Machining Stuff,,The Law of finding center

As long as you have desire to learn, all else is easy. I use a coax indicator regulary, and it helps find centers of holes (or shafts) easily and quickly. I've seen cheap ones on ebay for as little as $40 and they work well enough. As long as you have a drill press with a chuck and a bit of patience, you can do it. If you have access to a milling machine, use an edge finder, I've bought a few from Enco for under $10 each.

 

You ain't gonna learn no younger!

The front bearing retainer locates the transmission in the bellhousing, not the bolt holes.

Cheep Dial Indicators

 

yeah...I understand that. my buddy was a machinist for many years and a good one. high school drop out and learned his trade in the navy and could do amazing calculations and find perfect center point. I went to college, became a business man, but I couldn't find my *** with a search warrant and a spotlight.

 

Little Wing,

I made an adapter the other day for that bell housing. Do you have the transmission that goes with that bell? I took the input shaft housing off the transmission, it is a tight index fit to the inner hole of the bell housing. I did some quick layout by laying the bell on a Flat plate of your desired thickness and then inserted the input shaft into the bell. Using transfer punches mark the four holes for the input shaft housing. Drill and tap those 4 holes with a tight fitting bolt. Bolt down the Input shaft housing using GOOD bolts with locktight, you will never be taking this apart again. You now have a plate with a mount that will chuck up in a lathe. I slid the housing in the lathe and bored a hole in the plate that will be a tight location fit for the donor transmission being used. In my application the donor trans slide inside the Ford input shaft housing. After the hole has been bored in, I then transferred the holes for the bell housing into the adapter plate, drilled and taped. After the bell housing and adapter plate are together, while in the car I transferred the trans bolt pattern to the adapter plate. this allows you to determine if you need to clock the transmission based on comfort and fit.

In this configuration, I was able to use all the existing Ford clutch linkage with the Ford bell also the Ford input shaft housing and ALL Ford clutch throwout bearing and pressure plate. The flywheel was Cadillac and the clutch is Chevy

 

If you are looking to do this on paper. Draw the circle on the paper that resembles the hole that you wish to find the center. Take a Comp*** and open it larger than the radius of the circle already drawn but not larger than the original circle. Now place the comp*** point at a guesstimated 12 o'clock position on the circle edge and draw a circle now. Now draw a circle with the same diameter with the comp*** point at 6 o'clock position again on the circle edge. The 2 circles that you just drew will intersect at 2 points, draw a line with a rule from one of the intersection points to the other intersection point.
Take the comp*** and repeat the same process as listed above, except the comp*** points are now to be placed at guesstimated 3 and 6 o' clock. Draw a line between the 2 new intersection points just as done before.

The intersection of the 2 lines that you just drew will be at the exact center of the circle. Simple little procedure with a comp***, rule and pencil.

 

The Packard retainer is 4 13/16
Chevy bell hole 4 11/16

Input shaft Packard 6 3/4 long
input Chevy 6 1/2 long

Chevy top mounting holes 8 1/4 wide
Packard 7 1/2

Chevy bottom mounting holes 9 1/8 wide
Packard 7 1/8


Distance from top holes to bottom holes

Cheyev 4 7/8

Packard 4 1/2

 

So you want a 1/4 inch thick spacer with a lip to locate on the Chevy bell. It might be easyer to bore the register hole in the bellhousing to 4 7/8 but not completly necessary. Some countersunk screws to hold the adapter on to the bell housing and bolt holes for the Packard trans and your homw free.

 

kinda what i was thinking..and i just realised I don't need to cut the big hole first,,I think that was what was making me worry about loosing cenetr for both holes

 

You should start with the big hole. Everything locates off of the big (Register) hole. The bolt holes can be oversize or enlongated or just plain sloppy and it won't matter. The bolts just hold it togeather. They don't locate anything. Flatness (parallelism) also counts on the faces.

 

i would start with a round piece of 1/2" plate large enough to cover both the bell housing patterns. take it to someone with a lathe and have them bore out the small hole and then take the whole plate down to 1/4" leaving a small ring the size of the large bell housing hole, now your trans will be lined up as long as the bell your using was correct in the first place. now you can add the bolt hole and cut the plate to the size and shape you need.

 

Ok Think I'm gonna cheat a lil

I have this adapter which I have NOOOOOOO idea what its suppose to fit,,but one side fits the Packard Trans,,but I cannot find any bellhousing that fits the

other pattern. or the jumbo pilot bearing


So Figure since this is 1/2 way built,,if I can center things and transfer the chevy pattern to this I should be good

other pattern is like top bolts 6 ( hemi and flathead are that wide )

bottom about 3 1/2 ( maybe you re drilled the bottom of teh bell to fit ??)

 

Google transfer screws and transfer punches.

 

I would toss the bellhousing up on the Bridgeport table and lightly clamp it down in 2 places. I would then (using threaded bolts with the heads cut off) square up the 2 bolt holes on the top of the pattern. This should get the whole deal square enough to work with. Then clamp it down for keeps.

