history... 1980 CB250RS, (4 valve, single cylinder, kickstart)

Needed new cam chain as the tensioner was at it's max (as far as I could tell) so over the weekend I fitted the cam chain, which necessitated taking of the right cover and removing the automatic timing unit and primary drive pinion. At the same time, I removed the head and barrel, as i thought I may have been able to get the cam chain free without having to pull the bottom apart (alas, no) and cleaned them up a bit while I had them off. Not having a spare head gasket, and knowing the old one was not very old (about 2000 miles) I re-used the old one. At the same time I cleaned up and patched the exhausts. BOlted it all back together, set the valves, incorrectly at first (clearances too big as result of not checking all valves closed - stupid mistake I've never made before) refilled oil and fired it up. Horrible clacking noise, failure to start, realised what i'd done with valves, fixed them up, started, sounded fine but died quickly. adjusted throttle stop screw so it would stay going, seemed okay.

next day, on way to work, realised bike not happy, pissing oil, no power, blowing badly. So, on the assumption that the head gasket was knackered (since that's where the oil was coming from) I got a new one and fitted it, along with cleaning fuel filter, new exhaust gaskets, new spark plug (just to be sure - the old one a bit sooty but not tragic)

Then fired it up, seemed much happier, backed out the throttle stop screw a little, no problem. Went for ride, still no real power, but seemed slightly better, up a hill, stopped (about 1/4 mile total), turned off, bike seemed hot. Rode home (only way to get bike back, and not far) using engine brakes a little down hill, at some point a horrible knocking noise started. I can't really tell where it's coming from, but it stayed when I pulled up.

What have I done? I'm hoping it's some stupid mistake and fixable.

To the best of my knowledge, the knocking wasn't there last week (before I began) - should have left well enough alone.

Am meant to be using the bike to get to work tomorrow, but somehow don't see that happening.

the best thing is to find out where the knock is coming from, the old screwdriver against the ear trick works well
you didn't use instant gasket at all? Hondas often use bolt holes for oil ways and instant gasket often blocks them, a m8 of mine total screwed a CB900 head by using that stuff
did you remember to tighten the 10mm head bolt thats kinda hidden near the cam chain sprocket

used instant gasket sparingly on the rocker cover, have done that before no worries though. the haynes manual actually says to do so.

not sure which 10mm head bolt you're talking about? there are 4 head bolts (2 inside rocker cover, on cam sprocket side), all 14mm, did them definitely. also 13 (count them!) 10mm bolts on rocker cover, did all of those too.

could you explain the screwdriver to ear thing? I've never quite gotten it to work and it sounds like a handy trick to know. Though to be honest I don't want to run the bike any longer than strictly necessary (i.e. preferaby not at all) in it's present condition

sorry i was thinking of the CBX250rs so disregard the 10 mm bolt

the screw driver thng is just a case of getting it in your lug ole in the right place, and just go around the engine where you think the noise is comng from
probably the best way would be to turn the crank with the cam cover off and see if the valves come back smoothly and none have a large gap also that the cam chain is tight and not suddenly going slack

Woodz is right one of the bolt holes on the CB 250 Rs head does have an oil way running through it.
I trashed the cam on a Z250 by using sealant instead of an o ring a long time ago.
You haven't upset the valve timing have you?

you should of seen the CB900, the cam cover and the little chrome caps at the side where blue you could fry eggs on it, and the horrid metal to metal squealing noise was unbelievable, the guy had just put a set of barrels on it because it had done the 900 trick of wearing a hole thro the front of the engine when the cam chain tensioner starts to wear out, but like the plank he was he used the old head gasket and a full tube of gasket sealer blocking the oilway to the left hand side of the head, it took 4 miles to get into the state i saw it, feckin the head, cam's and the cam cover

I don't think so, but anything is a possibility at this stage... will have another look tomorrow right after I look up bus timetable.

I seem to remember the same plank twisting the crank on his LC by riding it back from Scarborough on one pot!!!

haven't had a chance to look at anything yet - god public transport sucks here!! had to leave an hour and a half before just to get there in time!

ancient is meant to be coming to look at it friday to diagnose so leaving it till then

still not got anywhere with this, except that it appears to be coming from top. compression seems fine (cork in spark plug hole blew out with some force). cam timing is fine, no sign of slack in cam chain. have tried adjusting valves - got gap too big, no sign of tick, but hard to tell under the rattle. adjusted again and again, back to tick, no idea what power like as I'm slightly afraid to run it too far, so it could be the valves just bugger to adjust... anyone got any tips on this?? how much leeway is there on valve adjustment? manual states .05mm inlet .1mm exhaust.

alternately any other theories??

not sure how to check oilways without removing head again - the ones I can see are clear - which I'd rather avoid if possible, but there is oil in the valve cover, so I'm assuming that means it's circulating okay since it runs down cam chain tunnel, so must be circulating to get back up??

links to mp3 of sounds - couldn't attach them - maybe too big??

right click and save or need quick time plug in

http://www.bsquiggle.com/bikevalverattle.mp3

http://www.bsquiggle.com/biketicking.mp3

Deffo sounds valve or cam chain related to me, something is very loose

cam timing or a sticky valve, has the cam chain tensioner cracked? it was a huge problem with hondas of that era

well, pulled it all apart again today...

took the cc tensioner out, played around with it a bit, all seemed to be functioning correctly, put it back in, checked the cam timing (it was fine), discovered one of the sprocket bolts not quite tight enough, released the tensioner and pushed to ensure it engaged, re-assembled machine, checked valve clearances, started it up....

no ticking!!!


didn't trust it since the noise started previously when on the road, so went for the very same ride, no noise - overrunning a bit, possibly the throttle stop screw needs sorting, since it was moved in the process, so stopped and did that, carried on for a total of 10 miles, varying terrain, got up to 50 mph (not top speed, but a speed i'm perfectly happy with on the local roads), all seems good , more responsive than previously, seems slightly louder, but that could so easily be paranoia, or the new exhaust gaskets bedding in, will check tomorrow afternoon.


thank you all for your help, it is greatly appreciated