New to the Thumper world... need a bit of help.

[Danny Boy]

Just bought my first Thumper (CB250RS) and wondered if anyone might be able to offer a bit of help. Was running a bit rough and ready when I bought it, but more or less OK. Thought I'd give it a quick service. Everything was fine until I got to the tappets. The exhaust side felt really tight (couldn't get the feeler gauge in there), so I attempted to reset 'em. It seems really b***dy difficult to get a feel for the clearance in there. Wind the tappet right out and it still feels tight. Eventually, managed to set 'em... or so I thought. Kicked him up and there's now an annoying but very distinct metallic tapping from the valve area. Get in there again. Reset. Still tapping. Now worried that I've buggered something on the old fella.
Am a pretty decent fettler. Have been setting my Super Dream for years with no probs. Am I doing something stupid? Is there a trick to the RS?
Yours in hope.

[guest833]

Hi and Welcome to the Club

I don't do inside an engine but did you get a manual downloaded yet? http://www.filemirrors.info/download_Honda+cb250+rs+Service+Manual.html

I'm sure other Thumper Guys will point you in the right direction

Cheers

John

 

[Baldrick]

Hi Danny Boy,
Cb250 Rs a great machine.
You need to make sure that the decompressor cable is adjusted correctly there should be 2 to 3mm of free play, and make sure the cable is not partly seized through lack of lubrication. might be worth disconnecting it while you make exhaust valves adjustment.
I have found the most accurate way of adjusting the tappets is with overnight COLD engine, to remove spark plug and with the bike on the mainstand get an assistant to operate the kickstart by hand whilst feeding the feeler gauge through the gap it is fiddly but it is accurate,  2 thou in (0.05mm) inlet,   4 thou ins (0.10mm) exhaust.  These motors are prone to wear in the camshaft non bearing as they run in the alloy head, so regular oil changes are a must, I change every 1000 miles with a good quality semi synthetic 10w-40.  
 Poor running it is worth replacing the HT lead ( copper cored) as they do corrode with all the muck from the road, where they fit in/on the coil spike, also the ngk resistor plug cap can be a problem, I also found it worth while fitting an ngk iridium spark plug, might be worth cleaning the carb out, especially if it has been stood for a while, as many of these bikes have, and make sure its got fresh fuel cos this modern stuff goes off in no time.

All the best  "Baldrick"        XT350, CB250 RS, and plethora of MZ,s

[Danny Boy]

Cheers, guys. Really appreciate the help. What a great welcome to the world of Thumpers!! Thanks for the decompressor tip. Wonder if that's the problem. Re: the tapping noise. Am assuming that it's just cos the measurement's way out. Was only ticking over for a few seconds, so am hoping it's nothing serious. From what I gather these engines are virtually unsinkable.
Cheers again.

[themoudie]

From what I gather these engines are virtually unsinkable.
Cheers again.

Aye Danny Boy,

Only if you warm them up before thrashing and as Baldrick says "These motors are prone to wear in the camshaft non bearing as they run in the alloy head, so regular oil changes are a must, I change every 1000 miles with a good quality semi synthetic 10w-40."

Welcome to the Landy Rover, Primus stove, weather girl, grey Ferguson, canvas tent appreciation 'Madhouse'!

My regards, Bill.

[Danny Boy]

Hmm... this is beginning to bother me. Disconnected decompressor. Tried resetting exhausts again. Initially, not much luck. Back tappets right off and it still feels tight in there. Then, had an idea. Tighten tappets till just touching valves. Give it a spin by hand till valves are closed. Back tappets off. Finally!!! There's some space under there. Set the gaps. Give it a whirl by hand. Bugger! Feels very tight again. Just noticed there is a bit of weeping from the exhaust side rocker spindle. Have I got some wear on that spindle? Is that what's causing the trouble?
PS - Not much in the Haynes manual about that decompressor. Doesn't actually seem to be touching anything inside the cover. Just whirling about on its own.
PPS - apologies for being a questions-question man so early in my Thumper career. Hopefully, I can get to enjoy this brave new world soon. Instead of just thinking I'm a rubbish mechanic!!

[guest1069]

Some people in their ignorance hear tappets making a noise and tighten them up so they dont. I had this problem on a bike I bought recently. Set them to the correct settings with the piston at TDC on a cold engine. If they rattle - so what its an old bike. Oil leaks, RS250's weep from the rocker cover, again not a big deal.

[guest7]

Are you supposed to worry about strange noises from an engine? Hmmmm that explains a lot 

Graham (it's broken again) Carrick

GC

[Danny Boy]

Point taken. This sounds a bit worse than a rattle, though. A definite 'tink'. Very ringy and metallic. Why didn't I just leave the thing alone and ride it?? No time to whip the cam cover off at the mo. Am going to have one more crack this morn and see what happens.
Cheers for the advice and help, folks!!
PS - if anyone out there has got a top box rack for the RS, would love to hear from you.

