The Honda Owners Club

Hello. I hope somebody can help me out.. I've just been given a 1969 Cb250 K0. It's in nice condition, but has very rattly tappets and cam chain. My manual shows the cam chain adjuster with a bolt and lock nut, but on my bike there is just a bolt, tightened right down. Is this right? If so, how do I adjust the cam chain? Also, the manual tells me to match up the timing marks on the alternator to the index on the edge of the casing, but there are no index marks, just the LF etc on the alternator.. Where should I turn the crank to to adjust the tappets? It's due it's first MOT in 20 years next Friday and after a couple of weeks of fettling it feels quite roadworthy.. Only the top end feels like it's about to break out of the cases! I just don't want to blow the engine up on on the way to the test! Any help would be greatly appreciated. Thanks, Mike.

If you really can't find the timing marks the best thing to do is remove the spark plugs and turn the engine over by hand until the pistons are at top dead centre. This can be ascertained by inserting a pencil through the spark plug hole and allowing it to reach it's highest position. Both valves will either have some free play or will be partly depressed. If they have free play they can be adjusted to the correct setting. If they are depressed the crankshaft will need to be rotated a further 360 degrees to achieve free play. Repeat for the other cylinder.

The cam chain adjuster should have a lock nut. To adjust the engine should be warm and run at tickover. Undo the adjuster bolt until loose and then retighten but not over tighten. Then tighten the lock nut. For best results the engine should have a very smooth tickover. Balance carbs if necessary to achieve.

Regards

Chimpy

Thank you for that, Chimpy. It didn't mention in the manual that the engine should be running.. As for the lock nut, would just fitting one to the existing bolt be OK? It's obviously been tightened right down at some stage without a lock nut being used - hopefully that hasn't damaged the mechanism. I'll get on to both jobs tomorrow..

Mike

It won't do any harm to remove the bolt and check it is the correct type. A lock nut can then be added to the bolt. if the bolt has been overtightened damage may have been done to the push rod causing it to stick.

Regards

Chimpy

That worked quite well, thanks. The tappets are correct now and the chain is quieter.. it's still pretty noisy up top though and the plugs are sooty. I'm thinking the valves themselves might be to blame. That's going to be a job beyond me so I might ask the garage to have a look when they do the MOT. Probably be expensive, but better to be safe.

Thanks for taking the time to help a novice out!

Mike

Mike

I'd be surprised if the valves were causing noise. It's more likely to be some piston slap with an older motor. I wouldn't worry too much about it unless the engine is burning oil. Are the carbs balanced? If not the uneven running can cause noises at tickover.

Regards

Chimpy

Sorry about the delayed reply, Chimpy. Been working away this week.

Thank you for the advice.

Well now you come to mention it, it is rather smoky. I haven't had it on a run yet, due to the MOT not being until Monday, but revving the motor to about 6000 and shutting the throttle does produce fairly big puffs of smoke. Whether this is due to it not having been run for 20 years or needing some work, I don't know. I'm not sure whether it's smoky enough to fail an MOT. The tickover is very even and the noise gets louder with revs.

The garage where the MOT is taking place also do servicing and repairs, so I think I'll ask them to take a look. Would you happen to know roughly how much a rebore and new pistons should cost, if they are needed, just so I don't pay way over the odds?

Here's a picture of the bike, by the way.

(Edit) Sorry, It says Board attachment quota reached - so here it is instead http://img.villagephotos.com/p/2006-10/ ... bike22.jpg

Thank you again for your help.

It sounds as if it may be in need of a re-bore, but it's difficult without actually seeing and hearing the bike in person. if it hasn't been run for twenty years it's possible the rings have gummed up causing some oil to pass. It may well clear with use. I doubt it's bad enough to fail the MOT. I would run the engine for a couple of hours max and then change the oil again.

She looks a real beauty by the way and definitely worth spending money on. Re-bores can be had for £30-40 per cylinder and piston kits about £40 ish.

Regards

Chimpy

Thanks

I'll give it a roundabout run to the MOT and see if it clears, then run it for a week or so if it passes. If not, I'll let them keep it to do the work..

Thank you again for your help. I'll let you know how I (and the bike) get on Monday.

All the best,
Mike.

Just a quick update.. Took the bike for a pre-MOT run yesterday and broke down about 1/2 a mile up the road. Engine just died. A quick check over all the obvious things revealed the washer which holds the points cam in place had been left out when the bike was rebuilt, resulting in the cam moving along the camshaft and not triggering the points. This morning it won't run on main jets, even though the carbs have been cleaned. The garage think it could be the old rubber fuel pipes decaying on the inside, as apparantly new unleaded fuel has so many additives that it eats into older pipes, and throwing little pieces of rubber into the carbs. I asked them to replace them with clear ones, but it seems the new fuels eat them too, so its new black ones i'll be having - just not made of old rubber! I've asked them to clean out the carbs again while it's in, and have a look at the piston/ring situation. Obviously the bike was trailered in..

The bad news is that they're so backed up with work that it will be 2 or 3 weeks before the work is done, so I'll update again then.

Thanks again,
Mike