ZD30 Snapping Tensioner pully bolts

[brooky]

Hi All

I have a ZD30 that has been shearing the bolt on top of the fan belt tensioner. This has happened twice now. I replaced the tensioner 10000km ago and it seams to be running freely when it is pulled off. the air con and alternator both run freely. It has been snapping after a few days of fixing so it seams that something is ceasing up after some time. Please help

[mudski]

Can you take a pic of which bolt is snapping. Where are you buying the tensioner from?

[brooky]

84547

I brought the tensioner / pully from Barnsons Auto. the first time it broke it snapped some of the casing, i had to heli coil a new thread deeper for the second one. i used a 4.6 grade bolt the second time but it sheared it so it seams to be a sudden force that it snapping it

[mudski]

now that section has snapped off, the new tensioner wont be sitting level and would have caused the bolt to snap no doubt in my mind. i would file it flat and pack out the gap difference with a washer or two.

[brooky]

i have the piece that snapped off and used it as a spacer, not shown in the photo sorry. the strange thing is it was fine for 4 days after i fixed it then just suddenly snapped again. Could it be the fan or alternator clutches? it seems like something is locking up

[mudski]

Use a genuine tensioner. My guess is the aftermarket tensioner is not giving enough rebound I suppose you call it, putting extra stress on that mounting point.

[brooky]

Thank you for your help, I have ordered one. Thank god the old bolt came out easy so now just a waiting game to fit the new one

[mudski]

Maybe see if you can drill further in to the mounting point and then run a tap through it, then use a loner bolt. Just for extra strength.

[PeeBee]

A failure on a factory fixture where there are many units out there suggests you are not at root cause. tapping the bolt deeper won't reduce the incidence of shear. Increasing the bolt dia will reduce the incidence of shear due to larger section, however the point remains that a larger load is being generated. Was the part that broke off fractured to begin with? Is the engine running differently under any circumstances - a/c on, first start up, hot?

[brooky]

It happened when engine is hot after some time driving. No air con just seems to be random. could it be the fan or alternator clutch engaging?

[PeeBee]

It happened when engine is hot after some time driving. No air con just seems to be random. could it be the fan or alternator clutch engaging?

The fan load would be constant at speed. I dont know of an alternator with a clutch - simply have not seen one, but if the a/c clutch comes on, the sudden engagement is typically handled as belt slip for an instant - its not that savage an action. How many of these events have happened - two? It looks like a casting/housing failure to me, but hard to understand why the bolt is shearing as well.