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stuffing box temp

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bobct

Advanced Contributor
I got my boat back in the water, new shaft, fixed prop strut and rudder. After all that I'm stumped on re-packing the stuffing box.... 1.25" shaft, 1/4" GFO packing.

I used this stuff on the other side before I launched and it runs about 10 degrees hotter than the water temp which is great. It almost doesn't drip at all. Since it's running so cool I haven't touched it since.

On the side I just put back together, I can't get it to run cool no matter what I do. First, I just re-used the "new" packing from the spring since it only had about 10 hours on it. I couldn't get it to run cool enough at speed, I was getting around 150 degrees on the lock nut, a little less on the shaft. I tried loosening a bunch of times but never could get it.

So, I figured I would start from scratch. I removed all the old packing and installed 3 new rings just like before. Tightened it just barely so it was a steady flow at the slip and took it out for a break in run. I'm back in the same cycle as I was before. If I go really slow (less than 10 knots), the temp will get up to around 105, hotter than the other side but not too bad. Water temp is around 70. But I can't get it to drip when over 3k RPM's and then the temp shoots up to 160-170. I tried it as loose as a steady flow at idle and it still got hot.

After going through this cycle half dozen times again, I removed one ring of packing since there wasn't much thread left but no change.

Can you guys think of anything else I could be doing wrong? Since it drips at a slow speed but seems to stop at higher RPM's I started thinking maybe the strut is moving slightly which causes the shaft to rub against the shaft log. I got another 1/4 turn on the strut nuts from inside the boat. It feels fine, alignment is good.

Maybe I've got it TOO loose to start? Is that possible? I must have been lucky on the other side, I did that in one shot.

Bob
 
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Did the nut go on easily, without moving the threaded end?

The only scenario I can conjure up is that the shaft isn't centered in the 'box' and this is giving a lot of contact area and inducing the friction that is producing the heat.

Doesn't explain the lack of a drip though....
 
yes, it threads on easily. I'm wondering if the new shaft is fractionaly larger, I was thinking of trying 3/16" packing instead. The shaft itself doesn't get nearly as hot, the hot spot does seem to be the bronze box and packing nuts. There's no noise and I've been down there when the boat is running.

So, I think the shaft is staying reasonably cool but the box is heating up. The tolerance between the shaft and the tube is so small on this Buck setup I can't see how it wouldn't touch under some conditions (at least initially). When I talked to Buck during the spring, they told me that the shaft did have to wear into the bronze at first.

I know you thought that was odd and so did I but I could clearly see slight wear on the old bronze box parts but the original shaft was just fine. I assume there was an initial wear period and then it stopped. When I re-packed there weren't any grooves, I just cleanup up with some 600 grit and it was fine.

Maybe the 3/16" will force some add'l water flow. I can live with a little extra drip for now or the rest of the season.


Update - I called Buck and talked to their tech support guy who's been there for 20 years+. He didn't miss a beat and said the "new shaft has to get polished and the temps will drop over the next 10-20 hours. He said the bronze is a lot softer than the SS and confirmed that there is metal/metal contact happening (for now). As long as the temps don't get over 160-170 it's not an issue. The hose is the weakest link, those temps don't pose any issue for the metal parts or the packing".

I guess this confims what I thought and does make sense given that the shaft is brand new. I'm not sure what other stuffing boxes look like but as I mentioned above, the tolerance between the shaft and the box is fractions of an inch. Seems to me if you had much larger gap (i.e, shaft to sterntube), you would eliminate this issue. I always thought stuffing box was full of water. On mine it just dribbles in. Even if I removed the stuffing box and packing completely it's still not really that much water coming in.

With this close a tolerance, it doesn't seem physically possible that you wouldn't have some interferance at least initially. I'm going to cruise for a while and get my baseline high temp and then watch it for a while. Hopefully it'll start to come down over the next few weeks.
 
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hmmm.., wondering if I should just run 3/16" for now until I get past the break-in period. I took one ring out yesterday so just two 1/4" installed now.
 
If the gent at Buck never missed a beat, I'd trust him. I'd keep the two rings of 1/4" and put the time they suggested on it - keeping a watchful eye with the temp gun.

That lack of gap is not the norm, at least for what I've seen, for today's designs. Since the boat has a few hours on it, it just may be ok once 'broken in'. Let's hope with a slow and steady approach, you and Rich will be 100% functional early next month.
 
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