engine tapping noise

Joined
Jul 12, 2012
Messages
11
Location
Canton, TX
Bike
83 VF1100C
I just rebuilt a rack of carbs for a customer on a 94 ST1100. He has what sounds like a top end tap and I am hoping it is a common problem with that bike. After the carb install it ran a few minutes before the tap started. He says he can hear it while riding and at idle and he pulled the #2 spark plug wire and the tap went away. He did a valve adjustment. Any ideas?
 
Joined
Aug 10, 2015
Messages
2,029
Location
Fort Worth, Texas
Bike
91 ST1100/06 ST1300
If all you did was a carb rebuild, assuming it's something related...probably an air leak at the rubber connectors.
Lots of other questions. How many miles are on the bike? Has it been well maintained? Does he use a recommended engine oil. Does the engine vibration level worsen or get better when #2 plug is removed? Without examining the bike in person, it's difficult to venture a guess.
However, worse case, if engine vibration smooths out with removal of #2 plug and the noise goes away or significantly reduces, a bad rod bearing is a likely cause.
Eliminate cheaper causes such as an air leak first.
 
OP
OP
Joined
Jul 12, 2012
Messages
11
Location
Canton, TX
Bike
83 VF1100C
I know little about the bike at this point. I have never seen the bike as it is in GA while I am in TX. My understanding is the bike has been dormant for a few years and the guy is bringing it back to life. I was thinking rod bearing or wrist pin. Rod bearings are not a click, more of a hard clank at least in my experience. If I find out more info I will post it here. I did email him a link to this thread and hopefully he will jopin and add his 2 cents. Hoping for a common problem with these bikes. I am not an ST guy so don't know their individual quirks.
 
Joined
Aug 10, 2015
Messages
2,029
Location
Fort Worth, Texas
Bike
91 ST1100/06 ST1300
I know little about the bike at this point. I have never seen the bike as it is in GA while I am in TX. My understanding is the bike has been dormant for a few years and the guy is bringing it back to life. I was thinking rod bearing or wrist pin. Rod bearings are not a click, more of a hard clank at least in my experience. If I find out more info I will post it here. I did email him a link to this thread and hopefully he will jopin and add his 2 cents. Hoping for a common problem with these bikes. I am not an ST guy so don't know their individual quirks.
I refurbished my 'new' 1100 a year ago. Had been sitting in a garage for 20 years. I did all the service in the manual because I was unfamiliar with it....Beware of 'was running when parked'..... When done, the only noise was the belt whine. A year later and that has diminished but is still there.

Was thinking about the click/no click. Could it be arcing from the #2 plug cap or wire? A bad rod bearing was my first thought, had one display as a click initially....thought it was an exhaust leak...hammering will follow. Only other thing I can think of cylinder specific would be an air leak or such associated with that carb. A leaky exhaust seal would sound somewhere between a squeal and a fart (sorry, can't think of a better description) before it becomes obvious. Sorry, just making suggestions. These problems all have a range of presentations.
 
Last edited:

bdalameda

PaleoCyclist
Joined
Jan 13, 2009
Messages
2,423
Age
67
Location
Salinas, California
Bike
Africa Twin
Also if your carbs are not synched correctly or the idle mixture is off on one carb there can be an audible knock sound. This happens when the other cylinders are developing power and pulling the dead cylinder along. Make sure all manifolds are seated properly and all hoses connected correctly. Try synching the carbs and setting the mixture.
 
Joined
Sep 4, 2013
Messages
8,110
Location
Cleveland
Bike
2010 ST1300
How about someone (owner) getting a cheap mechanic's stethoscope and trying to localize the sound? Ok, if he is a doc, he can use his expensive stethoscope.
 

jfheath

John Heath
Site Supporter
Joined
Mar 18, 2006
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Ilkley, W Yorkshire, UK
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2013 ST1300 A9
2024 Miles
000679
STOC #
2570
Ah - I know exactly what that noise on the video is. It appears usually after removing the airbox.

Underneath the air box, there are two tubes which connect from underneath. A large one and a small one, each held in place by a circlip. The air box housing will not come off until the larger tube has been disconnected. The smaller tube will just slip off un-noticed.

In the nano second between removing the air box and stuffing any holes to prevent anything falling inside the engine, it is possible to catch the smaller rubber tube. Because it slipped off the airbox un-noticed, it is often forgotten that there was a circlip on the end of the tube.

The noise in the video is the sound of that circlip being hammered into the top of the piston as it strikes the top of the cylinder head.

Please don't ask me how I happen to know this.
 
Joined
Dec 22, 2009
Messages
68
Location
Nanaimo BC
Bike
1998 ST1100A
STOC #
434
That may well be, I was attributing it to a bent valve because one of the keeper halves was up too far and the valve won't close even with the cam out, I should pull the head and see if there is something in there.. The clip is still on the crank vent hose but who knows on a 20 year old bike, I did have the carbs off to do the rad hoses and pair delete prior to this happening..
 

jfheath

John Heath
Site Supporter
Joined
Mar 18, 2006
Messages
2,786
Age
69
Location
Ilkley, W Yorkshire, UK
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2013 ST1300 A9
2024 Miles
000679
STOC #
2570
You may well be right. I just heard the sound and instantly recalled that sickening feeling that I had all of those years ago when I fired mine up and heard the noise of piston hitting something.
 
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