noisy cam?

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croz2803

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Feb 6, 2013
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i've pulled my 850 mk2 almost to pieces trying to find a very loud "clunk" when the engine turns over. i believe its the contact between the follower and the cam on the exhaust. apparently its a 4S cam in there but i dont know how to confirm this. Has anyone with 4s cams in their bike able to confirm that this clunk is normal? it seems to happen when the piston on the exhaust stroke is about 8mm from the top of the barrel.

Cheers

Andy
 
Depending on circumstances it's possible for a lobe on a high lift cam to make contact with the casting on the barrel around the lifter. You would have to grind it down a bit if that is the issue.
 
checked that Rennie, with the head and barrel off there is no noise. its only when there is pressure down onto the followers that it makes noise, and only on the exhausts. when it was running it sounded a bit like this

http://www.youtube.com/watch?v=9sJyxm-CHok

this wasnt a video of my bike but its the same.

Andy
 
You could try the long screwdriver handle in your ear approach to the exam. With the handle pressed against your ear you touch different parts of the engine to pinpoint where the noise is coming from. Left side, right side. Head or tappet. They make stethoscope deals for it too. Obviously, there's more that one noisemaker in there but you shouldn't have much trouble locating the one that you're talking about.
 
Noisey Lifter ? ?

What valve springs does it run ? ? shoud have something fancy if its a 4S .

If the heads on the barrel , on the bench - operateing the Cam Followers ( use a bit of wood or set up a lever ) will see if it clunks
returnuing down .

You should be able to get a fair idea of the LIFT , useing a stright edge across the mouth .
Turn till lobes opposite , drop a stick on the heel , and put a shafp knife mark on the stick .
Repeat crank 360 / cam 180 degrees ( 1 Ex lobe UP , 1 DOWN ) Mark again .
Flog saomeones glasses and figure how many millimeters & thirds or quater millimeters it measure .

Now you Know .

If the heads off , see if the cam follower action is free or sticks . Ditto the rockers .

You sure the noise is down low , Not at the Head ? ?
 
Is this a newly built engine, or a well worn example ?

If its a new one, or newish head, something to possibly watch for is that the valves guides are not too tight, and a valve is briefly catching before letting go and closing with a thump....

As someone said, a 4S cam can need the surrounds ground a little to provide clearance for it to spin.
And the pistons need the cutouts cut to clear the valves...
 
My 4s cam makes a loudish click when turning it over with the plugs out , no idea why , but its been a real good runner now for around 8000 miles and still no difference to the clicking noise .


Edit
Just seen the video :oops: , my noise isn't like that at all , no noise when running .
 
The cylinder follower tunnels wear a step in the follower bore, replacing with a high lift cam will cause the follower's to now hit the step...hope that makes sence :?:
 
Hi, could be a pushrod out of his seat in the rocker.........or, something else, does it happens suddenly,or after a rebuild??
 
one more : take out the rockers covers (all four) and the timing cover , and turn your engine by hand till the clunk appears, you shoulsd see what is wrong , if not ..........more answers will come later on....
 
Anything that click/claps in our engines rings the whole thing so hard to tell the source. Sounds similar to cold loose piston slap in bores or rod shells slack or worn cam lobe/lifter lash gap, which IIRC is quite large in 4S cams anyway. Sounds half as loud as a push rod out of liter socket. Lobe striking cylinder extension would only happen a few time before knocked off cast iron so relax about that worry at this point. If nothing jumps out on exam so far likely just need to get used to it and brave road fates like the rest of us, till eventually something does become obvious as nil warning before seizures or blow ups anyway.
 
If you have a S4 or some other high lift cam do you have radiused followers in?
Flat type will make more noise as the followers drop off the ramps more quickly.
Mine made noise like the video an hardening had gone on both inlets :-(
Now in process of rebuild rebore an installing a PW3 (that's blown the bank balance again).
 
pulled off the timing cover and it seemed the chain was a bit loose.. not sure how much is too loose. my followers arent radiused so im thinking Toppy might have the right of it. the combination of the follower coming off the ramp sharply and the chain being a bit slack causes the follower to "jump" onto the next section of the cam.. that would explain why it happend on both pistons at the exact same point in their cycle.. im putting her back together today and ill let you know how i've gotten on... thanks all :)

Andy
 
Hm, set me straight but I thot all the S's 2 , 3, 4 were flat tappet grinds and took special order for radius lifter cam. Cam chain slack changes in its cycle around as cogs never perfectly centered and springs tug and release. Manual has the details on 3/8" slack setting. Big lash cams make racer like noises.
 
noisy cam?

The pointy end goes against the engine :D


noisy cam?

This one's for wimps.

noisy cam?

This one's for someone who got caught in one of those really bad tornadoes.
I suppose you'd have to have seen those pictures of pieces of straw pushed through a picket fence.
 
Naw he's using bone conduction on back of skull if anyone even use a broom handle. Best wishes trying to really tell where the sound source is on a running Norton though there may by some use for ping detection while running. Might practice placing probe on a church bell to tell where someone struck it to ring, ugh. You'll get great fidelity of the detailed phases of ringing but the striker location... An IS size tank conceals most of this on the fly and header wrap takes out a lot of the pipes ringing annoyance too. So put on the stethoscope and tap engine in a few spots to see what ya up against.
 
and its fixed.. tightened the timing chain and the noise it completely gone. time to get riding :)
 
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