What is "piston slap", and what can silence it?
Road Captain
Joined: Aug 2008
Posts: 559
Likes: 0
From: Berwick, Pa.
If the moco agrees that it is piston slap they have to stand behind the warranty. Is it possible you are bringing the bike to them warmed up and the extent of problem is not observed? Anyway if your guy isn't helping call other dealers, even at a distance, and ask their opinions on repair.
Two quick things. Ethanol or better the amount of ethanol will cause problems with pistons. To me it's akin to putting sugar in the tank. Second, to help with bad gas and cooler top end running, I've been useing Marvel Mystery Oil this summer. 2-3 ounces per tank. Top end sounds better and runs cooler while lubricateing top end.
Two quick things. Ethanol or better the amount of ethanol will cause problems with pistons. To me it's akin to putting sugar in the tank. Second, to help with bad gas and cooler top end running, I've been useing Marvel Mystery Oil this summer. 2-3 ounces per tank. Top end sounds better and runs cooler while lubricateing top end.
Extreme HDF Member
Joined: Sep 2005
Posts: 11,615
Likes: 50
From: Baton Rouge, LA
I have a '66 Corvette with a factory 427ci engine and it has piston slap that lasts about a minute when cold, then goes away. This is considered normal for these old motors with forged pistons, which weren't put together with exacting tolerances, but I wouldn't expect piston slap on a new HD or any other modern engine. I'm not sure what you can do except tolerate it, as their unwillingness to fix it doesn't surprise me, and I agree it probably won't hurt anything. OTOH it would be a nice excuse for installing a Stage II kit if you were otherwise on the fence about it.
Road Master
Joined: Jul 2007
Posts: 914
Likes: 1
From: Republic of Texas
I read to the end of this, and everyone seems to just accept your diagnosis of the cause of the problem without question. But to confirm that it actually IS piston slap, it'll require a tear-down.
From your description of the problem, "only when the motor is cold, I get a clanking sound coming from the engine", a lot of things could sound like that. One that comes to mind is rod knock. Rod knock wouldn't really ever "go away", but traffic/road sounds/wind/etc would tend to mask it at higher riding speeds. Same thing could be said about piston slap.
Another might be lazy lifters - one or more lifters that don't pressurize as soon as you start the engine. Could be other things as well. Just keep an open mind until you find what it really is.
I agree with others that you shouldn't be having any kind of problem with a low-time engine. But it happens.
From your description of the problem, "only when the motor is cold, I get a clanking sound coming from the engine", a lot of things could sound like that. One that comes to mind is rod knock. Rod knock wouldn't really ever "go away", but traffic/road sounds/wind/etc would tend to mask it at higher riding speeds. Same thing could be said about piston slap.
Another might be lazy lifters - one or more lifters that don't pressurize as soon as you start the engine. Could be other things as well. Just keep an open mind until you find what it really is.
I agree with others that you shouldn't be having any kind of problem with a low-time engine. But it happens.
Last edited by racklefratz; Oct 14, 2009 at 11:26 AM.
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Road Master
Joined: Oct 2008
Posts: 880
Likes: 81
From: California
I know you guys are right about taking it to the dealer, but I absolutely HATE taking it in. I've had a few other issues with my bike (clutch cable, fuel top plate, stalling), and never once have I been happy with the performance of any of my local dealers. They take too long, don't correctly diagnose the problem, and then I have to wait days and days for parts to come in. And, with their track record, chances are that I'd still have the same exact problem when I get it back. Dealers truly frustrate me to no end; to the point that I'd just about rather live with problems, or better yet, deal with them myself. In fact, every single problem that I've had, and that I've taken it to the dealer for, I've ultimately ended up fixing the real issue myself. Pathetic! But I'm resigned to the belief that my local dealers suck, and I'm not willing to go further to search for a better dealer.
Racklefratz, Thank you for the insight into other possible causes. To address a few of them, the noise absolutely does go away once warmed up. In my case, road conditions or other ambient noise is not playing a part in the silencing of the sound. So based on your info, my lifters may be lazy? Hmmm...
Racklefratz, Thank you for the insight into other possible causes. To address a few of them, the noise absolutely does go away once warmed up. In my case, road conditions or other ambient noise is not playing a part in the silencing of the sound. So based on your info, my lifters may be lazy? Hmmm...
Road Warrior
Joined: Feb 2009
Posts: 1,661
Likes: 0
From: East Northport, NY
Sir, it appears that when you washed your bike, you used a $2.95 microfiber cloth instead of our $14.95 HD microfiber cloth, and that not only is causing you engine problems, but voids your warranty