[Dick Scratcher]

Hello Danny Boy, Oil leak from a rocker-shaft eh ?, you'd think that this would be a p-o-p to put right, it's not. I've got a 250RSA also leaking from there and to do something about it is a real pain in the butt. The shafts are secured in the cam-cover by two pressed-in dowels, one in each. I don't think Honda ever envisaged anyone needing to get these shafts out as the dowels are the very devil to try and remove. Honda's recommended method of removal is to use a small grinder (Dremel ?) to cut a 'V' in the dowels and using a suitable (whatever that means) drift and drive them out, the reality is that you can't get a straight shot at it, you're coming from an angle of about 45 degrees, knocking them sideways which achieves b-all. The option of gripping them with some form of self-locking wrench is also not very likely as there's only about 5mm of dowel sticking out and it's partially shrouded by the mating surfaces of the cover. I'm now contemplating, if I can locate someone competent with a mig/tig welder, having a few inches of 6mm threaded rod welded onto the end of the dowel and creating a puller of sorts and with the help of a heat gun, draw them out.
If you come up with a better way or manage it at all put a posting up on this site describing your method.

[Danny Boy]

Ah... I did read that bit in Haynes and wondered how tricky it was going to be. The oil leak ain't that bad, really. I just wondered if that had something to do with the wayward rocker arms. Have actually managed to stop it making the pinging. It was just serious tappet noise. What seems to be happening is that, after you set the tappets in the usual way, they open up a bit more as soon as you turn the engine over.
This made me think there was some movement on the spindle... hence the interest in the oil.
If I sneakily the tighten the tappets a bit more than I would normally, the noise - as you'd expect - disappears. I'm loathe to start digging into the head/spindle at the mo. Just bought the damn thing to get me about over the summer. My only worry is those tappets. Am trying to work out a method to get them set (roughly) while there's all that movement in there. Back em off till the pinging starts and then tighten till it just stops??
Apart from that, it's a lovely thing to ride around town. So small and light... easy to get between gaps and chuck around when car drivers are trying to kill you. And, my god, is that horn loud! Does tend to shimmy and shake and rattle the chain a bit when it's pulling at very low revs. Never had a big(ish) single before (I guess Suzy GP100s don't count as Thumpers!!), so I'm not sure if they all do that, sir.
Anyway... cheers loads for your time and help, guys. Much appreciated. If I have a dig into the spindle, will let you know how it goes.

[Dick Scratcher]

Hi Danny Boy, Yes, I'd regard the oil leak from the shafts as a nuisance, something to be dealt with when and if it becomes a problem you really can't ignore bearing in mind that thirty-year-old neoprene oil rings aren't going to work forever and if my experience is right things will deteriorate.
              Setting the valve clearances on the 250RS is a right pain as every damn' thing is so small and access isn't the best in the world either. The correct clearance is best to stick with, closing them up is asking for trouble as there's really very little in the first place.
              Like all (relatively) modern singles, especially with a virtually non-existant cush-drive, 'slogging' the motor is no way to go, rev 'em as there's b-all power below 4/5000 revs anyway. You'll find that your bike will knock the s**t out of the final drive chain, again because of the c-d. Chain and sprocket sets are OK from M & P and not daftly priced. Be sure to change the engine oil at no more than 1000 mile intervals, Jap engines will stand any amount of abuse but not dirty oil, engines are expensive, oil is (still) cheap.
             CB250RS's are great little bikes, I've cruised from Cornwall up to Stafford (M5/6) several times holding 70mph and now got over 50000 miles on the clock, and the bike only cost me fifty quid in the first place. Love to get another around the same price !.
             Look after it and it'll look after you.

                                 Take care, ride safe,            Dave.

[Danny Boy]

Dave - cheers for the info. Yep, had a bit of blast on it yesterday and finally seemed to be getting the hang of it. Anything below 4000 doesn't work. Keep it singing and everyone's happy. Surprisingly enjoyable on windy, country roads, too. So small that you can really chuck it around.
Am going to have another nose at those valves this week. Suspect there'll be some head-scratching.
Ta - Danny

[Danny Boy]

Reckon I've cracked it! Not sure what I was doing wrong before, but tappets seem OK. Fingers crossed and all that.
Just one question if anyone's got a minute. The decompressor. Am assuming that when you pull the arm and the cam comes down, it's supposed to open up the the exhaust valves via the rocker arm.
The cam on the this one is actually sitting at the top. No matter how far you pull it over, it hits the stop before it hits the rocker arm. In effect, it's doing bugger all. No amount of cable adjustment gets it anywhere near the cam. Has someone put it back the wrong way around??
Have just grabbed a shop manual off the internet to see if there's more info.

[Dick Scratcher]

Hi Danny, I removed the decompressor cable on my bike years ago, I found it unnecessary, more troble than it's worth, after-all it's only a 250 not a 500 Goldie or a Velocette or if it comes to that a Japanese 500/600/650 single where you can get a kickback if you're not careful. Must have fitted these things on the off-roader model for those girly-types over the water so thought they'd better use one on this model.
                                        Regards,              Dave.