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Discussion Starter #1
About a year ago I was having a discussion with a Melling engineer about oil pump breakage and different causes, in small blocks.

One item that he brought up was the way the oil pump drive shafts are made. The OEs supposidly always have the slot for the dist drive and the "tang" that engages the pump in line.

He said that some aftermarket drive shafts did not do this and were an issue with various pump failures.

I didnt really think much about it but today I did notice that he was correct in that some aftermarket shafts are not in line. So maybe he has point of interest?


I dont have an opinion on this, (yet).

Im just wondering what you guys think?


Thanks

Jeff
 

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I don't really see how this could have anything to do with pump failures. Now it were shaft failures, maybe, but I still doubt it. I don't see how the alignment of the slots could possibly change the dynamics of the rotational torque enough to harm the pump, especially since the drive rod 'floats' on the pump tang. Plus the rod is somewhat supported by the block. There should be no side loading of the pump that would be affected by the position of the distributor gear tang. It's rotational force and any side loading would be consistant no matter what the phasing. Now it they were breaking off the drive tangs or something like that, I still don't think so, but the argument could be made a little more I suppose.
 

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Discussion Starter #3
I can see as where if the slots are aligned there would appear to be an avenue to allow more misalignment than having the slots non-aligned?
 

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I have always stuck with Melling shafts.
One they are OE Manufacture and the cost is better.

A Melling IS55E has always been better priced than any other. And has correct fit.

http://www.summitracing.com/parts/MEL-IS-55E/
Not ChevyII 62-67

IMO
AL
 

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I can see a problem there!! The shaft is "Captured" by the block but it's not necessarily "Supported". It is captured by the distributor and the oil pump collar. If the slots are out of alignment, there would be one hell-of-a lateral vibration that would wreak havoc on the oil pump's neck whick just happens to be where they have a tendency to BREAK.:yes: Think of how heavy the drive shafts are and how fast they have to spin. It wouldn't take much to become a BIG out-of-balance problem!!
 

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JEFF AFTER THINKING A BIT.... I know it's dangerous..... but if the to engagements were at 90 degree to each other.. and given the amount of slop the fitments has I could see a fair amount of angularity deflection between the two..

However, if they were in align.. then any deflections would be the same as the centirificial force could possibility throw it to the same side and reduce binding.. more or less becoming a concentric rather than a pitched to one side on the distributor and pitched 90 degrees opposite on the pump....

I could see some binding in latter scenario
 

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I don't think was ever a big issue until the quality of the casting went to "S*#*"!

And "S*#*" they all are! All of them period!

Al
 

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I don't think was ever a big issue until the quality of the casting went to "S*#*"!

And "S*#*" they all are! All of them period!

Al
I think that's the problem right there, and they're looking for something else to blame. Ok, I can see the issue of binding possibly once centrifical force is thrown in to the mix, but with one end captured by the distributor gear, and the other by the collar on the pump shaft, that should not be an issue. And even if it was, I don't see it throwing around enough weight to break the pump casting unless the casting was p*ss poor to begin with. Funny though, how I don't see this problem with any other pumps but the Chevy stuff mainly. I'm sure they're are, but not like the reports from the bow tie camp. If it was the shafts fault, then the Pontiacs should be having the same issues as well, but I odn't hear of any. HHHUUUMMMMMM???????
 

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SB Ford had an issue in the early days of the 5.0 because all of their Windsor motors use a 5/16" hex drive.:eek: They were twisting and breaking all over. Seems Ford Motorsports division (along with ARP) stepped in and came out with an affordable fix for their camp.:rolleyes:
 

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Discussion Starter #11
Personally I think the weakening of the casting was the MAJOR issue in most pump failures, and to Mellings credit all of the 55HVs I have purchased lately are very nice heavy built castings.


I have never had the pump break, but I have seen many that have. Im always curious about the issues and and I firmly beleive that if you think you have something figuered out you are just fooling yourself if arent constantly revaluating what you "assumed" was accurate.


When the topic of this shaft came up I never even considered the phasing of this to be an issue, but I can see how it may be.

One of the major suppliers of very high quality parts also supplied these shafts. According to the engineer use of their "early" shafts greatly increased the risks of pump failure, ANY pump failure not just Mellings. Aparently they changed their design and the slots are now aligned.

I have looked at their current product and all I have seen are aligned and I wasnt sure they ever supplied any that were not.

But today I found an apparent early one that is not aligned and it may be a coincedence but this was on a circle track engine with not much time on it, with the "early" 55HV (before any issues), and the oil pump screen was was broken in 2 seperate places. One where I had tig welded the screen in, and it actually fatigued the metal and broke the support off the screen assembly itself, destroying the metal not the weld. If you like I can try and ost a pic.

This luckily caused no damage to engine, but Im sure it would have if it would have ran longer. We just took it apart to freshen it up, and found this.

Like I said, it may well be coincendence but I dont think I will use any non-aligned shafts in the future.

I did find one other "old" style shaft the sold that was non-aligned and does seem to have excessive wear, but who knows why? Most of this stuff lives a tough life anyway.

Im not saying there is any validity to any of this but its kind of interesting to me.

By the way where does the block support the shaft?

Jeff
 

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Melling says right in their instructions to not use the plastic sleeve with their High Volume pumps. I had one of the HV pump input shafts break with the OEM GM drive shaft and nylon sleeve.

As you know I make Chevy II short pump shafts. I can tell you it is a bear to get them to spin true. It took me a while to figure out a way to get that right. I scrapped a bunch of shafts getting it worked out. Getting the tang square and centered isn't the problem. It's getting the sleeve on straight and true.

I think it's possible that some aftermarket shafts are being made to less stringent quality standards. I haven't spun all the available shafts on my lathe to check for wobble and runout, but the ARP shafts are pretty good.

I can't say why all these pump failures are happening now after decades of no problems with the tried and true Chevy Design. Clearly there is a problem. The oil pump makers choose to explain it as someone else's fault.

1. GM (or Autozone or unknown Major buyer) made us cheapen the casting.
2. You have to buy a more expensive pump now.
3. Aftermarket driveshafts are to blame.
4. You didn't install it right.
5. The Chinese didn't make it right. Not our fault we sourced them overseas. US buyers want cheap products, not quality.
6. We know the Chinese quality is inferior. Not our fault we sourced them overseas. Our management wants more profitability, they could care less if the parts are junk because we can sell an even more profitable billet pump as an alternative.
 

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The other day I was reading thru my brothers giant PAW catalog and when I got to the oil pumps section, there was a big introductory paragraph and the first line said something to the effect of...."The oil pump is the most vital part of your engine", or something like that. I can not for the life of me understand why anyone would want to put a $16.95 oil pump in their car. Obviously cost can be an issue for many. It is for me but I believe there are certain things you just don't skimp on. That's why I got the Wright pump :yes:
 
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