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  #1  
Old 06-18-2017, 09:07 PM
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Location: Eastern CT
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1980 240D water pump / crank pulley clearance

New to me car last week. Runs good, but overheats after idling for extended period of time. Noticed light grinding noise from front of motor. Friend with me when I looked at said sparks came from area of water pump/crank pulley when revving. Bought thermostat and water pump to replace. Looking once home, it appears those two pulleys are extremely close to each other. Both pulleys look they they may have a tiny bit of rubbing, but not heavy.

Is that tight clearance normal? Is one of the pulleys the wrong size? With a pry bar, neither pulley seem to have any play.

Feel free to tell me I missed something in my searching and point me in the right direction!

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Old 06-18-2017, 10:19 PM
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Tight clearance is not normal.
Sounds like the crankshaft bolt on the main pulley is loose or the vibration damper is starting to let loose.

Don't run the engine until you get this fixed.
You can ruin your crankshaft nose.

On my 78 W116 300SD, the main crankshaft bolt worked loose and took out the harmonic balancer and bent the shaft of the water pump.
Fortunately, the crankshaft nose was not damaged.
In the photo you can see the fresh exposed metal on the rear of the crankshaft pulley and the front of the water pump pulley where they were in contact.
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1980 240D water pump / crank pulley clearance-crankshaft-pulley-water-pump-pulley-made-contact.jpg  
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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022
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  #3  
Old 06-18-2017, 10:26 PM
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Interesting. I did notice the water pump and crank pulley were slight misaligned which I thought was weird since they run the same belt. I will check the balance bolt tomorrow when I have it apart for the water pump. Is it a matter of cleaning it up and using some loctite and torquing it properly?

It still looks to me like the two pulleys will be very close to each other even in normal operation.
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  #4  
Old 06-19-2017, 03:07 AM
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Oops! Wrong assumption on my part, looks like the 240D doesn't use a harmonic balancer.

At any rate, check the bolts that mount the pulleys.
If either pulley is loose, the wobble that results at high rpm can cause the pulleys to strike each other and generate the sparks that were seen.

If crankshaft pulley bolts are loose, remove them, clean and degrease the bolts and threaded recesses and reassemble with a dab of blue Loctite to the right torque.

The pulleys are close, about 2mm apart, but they shouldn't contact each other at any time.

I replaced the original water pump pulley on my 78 W116 300SD with a smaller one from a 1985 300SD to get better coolant flow.
The Contech V belts were changed from the original size of 10 X 1035 to the smaller 10 X 1005 size V belts when the water pump pulley was changed out.

Be careful removing the fan bolts, they tend to get rounded if you don't use a thin closed end wrench.
Replace any rounded bolts.

Be extra careful removing the bolts that mount the water pump the aluminum housing.
They can get corroded in place and shear off.
Use some penetrant, get the engine hot, and use a six point socket.

Use nickel antiseize when reinstalling.

Best of luck on replacing the water pump.
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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022
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  #5  
Old 06-19-2017, 07:02 AM
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Great post! Thanks for pointers!
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  #6  
Old 06-19-2017, 10:02 PM
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Join Date: Feb 2014
Location: Eastern CT
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Job done. Was a breeze. No more boiling over, idles around 100c which seems a little warm. I am guessing it will do better with some air flow on the road, tires and plates tomorrow.

Also found the grinding noise. Unused RPM sensor bracket with missing bolt. Removed and sounds great now. Water pump was probably fine all along, but followed through with it while it was apart.


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