Shaft Coupling Bolts

[Tony Meola]

Come by me, we'll sit in the parking lot looking at the boat and tell fish stories...maybe go inside, look at the boat and tell fish stories over a cold one. Or maybe I should just work on mine.... nah. Cold one and fish stories.

Just make sure the wife is not around. Everytime my wife comes to the Marina in the spring to give me a hand, she is always saying to me no wonder you never get anything done. All you guys do is talk to each other.

[Carl]

Just make sure the wife is not around. Everytime my wife comes to the Marina in the spring to give me a hand, she is always saying to me no wonder you never get anything done. All you guys do is talk to each other.

They do seem to have knack for showing up at those times...

[Joseph Fikentscher]

I vote for cold ones and fish stories. I used to be able to catch fish.

[Joseph Fikentscher]

Got it back from the machine shop early. $80.

Lining up the splines is no fun. Taking a break. It's quite heavy.

https://www.facebook.com/enduranceb25/p ... =3&theater

[Carl]

4 x 4 or pole across gunnels
Use a rope, tie off and shim the cross beam to adjust to the right height.

or come-a-long, cheap block and tackle

Changing my trannies I used a JC Whitney Block and tackle...1/4" rope plastic pulleys..cheap but worked perfect.
Tied off to tower..brought up to height ...one hand let me bring up or down a bit...knee's guided, other hand wiggled and pushed.

[Joseph Fikentscher]

After 5 hours, I still can't line this up. UGH!!! It should just slide in.

[Yannis]

Joe,

Talk nice to it, it might help!

[Tony Meola]

Joe.

If you need a second set if hands give me a call.

[Joseph Fikentscher]

Finally got it back together yesterday. Seems to be ok. Ran in the slip only. How long does the red lock tite take to set up?

I figure I’ll take it out tomorrow for a run.

Thanks for the offer Tony.

[Joseph Fikentscher]

Well, now that it's back together, I ran it in forward at the slip for about 20 minutes. Sounded good.

Then I put it into reverse and heard some loud noises and the engine stalled. Started it up again and forward and reverse was ok. Forward and reverse a couple of times and the sound came back and the engine stalled again.

Maybe I found why the bolts were shearing? Not sure what it is called but could the part with the springs between the engine and the trans be shot?

I haven't taken it apart yet as the engine will need to be raised a bit to get the whole trans out.

What do you guys think??

Thanks,

Joe

[Carl]

Pressure plate.


I know when mine went I thought transmission was coming apart.

It was also at low rpm when it sounded horrendous and kinda got better as rpms came up.

But always at low rpm in gear...makes me wonder how a broken spring or two can only be broken sometimes.
Not saying yes or no...I am not a mechanic.

[Joseph Fikentscher]

Thanks, carl. That's what I thought.

[Tooeez]

I have been following this thread with interest, because I thought that I was the only one who ever had these impossible to figure out, nobody ever heard of such a thing kinds of problems. And since I never worked on a v-drive I was hesitant to offer an opinion. However, I know how frustrating this kind of thing is, and how you can get so into looking for an answer you begin grasping at straws, and that leads you further away from an answer to the real problem. Therefore, let me offer you an objective look at your problem:
You described the problem as the bolts "shearing", and that word got us thinking about the problem in a certain way. Let's go back to basics, and consider how a coupling works: one side is connected to the driving force, the other side to the load to be driven. The faces of the two sides of the coupling meet, and should be as close to parallel as possible, so that when the coupling turns the only force on the fasteners is shear--side to side load. There should be no tendency for the faces to runout, or try to pull apart--that would put a tension load on the bolts. In order for the bolts to shear--to be cut off at the face of the coupling--the driven side of the coupling would have to stop dead, while the driving side continues to apply torque--and enough torque to overcome the shear strength of the bolts. I don't think that any gas engine--especially at low rpm--can supply that kind of torque. And if it did all four bolts would be sheared even with the face of the coupling.
When I re-read your posts I noted that both times the bolts broke there were portions of the shank of some of the bolts protruding from the face of the coupling that they were screwed into. I think that means that they were not broken by a shearing force--they were pulled apart by a tension load strong enough to pull the heads of the bolts off.
Think about how a coupling looks in a side view--if the two faces are parallel as it turns the space between the faces remains even all the way around. If they are not parallel--if, for example, they are closer together at the bottom than at the top--as the coupling turns the bottom edges will be pushed together, and the top pulled apart--maybe, eventually, fatiguing the metal in the bolt until the head breaks off. If that happened to one or two bolts the remaining bolts would be unable to handle the shear load and would part at the coupling face.
This might all be wishful thinking, but for what it's worth here's my thoughts: your problem is most likely caused by a radical misalignment between the v-drive and the shaft. Although it just might not be lined up correctly, I think it more likely there is a problem in the engine mounts that allows the engine to shift position under load. It could be one or more broken motor mounts, failed rubber bushings, rot in the engine beds, broken lag screws, etc., or a combination of that sort of thing. And it might not be apparent--I saw a lag screw one time that seemed to be socked down tight, but turned out to be frozen in the motor mount, and broken off underneath. It's also possible that the shifting of position is coming from the shaft end, but this seems much less likely to me--somehow the strut would have to been moved way out of position.

