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rdog, this is too broad a question to get a reliable answer.

Some history on the engine condition, recent work, and actual symptoms, will give someone an idea on just what the problem might be.

Assuming the mechanicals are OK, detonation will cause the engine to knock at low RPM under load. This is just a wild guess, but if the engine is detonating, big trouble is sure to follow unless you get a fix.

Get high octane gas into the tank, 98 RON would be good. Ensure the ignition timing is correct for the model. Avoid loading up the engine at low RPM (lugging).

Remember, you tell us under what circumstances the engine knocks and good advice on a fix will surely follow. RR
 

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If it only knocks under load, it is probably too low of octane fuel or advanced ignition timing. If it knocks all the time, it could be rod or crank bearings, loose/worn gudgeon pins, piston slap caused by too much skirt clearance, clutch hub play, a loose rotor, a burr on a timing gear, or any number of other mysterious gremlins. Loose tappets create more of a rattle than a knock.
 

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BESIDES worn rings and/or bad pistons, valve problems or bent pushrods, possible causes of knocking sounds in an engine:

Pre-ignition due to bad fuel
Pre-ignition due to incorrect timing
pre-ignition due to excessive carbon buildup
Alternator rotor body loose on it's center hub
Connecting rod big-end bearing shells excessively worn
Connecting rod small end bushes excessively worn
Loosening connecting rod bolt (danger Will Robinson!)
Crankshaft main bearings damaged (more of a "rumble")
Damaged camshaft lobe(s)
Damaged cam follower(s)
Incorrect valve lash adjustment
Cam followers sticking in guide blocks
Valves sticking in guides
Transmission gears with damaged teeth or grooves
Transmission shafts with damaged splines
Damaged / deteriorated clutch cush hub rubbers
Damaged or missing clutch roller bearings
Damaged woodruff key on alternator rotor, engine sprocket or clutch hub
Damaged oil pump plunger
Damaged oil pump slider block
Damaged camshaft/drive/idler pinion gear(s)
Sticking primary chain links

I know I'm forgetting several other possibilities, but this ought to get you started...
 

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Take a long, thin screwdriver and set the tip in various spots on the engine at idle (high or low idle, wherever the noise is greater), and hold your ear to the handle.

Point a big fan at the engine when the bike is sitting idling for more than a couple of minutes.

When you seem to localize the source of the noise, report back...

Top to bottom, front to back, side to side. Don't stop when you THINK you've spotted it, because it could be louder somewhere else.
 

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As a rule, a typical engine knock is caused by a clearance being too large, in other words out of spec. Normally this is a bearing clearance and it allows two mating parts to move more, relative to each other, than designed and results in them hammering each other, producing the knock. Since these engines are reciprocating, you get the knock each time the pistons change direction. Once an engine starts to knock, it is like a hammer working on the knocking parts. It makes the clearance larger, increasing force of the hammering until something fails. The hammering also overcomes the oil film because of the sudden spike in pressure at the point of contact and because things are not staying in relative contact and maintaining an oil wedge. All bad stuff.

Piston slap is also caused by excessive clearance as already stated and is just that, the piston slapping against the cylinder wall as it changes direction. It's actually rocking back and forth on the wrist pin.

Old gasoline commercials used to refer to "engine knock" which was really "ping". This is the sound made when the fuel mixture combusts too rapidly and normally on more than one flame front causing a detonation in the combustion chamber and the resultant pressure wave is transmitted thru the engine casting. Ping normally sounds more like a coffee can full of nuts being rattled.

Valve clatter is usually constant. Some of it is just inherent in a particular design. Some is caused by excessive clearance at the rockers, some perhaps by worn guides or worn rocker arm shafts. Some is just normal. Engines with solid lifters like yours, will always have some valve train noise.

What causes knock? There is probably an endless list of potential reasons, but most common are:
1. Loss of lubrication because of old oil, cheap oil, wrong oil, low oil, bad pump or dirt/crud plugging oil passages.
2. Abuse as in over revving, over heating, over stressing when cold, etc.
3. Clearances under spec when assembled causing limited or no oil wedge and early bearing wear.
4. Normal wear over time.
5. Bad material as in soft journal, bad babbet, bad race, ball or roller in bearing.
6. Hard use like racing versus day to day street use.

From your guesses at what might be wrong, I would suggest that you go on line and find a good website that describes how a reciprocating engine works. It will give you some insight as to what is in play and help you understand what forces are involved and hence what might fail and why. You also need to find somebody locally to help you understand what you are hearing. What you might call a knock, a trained ear might call a ping or rattle. My point here is not to dump on you for guessing, but to get you started on the right foot now. If you have a mechanical mind (not everybody does) you'll soon start to understand what is in play and why one part might wear out where another won't.

