Engine mount failures

Re. CAT C12 and Isoflex engine mount failures

Interested to hear from any builders or operators that experienced premature failure of Isoflex engine mounts. We launched 4 aluminium sister 15m Pilot boats less than 10 months ago.

One Pilot required all CAT C12 engine mounts (sheared stud bolt) replaced after just 8months, now another pilot has the same issue.

Shaft alignment and engine bedding was check after launching and again at 6 months.

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Discribe the motor shaft and gear box set up . The full thrust of the prop is pushing onto the engine Then through onto the mounts ??? is it only the mounts that are crapping out????
When you shift from forward to reverse does the engine move back and foreward on its mounts ?? Post some pictures of the whole box and dice you have ,mounts , gear box , motor , propshaft , lets see what you have and how everything is set up !!!
We await you reply !!!.

What part of China are you in ?? I was in Suzhou last week and just shifted !!

 

The set up is standard, nothing ouside the box.

C12 500hp @ 2300rpm C rating ZF325A gearbox with flex coupling/Henley stern gear and Austral 29in 4 blade prop.

Engines don't fwd/aft shunt under drive/reverse changes, minimal engine rock, vibrations well within normal limits thru ought engine speed range. Boats do work hard, 20hr plus per 7 days in all conditions. Seas dont get big but waves get short & steep.

Boat Capt. are reasonably conservitative drivers not full throttle jocks like some pilot operators.
I RC hardness tested the broken (sheared) 24mm dia bolts - all were in 63-65Rc range, tensile strength unknown.

 

Hi tunnels, check your pm

 

The broken engine mounts that Ive seen were, as Tunnels pointed out, caused by prop thrust or poor installation. Mounts must be correctly aligned and fastened on the engine beds so that the mounts studs are perpendicular to the engines crankshaft and the engine must not be jacked up to high on the studs.

 

All engines mounts were set up correct, min. amount of bolt extension, 20mm clearance between lower lock nut and flex cover plate as per install instructions. All monts were set up by a highly experienced marine engineer as team leader and checked, bolts had correct verticle loading @ 90 degree to cover plate/plate true to engine bed.

All bolts were in compression, none in extension. We recently recieved advice that one set engine mounts in third vessel have also failed. I think bolts were excessively hard/incorrect heat treatment. The manufacturer and agent doesn't have the professionalism or courtesy to respond to my latest emails.

 

Send the bolts to an authorised independent testing house and get them to establish the grade, temper and yield stress of the bolts. Also have them check for poor QA during manufacture too, since poor threads etc can lead to fatigue failures quickly if not done correctly and within a tight tolerance.

 

Correct engine mounts on a flat bed with correct adjustment don't break.

I think you too high on the mounting bolts.

Are you using 4 or 6. Is the shaft straight from the gearbox or a down angle.

 

Hey Frosty, in my previous post: 'min. amount of bolt extension, 20mm clearance between lower lock nut and flex cover plate' should have been max. amount of bolt extension (I'm back at my desk with 14hr flight jet lag, plus bloody 6 hr delay connecting flight and 4 hrs sleep = brain death).

All 8 gearboxes are ZF325 A.

 

All engines were 4 mount only, and when replacing failed bolts I also added a fabricated 12mm steel bracket to each engine block rear to bolt/transfer load to gearbox mount.
The design allowed for 4 mounts only - I didn't agree with this arrangement as ZF325 gb case is alloy and I don't believe strong enough to hang a 1200kg CAT engine onto without distorting or cracking eventually.

 

Over torquing the stud nuts could lead to failure.

Is the weight distribution, balance, of the engine normal ? a heavy PTO on the front end... a heavy exhaust system ?

 

The bolts are 24mm dia & access/swing restrictions due to mount position & boats internatal structure (outboard of engines) makes over torque impossible - also another issue I've asked the designers to resove & improve for next generation of hulls already in production.

Engine wet exhaust system has minimal weight interference on engines - Vynilester pipes with flex exhaust hose connection after mixer, waterlocks have no cracks or indications of unusual stress.

Engine additional gear is nothing out of ordinary: one big frame belt drive 120amp alternator (port block), belt drive fire Jabsco pump (std block).

The only non standard kit on a very much stock standard shaft drive CAT C12 set up is the mounts.

 

The boats, a typical broken mount in place, the failed units

 

Hmm...thats a clean break...no corrosion...virtually new mounts and a standard motor installation.

Did you send a mount back to isoflex for comment ?

Also might be educational to remove the flex coupling from the prop shaft and examine for signs of wear or mistreatment, operator error. .

 

Looking at the pictures of the mounts , brackets and the weight and size . Thats one hell of a lot of weight and thrust on the engine mounts massive brackets ,massive beds , massive weight ,massive push and pull , all on 4 spindly little bolts
One of two ,add more mounts or fit a thrust bearing to the actual prop shaft and take all the push and pull off motors and off those bolts !! Even if the bolts were Titanium they would crap out in time