[llwta76]

1) Relative to the crank center line are all Pontiac block( 455) dowel pin holes positioned precisely ( within a few tho) in the same location?
2) Are the four transmission mount holes in a scatter shield positioned so precisely that the center hole can be relied on as being dead center when using this hole to align the bell housing using offset dowels and a dial gauge? Now that's assuming that my transmission input shaft center line is dead center of the four mounting holes on the transmission.

These questions occurred to me when aligning my scatter shield yesterday.. I found that my center hole was out of alignment so much in the 12 and 6 o'clock position that I need to use the max offset dowels ( .021") to get it to .004". Side to side was right on but was .050" off toward the top of the block. Almost as if the crank center line was too close to the cam tunnel.( I will check that distance myself later). The machine shop said that they measured the crank to cam tunnel center line and said it was only .004" closer than the factory spec. This same Lakewood scatter shield was used on a different block of mine and never needed offset dowels. Just raised my curiosity and concern. Thanks, Larry

[gtospieg]

You need to check the bellhousing for parallel first and then check for concentricity The first affects the second.

[flamedabone]

Check for trans mounting surface to crank surface parallel first, then make sure your center hole is round. A few thou off on the center hole makes a huge difference in alignment numbers.

I like to center the top then dial from there.



Another thing I noticed, if you set the block vertically, it eliminates any thrust tolerance and keeps the weight from the indicator itself from having an unintentional effect on your numbers.



What are your 12, 3, 6 and 9 o'clock numbers? .050 seems like a lot...

-Abone.

[Tom Vaught]

My Browell Tool does exactly the same thing and everything is indexed exactly to the crankshaft centerline.

That being said, "1) Relative to the crank center line are all Pontiac block( 455) dowel pin holes positioned precisely ( within a few tho) in the same location?"

NO!

2) Are the four transmission mount holes in a scatter shield positioned so precisely that the center hole can be relied on as being dead center when using this hole to align the bell housing using offset dowels and a dial gauge?

NO!

Now that's assuming that my transmission input shaft center line is dead center of the four mounting holes on the transmission.

NO!

I have seen offsets as much as .009" in both directions.

Tom V.

[llwta76]

Originally Posted by Tom Vaught

My Browell Tool does exactly the same thing and everything is indexed exactly to the crankshaft centerline.

That being said, "1) Relative to the crank center line are all Pontiac block( 455) dowel pin holes positioned precisely ( within a few tho) in the same location?"

NO!

2) Are the four transmission mount holes in a scatter shield positioned so precisely that the center hole can be relied on as being dead center when using this hole to align the bell housing using offset dowels and a dial gauge?

NO!

Now that's assuming that my transmission input shaft center line is dead center of the four mounting holes on the transmission.

NO!

I have seen offsets as much as .009" in both directions.

Tom V.

The only method I know is to align the bell housing using a dial indicator. If centering the crank on the bell housing hole isn't necessarily going to put the crank and input shaft in alignment then I am at a loss as to how to proceed.

[llwta76]

Originally Posted by flamedabone

Check for trans mounting surface to crank surface parallel first, then make sure your center hole is round. A few thou off on the center hole makes a huge difference in alignment numbers.

I like to center the top then dial from there.



Another thing I noticed, if you set the block vertically, it eliminates any thrust tolerance and keeps the weight from the indicator itself from having an unintentional effect on your numbers.



What are your 12, 3, 6 and 9 o'clock numbers? .050 seems like a lot...

-Abone.

12:00 = 0 . 3:00 = .015 6:00 = .050 . 9:00 = .016. I repeated the process 3 times and came within .001
Note I used 12:00 at the bottom of the engine as the block is on a table with the mains facing up

[flamedabone]

Definitely try setting the block vertically, it may make a difference. Also, put zero in different clock orientations and see if the .050 stays in the same spot. If so, get the big offset dowels, get it in spec and don't worry about it anymore.

Good luck and please keep us posted.

-Abone.

[Tom Vaught]

Read this article: Easy peasy.

http://www.hotrod.com/articles/hppp-...n-bellhousing/

I have seen Dial Indicators that were "off". Darn hard for a feeler gage to be off (especially if it is checked for thickness with an accurate micrometer before hand).

Tom V.

[llwta76]

I received my RobbMc off set dowels( the .021 ). With 12:00 at the top of the block rotating the crank my dial gauge reads : 12:00= 0 ; 3:00= .004 ; 6:00= .007 ; 9:00= .005.

[ITSBACK]

I’m buying that alignment tool for sure. I had to take my dowels out to get block plate off today to find leaky freeze plug so I’m gonna have to align all over again. No time to play, that tool is it for me.

[Scott65]

Just an observation, but you may have an imperfection in the bore or something as your numbers don't add up as would be expected. The sides should equal the vertical amount. Much closer in the second set of numbers if one of those is plus and one minus.

[geeteeohguy]

Just went through all this on my '61 Corvette with the Lakewood scatter shield and block saver plate. Time consuming but worth it. If you are running the block saver plate, you will need to upgrade to an extended pilot bushing. Otherwise, you won't be supporting the input shaft of the trans fully, as the trans will be further away from the engine. Paul at 5Speeds.com fixed my up for my application.

[Schurkey]

How far off are the original, OEM parts?

I never understood how GM/Ford/Chrysler/AMC/Imports could knock out a million bellhousings a year and get the alignment right, while the aftermarket parts need to have every single one dialed-in individually.

Are the aftermarket bellhousings really that poorly made?

[lust4speed]

Another pesky problem is that the big hole can be slightly oval. My old Lakewood wasn't out much at about .005" larger diameter in the 9:00 - 3:00 compared to the 12:00 - 6:00. As long as you are comparing opposite sides it doesn't matter, but does cause a moment of concern until it is taken into account.

As far as poorly made, my scattershield has survived 35 years, but I get a little different measurements depending on the tightening sequence of the six bolts to the block. We checked it for square and it was good, but between the engine plate and the position of the moon, numbers will shift a little every time we retighten it.