Valve noise?

I notice that my new (old) bike seems to idle nicely and quietly right after
startup. After around 90 seconds and the engine warms up, what sounds like
the valves begins to make a bit of noise at the front end of the bike. Is
this really the valves working, or is it something else? It makes more
noise when decelerating, but that could just be because the exhaust drowns
out the noise.

Previous owner always filled up with premium. I filled up with regular when
the first tank got low about a week ago. The bike makes the same noise on
the premium and regular.

 

The fuel has nothing to do with it. It sounds like a sticking camchain
tensioner.

Telling us what bike it is might help.

 

I read complaints about "ticking noises" in the top ends of CBR-600's
frequently. You might want to google around for CBR-600 forums that
have discussed this problem.

It just might be that oil on the valve buckets is thick enough when
it's cold to take up clearances between the buckets and the cylinder
where they slide up and down and that quiets the valve train until the
oil thins out a bit because fresh oil is lubricating the valve train
better.

The cam chain gets lots of oil, it's better off than the drive chain in
that respect, but it does live in a hellish environment of rapid
acceleration and deceleration, with riders suddenly blipping the engine
up to 12,000 RPM frequently just to hear the exhaust sound. It doesn't
take much horsepower to turn the camshafts, but when the rider blips
the throttle, he's demanding that the poor little chain take up any and
all slack and *jerk* the camshafts into motion.

Not smart at all. The chain link pins can wear, the chain can snap. My
buddy's cam chain snapped during a heat race on Willow Springs once.

The plastic chain guides wear too. You see tiny plastic shreds in the
bottom of your oil drain pan while you're looking for metal chips
indicating major problems.

Chain guide wear is normal from the steel chain sliding hard against
the miracle of plastic. Chain guides don't last forever, but there's
enough plastic on them to go 100K miles. Most motorbike owners don't
even know they have chain guides to wear out.

The chain gets loose, the automatic tensioner is supposed to take up
the slack, but it doesn't always manage to do that.

Honda changed some part of the cam chain system in 1995, but I'm not
sure exactly what it was. Maybe www.bikebandit.com has part numbers on
their parts fiches and you can see what was changed. Www.partsfish.com
doesn't have part numbers on their parts list.

The automatic cam chain tensioner should be on the right hand side of
the engine where the cam chain lives.

Automatic cam chain tensioners like the CBR uses will have an access
plug so the owner can push gently on the plunger and move it toward the
chain, taking up any excess slack. Maybe if you do that you'll hear one
or two clicks as the rachet pawl passes a tooth on the plunger. The
ratchet pawl keeps the tensioner plunger from backing up.

Before messing with the adjuster, you should accurately locate the
source of the sound.

If you run the engine and hear a rattling, but the rattling mostly goes
away when you pull the clutch lever, that's the clutch basket. Maybe
the big nut holding the clutch inner sleeve is loose.

If the rattling doesn't go away, it's possibly the starter clutch on
the left side of the engine. Broken bolts securing the starter clutch
to the back of the alternator will allow the starter clutch to slap
against the alternator.

So, you have funny noises in your engine? Time to make a mechanic's
listening device.

Remove as much of the fairing as you need to gain access to the top and
sides of the engine.

Get an old wooden broom handle or a piece of 1-inch wooden dowel about
1.5 feet long.
The harder the wood, the better, it will transmit sound better.

Start the engine and put the dowel against the cylinder head cover on
the right hand side of the engine and put your ear against it and
listen. Do the same thing on the left hand side of the engine, down on
the alternator cover. Listen to the clutch by putting the stick against
the clutch cover.

You'll hear an amazing amount of clattering and grinding and rumbling
sounds coming from the greasy guts of your engine. What does it all
mean? The low frequency stuff could mean ball bearings are worn out.
But the sharp, high frequency cracking sounds should give you cause to
worry. Nothing in the engine is supposed to go snap, crackle, and pop!

Well, if you were hearing pinging from low octane gas, it would be
while you're accelerating, and it would take more than 90 seconds for
the pinging to start. It would take more like 10 minutes for the engine
to get that hot.

 

As CK knew, '93 CBR600F2.

 

Yes, a quick google search on "ticking CBR600" yields plenty of results that
sound like my situation. They call it a "sewing machine" sound. Very
characteristic of the noise.

Hmm... that sounds plausible.

37k miles on this '93.

And that's all that needs to be done? Is the automatic one supposed to do
all this for me, but I'm just helping it out a bit?

The noise is definitely at the top of the bike.

Great suggestion - I will try that one out the first time I get the bodywork
off.

