Distributor shaft cracked

Dizzy shaft cracked at pump drive end.
On an early rebuild my engine builder noticed a hairline crack on my MSD distributor at the bottom of the shaft where the oil pump drive locates, when he put the drive in and loaded it up the crack opened up and broke a piece off. This was a second hand dizzy so we put it down to fatigue. Currently refreshing motor and he checked the Accel dizzy (a known dizzy, only done a few 1000 miles) and the same thing has happened again.  
Anyone had this experience and found a cause?

Alignment issue? Same block?

dfree383 wrote:Alignment issue? Same block?

The MSD was in a D1VE block, this time an A460 block.

Just checked another old dizzy from an older build an it's fine. Checking oil pump tomorrow (KAASE) MSD & Accel have been driving that, the old dizzy in good cond. drove a Mellings.

What oil pump drive shaft? I have found the ARP shafts to be a touch long and need a little trim . Not sure it'd cause that but just a thought anyway

Gregaust wrote:What oil pump drive shaft? I have found the ARP shafts to be a touch long and need a little trim . Not sure it'd cause that but just a thought anyway

It is an ARP one Greg, will check it out.

Some shafts are smaller than others and don't fit in the block that end looks to be the smaller one,is it .490 or something?

cool40 wrote:Some shafts are smaller than others and don't fit in the block that end looks to be the smaller one,is it .490 or something?

The MSD one pictured is a large shaft that takes the .530 gear and is stepped down to about .512. Hole on block is .517, The Accel that broke is one that takes the .500 gear and doesn't have a step down.

bbcoupe wrote:

Gregaust wrote:What oil pump drive shaft? I have found the ARP shafts to be a touch long and need a little trim . Not sure it'd cause that but just a thought anyway

It is an ARP one Greg, will check it out.

Bolt the pump up , ensure it has a little endfloat. The ARP ones i used required a slight linish from the overall length
I have used a few Ford racing shafts fit nice
M-6269-A460

Also, I've seen oil pump drive shafts where the hex wasn't machined long enough on both ends. This sort of makes each hex specific to either the oil pump or the distributor. Meaning it only goes in one certain way. I've seen this on a Windsor/ARP shaft before but haven't run into it yet on a BBF but definitely something to check.

If you stick the end with the short hex in the distributor shaft it will bottom out where the hex transitions into the round shaft making the distributor/oil ump drive shaft assembly too long overall. When you tighten down the distributor hold down you'll split the distributor shaft. ..

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