Cam chain rattle from an honda cb100n. Help, save me!

[Arachnoblaster]

Ok, I know it ain't a thumper but does anyone know why the cam chain on my 15000 mile old cb100 rattles so badly? Turning the adjuster either way just makes it worse. The adjuster is free & there is plenty of fresh oil in an otherwise perfectly normal sounding engine (i.e. no excessive tappet, piston or end noise). I have removed the locknut & cleaned & lubed the adjuster but the noise remains the same although there is a point when it lessens very slightly but that is negligible. I have heard that the cam chain assembly on these little bikes can be, & often is, a problem area - my old '72 cb125s rattled like this just before its demise 3 miles outside of Wokingham so I don't want to suffer that indignity again if I can help it. The noise doesn't exactly inspire confidence & not being able to work out why its rattling is bugging me. I mean surely the cam chain can't be worn out at this mileage? If the engine had suffered oil starvation or neglect it would show up elsewhere & this isn't the case. Are they all like this? I bought it as a winter hack to teach my squeeze how to ride for less than the price of two tyres for my SRX (ha ha), so I don't want to spend loads getting a new cam chain fitted unless there's no tensioner mod available. So come on gents, One of you must have come across this problem before (the tensioner, not my bird), & any advice would be greatly appreciated 'cos I'm in two minds. The fate of this little honda lies in your hands either it'll be pampered as my girlfriend's first bike or I shall courier the piss out of it...

[guest27]

Is it an auto tensioner or a manual one?

Cam chain should not be too expensive and on a 100 will be a split one so only need to run it in with the old one - couple of hours?

100 - is a Thumper as I remember - albeit small.

R

[Arachnoblaster]

I dunno if its auto - good point - & I dare say the obvious place to start, but if it is auto it ain't cutting the mustard. It sounds like its cutting the alloy! I'll have a look & re-post when I'm done but it may take a while 'cos I can't find my impact driver. Its an '84 model and unmolested according to the bolt heads. And I didn't know that split cam chains were available either. Cool! Thanks for the reply mate.

[pigafetta]

Cam chains are a tenner or £12 for a genuine from David Silver. They do tensioner blades too for about £16.

Dave

[Arachnoblaster]

I've just had a good old look & the cam chain seems to be fine. Its all totally pristine - the tensioner blades look sound & the tensioner is working correctly so could the racket be the cam itself? I think the noise is coming from the upper part of the head - setting the tension divorces the two different noises and noise remains after the cam chain is set. What are the bearings like in the cam area? Does it even have a bearing? Maaan, I knew I should have bought a haynes manual. I'd always thought Honda bearings were the mutts too.

[bullet350]

honda had a habit of running the cam in the head (assuming its overhead cam), with no bearing!

its not quite as stupid as it sounds so long as the right oil is used and its clean, after all the layer of oil should separate the two surfaces.

if you take the top off the engine, just the cam cover, you will be able to see the cam lobes. if one area of the valve gear is worn then the chances are so are the other parts.
so worn cam lobes usually accompany worn cam bearings

this way you will not disturb anything complicated, and will be able to see if there is excess wear at the top of the engine.

bullet350

[Arachnoblaster]

Bullet, sound advice & I shall get amongst it right after my hangover subsides. And fellas, I must say that unlike some of the other biker sites on the web, this one is the Don. Good advice, cool humour & a mature acceptance of novice inadequacies makes for an online environment that is a pleasure to be a part of. Ladies. Gentlemen. I salute you. Oh, & there's no points for guessing I'm drunk either, but, even I in my most inebriated state even I wouldn't consider running a cam in an ally head wit no bearing. I mean what? Eh? Little bike, learner abuse, OHC, no bearing? No sodding bearing? Err...

[guest295]

Not that strange, actually. Most manufacturers have been doing it for yonks. Aluminium isn't a bad bearing material. The problem is that when the thing's been sitting for a while the oil squeezes out on the side where the cam chain's pulling down, and when it starts up again the metal surfaces rub furiously until the oil gets up there. People have been known to line-bore the head and install sintered-bronze bushes or even (gasp!) needle bearings. Check your oil filter for alloy swarf, and change the oil often.

[guest27]

My K4350 has the cam running directly in the alloy of the head, it is worn and leaks oil out of the points cover.  Have seen them fixed in many ways - line bored and sintered bushes, needles, welded up and re-bored, cam welded and recut to a larger dia to fit a larger bore on the cap (WHY!!!!?).  Mine - well it just rattles like a good un.  I will get it sorted sometime.  Replaced the cam chain about 10,000 miles back.

It stands for years at a time - so no help to the lubrication - but I do try to kick it over a couple of dozen times before starting it - lame hope that it will get the oil back up the top.

As to the good burgers of this site being open to all - I think the problem is that we all still make mistakes, we put plugs in and strip the thread, forget to torque the head, get water in the carbs etc.  A beginner just makes the same mistakes but probably with less effort.  We are all the same here, male female, newbie, crusty old git.  Some one forgot to tell us about elitism and hierachy.

Damn even the Yamaha boys with their SRXs will talk to the Honda lads with their XBRs 

R

[Julian217]

I had a CB100n.  It also had a noisy cam/ chain, with noise coming from the top.  I dont know the technical term, but there's a cog which the chain goes round in the top of the engine. This is attached to another bit (cam?) by a couple of bolts. These were a bit loose, tightening them reduced the noise.

[guest7]

Here in Cardiff there was an engineer who (in the late 70s, early 80s) had a good sideline in repairing worn single cylinder Honda OHC heads... in the days that half the world ran a CB 100 or 125 he had a roaring trade. 

As people have said, it's not a terrible idea, but not the best approach for a bike generally sold to novices and teenagers.

GC