[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?

[lust4speed]

Never much room between counterweight and shaft, and I would suspect that contact was after the failure. Sounds like a manufacturing defect - very strange way for the shaft to die - usually just shears off the tangs from one end or the other. Should worry others that have recently installed one from the same manufacturer. Source of shaft?

[GOAT8U2]

Sorry to hear this, I just built an new engine after a shaft broke and replaced it with a Melling shaft. Makes me nervous to hear this but maybe you have a pump shaft issue that's creating too much force on the oil shaft to turn it.

If the pumps out, consider turning the shaft on it and see if there's a high amount of resistance.

Obvious answer is the shaft is just too brittle etc and just snapped on you.

[wakesupremo]

I have installed another shaft and it turns freely enough but there is very little clearance between the shaft and the counter weight on the crank. maybe 0.002"

[taff2]

I would want a minimum of .050" clearance, that pump shaft does oscillate in use.

[Tom Vaught]

I know of at least 2 examples where the DRIVESHAFT for the oil pump (from the distributor to the oil pump) clearance was too small and the the cast in boss that retains the DRIVESHAFT was broken from the block. NOT GOOD. Go for the .050" clearance as recommended above.

Tom V.

[wakesupremo]

How do I get that 0.050 clearance when the rotating assembly was sent to me from US as a balanced assembly?

[lust4speed]

Would be good to have photos and confirmation shaft did split lengthwise.

Most of us have seen shafts fail and the tangs break off and seen shafts bowed, but if "the oil pump driveshaft ( a Melling billet shaft) had split down the centre.." then we could be dealing with a manufacturing defect.

Most failures result from improper installation and the shaft gets destroyed within a few revolutions because tangs aren't properly engaged on installation - but I've never heard of a shaft failing lengthwise.

[mgarblik]

As far as balance is concerned. If you have to carve a bunch off the counterweight, it will have some effect on the balance. How much you might ask? A typical 1/4" ARP flat washer weighs 1 gram. Actually, that's what I use to make up the Bob Weights on my system to balance. So if you can picture that much metal and where it would need to be carved out of the counterweight, you get an idea of the imbalance possible. This is the street thread, so I wouldn't be too concerned with removing 3 grams of material or so. If you need to remove more, a re-balance might be a good idea. My old balancer will get a crankshaft +- .5 gram on each end. Many of the rotating assemblies purchased with Chinese components, if it's within 5 grams, they ship it.

[taff2]

Who in the USA did you buy the balanced rotating assembly from? A rebalance over here will cost around £250- maybe you can get the supplier to pay towards it, as the crank they supplied must be out of tolerance on that counterweight.

[Vid]

Just throwing this out there but as for shaft vs counterweight clearance wouldn’t it be easier (and not upset the engine’s balance) to carefully turn down the shaft .040-.045 in the area of concern on a lathe? The tensile strength of the shaft really shouldn’t be comprised.


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[Tom Vaught]

The question in my mind would be is the Oil Pump shaft heat-treated vs case hardened or Nitrided?

Nitriding can be done at lower temperatures than carburizing. The diffusion of nitrogen gas normally occurs at low temperatures, and hardening occurs without quenching. Only the surface is hardened, the core remains the same. When a steel has undergone Nitriding process, it has excellent wear resistance.

Key thing being: "Only the surface is hardened, the core remains the same."
So by turning down the shaft .040-.045 are you making the shaft much weaker in the area of the modification to get some extra counter-weight clearance.

So do you actually know what the the tensile strength of the shaft really is?

That is my question on your proposal.

Tom V.

[Vid]

Originally Posted by Tom Vaught

So do you actually know what the the tensile strength of the shaft really is?

Tom V.

Tom, I do not. It just seems like a logical approach to me. My reason being that an oil pump shaft in properly applied normal service (no mechanical interference from counterweight for example) really isn’t subject a tremendous amount of stress. If it was, the typical V8 would likely have a much more sturdy way to spin the pump. I envision a piece of lumber, a 2x4, say 6’ in length. If you tried twisting it from each end, it would take a lot of force to break it. Now put that same 2x4 between two saw horses and try to sit on it - SNAP! Different story. Personally I don’t see how turning it down .045 would significantly weaken it, but I am neither scientist nor engineer, merely a shade tree mechanic.


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[steve25]

You underestimate how much stress those drive rods are under with a 60 psi pump, no less a 80!
Next time you have the chance to do so and have real good size electric drill, just try spinning one fast enough to get the pump bypass to open!

[Formulajones]

I don't know about turning it down, but just for reference, shafts are made in other engines with thinner sections to clear crankshafts. The 400 SBC is one that comes to mind. However it is "made" this way, not modified.

So this is not a new concept.

[Tom Vaught]

I am sure that if you had a bunch of the Pontiac Oil Pump Drive shafts, you could clean them up in a glass beader, make your modification to the shafts where the crank counter-weight is close to the shaft, and remove metal there.
Then you take your 50 modified oil pumps shafts to Joe at Moldex Crankshaft and he nitrides them the next time he does a custom crankshaft. You pay him the money and for the next 20 years you look at the 49 other oil pump shafts sitting on your parts shelf. I have better things to do.

Tom V.

[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.

[lust4speed]

Not going to get any photos are we? Thousands of 4.25 stroke crankshafts made and one pops up too wide? I still think it was improper assembly without the tangs properly seated.

[steve25]

In terms of post 17 what make crank was this as the normal thing done to fit these cranks in a 3” main block it to clearance the block as needed?

[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?

Do you have a part number or link for the Melling billet shaft?