[Joseph Fikentscher]

To clarify, the bolts sheared off even with the coupling face. There was about 1/8" protruding on the back side of the coupling. I was able to remove two with vice grips but the other two wouldn't budge. Therefore I had to remove the v-drive and take it to a machine shop for removal of the last two bolts. The head portions were found in the bilge.

I have checked the alignment and all seems ok.

There was some major noise in reverse after I got it back together. And before this all happened it was intermittently stalling when I put it in reverse.

I am attributing the noises to the pressure plane/dampening plate.

I order to fix that I will need to raise the engine to get the whole transmission off.

[mike ohlstein]

I HAVE NO IDEA HOW THESE COUPLINGS WORK

But, I know a thing or two about steel and loads and shear.

When you mechanically fasten two pieces of steel (beam to column, for example) and put the right amount of torque on the bolts, there's so much friction between the two faces that (perfectly parallel or not) it would take a monstrous force to overcome the friction alone. The only way to even get past the friction to test the shear strength of the bolts would be the application of an enormous shock load. Which begs the question, are you torquing the bolts to the proper spec?

[Joseph Fikentscher]

Mike, They were tight. But, that being said, I'm not sure what the spec should be.

[Joseph Fikentscher]

Stumped Mack Boring with this question.

[Joseph Fikentscher]

Just got a call back. 3/8" bolts are 50 FtLbs. 5/16 bolts are 25 FtLbs.

[CamB25]

I hesitate to weigh in on this...I would like to see photographs of the failed hardware. It's hard to imagine a pure shear failure of all bolts at once that didn't coincide with a catastrophic failure of some kind. My guess is they are failing in fatigue due to alignment issue or repeated overloads (shocks), or a bad bearing wobble, or the couple faces are not making good, uniform contact. Anything out of alignment may result in eccentric loading of the fasteners, resulting in a progressive fatigue failure of the hardware, one by one. See Tooeez post

It's happened twice on the same side. This last time you were putting around at 1200rpm. Low loads..points to fatigue failure. You had/have a stalling issue in reverse, which means something ain't right with the entire assembly. The coupler failed as the weakest link.

I think you need to dig deeper into the engine and drive to find the root cause. The coupler is like a fuse, it is letting you know something is wrong.

[CamB25]

50 ft-lbs on a 3/8 grade 8 bolt? That would be for fine thread, not coarse thread.

[Joseph Fikentscher]

Cam, I agree somewhat. I will be replacing the dampening/pressure plate. We'll see what that does. Maybe they were just loosening up? I didn't use locktite before.Did this time.

The bolts are fine thread. I tossed the old ones already.

[Carl]

Coupling bolts are fine thread.

The idea of a large, clean, face on the couplings is to create high amounts of friction to transmit the load. The bolts are in tension creating the friction as Mike said.

Soon as bolts loosen...the game changes as friction is lost between the coupling faces and the bolts are left to take side loads...and shear as they are not meant for that.



Bad alignment of motor to shaft may stress the bolts some as mentioned...but usually what happens is the shaft takes the brunt of the misalignment bending slightly with each rotation. This fatigues the shaft and causes the shaft to break...usually right at the key behind the coupling.

[mike ohlstein]

You probably know this but......

Proper torque is critical. Don't use your grandfathers rusty torque wrench.

Don't torque down one bolt and move to the next one
Do sneak up on tightness and do it in a 'star pattern' (do one, then the one opposite, then to the left, etc.) Sung each. Torque each. Re-torque each.

Do use hardened steel (grade 8 fine thread).
Don't use titanium. As Uncle Vic used to say, "The enemy of good is better". Titanium is extremely strong, but it stretches. Getting Ti bolts properly torqued is tricky. (This is good advice for Ti hose clamps too)

[Tooeez]

Here's another thought: you have a noise in reverse, but not neutral, which makes one think that whatever is making the noise only turns with the engine in gear. That means everything aft of the transmission output shaft, which in your case is the v-drive. Maybe there's a bad bearing in the drive that is allowing the coupling to wobble. If it was the rear bearing I think it would destroy the oil seal, and you would see oil in the bilge. But I assume there has to be a front bearing on the v-drive output shaft, and if that went bad the front of the shaft could move around while the back stayed in place, causing the flange to runout while turning. Loose ball bearings in the case could also explain the stalling: if one of them gets between gear teeth it could lock the unit up, then fall out when the load is released. The damper plate turns all the time, but there is no load on the springs in neutral, so maybe in neutral a broken spring wouldn't make noise. I have seen a few of these go bad, and it always showed as a hard bang when going into gear, with maybe a rattling noise in gear at low rpm. I can't imagine how a broken spring could cause a stall.

[Carl]

Spring or two goes bad in pressure plate you can get a bad case of gear slap...that self destructing noise.
I'd say its a good shot that could stall a motor at a low idle.


Issue with just relying on torqued bolts is the torque is usually a dry assembly and Joe is using loctite.
Which I think is a good idea especially as he is not bolting into a grade 8 nut...but a soft steel tapped flange that has less then perfect threads.