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Fan Hitting Fan Shroud on Acceleration

 
Old 05-10-2019, 02:42 PM
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Chip Robie
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Default Fan Hitting Fan Shroud on Acceleration

My 1976 c3 L48 with automatic transmission has problems with the engine fan making contact with the inner surface of the fan shroud near the top. Happens when I accelerate from stop or low speed.
What is the appropriate clearance that should be between the tip of the fan blades and the inside perimeter of the fan shroud? It looks like there is a little more clearance at the bottom than the top--is the shroud adjustable?

Could this be a sign of tired motor mounts? How much of an ordeal is it to replace those?

It's a harsh clatter that only lasts a second but it's not good. Thoughts?
Thanks,
Chip in Cary
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Old 05-10-2019, 02:51 PM
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suprspooky
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I would guess new Motor Mounts will solve the issue as the rubbing is a classic symptom of a broken drivers side mount (if the car has always made the noise there may more troubleshooting involved), it not a tough job if you are working on Ramps etc. I'd budget a half day. I have a BB so it may not port over, it seems like my shroud didn't have much room to move for changing clearance.
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Old 05-10-2019, 02:56 PM
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Gordonm
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I broke one years ago. The rubber just gets old and separates. Not a bad job to replace. You can actually see it if you pop the hood and stand on the brake and rev the motor a little .You will see the motor pick up.
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Old 05-10-2019, 03:01 PM
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CanadaGrant
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If clearance looks fine with the engine off then check your drivers side motor mount to see if the rubber has come apart. Another way is to raise the hood, put it in gear with your foot on the brake and step on the gas (like a brake stand) and see if the left side of the engine lifts up.
Edit: That Gordon beat me to it again!

Last edited by CanadaGrant; 05-10-2019 at 03:05 PM.
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Old 05-10-2019, 04:58 PM
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Tampa Jerry
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I would check the transmission mount as well. My Chevelle poly mount went south and allowed the fan to hit the shroud. A lose or bad transmission mount will do the same thing. Jerry
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Old 05-10-2019, 08:38 PM
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drwet
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+1 on the motor mount. Happened to me a few years back. I ended up adding a cable to hold the engine down on the drivers side.
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Old 05-11-2019, 12:59 AM
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OldCarBum
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Just be sure to purchase a good quality motor mount.
There is a difference, so don't buy cheap.
There are some good rubber mounts that have a steel safety device molded into the mount that prevents the motor from raising if the rubber part of the mount fails.
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Old 05-11-2019, 09:04 PM
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Goody
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Never tried to replace a motor mount on a C3 yet so I can't tell you how to accomplish it yet, but I suspect that is the issue as well. Do the tests as others have already posted.
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Old 05-12-2019, 08:35 AM
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I had the same problem with my stroker. Turns out the left stock mount tore in half from all that torque. That allowed the motor to lift and fan broke the top of the shroud. I put a solid mount in the left side while engine was in car. I little challenging but patience will prevail.
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Old 05-12-2019, 09:10 AM
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jackson
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^^^^^^^^^^^motor mount
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Old 05-13-2019, 03:26 AM
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We had same problem back in the 60's with modified engines pushing more than stock torque.
It was always a separated/broken driver's side motor mount. The rubber separates from the backing plate.
If you think about it, it just makes sense as the engine torques clockwise which pulls on the driver's side mount and pushes down on the passenger side mount.
Our solution back then was called a "torque strap".
Take a huge turnbuckle and mount one end to the frame and the other end to a solid stud/bolt coming out of the block. Tighten it down and check periodically.
Had that issue with my 67 Camaro.
After the torque strap, I would end up lifting the front wheels on takeoff. Little higher on the left of course.
Nowadays, I use solid engine mounts up front and a rubber or poly transmission mount behind the trans.
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Old 05-15-2019, 11:13 AM
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Chip Robie
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Seems like a no brainer. Ordering a good set (not the cheap ones) of motor mounts, and might as well do the transmission mount too.
Thanks for the advice.
Can I do this with front ramps or do I need to jack the whole car up? I have a low profile jack and some shim blocks to help lift up the motor from the bottom.
Chip
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Old 05-15-2019, 11:30 AM
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jackson
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Depends on ramp height & your girth.

You'll be working near HOT starter cable ... Disconnect battery POS.
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Old 05-15-2019, 03:24 PM
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A local garage that works on classics quoted me $100- per mount (2 engine, and 1 transmission). I replaced the driver side engine mount myself. Having the garage do the other two will be easy money spent. It's probably not a hard job, but even with the exhaust removed, it wasn't easy.

In my case, when I removed the drivers engine mount, my engine tried to climb into the passenger compartment. I had to rig up a contraption with some straps on the ceiling to pull the engine up and forward, while jacking the engine up and forward from below. And this was with all four wheels on my Kwik-Lift.

Hopefully your install goes more smoothly.

Last edited by Bikespace; 05-15-2019 at 07:06 PM.
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Old 05-15-2019, 05:06 PM
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Had one go on a big block K5...that gian clutch fan took everything out. Water pump, shroud, hood, radiator, the carnage was spectacular! lol
Sure was fun though.
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