'79 FXEF top motor mount broken, Why? : V-Twin Forum: Harley Davidson Forums

94BruceM · 06-23-2009, 05:54 PM

I have a '79 FXEF 1200, 4 speed, Super Glide.

We punched it 0.020" over and put new pistons in it, last year. Since then we put 9,000 miles put on it. The top mount was bolted to the rear cylinder,the front cylinder and then the frame mount. All cold. The front cylinder mount is slotted. I have a large flat washer on the bottom and on the top of the cylinder mounting studs sandwiching the mount. The mount has a single flange that bolts to the top frame plate.

The Problem: I was in the process of switching to 5 Gal. gas tanks and noticed that the top mount is broken in three places. Now, I had the mount bolts cranked down pretty good. The motor is bolted in solid. The Trans and Primary look good, and I don't see any cracks in the frame.

Anybody seen this before?

Thanks,

BruceM

Michael M · 07-05-2009, 09:20 PM

Yep, I had a bored and stroked 76 shovel head that did the same thing. It was either metal fatigue or it was already defective and slipped through AMF's world class quality control program.

94BruceM · 07-06-2009, 05:42 PM

Michael,

Thanks for your input. I found a rubbing witness mark between the vertical part of the mount and the frame mating plate. I figure the bolt worked loose, and the mount self destructed due to vibration. I have replaced the mount, and double checked everything. Locktite 242 is my friend.

I'm back to riding it and am keeping a sharp eye on that thing.

Shovelheads forever!!

Shinny side up,

BruceM

Klammer76 · 07-06-2009, 08:04 PM

Back when I had my shovel (1980's) I broke two mounts before I figured out the problem. The mount needs to be shimmed at the frame to mount point.I recall I used a few washers between the mount & frame so there was no stress on the mount when tightening. Even a very small gap will cause stress combined with vibration will cause the mount to crack. It can't be torqued with any stress on it. I also used nylock nuts and never had another problem.

Of all my Harleys, I wish I could find that 75 FX & get it back.

Good luck,
Klammer

94BruceM · 07-06-2009, 10:33 PM

Klammer,
You mean the mount points at the front of the motor? I'll try your suggestion.

The mount I used as a Replacement (J&P) has a slot at the front cylinder and a vertical slot at the frame pick up point. The Frame plate has a horizontal slot. Any residual stress should be between the frame and the motor, not the top motor mount. I know the cylinders grow 0.90" as the motor warms up.

I did pull the primary when I changed the Stator. (Former owner had a 4" wide battery that shorted to the oil tank). The motor could be stressed in the frame mounting.

This Shovel will idle at 400 RPM and run with most Harleys. Parts and tools are cheap, and I don't need 2 grand in tools to work on it. No computer crap on it, either.

Mustang seat, no Monkey Bum, you know?

Thanks,

BruceM

Klammer76 · 07-07-2009, 07:38 AM

Quote:

Originally Posted by 94BruceM

Klammer,
You mean the mount points at the front of the motor? I'll try your suggestion.

The mount I used as a Replacement (J&P) has a slot at the front cylinder and a vertical slot at the frame pick up point. The Frame plate has a horizontal slot. Any residual stress should be between the frame and the motor, not the top motor mount. I know the cylinders grow 0.90" as the motor warms up.

I did pull the primary when I changed the Stator. (Former owner had a 4" wide battery that shorted to the oil tank). The motor could be stressed in the frame mounting.

This Shovel will idle at 400 RPM and run with most Harleys. Parts and tools are cheap, and I don't need 2 grand in tools to work on it. No computer crap on it, either.

Mustang seat, no Monkey Bum, you know?

Thanks,

BruceM

Bruce,

As I recall, there should be a thick washer on each head under the mount and another large washer on top of the mount followed by the nylock nut. I tightened the nuts on the heads first then filled any gap that was between the top of the mount (verticle slot) and the frame with appropriate washers to make sure there was no stress on the mount when tightened at the frame. You should also make sure the engine is shimmed in the frame. This is done by loosening the front & rear mounting bolts as well as the top. Then torque the rear bolts, check with feeler gages for any gap between the front mount and frame and shim if needed (pieces of shim stock, feeler gages or alum can cut to proper size can be used). Torque the lower bolts and then do the top as I described.

You cylinders are cast iron with the cases and heads being aluminum. I don't think the cast cylinders grow 0.90 (that's a lot). The later evo & TC's aluminum cylinders do grow a bit when warmed up.

Klammer

94BruceM · 07-07-2009, 01:46 PM

Klammer,

You are right it was late out. The cylinders grow 0.090" (I can't type).

I've got the fat washers on the top mount.

I'll try your suggestions. Thanks.

We'll let you know,

BruceM

vindex1963 · 07-07-2009, 03:29 PM

The top mount on my '79 used to break also. I bought a HEAVY DUTY mount...extra thick.....used care in shimming it and it never broke after that.
If you're idleing at 400 rpm you might as well buy a rebuilt kit for it now. You're killing that motor to sound "cool"????

94BruceM · 07-08-2009, 11:29 AM

Hi Vindex,
In reverse order. This bike carries 18lbs oil pressure at 400 RPM, warm. Oil pressure gauge on it. I actually idle it at about 600 RPM, so there are no cold idle problems. That's with H-D 50wt. oil.

The newer bikes wont idle that low. Redesigned oil pump, thinner oil, and the electronics won't let you, sorry.

Based on Klammer's input, I loosened the motor yesterday. It sits flat on the mounts. No shimming needed.

I have wondered about lousy after market parts quality.

What mount did you use?

Thanks for the time,

BruceM

vindex1963 · 07-08-2009, 09:32 PM

Quote:

Originally Posted by 94BruceM

Hi Vindex,
In reverse order. This bike carries 18lbs oil pressure at 400 RPM, warm. Oil pressure gauge on it. I actually idle it at about 600 RPM, so there are no cold idle problems. That's with H-D 50wt. oil.
The newer bikes wont idle that low. Redesigned oil pump, thinner oil, and the electronics won't let you, sorry.
Based on Klammer's input, I loosened the motor yesterday. It sits flat on the mounts. No shimming needed.
I have wondered about lousy after market parts quality.
What mount did you use?
Thanks for the time,
BruceM

I used a Custom Chrome mount.
Don't be sorry I wouldn't idle my bike that low anyway, even the 20+ years I owned my '79 I idled it at 800-900. Funny thing about that old Shovel...it went 167,000 miles with original internals and had near zero oil pressure with 50wt at idle.

94BruceM · 07-13-2009, 05:05 PM

Thanks for the input Guys.

I consider this thread closed. I've replaced the mount. Correct bolts, nylock nuts. Locktite 242 on all. Motor sits square, and flat, when loose mounted. I'll put a few thousand miles on it. If it breaks again I'm going to make a stronger top mount from scratch.
BruceM