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Author Topic: Engine Knocking on Reducing RPM  (Read 1039 times)

IronHead

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Engine Knocking on Reducing RPM
« on: April 23, 2013, 05:54:59 PM »
Greetings from Sunny South Africa.

After 11 years of waiting I am the proud owner of a Bullet 500, and have been using the past few weekends to sort out minor niggly issues such as the brake and indicator lights.

According to the papers it is a 2007, but the VIN plate says 2002. That being said, it has the later type crankcase breather from the top of the case with the return going into the timing cover (?), so the jury is still out on that one.

The only mod I have done so far is the 'Australian Fix' for the breather, by turning the pipe around.

Since I got her the idling has been a bit high to my liking and after adjusting it yesterday, when stationary and  twisting the throttle, upon release as the RPM drops there was a knocking sound, which then dies down and the engine returns to idle.

I then adjusted the points and timing this afternoon, with the knocking being reduced, but still there. I suspected the ES was maybe shot and took off the primary cover to check for loose bits, but all good in that respect.

After putting everything back I started her up again, and the knocking was gone - bear in mind that you could feel it through the handle bars - which made me wonder if maybe it was pre-detonation.

I suspect that with the time taken to test and adjust the idling etc., with all the stationary idling there is a hot spot that causes pre-detonation, which is why it only happens when the engine gets warm. The time taken to refill and put back the primary allowed the engine to cool down again, of course this is speculation.

I took her for a test drive and listened over the valve clatter as well as revved a bit when stopping to test, but no more knocking.

Am I correct on my guess as to the cause of the knocking and the 'fix' or can something else be causing it?
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ace.cafe

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Re: Engine Knocking on Reducing RPM
« Reply #1 on: April 23, 2013, 06:29:25 PM »
We cannot say. We don't know what this "knock" sounds like.

However, if it is a popping in the exhaust pipe on deceleration, that would be something else, and we might be able to guess that.
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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jedaks

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Re: Engine Knocking on Reducing RPM
« Reply #2 on: April 24, 2013, 10:42:45 PM »
I don't think electric staters were available until 2003/04.

Ace is the man to diagonse, but wouldn't detonation at idle be very unusual unless your combustion chamber and piston crown are absolutley filty? How many miles on the bike? 

IronHead

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Re: Engine Knocking on Reducing RPM
« Reply #3 on: April 25, 2013, 11:29:22 AM »
1658 km when I got it, currently just under 1800. The original owner apparently used it as a display piece in a pub, and I think it stood outside or at least where it got a lot of sun, the red is faded to a pretty dark orange.

The weird thing is that it is there only briefly, when letting off on the throttle.

At Idle: valve clatter and exhaust note.
Increasing RPM: valve clatter and exhaust note.
Letting go the throttle: as the RPM drops, just before it returns to normal idle, there is a clack-clack-clack for a few seconds, then it disappears and returns to normal idle.

Together with the noise, it feels as if something is knocking the handlebars as they vibrate like crazy at the time.

I have checked the head stay screws and are all pretty tight, and to me it seems like it is inside the head/cylinder and not lower down.

As said, it appears to have disappeared, but it would be good to know what is causing it. I have searched and from the descriptions elsewhere on the forum it doesn't sound like pinging as the sound is pretty low pitched, the frequency is below that of the valve clatter. I tried to record it but it is too soft to be heard over the valves.

(On a side note I am very glad to have found this forum as I can see lots of time ahead tinkering in the garage and the information so far has been exceptional.)
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ace.cafe

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Re: Engine Knocking on Reducing RPM
« Reply #4 on: April 25, 2013, 12:04:42 PM »
Sometimes it can be from sympathetic vibrations of something else rattling when the engine vibrates at a certain frequency.

However, knocking on deceleration CAN possibly be a bearing knock, indicating a bad bearing, so you must assess that situation, just in case. Low mileage is not necessarily an indicator of bearing health. I'd use a stethoscope on the engine case to see if the noise is coming from within the engine.
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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Arizoni

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Re: Engine Knocking on Reducing RPM
« Reply #5 on: April 25, 2013, 05:54:29 PM »
Is it possible that the primary chain is loose?
If it were the momentum of the clutch and transmission input shaft and gears while the engine speed is decreasing  might cause the chain to whip or slap something like a loose chain tensioner.
Jim
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curtisbelford

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Re: Engine Knocking on Reducing RPM
« Reply #6 on: April 26, 2013, 06:03:06 AM »
My 99 had a similar vibration and I discovered that my valve seats where dropped. SSOOOO upon further investigation it also cracked my head and I bought a new one ($450.00 ouch that one hurt) and all is good. Also had to keep setting my valve lash too.

barenekd

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Re: Engine Knocking on Reducing RPM
« Reply #7 on: April 26, 2013, 05:30:08 PM »
Would highly doubt that preignition is the culprit in the noise you're hearing. Deceleration is the least likely spot to hear that.
You have something mechanical banging around in there.
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grumpyed

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Re: Engine Knocking on Reducing RPM
« Reply #8 on: April 27, 2013, 02:45:23 PM »
My 96 started doing that at about 50-75 miles.It was a loose exhaust seat.Had a new one installed and that fixed that.

IronHead

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Re: Engine Knocking on Reducing RPM
« Reply #9 on: May 06, 2013, 03:00:17 PM »
I am beginning to suspect the electric start, coupled with very old primary chain oil.
When I drained it the first time around it was black and smelly, wiffed liked a drain pipe! After replacing it with fresh clean oil everything seems smoother and better.

I also recall that the day before I first encountered the noise, when kickstarting at the end of the day to head home, I heard the same whine as when the ES does not start the engine and you release the starter button, not sure what you would call it.

Haven't heard or felt the noise/knock in the last two weeks, so hopefully all good, but still planning to have a look at the valves as soon as I can get a chance.
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Blltrdr

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Re: Engine Knocking on Reducing RPM
« Reply #10 on: May 06, 2013, 06:04:20 PM »
A few years back it was recommended that an additional amount of oil be added to the ES model primary for proper lubrication of the sprag gear. I'm sure someone will chime in with the correct amount.
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D the D

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Re: Engine Knocking on Reducing RPM
« Reply #11 on: May 06, 2013, 07:30:31 PM »
I've read on this and other forums 820ml for ES Iron Barrel primaries.  I've never seen the actual factory bulletin though.  Members of the forums in India say it is a US/Britain or Export bulletin.  Some Indian owners of ES Iron Barrels say they are using 3/4 to 1 liter because of the Export bulletin.
I used 840ml 'cause it won't hurt if it doesn't help.  "Drag!" I've heard some say, but I don't notice it.  I'm not racing an HP machine on Isle of Man either. It's probably more what fluid makes your clutch feel the way you like than how much is under the cover.
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