[Lokidog]

For the last few months I've been getting a random bearing squeal when I first start my sierra. It doesn't happen every time and it only lasts for 1-2 seconds. It is definitely not a belt squeal and I've just replaced my alternator today. This leads me to believe it's the water pump bearings, but I would have thought that it would be a constant squeal. A neighbour suggested that it may be the outer race of the bearing slipping with the initial torque on start up. Thoughts?

[jdk81]

Remove the fan belt, and give the water pump a wobble to check it. If it wobbles, its probably the cause.
disconnect the plugs and try cranking it over (with no plugs connected and no fan belt)
You want to get the oil pressure up and listen for whats happening.

Could be the starter motor clutch.
If it gets filled with crud it can squeal.

Could be the engine bearings, when its low on oil pressure.

If it seems to not squeal with the belt and leads off, its probably the waterpump.
But it could also be intermittent problem too.

[want33s]

As above.. remove the fan belt and run engine briefly.
This will eliminate the fan belt and if it still makes the noise it must be the timing belt tensioner bearing.

[Lokidog]

I replaced the timing belt tensioner not long ago. A couple of months ago I was going to change the alternator with a new one I bought of eBay. It was an aftermarket one which didn't fit as the plug on the rear of the alt was fouling on the engine mount. I checked the water pump for play then and everything seemed ok. In saying this I'll check it again and then turn it over with no fan belt. The comment about the starter motor intrigues me... Could it be making the squeal as it's only on start up???

[Red89]

The starter can run on at startup

[PORL]

^^ that's what mine does.

[Lokidog]

The more I think about it the more I feel it's the starter motor. Took the Zook out a few times today and it only squealed twice out of six starts.

[PORL]

Over engagement will cause a grinding type high pitch squeal. It's annoying

[Lokidog]

Well a couple of days after installing the new alternator the squeal has gone. Starter motor does run on a little, so that's my next job.

[jonno_racing]

Bendix drive on starter!