My CAV GT40 has been suffering with difficult gearchanges and clutch disengagement problems for a while especially when driven hard. Recently I decided to pull the Renault 21T transaxle out of the car and check the one piece bellhousing for concentricity and was horrified to discover that it was out by 2.5mm (100 thou ")vertically. I sent the gearbox away to be rebuilt while I concentrated on solving the misalignment. My local machinist made me affset dowel pins which have reduced the misalignment to 30 thou". As there is a bit of play in the input shaft,I am hoping it is going to be OK. Your input and similar experiences would be welcome.
bellhousing alignment
- Thread starter cavgt40
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Sibbat
You didn't specify what material your bellhousing is..I am assuming aluminum. I had a similar problem with a 4 speed box attached to a motor and we solved it by welding closed the holes, then re-boring them in proper alignment. You can also drill out the bolt holes and bush them with offset bushings. Most aftermarket scattershields come with overdrilled holes and offset bushings, and I would bet your machinist friend could do that in short order. I wouldn't be concerned about a tiny bit of play in the input shaft, but I would make sure that my pilot bushing was in good shape to support the shaft.
Cheers
Phil
You didn't specify what material your bellhousing is..I am assuming aluminum. I had a similar problem with a 4 speed box attached to a motor and we solved it by welding closed the holes, then re-boring them in proper alignment. You can also drill out the bolt holes and bush them with offset bushings. Most aftermarket scattershields come with overdrilled holes and offset bushings, and I would bet your machinist friend could do that in short order. I wouldn't be concerned about a tiny bit of play in the input shaft, but I would make sure that my pilot bushing was in good shape to support the shaft.
Cheers
Phil
Hello Sibbat !
This is the way most racers correct the blocks around here. BHJ makes some of the best correction fixtures around. The nice thing about having one of these fixtures, is you can do a few blocks for others and soon it will have paid for it's self.
Dowel-Tru Blueprinting Fixture: BHJ Products, +1 (510)797-6780
Blueprinting Fixtures
Dowel-Tru Kit
Download this item's Catalog Page Back to Previous Page
Part Nos:
DTK-CH, Chevrolet
DTK-FOB, B. B. Ford
DTK-FOS, S. B. Ford
DTK-MPB, B. B. Mopar
DTK-MPS, S. B. Mopar
Use of the Dowel-Tru requires the 2-Inch Precision Support Bar and Main Bearing Bore Adapter Rings which are purchased separately.
Most high-performance engine builders have experienced the time-consuming operation of "dialing in" bellhousings using troublesome offset dowels. Use of the Dowel-Tru will quickly and easily correct bellhousing dowel hole locations by placing them in the proper relationship to the crankshaft centerline.
The Dowel-Tru plate installs on the block using the 2-Inch Precision Support Bar and Main Bearing Bore Adapter Rings (sold separately). Once installed, it is adjusted into place using a pair of jackscrews and then bolted to the block. The dowel hole locations are remachined with a special size reamer from the kit, guided by drill bushings in the fixture plate. After machining, special stepped dowels are driven into place.
The Dowel-Tru is available to fit most popular GM, Ford and Mopar blocks and includes a manufacture specific plate, six stepped dowels and one special reamer.
Additional Stepped Dowels are available in six packs. We offer standard length and special extra long length for use with a motor plate.
Download this item's Catalog Page
Regards Brian
This is the way most racers correct the blocks around here. BHJ makes some of the best correction fixtures around. The nice thing about having one of these fixtures, is you can do a few blocks for others and soon it will have paid for it's self.
Dowel-Tru Blueprinting Fixture: BHJ Products, +1 (510)797-6780
Blueprinting Fixtures
Dowel-Tru Kit
Download this item's Catalog Page Back to Previous Page
Part Nos:
DTK-CH, Chevrolet
DTK-FOB, B. B. Ford
DTK-FOS, S. B. Ford
DTK-MPB, B. B. Mopar
DTK-MPS, S. B. Mopar
Use of the Dowel-Tru requires the 2-Inch Precision Support Bar and Main Bearing Bore Adapter Rings which are purchased separately.
Most high-performance engine builders have experienced the time-consuming operation of "dialing in" bellhousings using troublesome offset dowels. Use of the Dowel-Tru will quickly and easily correct bellhousing dowel hole locations by placing them in the proper relationship to the crankshaft centerline.
The Dowel-Tru plate installs on the block using the 2-Inch Precision Support Bar and Main Bearing Bore Adapter Rings (sold separately). Once installed, it is adjusted into place using a pair of jackscrews and then bolted to the block. The dowel hole locations are remachined with a special size reamer from the kit, guided by drill bushings in the fixture plate. After machining, special stepped dowels are driven into place.
