Broken prop shaft!

Poor alignment most likely I think.

juniorwoody wrote: Poor alignment most likely I think.

Absolutely agree.

Both couplers have to be dead. Not a .01 of wobble, and both faces must be absolutely perfect. Correct me if I'm wrong

Thanks for the response. I did align with a feeler gauge last time, and I THOUGHT it was good. But,as I said, as I did it, it seemed like it was arbitrary. My new shaft is on its way, . I'll give it another try!. Just for curiosity sake, I'm going to try and do it mathematically,,just to see if there's anything I obvious.

TRBenj wrote: Maybe one of our resident ME’s can comment how one might align with “math” instead of measurement.

I'd sure like to know how too.

You can verify your couplers are pretty darn straight by using the technique of adjusting the gap to as close to zero as possible and then rotating the prop shaft and double checking. Your gap should be the same before and after rotating the prop shaft 180*.
Far as I know this is the industry standard and you do not need to revisit the technique. It works, if yours broke something was wrong with the shaft or your alignment.   Hope the repair goes well. As mentioned early in this post, the tapered shafts save a lot of time on install and if you ever need to repair and are nearly the exact same cost as a standard shaft.

Pete could align an engine under .001" with a stick of gum on a cold enough day, i think you're going to learn something on this project

Thanks guys.! now that I'm home on my laptop, instead of my phone, I can elaborate..I have a 47-3/4" x1" double taper shaft. I very carefully checked the alignment with my feeler gauge. My thinking is: there's AT LEAST 4 things using the feeler guage wont tell you.
#1 is the trans coupler true to axis?- if not, no measurements are valid- and how would you know?
2. is the shaft coupler perfectly aligned to its axis? AKA 'wobble"
3 Was my old shaft perfectly straight? "
4- are both mating faces PERFECTLY clean.- or feeler guages dont work

Id bet its rare not to have at least one of these issues. No?

Dont take this I'm being argumentative-I just think of why things might not work constantly..
- I remember spinning the couplers while I was installing the shaft- thinking both couplers could be off axis equally and mated together,but as long as the engine and shaft are in alignment it wouldnt matter and could have been fine since manufacture.. couplers could wobble together and everything be just fine,, and then when you try and rotate them 180 you could get a big difference and massively out of whack .. I know I'm going down a rabbit hole for no reason,, but I'm just sayin = you cant try to be VERY accurate and have variables at the same time..

MourningWood wrote: . He convinced me that the best way to do it was in the water, although not very practical all the time.

If I remember right one of the PCM books I have even mentions checking it every time it is launched as well. I believe their thinking was for large boats not trailer boats but that was not stated.

briandarf wrote: one more question.. how can you spin the shaft 180 and know for sure it didnt slide forward or back?

I used to put a .003 shim in the tightest spot, near a bolt hole. then tighten the bolt finger tight, just enough so the shim (aka spare feeler) wouldn't fall out. Then you can gage from there (.003-.006), rotating to see if it changes (it always did for me).

I think Brian's taking the 'measuring' too literal.

Sub-0.001" angular alignment is possible, using any single feeler gauge in stack, by blunting the couplings together with the gauge inbetween and feeling for uniformity.

After getting it close one then rotates each coupler individually to re-verify their squareness. if it goes wayout, stop and correct the flanges else chase it forever with bad results.

then upon clamping the couplings, if it takes more effort to rotate the system, or has a difficult spot, something is still amiss and will translate to vibration or worse yet, failure.

Thanks gottaski. These are the answers I was looking for. You guys are awesome

One more, have you watched the alignment video? There's a link in the FAQ thread in the maintenance section.

Briandarflinger wrote: Can't check the coupler the shaft is broken and still in it.. I guess I could check the shaft for straight if I had a glass coffee table.

Brian,
The alignment video has a short mention of using a dial indicator for checking the shaft.