indestructible oil pump shaft....WHY?

[PROFESSOR FATE]

I'm in the middle of assembling my umteenth FE motor. While looking through the old tool box, I ran across a couple of those chromemoly oil pump shafts and, of course, some stock ones. The chromemoly ones were new. Don't know where I got them or why, but there they were. So, should I use one? For nearly 40 years I've used the stock shafts without a problem. I've built motors with anywhere from 70psi to 120psi of oil pressure. Never even twisted one much less broke one. But, there they are, free, just sitting there in the tool box. Why not use the bulletproof shaft? Of course, they are kind of heavy. And, if you think about the stuff they're attached to (oil pump, distributor, distributor gear, roll pin, and cam gear), if one of them starts to go, which would you prefer to have catastrophically fail? I'm thinking the $5 stock shaft.

Can anyone give me a good reason to use an indestructible oil pump shaft?

[Jac Mac]

Had a 302w that popped a circlip out of a lifter a while back. That circlip found its way down into the pan, wriggled in thru the pickup screen & locked up the oil pump. The stock drive then screwed itself up until it looked like a coarse thread bolt before it became short enough to lift out of the pump and then the light came on. Fortunately the owner "saw the light" & switched off. When I stripped the bottom end down there was no other damage [ I magnafluxed cam& distributor gears along with distributor/oil pump hex drives.]

Now if that had been an 'indestructible' type drive would we have got off as lightly, I doubt it. I have seen motors fitted with HV pumps twist up std drives just from a throttle jockey on cold starts. They then blame the pump drive. It is not the problem, just the messenger to a driver that wont listen.

Use the std shaft & keep a good scan on your gauge's/light's, this has never let me down yet!

A better use for the " heavy " shaft is as an extension allen type socket screw driver for awkward place's.

Cheers Jac Mac

[PROFESSOR FATE]

Jac Mac, Thanks for the reply. I just finished assembling the motor with the stock shaft. I was particularly pleased to hear that the stock ones are ductile enough to twist as much as you described. I never would have guessed that it would fail that way.

[SCOBRAC]

One cold day and you may find yourself wishing you had used one. Like everything else it's all about how much power you want to make and how fast you want to go.

The chances are your stock shaft is a used piece which was made in the 1960's and has tens of thousands of hours in service and possibly hundreds of millions of reveloutions under load. How that load was applied will make the difference between one which might fail and not fail. Do you know where your stock oil pump shaft had been? I guess if you are assembling a stock 390 from parts you perviously owned it doesn't matter. If you grenade the motor it shouldn't cost you more than a few hundred to pull one out of an old truck and slap another $900 into the rebuild.

If on the other hand you have $15,000.+ invested in a .015" over side oiler and it will cost you $5,000 to repair the damage from a failed shaft then I'd recommend spending the extra $15. for a high strength unit from Ford Racing or other reputable source. Um, ok. On second thought I am sufficiently lazy to think the high strength unit is a good investment whether you are at the $1500. or $15,000. pricepoint.

[Scufty]

after my engine did the EXACT thing as mentioned above ..with the lifter clip..I am glad that the shaft broke..dont get me wrong I wish nothing would have happened in the first place..I did talk to a top fuel guy who says that they run a magnito or something like that so that if the shaft breaks it automatically shuts down the ignition...I think these are pretty rare occurances but I may be wrong? Mine broke after the oil pump sucked up a piece of that clip. I noticed the oil pressure was Notta and shut er down ...427 side oiler ..took it all apart and thank god nothing was broke but do wonder why the hell that clip broke?

[cobrarkc]

Years ago I had a 289 that sucked up a piece of nylon that broke off the stock camshaft timing gear, it twisted the shaft up like a licorice stick and snapped in half. When I took evrything apart and discovered the problen I altered the screen in the stock pickup and it never happened again. I did find more pieces in the pan after the next oil change. Finally change the timing gears. They make the stronger shafts to prevent any spark scatter in the distributor not to prevent them from breaking. I you are building and decent motor I would hope you would not be using a stock pick up in it. Go buy an aftermarket on that was a strong screen on it that nothing can get through to the oil pump.

