The factory Jaguar v12 locating dowels are .621” , upon test fitting in the bell housing, they seem loose. I also test fit a .625” dowel to compare and even this had some play. So there is at least .005” tolerance, probably more.

I know not many have converted to manual but the collective mind of this group is usually pretty helpful.

I feel like my baseline alignment numbers will e skewed right off the bat

 

Generally dowels are at minimum a parallel fit, the clearance that you have measured kinda defeats the purpose of them. But it might alleviate the need for offset dowels to align the bell housing register to the crank….

 

That was my thought as well. The dowel should locate the bell, not sure how this would occur if there is too much movement.

 

They are a parallel (almost interference) fit, any clearance at all obviates their purpose
You might want to invest in a set of oversize/offset dowel pins, as it is critical the centreline of the gearbox matches the centerline of the crankshaft
Set up a dial indicator to the flywheel with the tip registering on the register bore of the bellhousing, max. runout is TIR .005
A screwdriver slot in the end of the offset dowels will allow you to adjust to centre....l would then bolt the bellhousing solidly and drill for a couple more .250
alignment pins to prevent future drift
Many aftermarket bellhousings are well out of tolerance, unfortunately.

 

And the instructions that come with some of those bellhousings say the alignment problem is because of the block dowel holes being not in the right location, so you need to buy offset dowels... I really can't believe they actually blame the OEM motor manufacturer for that.

Doug

 

One of the main reasons I am
replacing the bellhousing was due to the sloppy tolerances of my current one.

i may be overreacting as i am
yet to take a dial indicator reading. Will have to wait and see.

 

Any supplier that would states this

just demonstrates their incompetence as design engineers and should not be given custom - dowel holes are machined and it ain't difficult to put them in the right place if your design is good, there's even less of an excuse with the tools available to engineers today..

The alignment formed by the dowels matters because it ensures that shafts are centred along their axis within tolerances - i.e. the pump drive in the torque converter or the input shaft in the crank bearing / bushing. Sure if they're out of line things may be a bit 'tight' but things will wear because of it, the dowels are what aligns things - not the bolts which only clamp things together.

 

A rule of thumb is the centreline of the crankshaft and transmission can be out of alignment up to about 0.015". Depends on the engine and transmission (manual vs automatic), but with 0.005" I think you should be ok.