Stuffing box packing

[doublec9]

Hello all,

I have stuffing box curiosity. Is there a standard packing size for A4s? I ask because I just pulled the old packing out of my stuffing box for the first time and found way too much packing in it (count 'em, 8 rings!). Luckily, the shaft is not scored and is in good shape. Unfortunately, I pulled 3 different sizes (and I think 3 different types) of packing out of the stuffing box, so I'm left guessing the right replacement size. I'm hoping there is a standard A4 packing size so I don't have to buy three different sizes. Shaft is 3/4". Boat is a '79 Pearson 30. The attached picture shows what I discovered.

Thanks,
Carter

[roadnsky]

Carter-
It looks like you're lucky not to have scoring.
This is the best explanation and description of the stuffing box re-packing procedure that I have found:
http://www.pbase.com/mainecruising/stuffing_box

There are also various other threads here regarding the procedure.
Search "Stuffing Box".

Also, just for future reference, watch your file sizes when you post pictures.
This site allows for some pretty high rez postings which cause the viewer quite a bit of scrolling.
Smaller images work best.

[roadnsky]

Oops. I didn't actually answer your original question about the packing size...

The size will be determined by your shaft diameter.
(Hmmm, can I say that on this site??!)

[rigspelt]

I had to estimate this for the first time too. Don Casey: "measure the space between the shaft and the inside of the packing nut to determine the correct flax size" (http://www.boatus.com/boattech/Casey/StuffingBox.htm). So if I've got this right, then size of stuffing C = stuffing box gland inside diameter A minus shaft diameter B divided by 2, since there are two sides to the diameter. Someone said that since packing won't compress down but can expand up a bit, go with the smaller size if between two and the larger is greater than C. Hope that's right.

[jayw]

When you install new packing it is very easy and very common to overtighten. New packing will compress down for a while after it's first put in and will require a few initial adjustments as it wears.
Best approach is to first tighten the packing nut until the water drip is slow (like about 1 drop per second or a little less) then run the engine for a few hours and re-tighten to the same drip rate as before. This type of packing is supposed to slowly drip water for its life as the water cools and lubricates. Overtightening to the point of no drip causes the packing to heat up and wear quickly and may score the shaft.

[doublec9]

Thanks for the great replies. Sorry for the large photo...and thanks for resizing it for me. As soon as I uploaded it, I realized how large it actually was, but couldn't figure out how to resize it.

I made some measurements when I extracted the packing, but my measurements didn't correspond to typical packing sizes. I measured between 5.5mm and 6mm as stuffing size "C," but that leaves me between 3/16" and 1/4". Of course, the problem could be the measurer, considering I was making the measurements at arms length.

Speaking of bad measuring, when I measured the shaft diameter, I got 15mm (roughly 5/8"). Does that sound like a normal shaft diameter or a bad measurement? I was expecting 3/4" or 1" diameter.

I'm probably safest buying 3/16" and 1/4" and doing a little trial-and-error experimentation.

[Dromo]

I used a caliper to measure the shaft on my 25ft boat.

I thought it would be 1'' or 1-1/8'' using a tape measure, but with a caliper I got 7/8''.

I'm thinking a 5/8'' prop. shaft sounds a little small for a 30hp inboard engine.

But I could be wrong.

Rick

[smosher]

I have a 74 P30 and its a 7/8 shaft and I used 3/16 packing, 4 rings

[m_galligan]

I have a Catalina 27, and I use 3/16" packing.

[tenders]

Buy all the sizes that might be right and write the proper size down for next time. You don't wanna be in the situation where the boat's in the water and the shaft is leaking uncontrollably.

By the way it looks to me like you've pulled out 9 rings, not 8!

[rigspelt]

Over or under size?

So, does slightly smaller packing expand up a bit as it is compacted by the packing nut? It makes sense to me that if one had to choose between a packing sized slightly less than C or larger than C, it would be risky to try to stuff the larger sized packing into C.

I measured C at 4.5/16" = halfway between 1/4" and 5/16", so bought 1/4" Teflon-impregnated packing, which is only 1/32" smaller than C. Would it be better to drop even smaller and start with 3/16",which is 3/32"" smaller than C?

[67c&ccorv]

Oh boy, just looking at this job gives me the willys! You should the tiny little work area I have to somehow squeeze into (probably with my wife holding on to my bootstraps) in order to redo the packing gland on the Corvette!

[doublec9]

Just wanted to send a follow-up. Successfully repacked the stuffing box this weekend. Started the job with a pack of 1/4" and a pack of 3/16" GTU packing. The four loops of 3/16" fit the bill perfectly.

By the way, remeasure the shaft at 1-3/16". Now I need new zincs and am guessing I should go with 30 mm: West Marine carries 1-1/8" and 1-1/4" anodes, and also a 30 mm.

[rigspelt]

Just wanted to send a follow-up. Successfully repacked the stuffing box this weekend. Started the job with a pack of 1/4" and a pack of 3/16" GTU packing. The four loops of 3/16" fit the bill perfectly.

What happened when you tried 1/4"? Just would not fit in? Just interested in learning more about this procedure, since I'm about to do it for the first time.

[tartansailboat]

packing gland

When I first tried to replace the packing material, measurements indicated that 1/4 inch material was correct. After installation I found that I could not get any dripping even with the nut backed way off and after running for a minute, the shaft was very hot. I redid the packing using 3/16 material and the shaft ran cool. All boats are different but I suspect you want the smallest diameter packing that still does the job, to prevent scoring of the shaft.