[Dragncar]

This

http://nitemareperformance.com/pumpshaft.html

[Formulajones]

Originally Posted by wakesupremo

Thanks for all your replys. it makes for very interesting reading. The one thing that hasn't been discussed is the 'snowflake ' minds of English engineers not being prepared to do any works that might mean a failure of that particular component and future reprisals. I tried for 2 years to find an engineer that would turn down my 455 crank journals to fit in my 400 block to no avail.

That's odd, I've had no problem finding a shop that would turn the cranks down to 3" mains. In fact if done properly with a radius many engine builders will tell you it makes the crank stronger. I was doing that stuff almost 30 years ago before 3" main aftermarket cranks were a thing.

[taff2]

The OP is in the UK, it's very difficult to find anyone over here that can be trusted to do any Pontiac high performance mods or machine work. The reason I built my own mains girdle was because I didn't trust any UK shop to machine/fit 4 bolt splayed caps.

[Vid]

This seems like an opportunity for someone brilliant to come up with “something better”. The problem is the tang on the pump. That dictates the necessity of a fork in the shaft. There is a property called modulus of elasticity. It's basically the same for all steel alloys. It controls the stiffness of the material. So it doesn't matter what alloy is used. The forks will bend the same amount. Strength is different than bending. Alloys can take more abuse before reaching the breaking point. But you need both properties working for you or you reach a "zipper point" and the fork will fail. So you need a different pump shaft and drive shaft interface design. Not just a stronger fork. My guess is that something like a splined end would be much stronger, think along the lines of a manual trans input shaft. You don’t see axles and transmissions driven by cheesy “tangs”.


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[Bill Hanlon]

Originally Posted by Vid

You don’t see axles and transmissions driven by cheesy “tangs”.

Except for Ford Model A rear axles with a key to attach the axle to the hub.

[steve25]

But how hard can it be to get a crank cut on your side of the Pond?
I mean Gez , in terms of bring down a counter weight some that’s done off the crank center line so it can be done in a big enough lathe, you don’t even need a crank grinder!

[grivera]

Originally Posted by wakesupremo

I finally got my 469 fired up yesterday, its been a long time coming. We shut it off immediately as there was no oil pressure. Upon tear down again we found the oil pump driveshaft ( a Melling billet shaft) had split down the centre.. The motor has an Eagle 4.25"crank and the clearance is very minimal. is this normal?You can see where the crank has touched the oil pump shaft previously but, obviously, we don't know if that was before or after the shaft split. Any ideas please?

Originally Posted by Dragncar

This

http://nitemareperformance.com/pumpshaft.html

OP said it was a Melling Billet shaft - I wasn't aware of Melling producing one.

[mgarblik]

Originally Posted by Vid

This seems like an opportunity for someone brilliant to come up with “something better”. The problem is the tang on the pump. That dictates the necessity of a fork in the shaft. There is a property called modulus of elasticity. It's basically the same for all steel alloys. It controls the stiffness of the material. So it doesn't matter what alloy is used. The forks will bend the same amount. Strength is different than bending. Alloys can take more abuse before reaching the breaking point. But you need both properties working for you or you reach a "zipper point" and the fork will fail. So you need a different pump shaft and drive shaft interface design. Not just a stronger fork. My guess is that something like a splined end would be much stronger, think along the lines of a manual trans input shaft. You don’t see axles and transmissions driven by cheesy “tangs”.


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Just an observation: If the Pontiac oil pump drive looks Mickey Mouse to you compare that to the 1/4" Allen Wrench a Ford uses to drive their pump! It's 7 1/2 inches long too. I may be the luckiest man alive but I have never broken a Pontiac oil pump drive shaft from basic street engines to the 1500 HP Grocery Getter replica we ran with a stock Melling M54 pump for almost 20 years. May break one tomorrow, but so far, no blems in hundreds of builds over 40 + years. I have used some of the Nightmare Performance parts over the years. The Camshaft thrust plates in particular. Their products are top notch and may provide some extra insurance if worried about shaft failure.

[GOAT8U2]

The Nitemare shaft seems like a must for those of us who've broken one or don't care about an extra $50 for an important part to not brake and destroy $15k.

[steve25]

I have never busted one also, but that being said I have had a few stock ones showing near a 1/8th of a turn twist in them.
Race motors are not as hard on them as a every day street car that has to start up in the dead of winter when it’s -10 to -15 out without the chill factor!

[taff2]

There's probably only one small spot at the largest diameter of the counterweight that will be close, I would grind a small flat at that spot - just enough to give .050" clearance. As Mgarblik said it's probably around a gram, doubt you or the engine would ever notice.

