A Perkins water pump drive coupling question

I am in the process of rebuilding the raw water pumps on my twin 200HP Perkins ST 6.354.4M's.* All was going well until the spider coupling hub on the pump shaft broke in half when I was removing it from the pump shaft.* While it could have been caused by me when I was tapping a screw driver in the gap to open it slightly to allow it to slide off the shaft, the markings indicate it was probably already cracked.* It cracked from one corner of the keyway slot and broke completely in half.* The broken coupling looks to be made out of cast iron, really looks like grey iron.* That hardly seems an appropriate material choice for something that has to flex slightly to remove and clamp.* Long story, short a new one from Perkins was quoted to me for $122.* And that is only*one side.* Worse, I can't get it to me before next weekend.* The coupling is a 3/4" ID bore with an ANSI std. keyway.* I can buy a generic spider coupling made of steel, not cast, same bore, keyway, overall length, with about a half inch smaller OD.* Rated at 25 HP at 2000 RPM.* The only real difference is that it is secured with a 5/16 set screw instead of the split hub/ 1/4' bolt like the Perkins.* Set screws work for prop shafts, I can't imagine why it wouldn't work here.* Best part, for $60. I get* both sides, plus Hytrel spider, I can have it on my door step at 10 AM tomorrow.*

Can anyone think of a reason this wouldn't be as good, if not better, and way cheaper.* I think I will try it regardless, but I appreciate your comments.

When I had my Mainship with the OEM 160 Perkins, it had a coupling made of phenolic material. I had one of the toolmakers where I worked make one up for me as mine was worn. That one was still in good shape 5 years later when I repowered.

I would go for the generic "standard" as a replacement. You can always grind or file *a small "flat" on the shafts for the set screw to bite into. Use loctite on the set screw and forget about it.

I have the 6.354 M *NA's and I don't know if I have the same joint or not (sounds like it though) and I have never replaced one, but I'm with*jleonard.

Only question I would have is the 2000 RPM rating? *My Perkins runs up to 2800 rpm (not that I often run them that fast). *Is this joint rated for that high of an RPM? *Other than that I don't think I would be afraid to try it. *Since you have twins, you have the security of a back up.

Larry B

PS. love your blue hull; was that an option on the later 34's or a repaint?*

Thanks for the responses. I ordered the coupling today, will have it tomorrow. I might have screwed up and ordered a slightly too large OD to clear the pump bracket. I had the broken hub but left the pump and bracket at home. Now that I have seen it, I think I will have a slight interference. The original is about a half inch larger OD than what I ordered, but the end nearest the pump is only about 2" OD. Soooo, tomorrow I'll have to decide if I send it back and wait another day, or turn it down on the lathe on the end.

Actual coupling is rated 7000 rpm. I used the 2000 rpm figure to calculate HP ate the rated 723 in-lbs torque rating.

Blue hull is not original. It's Interlux Interthane paint.

I will post a picture when I get it together.

OK, that makes sense then. *I wonder if I do have the same couplings. *I've never taken them apart, so I think I will check them for cracks. *I have Sherwood pumps. usually I just put a new impeller in every couple of years and she's good to go. *Let us know how that works out for you.

Larry B

how did you get a quote from Perkins? I have same problem. I broke both mine.

I broke both of mine (same way) now i need to get 2 from Perkins. How did you get ahold of them??

Capn Craig said:

I am in the process of rebuilding the raw water pumps on my twin 200HP Perkins ST 6.354.4M's.* All was going well until the spider coupling hub on the pump shaft broke in half when I was removing it from the pump shaft.* While it could have been caused by me when I was tapping a screw driver in the gap to open it slightly to allow it to slide off the shaft, the markings indicate it was probably already cracked.* It cracked from one corner of the keyway slot and broke completely in half.* The broken coupling looks to be made out of cast iron, really looks like grey iron.* That hardly seems an appropriate material choice for something that has to flex slightly to remove and clamp.* Long story, short a new one from Perkins was quoted to me for $122.* And that is only*one side.* Worse, I can't get it to me before next weekend.* The coupling is a 3/4" ID bore with an ANSI std. keyway.* I can buy a generic spider coupling made of steel, not cast, same bore, keyway, overall length, with about a half inch smaller OD.* Rated at 25 HP at 2000 RPM.* The only real difference is that it is secured with a 5/16 set screw instead of the split hub/ 1/4' bolt like the Perkins.* Set screws work for prop shafts, I can't imagine why it wouldn't work here.* Best part, for $60. I get* both sides, plus Hytrel spider, I can have it on my door step at 10 AM tomorrow.*

Can anyone think of a reason this wouldn't be as good, if not better, and way cheaper.* I think I will try it regardless, but I appreciate your comments.

Click to expand...

Did you look in mcmaster-carr? They seem to have everything.

Warp 7 said:

I broke both of mine (same way) now i need to get 2 from Perkins. How did you get ahold of them??

Click to expand...

HELP!! Anybody know where I can get 2 of these couplings for less that $862.00 each ?? They are best described as "split collar couplings for a keyed raw water pulp shaft" I fear I am the one getting the shaft from Perkins Parts.

See post #2 above

I don't know. If you're more inclined to keep everything stock then bailout of the below.

I would get creative, especially if I had two engines - but only because I am cheap and enjoy solving these types of problems. Certainly risk is a big consideration here, as this is a critical component. Failure of the coupling wouldn't render you immediately without an engine but you would only have a small amount of time before you must shut down or suffer damage/failure. Lets say you don't have Murphy gauges, have only a single engine, and commonly transit a bar or other dangerous waters. In this case I wouldn't waver far from the stock solution. However, let's say you have an alarm on your raw water flow, have two engines, and stay within calm waters where you can almost always just anchor and call for Vessel Assist. Then I would feel more license to come up with a coupling that is farther away from a stock solution.

Let's say you're in the latter of those two groups, since if you're in the first group you need stay with the stock solution.

I have the same water pump setup on my mainship so I have some context. I believe the purpose of this coupler is to allow for some axial play between the water pump and the PTO shaft. This is a common problem in machinery. The Perkins solution is certainly tried and proven, however there are likely alternatives. The interface between a PTO shaft and a power consuming device, such as a water pump for a marine diesel, or a fertilizer spreader for a tractor diesel, are similar. There are hundreds of different types of couplers that allow for alignment and play between two shafts. The specs would be the shaft diameters, keyway size, RPMs, torque, tolerance, etc.

I don't know what the torque on a water pump shaft is. Here are some shaft couplings in the $50 - $250 range with ratings between 140 and 3700 in-pounds.

McMaster Carr offers these:
McMaster-Carr
McMaster-Carr

If you're not comfortable or have any concerns then stick with the stock - it's tried and proven. These might work, but like I said earlier, I don't know.

I would pick the largest outside diameter "lovejoy" style coupling that would fit. This type of coupling is used every day in all kinds of applications.
We have them on hydraulic packs that have more heat and higher torque than a raw water pump on a diesel engine. And they last a very long time.

OR buy some phenolic material of the same thickness as your oem is and take it to a machine shop along with your two coupling halves. I would estimate one hour to make two ($100).

I was just about to order a replacement "spider" from Perkins parts shop for about $140! The original was about 75% worn away. I flipped it over backwards to torque on the unused faces for now. Thanks for the McMaster Carr link.
Another project for when we get home.