The Dowel-Tru is available to fit most popular GM, Ford and Mopar blocks and includes a manufacture specific plate, six stepped dowels and one special reamer.
Additional Stepped Dowels are available in six packs. We offer standard length and special extra long length for use with a motor plate.
Download this item's Catalog Page
Regards Brian
Attachments
Hello Andy !!
Here are a couple of wright ups about it.
http://www.lakewoodindustries.com/pdf/bellhousing_align_procedure.pdf
Bellhousing Alignment | Circle Track Magazine Article at Automotive.com
RobbMc Performance Products - Bellhousing Alignment Dowels
Bellhousing alignment and installation - Moparchat - Home of MOPAR enthusiasts worldwide!
Regards Brian
Here are a couple of wright ups about it.
http://www.lakewoodindustries.com/pdf/bellhousing_align_procedure.pdf
Bellhousing Alignment | Circle Track Magazine Article at Automotive.com
RobbMc Performance Products - Bellhousing Alignment Dowels
Bellhousing alignment and installation - Moparchat - Home of MOPAR enthusiasts worldwide!
Regards Brian
Like a porsche for example?, these register in a recess on the adaptor plate, so all that should be reqd is a dial gauge check of that register for both concentricity with the crank centerline and parallel to the flywheel & block rear face's. Both of these checks can be done with a mag base dial indicator mounted on your flywheel indicating off the respective faces of the adaptor. You can also check the trans register with a set of vernier calipers to the input shaft, although I think it would be fairly safe to assume that Porsches measuring machining standards might be a fraction higher than those of Ford/ GM, however it wont hurt to check, particularly if the trans has been welded or repaired in this area.
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I have often looked at the Audi etc that others are fitting & wondered how or if they even bother to check them.
To me the simplest way would be to make up a concentric jig or large spigot that would locate on the release bearing sleeve and in the register in the bolt circle recess of the flywheel. By standing the block assy on its nose the trans can then be located in the spigot & on the yet undrilled adapter plate for mark out & drilling of the bolts & dowels. Sorry this is an out of car deal---gravity plays to many tricks to try & do it any other way. I would imagine most of those who sell adapter plates use a similar method, the down side of which is you are crossing your fingers that YOUR block has its factory dowel's in the correct position.
To me the simplest way would be to make up a concentric jig or large spigot that would locate on the release bearing sleeve and in the register in the bolt circle recess of the flywheel. By standing the block assy on its nose the trans can then be located in the spigot & on the yet undrilled adapter plate for mark out & drilling of the bolts & dowels. Sorry this is an out of car deal---gravity plays to many tricks to try & do it any other way. I would imagine most of those who sell adapter plates use a similar method, the down side of which is you are crossing your fingers that YOUR block has its factory dowel's in the correct position.
Terry Oxandale
Skinny Man
Jac Mac, your post is what my next step will be for the alignment of my "alternate" transaxle. I'm using a 944 Turbo S transaxle, which has fitment issues separate from the Audi brethren. My process will be to have a "mock up" pilot bushing fabricated with a conical point in the middle of it that will fit into the lathe index hole in the end of the Porsche input shaft. With the transmission suspended over the end of the block, I should be able to get a very accurate position for the transmission on the modified bellhousing (I'm sure this will be a tedious experience, but time is on my side). I can then transfer the Porsche bolt pattern onto the plate welded onto the end of the shortened ford bellhousing. Fortunately, the 924 shaft has zero play in it so this should work out very well.
Terry Oxandale
Skinny Man
:lol: youz guyz crack me up!... I've refigured the alignment deal though. I found the Porsche torque tube coupler's OD is very close to the Ford pilot bushing OD, which means that with a very simple modification, I can use the modified tube coupler to index the transmission input shaft into the end of the crank accurately as long as the bellhousing plane is parallel to the rear block plane.
Look inside the gearbox bolt holes,2 are often dowled.
I have done a few conversions and I have always measured the rear of the eng and the front of the box.
I do a drawing of the eng
I do a drawing of the box face looking a it facing the flywheel.
I lay them over each other using the crank center and the box input shaft as the attachment point.
Rotate the box picture around crank center to the desired location.
Then use the mill to punch the holes and install dowl pins.
Or as per Jac's suggestion if you lack a cad program.
The conversion plate must be dowled to the block.
The box must be dowled to the conversion plate.
4 in total.
I cant understand why people want to leave them out(maybe it is all to hard) you need to be within about .002-.003".
Jim
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