And of course, as others have already said, give the forum a more detail description of what is going on and you'll get help to figure it out.
regards,
Rob
 

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Discussion Starter #7
Thank you all for the advise.

After listening to it idle trying to pinpoint the noise and not hearing the noise that I always hear when I ride, I was stumped. So I decided to work on another problem to clear my head. The clutch had been slipping so i figured It was time to take a look at the plates. When I removed the primary cover for the first time I could not believe my eyes. It looked like the previous owner had broken the primary chain tension tierod and rather than replace it had wedged a block or aluminum bar stock under the tension blade. The problem was it was only held in place by the pressure it placed on the primary tension blade. At some point it must have moved and pushed the end of the tension blade against the primary chain snapping it off.

To make a long story short, the "knock" was occuring when at high revs a bounce in the road caused the broken end of the tensioner to fly around the inside of the primary case.

I consider myself exceptionally lucky that this never jamed itself in the chain locking up the engine... Pretty scary to discover.

So after thanking my stars to be alive I replaced the "hack job" parts, chain, tensioner etc, clutch, closed up the case and.... no more knock!

Brings up an interesing question though, anyone else ever find something that "hack" in or on a vintage bike they purchased?
 

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Thank you all for the advise.
Brings up an interesing question though, anyone else ever find something that "hack" in or on a vintage bike they purchased?
There would be thousands of "hacked" motorcycles out there, plenty of them would be Triumphs. Dodgy Bros motorcyle repairers are everywhere!! RR
 

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I'm a firm believer that some people should not be allowed to own tools. Tell me that some of these are not familiar to others reading this thread:

Pipe wrench gouges on fork tubes, handlebars, and other formerly smooth round bits. Even saw the spring adjusters on a rear set of shocks with pipe wrench marks.

Destroyed knurls on tach and speedo cable nuts from pliers.

Metric bolts in SAE threaded holes or vice versa. Not to mention the whole Whitworth and other British variations of threaded fasterns used in or replace with metric or SAE stuff.

Stripped and cross threaded spark plug holes.

Motor oil in hydraulic brake systems.

Silicone sealant in copius quanties blocking off or at least restricting various flow paths.

Butchered slotted inspection covers.

Chiseled spanner nuts.

Wiring held together with masking take, surgical tape, packaging tape or just twisted together and stuffed into a nook.

Extra long bolt in an extra shallow blind hole.

Hammer marks on previously polished engine cases from trying to unstick a cover when removing.

Chrome with a scratched and scuffed finish from using a pot scrubber to clean it.

Gouged chrome rims from using screw drivers and who knows what to remove and remount tires.

Entire bike rewired with small gauge speaker wire.

Anyone want to add to the list. I'm sure it could become endless.

Rob
 

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T-dog,
From recent experience, this kind of bodge could be an early indicator of many many other horrors. What starts with a dodgy front wheel pretty much lead me on a journey that finished with a sludge trap on the verge of blockage. Along that journey there were at least 3 "I could have been killed" and many, many "that would have stuffed the motor for good".
Hopefully for your sake the bodge was a one off towards the end of the po's ownership.


Perhaps the more experienced might list a sort of safety list to scan for dangerous bodges before riding.

cheers
derek
 

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This one was "somewhat" modified from original, but I was able to put it back to stock with a little effort...
Where on God's earth do some people get there ideas from. What a hideous piece of gear you saved there Paul. RR
 

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Nice work GPZ :)

Talking of "one mans trash is another mans treasure" are you able to sell on some of the hideous custom parts, or do most of them just end up in the trash?
(Not that I want to buy any, just curious :))

Webby
 

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That sissy bar was ANYTHING but "dangling".

It was heavily WELDED to the frame rear loop.

I sold the springer forks (actually traded even for the entire project's powdercoating), also sold the oil tank; still have a few of the other bits like the sissy bar and foot control bodge bits.

I noticed nobody stated thier affection for one round headlight, one rectangular...
 

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This one was "somewhat" modified from original, but I was able to put it back to stock with a little effort...
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Well I suppose everybody is entitled to their own idea of what's 'cool' but choppers just make me laugh.

OK - I'll probably catch hell for saying this out loud, but... That very common riding posture where due to using raised bars and 'forward' controls for foot rests make one look like they just blasted in the belly with a cannon ball - ooof. Look like they're... (never mind)

Choppers crack me up, what can I say...
 
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