Grinding during acceleration

Post by **FireFox31** » 03 Dec 2020, 11:08

In my newly acquired 2000 V70 with 200k miles, there's a grinding sound under the front floor boards during acceleration. This only happens when the weight of the car shifts back, such as accelerating from a stop. I haven't found and spots where moving parts (belts, shafts, axles) are hitting non-moving parts. Are there any common faults I can check?

Post by **scot850** » 03 Dec 2020, 16:59

Is your car a FWD or AWD?

Have you checked your engine mounts? In particular check the top torque mount bush mounted at the top rear of the engine to the bulkhead, the lower torque mount under the front of the engine near the middle of the car, and most importantly the engine mount under the crank pulley on the RHS of the engine bay. It is prone to failure as it is a block of rubber bonded to metal plates and will fail and frequency is dependent on quality of the part.

To check the engine mount place a piece of wood ontop of a floor jack and try raising the engine on the right (passenger) side about 1" max. Look at the mount and see if it separates. Of the 3 this is most likely to cause the issue. Otherwise we are then looking at drive axles, carrier bearing on RH axle and wheel bearings and brakes.

Neil.

Post by **FireFox31** » 20 Jul 2021, 09:34

I believe the grinding sound is coming from a timing belt or accessory belt component. I need to determine if this repair will be so expensive (crankshaft!) that it makes the car not worth fixing.

The grinding sound is rapidly cyclical when the engine is under heavy load (accelerating hard from stop). It scrapes maybe six times per second at 2000 RPMs. I also hear a slight whir at idle suggesting a pulley bearing is bad. I will replace the timing belt (it's due), idler, tensioner, and coolant pump.

There's oil leaking around the crankshaft pulley which has me fearing the worst. I'll research replacing its gaskets. Could an oil pump failure cause that pulley to wobble? Could the crankshaft be wobbling, causing damage to the engine block? When I have everything apart for the timing belt change, how can I test the crankshaft to find the problem?

scot850 wrote: ↑03 Dec 2020, 16:59 Is your car a FWD or AWD? Have you checked your engine mounts?

The car is FWD. Thanks for the detailed engine mount checking info. I will check them after I handle the timing belt change.

Post by **wizechatmgr** » 20 Jul 2021, 16:39

Any chance we can get audio or audio/video? Grinding noises are heck hard to identify without the noise. I'm thinking not timing or belt drive as if this were the case you could reproduce it by increasing engine speed while not moving generally.

Generally speaking if the issue were the crankshaft itself, you're talking new/different engine. I don't think this is it yet.

The good part about NOT having AWD is something like 2/3rds of the potential issues are already gone for you =)

Post by **scot850** » 20 Jul 2021, 17:39

You could remove the serpentine belt and start the car briefly and see if the noise goes away. If it is still there then you should have at least eliminated most of the stuff like A//C compressor, alternator, tensioner and any pulleys on the serp run.

If the noise is still there then I would suggest checking the tensioner for the timing belt.

Neil.

Post by **scot850** » 20 Jul 2021, 19:34

Sorry, went back and read further up in your post about the oil leak.

Oil may or may not be the crank pulley seal. Time consuming but not too bad if you are changing the timing belt anyway.

As for the wobble on the crank pulley it could be it has been bent by someone trying to remove the pulley and they bent it. Might be the reason for the oil leak and your rubbing sound.

Neil.

Post by **FireFox31** » 20 Jul 2021, 19:51

Here's a video of the sound. It's faint, but you'll hear roughly four grinds per second from 0:08 to 0:10 and from 0:29 to 0:32. I could not make the grinding sound by revving at idle but it always happens when accelerating hard.

scot850 wrote: ↑20 Jul 2021, 17:39 You could remove the serpentine belt and start the car briefly and see if the noise goes away.

Thanks, I keep forgetting that this is possible. This diagnostic might not help since the problem doesn't happen at idle.

I'll replace the timing belt and its tensioner (and idler?), accessory belt and tensioner, water pump, and maybe the VVT cam o-ring and oil pump/crankshaft seals. I want to be sure I get this grinding when I have everything apart.

Post by **scot850** » 21 Jul 2021, 14:29

If it only happens when moving and is not related to revving the engine, then check the brake dust shield on that side is not rubbing on the rotor.

Neil.

Post by **FireFox31** » 21 Jul 2021, 17:42

Thanks, I'll check that. One of my front brake dust shields is a little rusted through and not fully intact.

A YouTube commenter similarly recommended that the grinding is happening at road speed, not engine speed. He recommended I check the propeller shaft. I'll get back under the car and check for these things.

Post by **scot850** » 21 Jul 2021, 19:55

If your V70 is a FWD then it does not have a prop-shaft. If it is an AWD then it does. The AWD versions prop-shaft has a front bearing that fails as it is right beside the catalytic converter and a center rubber bearing support that fails with age.

If you have a FWD only vehicle, the front RHS axle has a center bearing support that can get noisy with age.

Neil.