82 XL250 / CB250RS Valve clearance problem.

[5m0k3y]

Hi all, new boy so please play nice. 
I'm having the same problem as Danny Boy in this thread: http://www.thumperclub.com/smf/index.php?topic=4756.0
I didn't want to revive an old thread, just incase it's against the rules or bad manners etc.

I went to set the valve clearances on my XL250 / CB250RS engine, as I was getting a lot of valve nock. I noticed the exhaust lash was nonexistent. I unscrewed the tappet screws all the way out and put them to one side. I noticed the rocker arms were actually touching the valve stems, without the tappets installed. On the other hand the inlet clearances were spot on, with no signs of wear, loosening or tightening.

I've had the rocker cover off and everything looks normal. The cam followers are in excellent condition, as are the cam lobes, journals and rocker arms.

Do I have streched exhaust valves or worn valve seats or something? Is this going to cost a fortune to fix? I just priced 2 exhaust valves at £47 each, from Wemoto... Ouch.

Any help would be greatly appreciated.

Cheers

[guest295]

Could that valve be stuck?

[5m0k3y]

Thanks for the input. I don't think they're sticking.
I had both of the exhaust valves out yesterday and although they're not pretty, they're still servicable. The tolerances between the valve face and seats were within spec...only just though (2.0mm). As were the stem/guide clearances. The bike has great compression and runs well, it's just a bit concearning that I can't set the exhaust valve lash for whatever reason. I have found some original Honda exhaust valves for for less than half the price Wemoto were asking, so I'll buy those and see what happens. Hope I don't need new rockers as that won't be as kind on the wallet.

[Dick Scratcher]

If the valves aren't deeply 'pocketed' into the head it's difficult to imagine that there's no clearance between the rockers and the valve. Compare your new valves with your used ones in case someone's bodged-in a pair of similar but 'strug' ones thinking "B****r it, that'll do to get me out of a spot". I must admit that on my 250RS there's only about an eighth of an inch clearance between the rocker and the valve which is roughly what you'd expect. By the way if you ever do have to remove the rockers be aware that it's a right b*****d of a task and definitely not the p-of-p that a recent article in a mag just claimed. I had to take both of mine out to replace tuppence-worth of neoprene seals, what a rigmarole !. Best of luck.

[5m0k3y]

I'd though it could have been due to wrong valves too Dick. Sadly the Haynes manual states every one of the valve's specs apart from the length of the thing. I'm going to ask the dealer to measure the new ones before I buy them, that'll clear that up.
Looks like the previous owner has had the rockers out already, as there are grooves ground into the retaining pins, which I understand is a recommended method for removing them. Hope I don't have to pull the buggers out. I'm off to pull a 2 stroke (swearing?) to bits as therapy.

[johnr]

doesnt the 250rs have a decompressor for starting? have you checked that it was disconnected before setting the clearances?

[5m0k3y]

The decompressor has always been disconnected John. When I stripped out all of the road required electrics, for the trails, I also removed the decompressor from the kickstart mechanism and cable. If you boot it after TDC it starts first kick and doesn't really need a decompressor.

[Dick Scratcher]

I'd though it could have been due to wrong valves too Dick. Sadly the Haynes manual states every one of the valve's specs apart from the length of the thing. I'm going to ask the dealer to measure the new ones before I buy them, that'll clear that up.
Looks like the previous owner has had the rockers out already, as there are grooves ground into the retaining pins, which I understand is a recommended method for removing them. Hope I don't have to pull the buggers out. I'm off to pull a 2 stroke (swearing?) to bits as therapy.

If you end up having to get the rocker locating dowels out come back to me and I'll tell how I managed it. The Honda method as recommended in the genuine workshop manual looks good on paper but in reality it's rubbish, you're literally attempting to drive the things sideways and not out and it's too easy to b****r-up the cam cover.

[5m0k3y]

Cheers, I'll bear that in mind. Hope I don't need to though. I've heard they're not easy to remove.

[blew]

It may sound too obvious,but you did set the timing marks correctly?

[5m0k3y]

Timing is bang on. When the cam lobes are facing down the followers aren't even touching the cam. They're just floating. (apart from the exhaust rocker, which is sprung)