[Jac Mac]

I live down the bottom end of NZ where it gets cold enough for me (we are on our 4th day of 6deg frost right now).
Micheal; I feel that the main reason apart from trash like circlips/plastic off timing gears/ stem seals etc of oil pump drive failure, is people that jazz the throttle on start up & or HV type oil pumps that have been fitted for the wrong reason. many owners/builders fit an HV pump to a motor that has seen better days to prop up sagging oil pressure, some time later the motor gets rebuilt but the pump looking brand new is refitted , to a motor which doesnt really need it. Chances are the promotion hungry salesman also told the guy that he needed a HD drive to go with the big pump. This is about where I enter the picture after the owner has visited every wannabe mechanic to cure any of the following ill's that he has created.
1. The oil filter blows out the ring when they rev it on start up.
2. It keeps shearing the roll pin in the dist gear.
3. Its on it's 2nd dist gear since the rebuild.
4. His mate has told him the drive gear on the cam is badly worn.
5. The lifters pump up real easy on cold mornings & and the motor dont rev like it used to.

I have many HV pumps that have been removed from 'new' motors for the above reasons.

The secret if you can call it that is to build the motor with the right clearances & on the FE enlarge the oil galleries so that the oil pressure you read on the gauge is actually being supplied to the bearings etc rather than just being 'created' by the restrictions in the gallery. Then use a pump [and cooler if necessary] to ensure that the oil pressure can be maintained at all times. Done in this manner you will usually find that you will have a reliable combo without having to resort to HV pumps etc.Defintely use a full screen pickup, that bypass hole on the original was only for old hi mileage purposes on stock engines where people used to change the car rather than the oil!!

Scufty, I think the circlip probably jumps out or fails after a long period between starts & the lifter has collapsed allowing the pushrod to knock it out or during an overrev with weak valve springs.
Hope I have not got to far off topic.

Cheers Jac Mac

[Carnut427]

SCOBRAC, you can lead a horse to water, but...

[PROFESSOR FATE]

To tell me that I should use a good shaft rather than an old used stocker is good advice, I suppose, but not exactly what I was looking for. I pretty much dismiss the idea that the old stock shafts fatigue. The only reason I have ever replaced one is because the ends that engage the pump and distributor had worn enough that the darn thing started sticking in the distributor, when I tried to remove it. I can't quite imagine $5000 damage resulting from a broken shaft, unless I pay no attention to my oil pressure gauge or am a blithering idiot. Let's ignore that last possibility/probability or we'll never resolve this. I guess what I'm looking for is real possible failure modes, in other words your horror stories. Ones where at the end you can say "Boy, I'm sure glad that I had that unbreakable pump shaft." or "Wow, if that stock shaft hadn't broken, it would have cost me a fortune."

Several of your responses have been just that. Thanks. The oil pump appears to be the most likely problem cause at the moment. If the pump seizes and the shaft doesn't twist, the gears may well experience several times their normal loads. The most likely weak link will become the roll pin. If that shears off, the distributor gear will turn on the distributor shaft, probably stopping the engine. But, how much damage is done? Has anyone suffered this kind of failure?

[My427stang]

Well, let me comment on broken roll pins. If they just twist off and spin you are lucky. I had a rash of bad rebuilt distributors from a supplier and 3 out of 6 broke on various motors over a years time, and of those 3, 2 put the pin into the gear an destroyed a cam too.

Now, does that apply here? Maybe in support of a stock shaft, but I honestly support your original idea. It just doesnt matter that much. I use a fancy one in my 489, but I have never used anything but Melling stockers with each rebuild and never had an issue

I do like the fancy ones though, and for the price, it sure doesnt hurt anything.

[edwhite7]

I got on mine a little to early when cold and sheared the roll pin. I have the big shaft. Sure was eaiser to pull the dist and replace the pin than the shaft. I was right next to a Sears and I did it in the lot. Sears is a good place to break.

[zipzip]

I just experienced an interesting situation that relates here. I feel like I keep a good eye on the oil pressure, but I'm glad that I have the stronger driveshaft in my pump. I was driving and the car quit all of a sudden. What had happened is that the oil pump had some debris enter the gerotor and create "tight" spots as it rotated. This caused extra load between the distributor gear and the pump which sheared the rollpin in the gear. All the pieces stayed in the gear, it just spun on the shaft. I feel lucky because if the driveshaft had twisted or sheared to the point that the oil pump stopped, I might not have noticed no oil pressure before it was too late. I like the fact that the engine quit along with the oil pump.... A new pump and rollpin and I'm on my way.