what is rattling on my 1976 husqvarna 125cr?

Question

my 1976 husqvarna 125 cr gp bike makes a sort of loud clattering noise all the time the motor has good compression and it usually starts on the first or second kick when cold but once it is warmed up it starts right on the first kick. the bike runs great i am jus kinda worried about this noise what is it?

the clutch plates had teeth on them that were dented or worn could this be the source of the noise?

Answer 1

Pull Cylinder head off and look for faint little scratches,,,
or even a "shiny,polished look" beginning at the top of the exhaust port.

They're bad ring snaggers,especially with a little wear/extra skirt clearance that's normal with age& run time.

Thats about as generic of a condition to hi-perf 2 strokes as having a spark plug.

If the port chamfer is inadequate or incorrect,,,that's not unusual either,,,& it's easy to fix.

Measure ring's width in that area,,compared to side's of cyl area.

End Gap alone dont tell ya all need to know about a 2 stroke ring,right?

Fresh ring never hurts anyway,,,better to beat up on it than piston

Or if ya just wanna fool with it,,,
Isolate the cylinder while it's running and see if that sharp,rattling,ringing sound is muffled.

Get a big bath towel or beach towel,,and wrap the cylinder and head,,,start it and listen.

If the sound is from anywhere but the top end,,,
the noise will be unaffected by having cyl/head isolated.

Or,,you can play Dr and use any number of things as a makeshift stethoscope.
Poke around different areas---which is Tricky becase ya really need to know which parts make what noises.
You cannot accurately LOCATE a noise,,so much as IDENTIFY the sound.

If you think the noise is your clutch,,jam a big wad of towels around the clutch cover while it's running and see what the sound does.

Does the clattering sound like "engine speed" frequency,,
or 1/4~1/5 Engine speed,,,which is what the clutch runs at.
( I guess 4 or 5:1 Primary,,heck I dunno)

Does it make the noise when clutch is DIS-engaged??

Or when it's all locked-up Solid and acting like ONE piece?
Like ,,,just in neutral?

Does the noise CHANGE when you pull clutch lever In/Out?
In Neutral,and in gear putting a little load on it.

If You tried hammering on it ,,it's "normal" and instinctive for many folks to try it in low gear.

Plug in High,,so you can wail on it good without worrying about bike going any where.

ANYYY fault whatsoever in entire primary thats causing noise will manifest itself under intermittent load.
Main bearing,,,primary gear/chain,,loose nuts on engine or mainshaft,,,Basket-to Hub Rivets,,hub damper bushings,,Basket bushing/bearing,,any thrust wasrs/brngs,,,dog-eared plates,,,notched-up hub or basket,,,,messed up primary teeth,,crapp stuck between them,,all that kinda stuff,,whatever's in there.

The sound WILL change as you Load/Unload it.
Also gives a better sense of what speed the noise is running at.
Since all the DRIVEN section of Primary and the Clutch run sooo much slower than engine.

Jack up back wheel if ya think it may be mainshaft bearing or anything on countershaft.

While you have it up,,rock back wheel and see what kind of noise you can make it do.
Or get a helper to do it while you listen.

Might be a problen in there somewhere.

1000's and 1000's of bikes have raggedy clutch plates and baskets and hubs.
Not many make any objectionable noise.

Without hearing it, I'd expect it's
Probably "just a 2 stroke" making top end noise as usual.
That's stereotypical.
It can get Loud and Ugly ,,,and it follows rpm precisely

Dont be mislead by it having all indications of good compression.

Keep in mind 2 strokes' rings are self sealing and can accomodate a huge amount of ring wear.

4 strokes' square rings Aint ---they dont have anywhere near the energizing,,,so they can remain free to rotate.

Plus the 4's wear circumferentially,,,360*
2 strokes dont--they'll maintain a large percentage of full contact till they are worn in 2 or break.
Typically more than 200*~250* circa

If you dont wanna bother taking the head off to check it,,
just look thru exh port to check it for snagging.

Go ahead and check the ring's wear thru the port,,,
just be sure to rock the mag a bit while holding pressure on the ring to make sure ring's butted on it's pin.
And same ol' rule-of-thumb applies like any "modern" 2 stroke from early~mid 60's onward.
All Ring>No Land.
If ya see any,,well there ya go.
Good compression or not.Shot's shot.

Good Luck with it,,hope it's nothing serious.

Answer 2

With good compression, the crankshaft and top end should be fine. Without seeing or hearing your bike , I'll take a wild guess and say it has something to do with the clutch. The clutch basket or it's bushings could be worn out. Drain the oil, remove the clutch cover and look around. It could even be a bearing on the main shaft (transmission).

Answer 3

It Could need a rebore kit and or an engine rebuild.

Answer 4

I would also check the exhaust where it connects to the head,possibly held by springs.

Answer 5

if it has compression and runs like you say it dosent need rebuilt it could be anything loose