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Proper bolt tightening for 4 blade white plastic fan.
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2015/10/31 1:41
From Jeannette, PA
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I had a catastrophic failure where I used Loctite instead of the bent metal tabs to keep the bolts from loosening. They did loosen. The pulley slid on the pump flange and the bolts hammered circumferential slots in the pulley (at least 1/2" of slot!). The pulley was also cutting into the bolts and eventually DECAPITATED THEM tossing the fan and destroying the radiator.

COOL OT RAD STORY: I had a alum aftermarket rad for a L20b in my L18 620. As soon as I bot that rad, some guy on eBay had a bunch of Eagle 481 proper brass rads for the 620 for something like $40 shipped (!) I was totally pissed - especially since it was the OE type. But I was so pissed I bot one anyway, put it on the shelf and laughed that I would never use it. (!) Talk about Serendipidy!

I reassembled with new tab strips and locked the bolts heads proper and tightened to a point where I thought I might be crushing the plastic fan.

Time passed....

Today I discovered my crank bolt was completely loose and backed out maybe 1 turn - it turned freely with 2 fingers and felt like a new bolt and crank - it was that smooth.

But I also found that the fan was slipping on the pulley a bit - the bolts were still safety tabbed.

The fan did not slip on the pulley when I assembled it, so that meant I had lost clamping force. I have not removed it yet, but I am concerned that if the fan is slipping, it's possible the pulley is slipping on the flange which could start the "slotting" failure I originally experienced.

So how to get this stack of parts to stay put?
Epoxy?
A Stud Bolt would be a great solution
https://uk.misumi-ec.com/vona2/detail/110300247310/#

Posted on: 5/5 6:04
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Re: Proper bolt tightening for 4 blade white plastic fan.
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For the Crankshaft Pulley bolt, the only thing needed is correct torque, a whopping 108-116 ft. lb.

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Posted on: 5/5 11:44
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Re: Proper bolt tightening for 4 blade white plastic fan.
Just popping in
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L18 Engine Vibration

Mine has a significant balance vibration (not some miss or ignition thing) that I can feel in the steering wheel, floor shifter and inside the cab in general. (I owned a 72 510 back in the day and never noticed any vibration issue - but that was many decades ago.)

This vibration loosens bolts all over the place (I've heard other people having the same experience.)

If I even have to put a clutch in, I would have the flywheel and clutch balanced just to be sure - BUT is this a Wild Goose Chase? - Do these engines simply vibrate like that?

OTHER ENGINE EXPERIENCE: no such vibration:

I had a 1600, 2002 and 2002tii BMW and there was no such vibration - in fact, the 1600 felt like an electric motor with a total absence of even the slightest vibration. it also wanted to rev forever (the 2.0's were completely different, not electric smooth and you could tell they were "straining" at redline.

Posted on: 5/5 17:09
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Re: Proper bolt tightening for 4 blade white plastic fan.
Just popping in
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UPDATE: Bolts hammering and slotting pulley holes AGAIN (and bolt safety tabs still in place.)

I'm going to drill and tap a 5th hole in the flange and pulley so I can put a cap or button head screw to positively clamp and hold in the place the pulley onto the flange. I'll scarf out some bolt head clearance on the back of the fan.

Then the wonky, loose fan bolts only hold the fan on and as they loosen (for whatever reason) the bolts will not hammer out the pulley.

Posted on: 5/5 17:44
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Re: Proper bolt tightening for 4 blade white plastic fan.
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before this, never heard of a fan problem. I imagine the engine shaking might be the cause

If the flywheel doesn't seat correctly it will vibrate. Just a little bit of burring on the flywheel-to-crank mating surface will cause it. You might not see it, but could feel it with your fingertips

Posted on: 5/7 21:13
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Re: Proper bolt tightening for 4 blade white plastic fan.
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Real butchers had this 620 before I got it.

EXAMPLE: They put a Rochester Monojet on it. The plywood adapter was cut out with what appears to have been a screwdriver and a hammer (!). The carb has a 2-bolt flange. They put one on a manifold stud, then aligned it diagonally and put a large washer on the manifold stud to "clamp the flange down". HOWEVER, showing some actual intelligence put a loose nut on the opposite side of the washer so when it was clamped down, it did not cock.

The truck has 130k on it and the clutch is still working. I don't know if the OE would last that long. Because of the vibration, I'm thinking they may have screwing something up IF they put a clutch in it. Judging on the work done, I doubt they would have taken the flywheel off (unless of course they ran the plate rivets into it.)

I won't inspect the clutch until I have to replace it. (and at that time I'll put my 1980 L20b 720 wide ratio 5-speed in it.) (If I ever get a 2nd car, I may just pay someone to do that job.)

Posted on: 5/7 23:30
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Re: Proper bolt tightening for 4 blade white plastic fan.
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Yes, the original Datsun clutch would last about 120k, depending on how it was driven

L18s are very smooth, and were blueprint balanced at the factory. Any vibration is not normal, in fact the factory redline was 7000 RPM

Posted on: 5/7 23:43
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