Then indicate the big hole, hit the DRO to 0,0 (everyone has a Digital Read Out on their B'Port, right?). Then indicate the 4 holes in turn using the bolt. It should come out to something fractional, for example the X axis on the upper right hole might be something like 3.625 and 2.375 in the Y axis. That way you'll know you're on the right track.

The holes should be symmetrical about the X axis, in other words if you want to do just the 2 lefthand holes, when mirrored over they should be the same on the right.

Bob

 

Bridgeport !! If I had a Bridgeport I would'nt be online

 

just eyeball it, then stick your thumb up in the air to make sure it's level..... GEeeeshh!!

I draw 2 equal length lines across the inside of the radius, mark the line at the half way mark, and use a right angle to draw lines that will intersect themselves at center.

 

C'mon over, you can use mine. Bring

 

Actually I have both transfer punches and screws here in my shop. What exactually will they get you? The relation of the bolts to one another. Which is worth nothing without the relation of the bolt holes to the register hole. The entire bellhousing is made in relation to the "big hole" that locates the transmission input shaft and front bearing. Any adapter will need to be made from this "0". That is the first thing you must understand to begin this project.

 

Not the best way, but what I have done is make the adapter and bore the center. Indicate the center hole in the adapter, then transfer the holes from the bell to the adapter.

 

Rich Fox pointed out the fundamental thing, which bears repeating...several people are missing it. The bolt holes do nor locate stuff that requires precision. Actual locators here are the block to bellhousing dowel pins on the flathead, the big hole, and the matching pilot ring on the trans. The bolts just clamp the parts together in the location established by those.
By the way, look for your old 8th grade geometry textbook...only stuff that stuck with me was a bunch of rally neat straightedge and comp*** ticks for finding centers, establishing perpendiculars, etc.

 

I don't know what you are going to do with that pilot bearing. That goes in the rear of the crank and is another issue from this. The adapter you have fits your trans, great. But you still have no way of accurately locating the trans on the bellhousing. Get it wrong and you may find your trans jumping out of gear and your front bearing having a very short life. There is a right way to do this and you are fighting it.

 

I'm so used to holding .0001 tolerances on lathe parts that I get carried away. Certainly the ****** front bearing retainer does all the critical locating. So hacksawed slots and fender washers get my vote for the rest of the adapter.

Bob

 

Pretty good lathe

 

not trying to fight just thought it was an option is all

 

This can be done with a minimum amount of tools, if you have to.

I mated a O/T 4cyl to the transaxle of an other O/T 4cyl with not a lot more than a drillpress, a angle grinder, a couple of good sharp files, and a good mig.
Didnt have a lot to measure with either, so I spent a lot of time to check what I was doing and make sure it came out straight & true.
( had the acctual adapter pieces flamecut to my cardboard templates )

I'm sure it wasnt perfect, but it was good enough for a couple of seasons of racing.
And I only took it apart because I got another car...

 

How about bolting that adapter up solid to the trans you are using....then take detailed pic(s) of how it fits around the packard trans bearing etc.

Then maybe that would spark some ideas with an actual fitting pic. What's to lose? film is cheap

and if I follow correctly, you then are going to the back of a chev bell?



edit: then maybe someone will suggest a dual diameter ring that fits the adapter center hole, but also centers itself to the chev bell centerhole...??

..and if that is impossible due to sizes, then there is a chance that you can center the adapter to the chev bell, then use dowels to keep it aligned. There must be a way to do this without rocket science. I still worry about trans reaching the pilot. Will it??

 

I will do that

Well seems the Chevy bell is same ( bolt pattern ) as the pontiac ,,but yes thats what I'm going with

 

hear ya be I used it on the 52 trans ,,plate is for the earlier 4 bolt but pattern is the same with all.

The outside box pattern is the Packard trans and where it bolts to teh adapter plate

and as I have said I have NO idea what the inner pattern fits

note : on the inner pattern the two top bolts come forward ( towards you like the input shaft )

The bottom bolts go the opposite direction

have found no bell pattern with that narrow a bottom pattern


oh and it is a 1/4 thick plate


plate is a perfect snug fit btw

 

Machine the retainer cir***ference down on a lathe to fit and use a 1/4" thick midplate like spacer between the block and the bell to move the trans/bellhousing back for input shaft clearance?
Redrill the smaller Packard pattern into the Chevy bellhousing.

 

Will the bolt heads from the bearing retanier clear the chevy bellhousing? It would be possable for you to put your "adapter" on the chevy bellhousing on the motor and mount an indicator on your crank flange or flywheel, whatever is there. Indicate th "Big Hole" to "0" with the "adapter" eyeballed straight and level. drill and ream for a couple of dowel pins so that it will be properly located. Drill and tap your bellhousoing or drill your "adepter" whichever is better and use countersunk screws to hold it in place. I think you said you had countersunk screws pointing to the rear that match the Packard trans so you should be OK. If you can handle the centering the two "Big holes".

 

after reading this from the start again i see i had things backwards, i just did ths to a ford 4-speed OD trans to mount it onto a y-block belhousing, i turned down the bearing retainer and cut 1/2" off the input shaft, no adapter plate required on mine.