backwards spin

[s2t]

Just curious
If you have a spin on track which results in you going backwards down the track and you dont depress the clutch resulting in a stalled engine what damage could be done

[snowdude2910]

none I wouldn't have thought you'd just be sucking in exhaust gasses and pushing them back up through the inlet system but I couldn't see it doing much damage.

[tertius]

s2t said:

Just curious
If you have a spin on track which results in you going backwards down the track and you dont depress the clutch resulting in a stalled engine what damage could be done

It will basically run the engine backwards, meaning exhaust gases, etc. will be sucked through the engine the wrong way, as I understand it this can result in blown seals, etc.. I imagine the injectors, fuel pump, air intake, etc. will all complain.

Try to depress the clutch next time.

I have done this but got away with it.

[slinky]

It won't just run the engine backwards, it'll attempt to stop rotating mass immediately and reverse its rotation, as long as, of course, the clutch/box/diff don't get out of the passenger door first..

[snowdude2910]

slinky said:

It won't just run the engine backwards, it'll attempt to stop rotating mass immediately and reverse its rotation, as long as, of course, the clutch/box/diff don't get out of the passenger door first..

no worse for the drivetrain then severe engine braking or using the gears to lock the back wheels surely?

[agent006]

You may like to read up on Dazren's experiences on here with a blown 996 turbo engine. If I remember correctly it was traced to being most likely caused by a spin and backward rotation of the engine (with someone else driving).

If you have a cam chain, turning the engine backwards can cause the tensioner to extend fully and stretch the chain.

[Steve H]

agent006 said:

You may like to read up on Dazren's experiences on here with a blown 996 turbo engine. If I remember correctly it was traced to being most likely caused by a spin and backward rotation of the engine (with someone else driving).

If you have a cam chain, turning the engine backwards can cause the tensioner to extend fully and stretch the chain.

This, almost.

Chain tensioners are generally the next cog to the crank so the crank feeds the chain to the tensioner which extends to avoid any slack (same thing tends to apply to cambelts with auto-tensioners). The actual tension on 90% of the chain/belt is then created by the crank pulling the chain against the resistance of the other pulleys, cams, oil pump, water pump etc. When a car spins it is possible for the engine to run backwards which can then apply that pull against the tensioner causing it to retract and allowing slack onto the chain as it then feeds in the wrong direction towards the other pulleys, it's rare but this can cause it jump.

Some BMWs, E46 330 for one, will sometimes put a management light on and drop into limp mode if spun and run backwards.

[silverthorn2151]

I span our Hyabusa engined Radical at Brands and didn't dip the clutch quick enough.

Turned the insides of the starter motor into dust. Millions of tiny pieces.

We have a special doodah now that stops that happening.

[AdiT]

As said above, it can let the timing chain/belt go loose and let it jump teeth; Resultng in anything from poor runnig to bent valves. Oil pumps don't like eing turned backwards and can empty themselves. If you're unlucky they might not re-prime when you start up again.
On bike engines it can result in the starter failing (particularly BUSAs)

[silverthorn2151]

in fact, this is what it does to a busa starter!

[s2t]

Thanks for the above - Have done various checks and think I have got away without any damage - save for a dent in my pride

[agent006]

Steve H said:

This, almost.

Chain tensioners are generally the next cog to the crank so the crank feeds the chain to the tensioner which extends to avoid any slack (same thing tends to apply to cambelts with auto-tensioners). The actual tension on 90% of the chain/belt is then created by the crank pulling the chain against the resistance of the other pulleys, cams, oil pump, water pump etc. When a car spins it is possible for the engine to run backwards which can then apply that pull against the tensioner causing it to retract and allowing slack onto the chain as it then feeds in the wrong direction towards the other pulleys, it's rare but this can cause it jump.

Some BMWs, E46 330 for one, will sometimes put a management light on and drop into limp mode if spun and run backwards.

Depends on the tensioner design. On my Shogun for instance the tensioner is on a ratchet system so won't retract once extended, hence having the opposite effect to your description.