The Why Of It?

[Harley George]

Searched and found fix, don't understand the why or cause and only on some dyna's.
Motor mount problems!
Have 09 FXDL 15000 miles, no problem. Nephew has 09 Super Glide 5000 miles just had to replace. Read many posts of problem, don't understand the why.
He rides like little old lady, can't be riding style.
Looking for enlightenment!
Thanks!

 

[89stroker]

It absolutely could be from the way he rides it if he is riding it like a little old lady! He may be lugging it badly, riding in too high of a gear and dyna's don't like that. I had an 08 FXWG and if I lugged it at all that motor assembly would rock on the mounts horribly, all my buddies' Dynas are the same. Continuous lugging will absolutely contribute to premature mount failures. Just sayin'.......

 

[Hoople]

Super Glide 5000 miles just had to replace.

Did the bond between the rubber and metal come apart or did the rubber turn into "gummy bear". Was it only the front mount. What was bad about the replaced mount.

 

[Harley George]

Hey, thanks for the replies. Didn't think about lugging 89, you may be correct, will ask him. Haven't been with him, lives in another local.

Didn't get into the specifics of the problem when he called the other day, Mott. I will ask and let you know.

Thanks again!

 

[R_W_B]

The specifics (as Hoople said) are important on that low a mileage. Some pics of the old mount would be a great evidence of what it might have been. Sometimes mounts are just plain defective from the factory.

Most times the problem with Dyna mounts is their OEM design/install. They not only mount the engine to the frame but they "stretch" the gap of the engine to the frame. HD's official stance on this is that design cushions the extreme vibrations of the TC engine (different crank components than the softails).

The "problem" is that this "stretch" will distort the rubber mount and over time (say 10,000 on up) will just plain deform it. Many folks (including myself) put washer shims on the front mount to allow the mount to stay in it's original position. I believe this prolongs mount life and seems (to me) to have lessened the vibration above 50mph.

Notice in the attached pics how the old mount is deformed in it's shape and the side view shows it stretched forward. The new mount is beside it. Also shown is a pic of the shim proceedure.

 

[Hoople]

Notice in the attached pics how the old mount is deformed in it's shape and the side view shows it stretched forward. The new mount is beside it. Also shown is a pic of the shim proceedure.

Great pictures & Info. So the primary issue is with the front mount. The rear rubber mount is pretty solid/reliable and longer lasting?

 

[R_W_B]

Great pictures & Info. So the primary issue is with the front mount. The rear rubber mount is pretty solid/reliable and longer lasting?

Well that depends, in my case it "appeared" that about 80% of the stretch occurred in the front mount. There is inevitably "some" stretch in the rear, however my rear mount did not appear to be deformed like the front.

When you look at the parts manual (see attached PDF) it "appears" that the OEM assembly would have the rear mounted first to the tranny and frame. Then as the engine is set in place the front mount is attached and the the torque would appear to pull it forward and downward (to me) leaving the rear "somewhat" out of the stretch factor. You can draw your own conclusions on that.

In any case both should be inspected if an issue is present. When I replaced my front mount, I did the shim at that time so as not to stretch the new mount. After installing the front mount with the shims I then pulled the floor jack out of the way and put the bike on the lift.

I then loosened the rear mount bolts and inspected the rear mount with a flash lite as best I could, but did not remove it. I then tightened the rear mount bolts but left them still a tad loose, I also re-loosened the front mount bolts, just enough to take the tension off, they were still securely attached.

Then while up on the lift in the vertical postion I did the vertical alignment (it's a lot easier to pull or push the the top of the engine with the mounts loose). The Vertical Alignment is a whole nuther story that has been covered elsewhere so I want go into that again here.

After I had Vertical Alignment done, while still on the lift with the mount bolts still loose, I fired the engine up and rev'd it a few times to let the engine "settle" in it's mounts. Then I torqued both mounts to specs. (it's easier to torque the rear mount bolts if you take the brake wire loose)

Keep in mind vibration can come from other sources besides a bad motor mount, or the preload stretch deformation. But the washer shim (and a new front mount) did help my bike.

I noticed when I put Tbars on my bike and installed the heavy duty riser bushings I now have more vibration in the bars. But I will have to live with that since I like the way the bars feel and handle otherwise. Before when I had to push the bike the bars felt flimsy.

 

[R_W_B]

Anyone wanting to do the front mount shim it is important to be "aware" of the amount of shim distance, and any other bracket thickness involved, as in my case I had the HD oil cooler bracket which eat up a good 1/8" of the front mount threads.

Couple that with the 1/4" stretch that I shimmed and I had to buy new grade 8 bolts. It's not always possible to find them fully threaded (in grade 8 anyhow). Some careful attention must be paid to assure you have at least 5/8" to 3/4" thread penetration into the mount thread and "also" if you are using bolts that have some bare shank, this bare shanked area cannot protrude into the mount threads. So buy your bolts accordingly.

Also keep in mind the OEM front mount threads are "not" open. You can only penetrate them about 1-1/8". Mine were just under that, I tested them first to find the penetration of them. Motor mounts is serious business, make sure you get all those factors right.