft lbs torque from the factory.

jhaa_lives writes, "The alignment is off by 0.015 "

Heck, this is significantly less than the margin of error of your measuring method. I would not give this amount a single thought.

Novak is a great place for information. I send people there on a regular basis, even buy parts from them. Few years back I had them add a part to their SM420 rebuild package; they forgot an important "freeze plug" like seal at a gear shaft end up front and bottom. Novak makes their own now. Nonetheless, this missing part informed me those boys are not fully experienced at some things, like rebuilding an SM420 truck trans.

Look at their photograph for measuring bellhousing alignment. What do you see inside? A pair of vise-grips clamped on a bolt head. How accurate is this? Not very!

Only way you can "accurately" measure your crank to bellhousing alignment is with a special jig which plugs into the pilot bearing and bolts to the bellhousing at the transmission bolt holes. You need a shaft which simulates your transmission input shaft and mounting surface. This is the only way to attain accuracy into the thousandths of an inch.

Measure your alignment six times. I bet you will find different readings for each measurement. I would not worry about this, you have far more wobble in your input shaft and clutch disc than this measurement you cite.

Billyray

I can't feature using a "special jig" which plugs into the pilot bearing hole. I would like to see one of them critters. I use a magnetic base and stick it to crank flange. I prefer a Noga holding system. It is very stable and it is easy to set up and I get the same reading every time. Clamping on to a flywheel bolt with a c clamp or a vice grip would probably be acceptable. However, the only way I have ever seen flywheel housing runout measured is by using a magnetic base on the crank flange.

maybe i misunderstand the picture but i don't see what the vice grips would have to do with a inacurate reading, they are just a mount for the magnetic base right. it seem it would take a little trial and error to get it perfectly centered, but i don't see why it wouldn't repeat itself. but i have to say i have never worried about his enough to measure it.

This is the holder I use http://www.noga.com/nogaProducts.php?prdID=DG61003 It will hold any one of my dial indicators without any other clamps. The 1954 GMC maintenance manual specifies .007 max runout. They also recommend oversize dowel pins rather than offset dowel pins. I am referring to Sec. 8, page 196. I don't know how in the world one would install an offset dowel pins. I see that my guys dial in a flywheel housing every time we pull a transmission. It only takes about 15 minutes to check one.

crenwelge writes, "I can't feature using a "special jig" which plugs into the pilot bearing hole. I would like to see one of them critters."

Here are several. I am sure there are more. Red billet aluminum method is the best. This a precision lathed centering device accurate within one - two thousandths of an inch. This is a "go - no go" method. Bellhousing is simply adjusted until the sliding ring slips right on in.

Two others in my graphic are similar, one is a centered bolt on, the other is a bolt on pilot hole centered method.

Bellhousing Alignment

Couple decades back I visited with a boy we met in Las Vegas. He is or was in the business of building NASCAR components. Cannot quite remember, seems we visited with him in South Carolina. He used a method which has a rod stabbed into the pilot hole and a machined cast iron "saddle" which bolted to the holes for a transmission. Dial caliper slid back and forth on this rod. This is probably the best method for duplicating how a trans will fit, this bolts right to the mounting surface as a trans does.

Most serious problem with a dial caliper method which is not securely bolted in place is the roughness of the hub hole in a bellhousing. You roll over bumps, depressions, ridge runs and such, leading to inaccurate measurements. This roughness will also move the whole setup, like a magnetic base unit, move the entire system around knocking off all measurements.

Billyray

Real question here is, "Do you need to align your bellhousing?"

Ever drive a 10 yard big rig dump truck? Get that puppy loaded up with a full ten yards of boulders, rocks and sand, drop her down into first under, ease out the clutch, the passenger side of the truck will raise up two feet before you move an inch. This is extreme torque. Yeah, you need everything in the driveline aligned.

Back in the Sixties, we ran a couple of super stocks, class A fuelie and class B fuelie, actually two bodies using the same engine. Set some records now and then, which were promptly broken. Green light and off the line, those puppies would snap your head off leaving your head bouncing around on the back seat. Quite a thrill ride. Marrs Brothers, those were our Glory Days. Yeah, you need a fully aligned driveline for this, and two hundred pounds of lead in the trunk to keep you on the ground.

I have a rust bucket, rattle trap, oil leaking, 100 horsepower inline six 3/4 ton '56 Chevy four wheel drive, weighs close to 5,000 pounds. My goodness, I can do zero to sixty in ten minutes on a good downhill run. Well, I think my truck will do this, never have been able to get it up to sixty, shakes apart first.

Am I going to align the driveline? Nope, I am pleased as punch if I can simply get the big ol' trans stabbed in. Heck, the driveline is so loose the truck will roll back and forth a foot before taking up the slack.

What worries me a lot more than driveline alignment, happened today, I am bouncing along, trying to think over all the rattling, clanging and squeaking, jerking the steering six inches to the left, jerking it six inches to the right, working at keeping the puppy going straight down the road, I hear that really annoying sound of some fallen off metal thing tinkling as it bounces along on the asphalt under my truck. Always look over my shoulder out the window, never see what fell off. I figure my truck will either begin spewing oil, the trans will do a face plant on the roadway, one of my wheels will go bouncing by me or... she will keep on trucking.

That ol' puppy keeps on going just like my old lady. Ain't worried about bellhousing alignment. I am worried about my driver's door which keeps popping open when I hit a bump in the road. One of these days I just know I am going to fall out. My ornery truck ain't gonna wait on me to catch up.

These old trucks most of us drive, if you can stab in the trans, this is all the alignment you need.

