Some input on couplings
Some input on couplings.
1) If you are removing a coupling that is more than say two years old, depending on bilge moisture, you should not re-use it. Solid couplings are a one time use after they have become "made on" as Mike the manager at H&H Prop refers to it as! Why is this?
When you remove an older coupling you will break a layer of rust free. This rust was your tolerance. A shaft and coupling are meant to fit together very, very snugly. In all my years of boating I have only had one coupling go back on and maintain the tolerance and that boat only had a few months of service on her. Re-installing a used coupling can ruin your shaft. Shafts are expensive coupling are cheap in comparison!
H&H Propeller, the machine shop I use & the largest shaft and prop shop in the North East, fits the coupling to the shaft with a tolerance of .0005". On a properly machined shaft, without any anti-corrosive agent like Tef-Gel, it will slide on about a 1/4 to a 1/3 of the way before you experience some serious resistance. This initial fit is often referred to as "lead" meaning they give you a little bit of leeway to get the shaft started into the coupling. The coupling and shaft are machined to exacting tolerances (.0005) so there can be NO wobble or play between the shaft and coupling. Any wobble will cause excessive shaft, key and coupling wear and could eventually lead to a failure.
2) The shaft is usually fine and can be cleaned and re-used. It is the steel coupling that gives up surface material, and this lost layer of rust means you can't re-use it. If the coupling just "slides" back on it is too loose!
3) When reinstalling a new coupling to an old shaft you should always have it fitted and faced by a machine shop or prop shop. H&H Prop charges $65.00 for a fit and face. While you are at it have the shaft trued. Shaft truing is more costly than a just a fit and face but a lot cheaper than a new shaft and it will get rid of any annoying vibrations. Another good practice to eliminate bvibrations is to "lap fit" the prop to the shaft and you could actually do this yourself.
If you hit something and bent the tapered end of the shaft near the prop the shaft is toast and most any reputable shop will not and should not straighten it.
4) When re-installing the shaft you should get it started with the machined in "lead" then lightly tap it home with either a rubber mallet or an oak or maple block protecting the shaft and a hammer. For this job need two people or many trips up and down the ladder. Pound it in while looking in the coupling holes until you see the dimples for the set screws. Don't over do it cause backing it off is more of a paint than driving it in.
5) Shaft keys should fit snugly but not so snug that they are "key bound". If the key has any play have a machine shop make you a new one.
6) Anti-corrosives like Tef-Gel can sometimes aid in future removal but it is no guarantee. As Mike at H&H says about using Tef-Gel or any anti-corrosives/seizes "It won't hurt nothin' but a properly machined shaft and coupling should shave any thing you put on that shaft off as you fit the two together". He says it won't hurt but in most cases it won't help either. You should also not use a neverseize product containing any aluminum, copper or graphite as it can add to galvanic corrosion issues.
Contrary to what Mike says I have been using Tef-Gel and had good to mixed results up to about two years with coupling removal. It does aid some in the removal but does not always mean it's re-usable. I will be pulling my coupling in a few weeks to do some tranny work, and it is also at the two year mark, and this time I will photograph any rust or lack there of.
7) If you can, I can't I have a v-drive, don't replace the coupling with a solid coupling and instead replace it with what's called a "split coupling". This will make future removal and re-install much easier. Even with a split coupling you should still have it fitted and faced after removal. The $65.00 +/- is well worth it.
Hope this helps..
Oh and;
Never use a hammer to pound directly on a coupling that is connected to the tranny. You can damage the bearings and the soft aluminum cases many transmissions are made of.
