Chasing Rattles On Both Harleys… It’s Those Darn Bridges!

A few weeks ago I began to notice a new noise coming from the Road King’s motor.  It was a very loud rattle that seemed to be in sync with the engine RPM coming from somewhere near the front of the engine. I checked around the shifter linkage, oil cooler cover and other hardware on the left side of the bike while it was at idle and as I rode trying to isolate the noise, but to no avail. The shifter linkage was rattling a bit, so I tightened it up, but that was a different and much more subtle rattle; but, good that I caught that.

Last Sunday, as I was headed back to the house on the Road King after running some errands I finally started to explore the upper end of the motor, around the horn and tops of the cylinders, as I remembered someone with another Road King CVO mentioning that his horn had developed a rattle.  Ah hah!  I finally found it!  It wasn’t the horn, it was the Harley-Davidson finned cylinder head bridge on the rear cylinder!

flh_bridge

These are purely cosmetic engine accessories that clean-up and finish the top of the cylinder heads around the head bolts and spark plugs.  I put them on our Wide Glide as well, as the engines just look like they’re missing something without them.  However, apparently the cap screws that hold the mounts to the cylinder head bolts backed-out or were worn down by the heat and vibration and were no longer “gripping” the cylinder head bolts, hence the rattling noise that paralleled the engine RPM / vibrations.

If you’ve never seen these things, here’s a photo of the kit alongside another photo of our Wide Glide with the front bridge removed and the mounting hardware removed from the front cylinder head bolt.

Screen shot 2013-12-08 at 12.58.42 PM fxd_bridge

There are a pair of cap screws in the mounting hardware that hold them in place against the cylinder head bolt, and then two other socket head screws are used to attach the bridges to the mounting hardware.  It’s that cap screw interface between the mount and the cylinder head bolts that proved to be a weakness.

capInterestingly enough, it was impossible to loosen the cap screws when they were cold; it took penetrating oil + heating with a torch to free them up. This is why I’m thinking that it’s the high engine heat + vibration that lead to these mounts coming loose.  Oh yeah, the reason the Wide Glide’s front bridge was off was because I also found that it was loose.

Anyway, I was able to get both bikes sorted back out and eliminate the noise. As you’d expect, H-D doesn’t sell the mounting hardware / caps separately so I’ll be keeping an eye on these bridges and pulling them off at least once a year for preventative maintenance.

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About TG

I've been around a bit and done a few things, have a couple kids and a few grandkids. I tend to be curmudgeonly, matter-of-fact and not predisposed to self-serving chit-chat. Thankfully, my wife's as nice as can be otherwise we'd have no friends. My interests are somewhat eclectic, but whose aren't?
This entry was posted in Miscellaneous ramblings on Motorcycling, Motorcycle / Equipment. Bookmark the permalink.

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