[Jay S]

My hunch is that Batson was likely correct and the pump shaft was not quite aligned right when the distributer was bolted down. It isn’t all that uncommon, and it can happen with other non pontiacs that have similar drive set ups. The couplings can get a bur on the coupling and will not seat quite correct, then when it is tightened down it puts a bind on the shaft and misalign’s it. It then splits the yoke on the shaft.

If you put it together and it breaks again, you better be looking at the counter weight clearance. I agree with taff2, I think the area would likely be small and not effect the balancing. I know of many of Pontiac engines running around with neutral balanced rotating assemblies and the oem flywheels that are not quite neutral with no issues. I have heard of some Butler rotating assemblies rebalanced found to be not all that dead to on and never heard of complaints either. My opinion anyway, I would clearance it an put it together if it is an issue.

I design/engineer a lot of drive lines. Sometimes you can over design the drive and it makes the smallest misalignment a big problem. My opinion is Pontiac engineers did fine on there design efforts on the shaft drive, for the most part it is not where the short coming are. My guess is the HD melling shaft was case hardened more to address the wear down at the drive points than shear on the shaft. I don’t think the weak spot on a oil pump drive for a Pontiac is pump drive shaft. We have never sheared a shaft or split the shaft at the unions. What we have done is shear the key up on the cam on the timing chain. We have sheared a couple of them, they were race engines with oil restrictors on the galleys, heavy weight oil and a 80 psi pump. They would run fine to about 95 psi, then key on the timing chain would shear, engine quickly stopped and proceed to bend several valves. That was with just and ordinary std pump shaft. Would have thought if the pump shaft was the weak link it would have sheared it instead. 60 psi pumps and those issues went away.

Could have saved your self some trouble and piece of mind by measure the counter weight clearance with some feeler gauges. But I have my doubt that there is an issue there, make sure the coupling seat together correctly before you clamp the dizzy down.

[PAUL K]

It shouldn't be an issue to turn down an oil pump driveshaft .050. It's the recommended procedure by AP to correct clearance issues. The drive in the picture came out of a World record setting Pontiac that made close to 1,000 horsepower and was spun past 8,000 rpm on every pass.

[Vid]

Originally Posted by steve25

Race motors are not as hard on them as a every day street car that has to start up in the dead of winter when it’s -10 to -15 out without the chill factor!

Funny you mention that Steve. The only time I did break an oil pump shaft was in a pretty stout 302 Chevy that I had in a ‘69 Nova. Ported heads, 12.5:1 compression, big ass Crower cam, etc. Being a 22 year old know it all, I just had to run Pennzoil “racing oil” in my hotrod. Never mind that it was Reno, Nevada in the middle of the winter and the race oil was straight 60w!!! Might as well have run 90w gear lube. That was the end of one damn good running little 302!


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[taff2]

Originally Posted by PAUL K

It shouldn't be an issue to turn down an oil pump driveshaft .050. It's the recommended procedure by AP to correct clearance issues. The drive in the picture came out of a World record setting Pontiac that made close to 1,000 horsepower and was spun past 8,000 rpm on every pass.

That shaft wouldn't be used in any engine of mine, not even a mild street type.

[Formulajones]

Originally Posted by PAUL K

It shouldn't be an issue to turn down an oil pump driveshaft .050. It's the recommended procedure by AP to correct clearance issues. The drive in the picture came out of a World record setting Pontiac that made close to 1,000 horsepower and was spun past 8,000 rpm on every pass.

Looks like a 400 SBC shaft

[PAUL K]

Originally Posted by taff2

That shaft wouldn't be used in any engine of mine, not even a mild street type.

Yeah, I know it won't. It's gotta go back in the engine, break a thousand horsepower and win more races.

[Dragncar]

Originally Posted by PAUL K

Yeah, I know it won't. It's gotta go back in the engine, break a thousand horsepower and win more races.

That shaft is still bigger than Fords with those pencil ends and they can make more power than any Pontiac.

[hurryinhoosier62]

Originally Posted by taff2

That shaft wouldn't be used in any engine of mine, not even a mild street type.

You guys really need to study metallurgy and heat treating. As long as the base alloy isn’t brought past its quench point( very unlikely in a normal lathe cutting operation) turning .050 off of it isn’t a cause for alarm. If it makes you sleep better at night, re-heat treat the shaft. The ONLY Pontiac oil pump drive shaft I have ever had fail was one I bought from H-O years ago. It didn’t break, but it was certainly interesting getting that steel “pretzel” out of the block. FYI....incorrect installation .

[hurryinhoosier62]

Originally Posted by PAUL K

It shouldn't be an issue to turn down an oil pump driveshaft .050. It's the recommended procedure by AP to correct clearance issues. The drive in the picture came out of a World record setting Pontiac that made close to 1,000 horsepower and was spun past 8,000 rpm on every pass.

Logic over emotion, Paul. Sometimes I am totally dumbfounded by the lack of logic among people who claim to be “performance oriented”.