Prop Shaft Bolts.

[hlb]

Why is my boat forever breaking prop shaft coupling bolts. There are eight of them. It also breaks engine mounting bolts for fun. Obvious one is engine alignment, but why should it be out. Any other thoughts. The mechanic is mending it now and he cant think why.

<hr width=100% size=1> <font color=blue> Haydn

 

[burgundyben]

Which bolts? the coupling ones? Whats the failure mode? cracking? shearing? what type of nut? what material have you been using? beware cheap bolts (were they bolts or machine screws)? esp zinc plated due to hydrogen embrittlement following the plating process, also, if not stainless then are they 12.9 (little number stamped on head)? that refers to the strength of the steel by measuring the number of breakages and how the breakages compare to the max UTS (ultimate tensil strength) of the material, I'm bit rusty on fasteners, there is a BS spec, cant remeber the number, either they are wrong material or are repeatedly under too much load caused by the application (torque or alignment) resulting in progressive work hardening and failure. In a previous life I specified bolts in aerospace.

<hr width=100% size=1>"Who was he?"

 

[byron]

<font color=blue>Send an Email to Princess Haydn. Perhaps they can throw some light on the subject.

<hr width=100% size=1>http://www.alexander-advertising.co.uk

 

[tr7v8]

What normally happens is that the bolts are not torqued up enough so start taking the torque in shear. Once one starts to stretch then the others will fail quickly. Find out what the bolt spec is, diameter, cap head etc. Engine mounting bolts can be vibration or misalignmnt or both.
Some one hasn't replace them with Stainless have they?
Same questions as BurgundyBen is asking....

Jim
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[paulineb]

Princess Haydn ? Who's that?

<hr width=100% size=1>Pxx

<A target="_blank" HREF=http://www.paulinebeddoes.co.uk/php-cgi/gallery>The Perils of Pauline</A>

 

[banus]

my job is with rally cars and the principle should be the same so here goes. If the bolts work loose due to vibration they will of course snap. Now then,why are they coming loose?. Try fitting lock taps. if you can't get at them to tighten them every trip Paint the bolts thro the nuts with a stripe of tipex. then by looking at them you can see if they are coming loose. I am sure they are. Make sure you get the locking job sorted before you fit expensive ss ones as the ss bit won,t stop them snapping

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[martinb]

The numbers refer to the nominal tensile ultimate strength (first number) and the nominal tensile yield strength (second number) as a percentage of the tensile ultimate strength.

For example, fastener material ISO property class 5.8 means nominal (minimum) tensile ultimate strength 500 MPa and nominal (minimum) tensile yield strength 0.8 times tensile ultimate strength or 0.8(500) = 400 MPa.

Martin

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[coliholic]

I reckon it's user error. Princess Haydn probably just wangs it in from full ahead to full reverse and wonders why the thing breaks.

Have a word with Grumpy\Happy, perhaps he can recommend a course for you to go on.

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[byron]

<font color=blue>OK I will re-write it for your sakes... Haydn, have a word with Princess.

<hr width=100% size=1>http://www.alexander-advertising.co.uk

 

[hlb]

Well I've been called some names in my time. But never a Princess. I dont know quite what to think.../forums/images/icons/frown.gif.../forums/images/icons/smile.gif

<hr width=100% size=1> <font color=blue> Haydn

 

[stamfordian]

sounds like the engine mounts are on the way out if he,s there tommorow get him to check em,sounds like too mucch movement ...if this fails use the other engine/forums/images/icons/smile.gif

<hr width=100% size=1><A target="_blank" HREF=http://www.arweb.co.uk/argallery/stamfordian>http://www.arweb.co.uk/argallery/stamfordian</A>

 

[omega2]

Haydn, Have you got R&D couplings between your gearbox and and shaft flange? if so you can check alignment by doing the following# Look closely at the bolts and you will find that one of them has a domed head the rest will be square, then place a feeler gauge in the gap between the head of the bolt and the flange at 12 oclock position get a nice sliding fit, the rotate to 3 oclock the gap should be the same then to 6 oclock and then to 9 o clock if the gap remains constant you are in line if not the measurment will indicate which way the engine needs to go to realign. If the original bolts have been replaced by inferior ones suggest you get the right ones that is presuming you have the above couplers.

<hr width=100% size=1>J HAMER

 

[Guest]

While you have the bolts loose (new or old) rotate the shaft by hand, inserting a feeler gauge or multiples of them (to take up the gap and check this gap as often as you can around the circumference of the two Plates) if the gap varies either by tightening or loosening by one or two thou there is a problem.

The cyclic stress applied to the bolts will cause them to strech and thus loosen them. When loosened they will now (Having lost any benefit of friction between the plates)start to be placed in shere (like very blunt bolt croppers the plates will attemp to cut through the bolts) If the bolts are hardened they will affect the plates elongating the holes and if the other way round the bolts will shere (over time) sometimes both will occur.

I agree with the person who suggested the "tipex" trick to see if they are loosening. I am told that it is generally believed that if the underground had paid attention to this system there would be no motors and bolts failing on there trains recently.

The remedy is to ensure that the holes are not elongated? if they are ream them out. and fit correct bolts (manufacturer specified) Then check that the plates are at 90 degrees to the shaft. then ensure that the engineand shaft is in alignment.

Hope this helps
Rob

<hr width=100% size=1>robinwdunham

 

[longjohnsilver]

Don't really care wots causing it, just get the bleedin things fixed b4 next week, spose that's another cancellation coming up /forums/images/icons/smile.gif/forums/images/icons/laugh.gif

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[mtb]

They have said it all already , but are the engine mountings hard enough, also I dont know your set up but hows the thrust being taken up, some times a thrust bearing can cause problems.
If it's standard shaft how long is the shafting and is the shaft supported correctely with plubmer blocks.
Oh yes a dial gauge would come in handy place it against the shaft in a few places to check the run out , spin it over by hand before any thing is undone .

Cheers
Mick

<hr width=100% size=1>smile you'l be on your boat soon ;-)
<A target="_blank" HREF=http://homepage.ntlworld.com/boats/>http://homepage.ntlworld.com/boats/</A>

 

[hlb]

Oh well. The bleeding thing will get fixed before the Weekend John. Thats not the problem and subject to weather of coures. Muckyfarter will be going out to meet whatever Shit hits the fan Weather eight bolts. three bolts or what ever. Theres always the other engine. Dont know whether it's four wheels on my wagon or one . But we can keep singing along!!

<hr width=100% size=1> <font color=blue> Haydn

 

[miket]

Don't know about the technical stuff.

I had a coupling part, after all bolts sheared/ bent and the result was about £2k down the tubes. New coupling and new shaft + sundry other bits that required replacement as the inboard end of the shaft bent an inch out of true. Not bad, it being only about 12 inches from coupling to shaft log!!
I was also only doing minimal speed when it let go. What the consequences would have been at 25 knots, I have no notion.

Don't mess around, get it fixed properly.

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