UL noise

Flathead noise

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Andygears
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UL noise

#1

Post by Andygears » Fri Oct 19, 2018 2:42 am

My friend George had me listen to his motor today, a '39 80 inch UL,. It starts & runs OK but has a noise like 2 flat pieces of metal slapping together. It only does it when you "Give it a rev." . At idle it's pretty much gone but as you throttle it up, it's intermittent but the same volumn each time, not terribly fast in relation to motor speed.

I told him weak or broken valve spring/s but I'm not a flathead guy and told him so. Was I way off?

Thanks

Andygears



Frankenstein
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Re: UL noise

#2

Post by Frankenstein » Fri Oct 19, 2018 12:11 pm

The list is long, but hard to pinpoint from here. :D Short answer, don't ride it!
Could be inadequate clearance between the rods and they are "kissing" each other, (the male rod slamming into the crotch of the female rod) at the bottom of each stroke, leading to a broken rod, cases, generator, etc, etc.

Piston slap,
loose rod bearings
piston hitting head from excessive rod bearing clearance
worn tappet rollers,
etc, etc,
All the worst engine failures you can and will imagine....
You're going to have to investigate.
I've had the rod thing happen twice, and it resulted in catastrophic case destruction
Investigate before you need to reinvest.
DD

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Re: UL noise

#3

Post by Andygears » Fri Oct 19, 2018 1:37 pm

Thanks for the reply. It doesn't sound as "Heavy" as a lower end and it's not banging on each revolution or every other. I was thinking a valve hitting the head but not knowing flatheads I don't know what that sounds like. He was saying how great it ran on a three hour 70 MPH ride recently. I was thinking that ride weakened a valve spring enough to float a valve intermittently. I asked if it got louder lugging the motor, he said "No" , it seems to just do it on hard acceleration of the motor RPM's. Am I correct in assuming a flathead valve can hit the head without bending it sideways? Thereby maintaining a smooth idle and good compression. I recommended he pull the head and could see evidence of interference. He's having other guys who know more than I, listen and give advise. I will post when he finds it.

Andygears

chuckthebeatertruck
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Re: UL noise

#4

Post by chuckthebeatertruck » Fri Oct 19, 2018 3:10 pm

I'm curious about the rod bashing comment.

My 4.75" stroke UL has plenty of clearance between the stock rods. It actually shocked me how much clearance was there. I still polished and peened the buggers -- but didn't have to grind out the "crotch." The cylinder notches and cases -- well that's a different story.

Did something go horribly wrong that it happened to you twice?

Or, did you learn these particular rods need more than the normal 1/16-1/8th clearance at their closest contact point?

Again, not busting or trying to dig at this -- I'm genuinely curious.

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Re: UL noise

#5

Post by Frankenstein » Sat Oct 20, 2018 3:47 am

So my experience with rods was for sure a rarity. First time, it was a UL. Second time a 62Pan.
The UL was my first build, didn't know to check rod to rod clearance. But, when the motor was fresh and the bearings tight, no noise, no clues there would be a problem. I think as rod bearing clearance increased the rod had enough movement so they would strike each other. Eventually, the female rod broke, and the rod stub trashed the cases and even whacked the aluminum end of the genny and banged it in. That's just a surmise on my part, all I know for sure was no noises when the motor was fresh, and about 8k miles later, the clicking noise developed, then boom.
On the 62, again no noises early on, then many thousands of miles later, the clicking noises, then boom.
I always check rod clearance now, and usually there is no problem, but the clearance does vary from set to set.
DD

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Re: UL noise

#6

Post by chuckthebeatertruck » Sat Oct 20, 2018 1:54 pm

Thank you.

This isn't the first time I've heard of this and I have a theory.

The machining on a lot of female rods I've seen is just terrible on the inside of the crotch. That's also one of the most stressed parts of the forging.

My theory is that when things get loose, the bashing causes a crack in those terrible machine marks, and the rod comes apart.

I've also wondered about poorly replaced races. I've seen some serious gouges on the outside of the race and rod, again just tempting fate.

