Safest way to lock engine to remove bottom pulley.

[ashley]

If you lock the crank so it isn't rotating, then there is no movement through it, and against the bearings on the rods...so the answer is to lock the crank before using an impact gun?

[mr2magic]

1) your run of the mill 240V impact gun has enough grund to loosen a 200NM Bolt......that's more than enough to damage the bearing surfaces
2) Yes! If you're going to use a gun the best way would be to lock the flywheel first.

[stecad]

Update: Bolt & pulley off.

Local mobile mechanic arrived (for cash). Bolt wouldn't budge with the cordless impact gun. Used an induction heater (amazing tool which sits on top of the bolt and heats it up in seconds) to apply heat direct to the bolt.
Straight out as easy as and all done in under 20 mins.
Well worth the cash, saves risking the flywheel, saves my blood pressure and stops the wife complaining about my swearing (at least for today).

[tiff_lee]

Impact driver?? On a crank shaft? You do realise there are conrods attached to the crank and that these have journal bearings... the bearing surface doesnt take kindly to repetative radial force of the kind caused by impact guns.

The above method is used (with minor alterations and special tools) by almost all manufacturers.

Can you expand on that at all? The crankshaft would barely be turning (if at all) using an impact drive so what radial force is there on the journal bearings?

Think about how an impact tool works for a minute. If running freely with no load it rotates without an impact. Only because the driven object (here the crank bolt) provides a counterforce does the hammer mechanism come into play. Now in our case the crank isn't in any way fixed, its able to rotate along its axis provided there is sufficient force, but it also presents enough force to the impact driver, to cause the hammer mechanism to engage. This becomes more apparent when holding the crank pulley while using an impact gun - you feel the pulley turning in your hand even though the bolt is being loosened.

The fact the crank turns isn't in and of itself bad. The problem arises in conjunction with the connecting rods and their bearings.The connecting rod bearings have play - yes it is a very small amount, but it is play. During normal operation oil pressure is sufficient such that the small lubricated area between bearing surfaces takes up the load imparted by the combustion without shearing or without being displaced. When we remove the oil pressure the remaining film is a) a lot less than during operation and b) able, through force, to be displaced even more. While hammering on the crank bolt with an impact gun we have no oil pressure so all force is acting on the remaining unstable and displaceable oil film.

As i wrote before the crank will (want to) turn during impact gun use and the amount it wants to turn is much greater than the oil clearance in the connecting rod bearings so basically the crank journal pushes up against one side of the connecting rod bearing half shell. Now even then it's not a big problem as long as the force remains constant or increases constantly. The problem arises because of the hammer effect. The force is being applied/removed/applied/removed.....and so on hundreds of times a minute all with the effect of ramming the crank bearing surface up against the half shell again and again. This causes flat spots and crushes the bearing layers together altering their composition.

The whole process is kind of akin to detonation during combustion which is known to cause bearing failure, just taht the force isn't being applied from the connecting rod to the crank bearing but from the crank bearing to the connecting rod.

That being said...using an impact gun doesn't automatically mean your bearings and /or engine is going to grenade on you. What it does mean is the application of unneccessery stress for the components of the engine - this may cause failure at some point.

I hope that clears my stance on the practice up a bit.

Thanks for taking the time to explain your viewpoint I see where you're coming from now.

Have you ever seen a premature failure brought on through a practice such as this? I dare say there are plenty of garages who would indulge in such practice.

[mr2magic]

I've seen numerous bearing failures on other vehicles but as you're usually left with bits of molten, smeared and crushed metal it's nigh impossible to correlate the damage with the use of an impact gun.

I would even go so far as to say most garages do it to remain competetive with their pricing (low real turn over time for repair compared to max time listed by manufacturer).

[MartinF]

Update: Bolt & pulley off.

Local mobile mechanic arrived (for cash). Bolt wouldn't budge with the cordless impact gun. Used an induction heater (amazing tool which sits on top of the bolt and heats it up in seconds) to apply heat direct to the bolt.
Straight out as easy as and all done in under 20 mins.
Well worth the cash, saves risking the flywheel, saves my blood pressure and stops the wife complaining about my swearing (at least for today).

I hope you are going to fit a new replacement damper\pulley as the rubber section is probably now knackered from the heat.

[SonicSW20]

Update: Bolt & pulley off.

Local mobile mechanic arrived (for cash). Bolt wouldn't budge with the cordless impact gun. Used an induction heater (amazing tool which sits on top of the bolt and heats it up in seconds) to apply heat direct to the bolt.
Straight out as easy as and all done in under 20 mins.
Well worth the cash, saves risking the flywheel, saves my blood pressure and stops the wife complaining about my swearing (at least for today).

I hope you are going to fit a new replacement damper\pulley as the rubber section is probably now knackered from the heat.

It will be fine, induction heating is much more precise than a torch - https://www.youtube.com/watch?v=MyZEaPQinO0

[stecad]

The heat is very localised. The pulley itself was cold to touch but the bolt itself too hot to handle. The bolt wasn't glowing red just very hot. Very useful tool and much more precise than a gas burner.
No need to replace the pulley albeit I was advised to replace the bolt.