I'm in the process of removing my oil pan. While in there, I'm considering replacing the oil pump and pump shaft because of the plastic coupling. Not that's it's broken, but after reading about how poorly designed this thing is and what could happen if it breaks, I'm worried about it.

The engine only has 42K on it, but if it's easy enough to do, it's worth the peace of mind.

First off, can I simply replace the shaft with the Melling IS-55E one? In other words, my stock pump is fine (great pressure all around), but it would be nice not to have to worry about the nylon coupler breaking later on.

Second, if I can't use the stock pump with the Melling shaft, I'm going to use the Melling 10554. I'm pretty (but not positive) that I won't need to remove the intake to install the new pump (insert the shaft from the bottom and bolt on the new pump). Do I need to remove the intake to access the gear in the valley (to line up the new shaft)? I'm trying to avoid having to remove the intake for obvious reasons.

Finally, am I paranoid for doing this? Is the coupler that prone to breaking? Getting the pan off is a major undertaking, that's why I'm considering doing the pump. I know SBC pumps are fairly bullet-proof, but than damn coupler is worrying me.

What do you think? Replace, leave it alone, replace just the shaft, etc.?

 

I've been running the nylon couplers for years with no problems.

 

I think I answered all this on another board, so there is not much more to say. The coupler is not "prone" to breaking (been used on every small block for 50+ years), but the IS-55E will directly replace the shaft and coupler. Paranoid? Maybe a little.

MHO, I would replace the pump with the 10554, using the higher pressure spring. No sense in leaving a worn unit in there when you could put a new in (given the effort it takes to get to it).

 

I'm not sure what your worry is regarding the nylon sleeve. If it broke and fell off it wouldn't mean that your oil pump would quit functioning. The drive rod can't disengage from the pump on the bottom or from the upper drive gear even if the sleeve is gone. I wouldn't worry about it unless you are going to take the motor out for a different reason.

c

 

From what I've seen if the plastic/nylon coupler breaks then yes it actually could disengage. I could be off on that though...What keeps it from disengaging if it does not.

 

The dimension of the hole in the main cap (approx. .480") doesn't allow enough lateral movement of the drive rod (.550" diam.) for disengagement. The vertical movement is restricted by the oil pump drive assembly at the top. I just mocked it up to make sure and the only way the drive rod could disengage would be for the upper oil pump drive assembly to completely fail at the moment the car was upside down. At that point, you'd have a lot more complications in your life than the plastic sleeve.

I think the sleeve is there primarily to make it easy to assemble the motor. I've disassembled more than a few 100,000+ mile motors and I can't specifically recall an instance where the sleeve was completely gone and I know that I've never seen one that had disengaged from the pump if the drive assembly (or the distributor in the case of Gen I motors) was in place. It would seem much more likely to anticipate failure of the plastic housing of the drive assembly bolted in the valley. Those things are almost always cracked when you take the core apart.

 

Wow...that's good news. I've got to say, I was concerned that the nylon coupler was the only the thing keeping the oil pump working. This is the first time I've read what it actually does...what a relief.

So, after a week of research here's what I now know:

1) The SBC oil pump is very durable and should last for well beyond 100,000 miles.
2) The nylon shaft coupler has been used for a great many years and all in all, does not fail very often.
3) If the coupler breaks, the pump will continue pumping.
4) If the pump is to be replaced, the Melling 10544 combined with the Melling IS-55E is a popular choice. If more pressure is desired, replace the stock Melling spring with the GM "white" spring.
5) When the pump is replaced, priming the pump is best. However, if that's not possible, filling up the oil filter, and cranking the engine a few times with the primary wire disconnected is sufficient.
6) Using a high volume oil pump is not recommended.

Am I missing anything?

 

Sounds like you nailed it to me.

 

Great post sir. That was the exception I was thinking off as well. I wander if a person would notice a slightly strange variation of oil pressure if it were (drive shafting it like that from an angle)...

 

I seriously doubt it but we're reaching the point of an academic discussion. In my feeble understanding of the way things work, RPM is RPM and that's what the pump sees but God knows, I'm just a retired school teacher, not an engineer. If the engine RPM is at 8000 (I love the sound of a small block at work), the camshaft RPM is 4000. At that point the gear on the camshaft is spinning the oil pump at an RPM that is mechanically determined by the number of teeth on the cam gear and on the pump drive mechanism. When the pump is turning at that pre-determined RPM, it forces oil upward into the system at a pressure that is ultimately controlled by the tension of the pump spring. The speed of the pump is going to move a given volume of oil at a given pressure, a slight angle of incidence in the drive shaft notwithstanding.

Hell, what do I know? I need to take a break after thinking through all those elements.

c

 

I have posted pretty extensively on oil pressure and oil pumps before. I won't regurgitate any of it except to say that it still escapes me why people feel compelled to replace the perfectly good OEM piece with a replacement that in many cases is of lesser or at best equal quality? The factory pump is fine for most motors as is the drive shaft and it will last a loooonnnng time.

Rich