I take the lazy way out and toss rods in the tumbler for awhile before polishing and peening. I fear busted rods.

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Re: UL noise

#7

Post by Frankenstein » Mon Oct 22, 2018 2:03 am

On both failures I experienced, you could see the shiny spot and wear marks on the two rods where they were beating themselves to death. Both times, motor was idling along at 50-55 level ground, when kaBooom! And suddenly, my Harley was running on one cylinder!
Ugh.
DD

flat38
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Re: UL noise

#8

Post by flat38 » Tue Oct 23, 2018 1:52 am

An easy way to help narrow down an engine noise is to put it in high gear standing still and let the clutch out to load the motor. If the noise changes, its bottom end or pistons and if it stays the same, it is valve gear.

Andygears
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Re: UL noise

#9

Post by Andygears » Tue Oct 23, 2018 10:35 am

flat38 wrote:
Tue Oct 23, 2018 1:52 am
An easy way to help narrow down an engine noise is to put it in high gear standing still and let the clutch out to load the motor. If the noise changes, its bottom end or pistons and if it stays the same, it is valve gear.
Thanks, I will try that, but what does a flathead sound like with a bad valve spring? And can the valve hit the head without bending? Pans & Shovels sound a certain way with a loose valve adjustment and a bad spring will make a noise I know or can feel in the pushrod cover, flatheads sound different.

Andygears

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Re: UL noise

#10

Post by Frankenstein » Tue Oct 23, 2018 12:03 pm

With aluminum heads, it will be noticeable it's coming from up top, Iron heads probably less noise, but still should be easily traced to being up top. However with original springs, I doubt it is the spring. They're not highly stressed and I've never seen a broken one. Aftermarket, who knows? But the one set I ordered, but didn't use, were much lighter pressure than stock, so breaking would seem to be a non issue. I'd also expect the machine to not run smoothly if a valve has taken on a mind of it's own. If the valve was hitting, I would expect it to get bent, which would spoil sealing at all speeds, and thus poor running at all speeds too.
You're going to have to investigate further. One more baddy I just encountered was a cam shim that had wadded itself, and the extra end play allowed a cam shaft to slide into the flywheel chest far enough to allow the crankpin nut to strike it! However, the noise was at any engine speed, but intermittent.
My first thought would still be piston hitting head, but almost impossible with a stock motorbuild, they're too far apart.
You're going to need to take a look-see. :(
DD

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Re: UL noise

#11

Post by nan00k » Tue Oct 23, 2018 9:44 pm

I know nothing, but isn't that the pointer if the noise is consistent with valve gear speed or faster con rod / piston rev;s?

Andygears
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Re: UL noise

#12

Post by Andygears » Tue Oct 23, 2018 11:30 pm

Frankenstein wrote:
Tue Oct 23, 2018 12:03 pm
With aluminum heads, it will be noticeable it's coming from up top, Iron heads probably less noise, but still should be easily traced to being up top. However with original springs, I doubt it is the spring. They're not highly stressed and I've never seen a broken one. Aftermarket, who knows? But the one set I ordered, but didn't use, were much lighter pressure than stock, so breaking would seem to be a non issue. I'd also expect the machine to not run smoothly if a valve has taken on a mind of it's own. If the valve was hitting, I would expect it to get bent, which would spoil sealing at all speeds, and thus poor running at all speeds too.
You're going to have to investigate further. One more baddy I just encountered was a cam shim that had wadded itself, and the extra end play allowed a cam shaft to slide into the flywheel chest far enough to allow the crankpin nut to strike it! However, the noise was at any engine speed, but intermittent.
My first thought would still be piston hitting head, but almost impossible with a stock motorbuild, they're too far apart.
You're going to need to take a look-see. :(
DD
Thank you, that's the info I was looking for! A first hand noise guy, I suspect this flathead was not really well built internally and an alternate scenario sounds plausible. As I said the slap noise isn't really fast but I knew I wasn't the guy to diagnose it. He's got other's looking at it, but thank you, I've learned more.

Andygears

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