Timing belt tensioner failure

[Stephen Edwin]

Originally Posted by monty400k

looks like the key on the crank sheared off so the bottom pulley is spinning, hoping it's on the pulley and not the crank as i've got a spare one, otherwise it'll be time for another engine.

ouch !!!


.

[TonyS9]

Is the middle bit separated from the outer (rubber moulded connection)?

Otherwise the Bolt should be tight enough to not rely on the key. If the bolt is missing or loosened, it means it wasn't assembled correctly.

It needs a big torque and something to properly hold the crank solid. Possibly they just tightened it until the engine turned, maybe held it by hand. That is only about 1/4 of the torque needed.

Edit to say - sorry I'm talking about red block, not sure about 6 cyl.

[360beast]

Sounds like they didn't know what they were doing all along!

[Laird Scooby]

The key between pulley and shaft is meant to be a form of mechanical fuse so it breaks if the torque rquired to turn whatever is being driven exceeds safe limits.
Two possibilities here, one the key was old and weak and just gave up the ghost. Two is that they didn't replace it, or if they did, it failed prematurely for some reason.

Either way, you need to get them to look at what caused the key to fail. If they set the crank 90 degree BTDC so the pistons are halfway down the bores, can the camshafts be turned easily? I think (although not 100% sure) there is an oil pressure restrictor valve in the top of the block. If this has failed, it will starve the camshaft bearings of oil causing siezure. If this has happened it's a head off job.

Think you said it was a replacement engine from somewhere? Was the oil and filter changed when it was fitted? Negelected oil and filter changes can cause those oil restrictor valves to block/fail.

Needs these basics checking out before they start replacing the keys and pulleys and whatever else and potentially turning the valves into bananas.

[monty400k]

Engine came out of my previous 960, had the head rebuilt 3 years ago as the valve stem seals had gone, regular oil changes, up to this point it was perfect

[Piet22]

It is not uncommon for a timing belt to slip a few teeth while parking on a steep hill. The reason is that the tensioner cannot handle a backwards rotating engine very well. It is therefore recommended to park in reverse if you are facing uphill and in 1st if you are facing down hill.

Piet

[monty400k]

Update, garage removed the crank pulley and it was good as new, out of options they took the head off, all good there too, valves look to be fine, however when they try to wind the engine over on the crank there is several points of resistance so it looks like it has spun a shell so engine is scrap.

Ive got the 2.5 that came out of the car that could probably be refitted although it wasn't running that well when I got it, I suspect the head gasket, wish Id done a compression check before taking it out, Ive got a 2.8 low compression engine that Id set aside to turbo charge at some point although this would not be a quick solution. I could source another 3.0, either way its probably going to cost me more than Im willing to spend and I need transport so it looks like Ill cut my losses and break it

[Laird Scooby]

What a bummer! Two possible suggestions, strip the 2.5 and rebuild it with a new head set, fit it and keep it as a known good runner (after the head gasket it should be, especially if you get the head checked/skimmed) or simply refit the 2.5 and flog it before anything else goes wrong!

[rwdkev]

Originally Posted by Stephen Edwin

Does the belt on this engine need re-tensioning after a "running in" mileage? If so. Was that done?

Tensioner on all white blocks is automatic. Hydraulic aspect is for damping, not the actual tensioning function.