Billyray

Amen, Billyray! Speaking from the perspective of 40 years of building dirt track cars, "Build it three times as strong as you think it needs to be, and don't be too surprised when it breaks!" It's definitely possible to get too anal about small stuff. Now, I get fussy about half a thousandth too much rod bearing clearance, but I'm not going to waste much time over stuff that's got lots of slop built in on purpose.

It's sort of like comparing a GI-specification 1911 .45 Auto pistol to a tricked-out Kimber race gun. The Kimber is a masterpiece of hand-fitting, and it needs 500 rounds or more through it before it functions reliably. The GI model rattles like a BB in a boxcar when it cycles. Drop the Kimber in the mud, and it jams. Shake the big chunks off the GI model, slap in a fresh magazine, and keep on shooting! Which one do you think I'd bet my life on in a firefight?
Jerry

Hotrod Lincoln asks, "Which one do you think I'd bet my life on in a firefight?"

Howitzer cannon. A person looking down the barrel of a Howitzer displays a lot of respect! Plug your ears!

This is like my girl in her hotrod Corvette. Drivers pay no mind to her, still tailgate, cut her off, knock door handles together, tight fit driving, alignment is a concern, until she hits her flame thrower button. However, she drives like she is in a destruction derby.

Driving our big bolt 3 ton GMC, people get the heck out of her way! Nobody messes with her. Kinda like this difference between carrying a Daisy Red Ryder BB rifle and rolling around a Howitzer cannon.

Point here is production line bellhousings are precise enough, alignment is not an issue for typical everyday use. Contrasting, high torque, high horsepower, high rpm usage, alignment then becomes an issue. If bellhousings were not well made, we would have to use really big hammers to get our transmissions installed, big hammers and a lot of cussing.

Had a hard time finding a tachometer for my '56 Chevy truck, little inline six. Finally found one with 4,000 rpm the top reading, red line is set to 3,200 rpm. Never take her over 2,500 rpm. Little over a hundred horse, redlines at the idle speed of many high performance engines, bellhousing alignment is not an issue, not something I ever think about. Parts settle in, wear in, get a little loose, all works well for a million miles.

With so many of us driving Forties and Fifties trucks, many still original equipment never touched, millions of miles racked up, no problems with bellhousing alignment, this is strong evidence bellhousing alignment is not an issue.

Your wife periodically realigning your head with a good whop upside your head is much more of an issue. Plug your ears!

Billyray

Sheeeeshz - I never gave bell housing alignment a thought but I've thoroughly enjoyed reading this thread. You guys are more entertaining than anything on TV tonight!!!!!

jhaa_lives , just get offset alignment pins. .015" is a bit off.

The tolerance for bellhousing mis-alignment is highly dependent on the transmission you are running. The later model O.D. 4 & 5 speeds really don't like to have their input shafts flopping around. Think about it, if you have 0.010" off-center from the crank centerline to the trans. register, then how far out is it at the input to mainshaft bearing area?

There is a angular check to be sure the trans. mounting face is square to the crank centerline & then a off-center check of the crank C.L. to the register bore.

Do a google of bellhousing alignment, there's a lot of info there.

I got into this after putting a MY6 behind the inline 292 in my '55 daily driver & experiencing some hard shifting & clutch chattering problems in the first couple months of running. Been 5 or 6 yrs. now, & no problem since.

Doug

desertdog writes, "I got into this after putting a MY6 behind the inline 292...."

A very strange transmission. This a manual version of the 700R4 automatic, really oddball gear ratios. I understand this trans is inherently hard shifting because of the size of the gears and the unusual arrangement for shifting into overdrive.

Did you need to have the bellhousing hub hole bored out to accept this transmission?

Billyray

In my opinion, the GM version of the NP 833 referred to as the MY-6 was a rather easy conversion. It used the GM input and tailshaft spline. 3.09, 1.76, 1.00, 0.73 makes a pretty good driver.

Thanks for the responses. Always an interesting bunch of people on this site!

Transmission is an SM420, old cast iron bellhousing that fits SBC pattern and 1958 bellhousing crossmember support, stronger than stock 292 (when it gets finished). Wanting to build a low RPM torque engine.

I did measure the bore alignment (crank CL to register bore) using the magnetic base attached to the crank flange. 0.015" total misaligment. Measured a second time, 0.015". Took the measurement again last night after taking bellhousing off, making sure surfaces were clean, put bellhousing back on, magnetic base back on, measured 0.014" off in the same direction as before.

Checked the angularity of the transmission mounting surface to crank CL using the same magnetic base attached to crank flange, but now with the dial gauge sticking way out as far as possible on the transmission mounting surface. Maybe 0.001 - 0.002" of out of squareness, but this is close to the noise of the measurement. I don't think I'll need any shims to correct this.

I read some other forums, and there's a lot of opinions on what should be done.

I'll get my machine shop to install the offset pins. Better safe than sorry.

I think you are doing the right thing. I find removing the old dowel pins, dialing it in, bolting it tight and then reaming the holes out and installing oversize dowels the easy way and this is what is recommended in the old factory maintenance manuals recommend and its still done today on Cummins Diesels. However, if your machine shop is more familiar with offset dowels, that's fine too. Again, I think you are making the right decision to correct it. Your clutch will work smoother and proper alignment relieves a lot of strain off the input shaft bearing and the entire front of the transmission. If you are looking for low end torque, you will have it in the SM420. It would climb trees if you could get traction.

IF you go with offset dowels, when you get them, you'll be able to see the direction of the offset, just holding them in your hand. Since you've done the hard work already of determining the offset & its direction, to then install the pins yourself will be a snap. Just align them to offset in the direction you need to move for alignment. Of course, both pins need to be clocked going the same way. Repl. your bellhs'g. & recheck for safety. You'll be happy, proud, & money ahead. Remember, they can always be pounded out & re-installed if necessary.
Doug