Knock sound when turning car off
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Re: Knock sound when turning car off
Originally Posted by Infinite
coolant doesnt make a knocking sound, nor does the throttle body.
The M112 motors have hydraulic lifters... When they lose oil pressure on shutdown they collapse, causing valvetrain chatter for the last few revolutions of the motor as it spins down. Thats what you are hearing. If it were the fan it would be a constant sound as the fan would be hitting that same point everytime it engaged.........................
The M112 motors have hydraulic lifters... When they lose oil pressure on shutdown they collapse, causing valvetrain chatter for the last few revolutions of the motor as it spins down. Thats what you are hearing. If it were the fan it would be a constant sound as the fan would be hitting that same point everytime it engaged.........................
Mine do the same thing, the chatter occurs at the instant I kill the ignition, clutch in or clutch out... doesn't matter. The chatter only starts immediately as the engine shuts off, and lasts less than a second.
Re: Knock sound when turning car off
Yea, its really not an issue as the motor stops so fast, it's just a byproduct of their design, over time (100,000+ shutdowns it could cause rocker arm wear but by that point other things would have worn out) you could run an accusump to prevent the problem on shutdown, but on a stock motor there really isn't a point.
Re: Knock sound when turning car off
Originally Posted by Infinite
Yea, its really not an issue as the motor stops so fast, it's just a byproduct of their design, over time (100,000+ shutdowns it could cause rocker arm wear but by that point other things would have worn out) you could run an accusump to prevent the problem on shutdown, but on a stock motor there really isn't a point.
Oil pressure keeps the lifters in contact and the pressure is not so great as to lift the valves. So?
Re: Knock sound when turning car off
most modern automotive oiling systems don't have one way check valves. And per our FSM, none exist anywhere in the system. Oil pumps have a pressure check valve that circulates excess oil back around the pump to keep pressure in check.
All oil pumps have a minimum operating rpm (i haven't datalogged rpm vs. oil pressure so I can't give a concrete number) but lets say hypothetically that limit is 200 rpm. During shutdown as engine rpm drops past that number, the pump isn't spinning fast enough to pull oil from the pan and pressurize it when this happens. And the fact that the lifters on our cars are basically the last thing in the oil passage circuit, they lose pressure first (the most important thing to keep oiled regardless are the main and rod bearings, which is why they are almost always first in the circuit, they pretty much keep residual pressure during shutdown and the starter spins the motor fast enough during cranking to deliver small amounts of oil pressure until the motor turns over)
Hydraulic lifters use oil pressure to force a piston against a spring which pushes down on the roller taking up the lash between roller and valve.
This is a cutaway of an LS v8 HLA (hydraulic lifter assembly) but they are all the same in construction and basic principle of operation.
When oil pressure drops on shutdown, the spring forces the piston in the lifter to its full retracted position. This causes excess lash between the lifter and valve, causing the chatter you hear on shutdown.
All oil pumps have a minimum operating rpm (i haven't datalogged rpm vs. oil pressure so I can't give a concrete number) but lets say hypothetically that limit is 200 rpm. During shutdown as engine rpm drops past that number, the pump isn't spinning fast enough to pull oil from the pan and pressurize it when this happens. And the fact that the lifters on our cars are basically the last thing in the oil passage circuit, they lose pressure first (the most important thing to keep oiled regardless are the main and rod bearings, which is why they are almost always first in the circuit, they pretty much keep residual pressure during shutdown and the starter spins the motor fast enough during cranking to deliver small amounts of oil pressure until the motor turns over)
Hydraulic lifters use oil pressure to force a piston against a spring which pushes down on the roller taking up the lash between roller and valve.
This is a cutaway of an LS v8 HLA (hydraulic lifter assembly) but they are all the same in construction and basic principle of operation.
When oil pressure drops on shutdown, the spring forces the piston in the lifter to its full retracted position. This causes excess lash between the lifter and valve, causing the chatter you hear on shutdown.
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Re: Knock sound when turning car off
Originally Posted by Infinite
most modern automotive oiling systems don't have one way check valves. And per our FSM, none exist anywhere in the system. Oil pumps have a pressure check valve that circulates excess oil back around the pump to keep pressure in check.
