Author Topic: metallic knocking sound  (Read 2003 times)

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mo goldie

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metallic knocking sound
« on: 20 June, 2021, 23:58:38 »
well the other day I was coming back from a ride on my RGS when it gets to about 65 mph there is a banging rattling sound
turned off on to a miner road and keep it at about 40 mph to get me back home but as soon as I open up to 60 - 65 it cam back....did not sound good at all..... so just striped the primary side down can`t find anything wrong there so took the timing side off as I just had my Dynamo sorted so wondered if I done something wrong in there.....but No everything is fine.

so any suggestions as to what it could be please as I still have it striped down ....... just hope its not an engine out Job.

Cheers Mo     

bikerbob

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Re: metallic knocking sound
« Reply #1 on: 21 June, 2021, 08:52:14 »
Difficult to say really but before stripping anything down I would normally use a mechanics stethascope to gve me a general idea as to where the noise is coming from you can use a long screwdriver just put the tip to various parts of the engine top end bottom end primary and timing sides and the handle to your ear this does help in identifying where the problem lies. But if you have already stripped the primary down I presume you have stripped the clutch down  to eradicate that , if you have just removed the cases and done a visual inspection then replace them and try the screwdriver test first. you could before replacing the cases see if there is any play on any of the moving parts and shafts. failing that it does seem to point to an internal problem and an engine strip down good luck. hope t is nothing to serious.

DAVE BRADY

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Re: metallic knocking sound
« Reply #2 on: 21 June, 2021, 09:20:44 »
Hi Mo,

So no noise at 40 but noise at 60.  Did the noise suddenly start or did it gradually come in?  Did it still sound the same at constant speed or was it more when under load when accelerating?  Is it speed related or revs related?

Dave.

idie

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Re: metallic knocking sound
« Reply #3 on: 21 June, 2021, 10:03:09 »
If you still have the timing cover off try levering the crank up and down. Use something like a tyre lever under the timing pinion. When this suddenly occurred on my Shooting Star in was the bronze bush. I had about 20 thou play. Also a very simple thing that might have occurred check the cylinder base nuts. If they come loose the cylinder goes up and down and makes a horrible sound like big ends failing. If left it will cause the barrel to fracture across the flange.

DAVE BRADY

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Re: metallic knocking sound
« Reply #4 on: 21 June, 2021, 10:52:08 »
Hi, 

Good thinking about the cylinder base buts.  This did happen to me once.

Just another thought.  If the timing has slipped that could cause some noise and vibration at higher revs.  This was the case with an A10 at the UK Inter. that felt like the bottom end was about to blow up when under load pulling off and at higher revs.  No problem with the bearings but timing, I think, retarded and/or auto advance not working properly.
 
Dave.
« Last Edit: 21 June, 2021, 11:01:59 by DAVE BRADY »

Dean Southall

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Re: metallic knocking sound
« Reply #5 on: 21 June, 2021, 13:02:31 »
I had a similar problem with my Super Rocket. Very worrying noise! So limped home at 30mph.
Turned out to be centre stand rattling in frame!
So double check it is an engine issue.
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Jim S

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Re: metallic knocking sound
« Reply #6 on: 21 June, 2021, 14:47:08 »
The fuel tank can also make quite a noise if it starts to resonate and is not properly secured on firm rubber pads.

mo goldie

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Re: metallic knocking sound
« Reply #7 on: 21 June, 2021, 22:14:15 »
Hi everyone thanks for you comments,

I have just striped off the rocker Box and the head and all were fine so then went a took the barrels off and the were great the pistons did not have any marks on them at all. took the bottom crank case plate off and found bits of some sort of steel in the strainer, also when I took the pistons down to there lowest stroke I found the pistons and made witness marks on the flywheel
even as I was holding them as upright as I can without the barrels when they came to that lowest point they hit that Flywheel....very strange.....the pistons are still on at the minute so have not looked at the inside to see who made them, and all they is on the tops is the mark 71.....so I was told they were 8,5:1 but thats all I know about them, so I assume that 71 means 71 mm but thats it so No +20 or +40       

DAVE BRADY

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Re: metallic knocking sound
« Reply #8 on: 22 June, 2021, 07:16:44 »
Hi Mo,

71mm is very close to 0.040 oversize and is common on pistons.  Usually rebore is done to match the pistons so there should be no problem there.  For the piston skirt to make contact with the flywheel indicates massive clearance in the big ends or the rods are out of shape.  Do the pistons.rods move up and down a lot?  Have both pistons marked the flywheel?  Although you are gong to strip the engine completely, check the bits from the strainer with a magnet to determine if ferrous or not.    This is quite intriguing.
Can you post some pictures?

Dave.

mo goldie

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Re: metallic knocking sound
« Reply #9 on: 22 June, 2021, 22:15:08 »
Hi dave

There is No movement at all in the pistons on the rods or the big ends... they are Gpm pistons which I have done a search for and found they are made in Italy or so it said..... the metal that was in the strainer was indeed steel and looks like a shim.... I have been told to take a few Thou of the skirt of the pistons as was told the bottom end is fin and Not to stirp it.... I took one piston off the rod and check it and it has only been just marking it a bit.....( well I here you say it should not even hit any at all ) so I will take a few thou as they say off and put it all back together in the next week or so and let you all Know how I got on....so fingers crossed  :-*

cheers mo     

DAVE BRADY

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Re: metallic knocking sound
« Reply #10 on: 23 June, 2021, 09:10:14 »
Hi Mo,

Make sure you remove exactly the same from the each piston and from each side to maintain the balance.
If it looks like shim material then this could explain why it started quite suddenly as the shim will throw out once it fails.   Is there a lot of end float?

Dave.

mo goldie

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Re: metallic knocking sound
« Reply #11 on: 23 June, 2021, 21:27:15 »
Hi Dave

Yes I have removed about 15 tho or so off the bottom of both the skirts on the Pistons and I have also made that weight of both the pistons are the same at  278 Grams each and both flat on the bottoms too, I have put them back on the conrods and they both Now don`t touch the flywheel when at there lowest point..... so Now I have done that I can Now get on with all the clean up of all the parts and even respray the barrels and hope to put it back together in about a week or so and will give all you Guy`s an update as to what the out come will be...so Fingers Crossed and everything else  ;D

Cheers Mo   

DAVE BRADY

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Re: metallic knocking sound
« Reply #12 on: 23 June, 2021, 21:38:56 »
Hi,

Did you check the end float to see if a shim has been thrown out?

Dave.

idie

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Re: metallic knocking sound
« Reply #13 on: 23 June, 2021, 21:49:35 »
Anymore then 3 thou end float will hammer the bronze timing side bush.

mo goldie

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Re: metallic knocking sound
« Reply #14 on: 23 June, 2021, 22:36:21 »
Hi yes there is very little and I mean little end float so that all seems to be good.