Good to know. Plus I smell a hint of gas smell when I'm idling at
stoplights. I wonder if it would be a slightly rich mixture, or if my bowls
are in need of replacement/adjustment. The bike runs/idles nicely otherwise
from idle to WFO.

So the big question is: is a loose cam chain a really big deal? When it
fails, does the bike just stop running due to no valve movement?

 

It's hard to say what that really means for a 12 year old bike without
seeing it. Maybe it was used daily for 3 years and stored for 9 years
or maybe it was only ridden a few weekends a year and spent much time
in the garage.

Yes, the automatic tensioner theoretically tensions the chain
correctly. But sometimes the plunger will stick and it needs some help.
You should also check the valve clearances to be sure that none of the
valves is tightening up. You'll find the correct settings on a decal
under the seat.

A tight valve will burn. Use an American feeler gauge set to avoid
going crazy with the metric gauges. The difference between blades in an
American set is 1/1000th of an inch but the difference between metric
blades is less than 4/10,000ths of an inch.

I wouldn't go through the hassle of re-shimming a valve if it was only
1/1000th of an inch too tight. But if it gets worse than that, the
valve definitely needs re-shimming. The camshafts have to be removed to
do that. It's a big job.

And you can even get into trouble checking the valve clearances. We had
a guy in here last summer complaining that he'd broken to part of the
cam bearing cap that the valve cover bolted to. He was trying to torque
the cylinder head cover bolts and they were oily. You can't torque oily
bolts without risking breaking the bolt or stripping the threads the
bolt goes into.

The float valve might be leaking on one carb, or the float might be set
too high or you might be smelling evaporated gas that recondensed in
the charcoal canister and is dripping out the bottom of the canister.
If you overfill the gas tank, you'll flood the canister and, again, gas
drips out the bottom.

Yes, a loose cam chain is a big deal. Besides the noise, the chain can
kink, and even jump a sprocket tooth. If you look at the camchain
diagram on www.partsfish.com you will see an upper chain guide that is
supposed to keep the chain from jumping sprocket teeth, but if the
chain is that loose it will be whipping around against the chain guides
and making a rattling noise.

If the cam chain breaks, the cams will stop with some valves wide open.
The pistons will keep moving for many revolutions and the pistons may
hit the open valves and bend them. Removing the cylinder head to
replace bent valves is a major hassle. It gets worse if the valves
damage the piston tops. The engine will have to be removed and taken
completely apart, since the cylinders are an integral part of the
crankcase.

 

ISTR some articles in Bike (UK magazine), about Honda's automatic
cam-chain tensioner often going out pretty early. On some models (e.g.
VTR1000) people pretty commonly replace it with a manually-adjustable
version.

Phil might want to check online for evidence one way or another whether
this is an issue on this machine. Evidence might be the easily
availability of manual cam-chain tensioners for his bike and/or web
pages detailing the replacement of the tensioner. It's worth looking
into, if web access is easy.

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.

 

In which case it is almost certainly a sticking camchain tensioner unit.

The CBR600 is notorious for it.

Very easy and cheap fix.

 

Utter nonsense

It's a sticking tensioner, I bet.<snip

It's a sticking tensioner. Google for CBR600 = sticking + cam + chain +
tensioner and you get a shedload of hits, all describing the symptoms
and cure.

 

It's a sticking camchain tensioner - just in case you didn't get the
mesage ;-)

 

OK, guess who I write for?

 

Hmmm.....T.W.O.?


I gotta say, Bike is a fantastic magazine. I used to read Cycle World
all the time, but after looking at the British magazines it just didn't
hold my interest any more. I was also rather irritated that CW never did
gear comparisons. Now I'm irritated that I have to wait until mid-month
to get the current issue! lol

I keep thinking that someday I'll look around here for a newsstand that
carries Motorrad, and see how they stack up, but I never seem to get
around to it. So I stick with Bike.

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.

 

Motorrad is *superb*. Bike has taken a lot of cues from Motorrad in
recent years, especially on the technical side. Unfortunately, I don't
speak German.

 

When you do replace that cam-chain tensioner, I'd suggest using an
aftermarket manual CCT (from APE) in place of the Honda OEM part. It's
a set and forget affair and will never need replacing. Cheaper than oem
too.

 

lol. Well, my german could be better. I'll poke around a bit over the
semester break, maybe. In the meantime, the Dec. issue of Bike should
show up here in another week. I'll just have to read back-issues until
then, I guess. Given the new Daytona 675, that's not hard to do really;
I just stare at the pictures.

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.