4M40 Crankshaft Pulley

edbo111

edbo111

New Member
I’ve got a 95 L400 with a 4M40 in it. There was a terrible noise coming from the fan/belts/pulleys the other day. I couldn’t tell what was causing it just by looking and it seemed to go away after driving it home. I’ve taken off the belts and the fan. The fan looks like it was rubbing on something but I’m not sure if this was the main cause of the noise. The idler pulley for the AC is very loose/wobbly, but that might be due to having no tension on it with the belt off. I’m wondering if the crankshaft pulley might need to be replaced. If this went bad would it make noise? Could it cause the fan to rub against something? Is it pretty obvious if this pulley is bad? Not really looking forward to removing this, but everything else I’ve taken off already hasn’t been fun. I would have taken if off already, but my sockets seem to go from 19mm to 24mm so I need to find a 22mm.

Thanks,
Ed
 
An idler pulley should not be "wobbly;" that's probably your issue. Failure of the harmonic damper/crank pulley is often readily apparent, but not always.
 
Damaged crankshaft pulley could cause front timing case oil leaking if not taken care of for a certain period and affect charging system.
 
Remove the idler pulley and inspect bearing by hand, if you are just checking it while loose, you could be feeling the through bolt wobbling. Inspect the rubber on the crankshaft pulley. Do all of your timing marks line up? Can check the cam position with the old fill cap removed. There is info somewhere here in the forum. How are your alternator and ac pulleys? How about the waterpump?
 
I'll take off the idler pulley so I can get a better look at it. Still confused by what could have been rubbing on the fan.

All the belts were replaced in Japan before the van was imported a few years ago and they still look good. May replace them anyway since I'm in there.
 
Got any pics of the fan rubbing marks? Do any of the pulleys wobble? If belts are good, proper tension when reinstalling most important
 
Remove the idler pulley from adjuster bracket. 14mm nut. Check the bearing. If it is not smoot and tight replace it. they press out and in fairly easily in a bench vise.
 
Any ideas for replacement bearing for the idler pulley? It doesn’t seem too bad when spinning it by hand, but would be an easy replacement at this point if a replacement is available somewhere. I’m going to order a new crankshaft pulley since that is most likely the issue, but I still haven’t removed it yet.

I think the fan was rubbing on one of the belts. Not sure how stuff got that far out of alignment, but not sure what else it could have been. I’ll try to post a picture of the fan.

1712936435238.jpeg
 
Looks too high relative to water pump center to be contacting crank pulley. Bearing number is usually stamped on bearing.

here is utube video of pressing a tensioner pulley bearing using a vise:
 
Update to this…

When I removed the crankshaft pulley it came off in 2 pieces. Pretty clear indication that this was the cause of my problems. I ordered a new one from DelicaUSA and finally got it (and everything else) put back together. Everything seems to be working the way it is supposed to be.

Thank you to everyone for your help.
 
How many miles on your engine. I wonder what contributes more to failure, old materials (the bonding agent in pulley) or mileage, how much vibration it can take.
 
The van has around 76,000 miles.

I was 1.5 hours into a 4 hour trip Saturday when the AC belt broke. I pulled over and removed the pieces. Everything else seemed OK but I didn’t want to continue the drive to a remote area so I headed home. Not sure why it broke. I did re-install all of the belts that I took off but they all looked to be in good shape. I may have nicked the AC belt when removing/installing it. I had turned on the defrost while going over a pass so the AC was engaged for 15-20 miles before it broke. I will need the AC in the coming months, but I’m going to leave it off for a little while to make sure that there aren’t any other issues.

I noticed that the alternator belts on my van were 5 mm shorter than what everyone has listed for the 4M40. Not a huge difference, but they sure were hard to remove and put back on. I’m now wondering if the AC belt was also a different size. There were no markings on it.

Now also wondering if something was going on with the AC and belt that contributed to the crankshaft pulley failure.
 
if the AC belt was loose or does not fit pulley groove well it can overheat and break. I have been through a lot of belts trying to find a combo that works. it looks like pulley is set up for an 11mm wide belt. I have not found one and have switched to a 10mm wide belt. This one while it sits low in the groove may have greater surface area contact on the V. I have not blown it yet. Hardly any miles either so it is not a real test yet.
 
I just rechecked my belt tension, it is that new. I am currently using a NAPA XL 25-7355 belt on my AC. It's spec 10mm x 919 OC.
 
While watching my engine run from underneath crank pulley I now see that your fan damage can easily be caused by crank pulley out of position.
Could you post a photo of broken pulley. I want to see what a broken one looks like.
 
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