All oil pumps have a minimum operating rpm (i haven't datalogged rpm vs. oil pressure so I can't give a concrete number) but lets say hypothetically that limit is 200 rpm. During shutdown as engine rpm drops past that number, the pump isn't spinning fast enough to pull oil from the pan and pressurize it when this happens. And the fact that the lifters on our cars are basically the last thing in the oil passage circuit, they lose pressure first (the most important thing to keep oiled regardless are the main and rod bearings, which is why they are almost always first in the circuit, they pretty much keep residual pressure during shutdown and the starter spins the motor fast enough during cranking to deliver small amounts of oil pressure until the motor turns over)
Hydraulic lifters use oil pressure to force a piston against a spring which pushes down on the roller taking up the lash between roller and valve.
This is a cutaway of an LS v8 HLA (hydraulic lifter assembly) but they are all the same in construction and basic principle of operation.
When oil pressure drops on shutdown, the spring forces the piston in the lifter to its full retracted position. This causes excess lash between the lifter and valve, causing the chatter you hear on shutdown.
All oil pumps have a minimum operating rpm (i haven't datalogged rpm vs. oil pressure so I can't give a concrete number) but lets say hypothetically that limit is 200 rpm. During shutdown as engine rpm drops past that number, the pump isn't spinning fast enough to pull oil from the pan and pressurize it when this happens. And the fact that the lifters on our cars are basically the last thing in the oil passage circuit, they lose pressure first (the most important thing to keep oiled regardless are the main and rod bearings, which is why they are almost always first in the circuit, they pretty much keep residual pressure during shutdown and the starter spins the motor fast enough during cranking to deliver small amounts of oil pressure until the motor turns over)
Hydraulic lifters use oil pressure to force a piston against a spring which pushes down on the roller taking up the lash between roller and valve.
This is a cutaway of an LS v8 HLA (hydraulic lifter assembly) but they are all the same in construction and basic principle of operation.
When oil pressure drops on shutdown, the spring forces the piston in the lifter to its full retracted position. This causes excess lash between the lifter and valve, causing the chatter you hear on shutdown.
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Re: Knock sound when turning car off
Holy smokes, forgot I even started this thread :|
It ended up being my cooling fan. Seems that it was slightly off-balance and rubbing around the outer rim of the fan.
Easiest way to find out if it's the fan is to have someone else turn your car off after the fan has been running.
It ended up being my cooling fan. Seems that it was slightly off-balance and rubbing around the outer rim of the fan.
Easiest way to find out if it's the fan is to have someone else turn your car off after the fan has been running.
Thanks
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Re: Knock sound when turning car off
You know, the fan motor/blades/housing is an assembly - why not just replace it?
I am 99% sure this fits - maybe 100/80 or Mr. Miata can verify.
Mercedes C280 99 00 SLK320 CLK320 98 04 AC Radiator Fan | eBay
I am 99% sure this fits - maybe 100/80 or Mr. Miata can verify.
Mercedes C280 99 00 SLK320 CLK320 98 04 AC Radiator Fan | eBay
You can buy the fan and shroud separately.
The SLK320 and SLK32 quote different parts to what is on my Crossfire. The shroud is a different number altogether and the fan is #000 540 15 88 and #000 540 16 88 on the SRT I have.
I believe the NA and SRT use the same fan and shroud - I'll check though.
Look at the parts on your cars the Mercedes part number is on most parts, even those made by Bosch etc.
I got the SLK320 and SLK32 parts list in the documentation thread along with other lists but why did I bother if nobody looks at them. I admit they may get out dated in a few places but the basics are there.
Re: Knock sound when turning car off
I have a spare fan/shield, I went out to the garage to look and all I could find was
333-55019-100 on the shroud, no numbers at all on the fan.
Google seems to think this is a good number for the crossfire fan assembly .....
333-55019-100 on the shroud, no numbers at all on the fan.
Google seems to think this is a good number for the crossfire fan assembly .....
Last edited by ala_xfire; 08-23-2016 at 07:30 PM.
Re: Knock sound when turning car off
Nothing wrong with that, I only can comment on Mercedes and Chrysler parts.
Re: Knock sound when turning car off
Thanks for the reply. My car is not a turbo and I understand what you are saying about the ticking of the cooling exhaust on shutdown. My issue is not those. I usually do let it idle a min. or so before shutdown. I am wondering why the clunk with the clutch pedal not pressed and no clunk when it is pressed in on shutdown. I have heard of thers with this issue I wonder if it is all 6 spds and is normal? I only run 93 octane. It dosen't sound good. Thanks.
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