Oil Pump driveshaft SBC Dart Sportman Block

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Oil Pump driveshaft SBC Dart Sportman Block

Post by banjo »

Hello All,

Long story short, SBC 406, dart sportsman block. When originally assembled, I broke two oil pump drive shafts in about a 50 passes, after the second one, did some research and found there was certain areas that need additional clearancing in the block and shaft. Well about 1000 passes later, this weekend, I broke another. When I say broke, it breaks off the two pieces that engage the bottom of the distributor. I haven't got the motor out yet, but I can turn the oil pump. Barring in obvious signs of clearance issues, would you chock this up to just a lot of passes or would you look deeper? Any areas to look at that may not be so obvious?

Just curious if when you all freshen up your SBC, do you replace the oil pump drive shaft? I didn't last time because we had to clearance the shaft before and it seemed to be good to go.

Worst part about it, It broke when I was done to five cars in electronics, and I had the bye. ](*,) Fire the car to make the run and no oil pressure.

thanks
74 Nova
SBC 406
3267 pounds
Speierracing heads

60 1.29 (10/15)
1/8 6.06@110 (10/15)
Best 9.87@131 on the rev limitor 1 Feb 2013
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by kirkwoodken »

I don't know about others, but I always use a small grinding wheel to polish out the tooling marks in the tang radius to get rid of stress risers. Also, you want to make sure the distributor is going far enough into the pump drive shaft.
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by banjo »

Makes sense about the polishing, I will give that a try.

I have a distributor with the slip collar, I will verify, but it should be right.
74 Nova
SBC 406
3267 pounds
Speierracing heads

60 1.29 (10/15)
1/8 6.06@110 (10/15)
Best 9.87@131 on the rev limitor 1 Feb 2013
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by Kevin Johnson »

Replace at 800 passes this time.
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by DCal »

I've heard of this issue with the distributor not being in alignment with the oil pump due to the intake manifold not being spotfaced correctly. I use a slip collar too and I'm wary of it for this reason.
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by governor »

I use ARP oil pump shaft very nice piece.

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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by banjo »

With the dart block, because they beef up the main caps, I originally tried to put in an ARP shaft, but if memory serves me correctly, it had to be cut down quite a bit to fit. Although at this point, I may get one and cut it down.

I started smoothing out the melling one and Its pretty rough to start out with.

I just don't think this is something I should be having issues with, so I plan to reverify all the clearances, Hopefully I will be able to spot the issue.

Thanks
74 Nova
SBC 406
3267 pounds
Speierracing heads

60 1.29 (10/15)
1/8 6.06@110 (10/15)
Best 9.87@131 on the rev limitor 1 Feb 2013
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by governor »

I think I would tend to clearance the cap before the oil pump drive, caps have a lot more material.

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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by chevyfreak »

governor wrote:I think I would tend to clearance the cap before the oil pump drive, caps have a lot more material.

Gov
Likewise, leaves more material on the shaft, only thing I can think off is if something is out of alignment, or maybe running at an anglefrom pump to dizzy,
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by needforspeed66gt »

What oil pump?
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by banjo »

I believe its a melling select pump, I would have to go back and look at my paper work.

The pump shaft isn't breaking where the machining is required, its the two fingers that engage the distributor.

Based on the instructions from dart, enlarging the hole could break into the rear main bore.

For the Dart block instructions
OiL PUMP DRIVESHAFT
On blocks with 400 main size you MUST use a 400 oil pump shaft which has a diameter of .425”. If you are using an
after market HD shaft or a 350 shaft, which are .481” diameter, you MUST machine the center of the shaft to .425” to
clear the hole in the block. If this is not done, you may experience oil pump and/or distributor gear problems. The 400
main blocks have a hole .062” smaller than a 350 so the shaft hole will not break through to the rear main bore.
74 Nova
SBC 406
3267 pounds
Speierracing heads

60 1.29 (10/15)
1/8 6.06@110 (10/15)
Best 9.87@131 on the rev limitor 1 Feb 2013
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by Kevin Johnson »

DCal wrote:I've heard of this issue with the distributor not being in alignment with the oil pump due to the intake manifold not being spotfaced correctly. I use a slip collar too and I'm wary of it for this reason.
^^^^^^^^^ You create a joint that accelerates and decelerates with every rotation, a non-constant-velocity joint.* You might consider buying some drill rod from MSC (needs to be very straight) and notch it to engage the oil pump. Center it in the manifold distributor hole with a plastic disk or collar machined with an appropriate OD and ID. Use a machined square block and travel around the circumference of the spot faced pad with the vertical surface pressed up against the rod. You will probably find it not to be square. Fix that.

* I am sure this does wonders for power output as well.
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by redsmokin57 »

x2 for checking the spot face on the intake manifold, may not be your problem but have had to correct a few on edelbrock sbc manifolds.
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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by CNC BLOCKS »

banjo wrote:Hello All,

Long story short, SBC 406, dart sportsman block. When originally assembled, I broke two oil pump drive shafts in about a 50 passes, after the second one, did some research and found there was certain areas that need additional clearancing in the block and shaft. Well about 1000 passes later, this weekend, I broke another. When I say broke, it breaks off the two pieces that engage the bottom of the distributor. I haven't got the motor out yet, but I can turn the oil pump. Barring in obvious signs of clearance issues, would you chock this up to just a lot of passes or would you look deeper? Any areas to look at that may not be so obvious?

Just curious if when you all freshen up your SBC, do you replace the oil pump drive shaft? I didn't last time because we had to clearance the shaft before and it seemed to be good to go.

Worst part about it, It broke when I was done to five cars in electronics, and I had the bye. ](*,) Fire the car to make the run and no oil pressure.

thanks
On Dart Sportsman blocks they use 1/2 inch hardware on the rear main cap. That being said on the oil pump drive side of the cap the washer has a notch that has to be clocked towards the oil pump shaft or it will cause a failure.

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Re: Oil Pump driveshaft SBC Dart Sportman Block

Post by banjo »

I will definitely look at that, I don't recall giving it any attention when we put it together. Thanks!
74 Nova
SBC 406
3267 pounds
Speierracing heads

60 1.29 (10/15)
1/8 6.06@110 (10/15)
Best 9.87@131 on the rev limitor 1 Feb 2013
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