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78 Honda XL250s cam chain adjustment.

5708 Views 2 Replies 3 Participants Last post by  RebelnDirt
Hi all,

I'm new here and any help/input would be very welcome.

I've owned a 1978 Honda XL250s for the last 15 years.

I mainly used the bike off road now and then and often it would sit for a year at a time in the workshop, before i'd fire it up again.

It will always start and sound healthy. However, over the years, I've never adjusted the valves or cam chain tension. It can't have done many miles at all over the time I've had it, but I am now re instating the bike for road use and would like to give it a major service.

My main question is the about the cam chain tension. The manual says to get the bike idling and then crack off the tensioner bolt and then tighten it back up again, as these are automatic. It seems odd to me to have the engine running, but nowhere does the manual state 'DO NOT RUN ENGINE' or anything like that. Is this correct?

Also, I assume its best to tension the chain and then do valve adjustments once the engine has cooled again? This way, Id imagine any slack will be removed before making your settings on the valves.

Also, after getting the bike running last night after its been in storage for 2 years, the clutch was stuck! I warmed the bike up and then kept operating the clutch and it freed off. Will this be enough, or should I dismantle the clutch assembly and service it??

Many thanks in advance,

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When I tensioned my can chain, I did it with the engine running, so I don't see a problem with that. If I were you I would adjust valves while it's cold so you don't burn/ hurt yourself.
Hiya Garfield!! Welcome

OK so the timing chains I have always adjusted with the engine running. On those spring loaded automatic adjusters you crack the bolt free, then tighten it up again is done to free up the mech of anything that may be holding it up. When they are manual adjustment you can use the engine running to hear when its good. When they are too loose they rattle and the engine may not run well. Tighten the adjustment nut/screw until they go quiet and then lock it down. It's pretty easy.

The valves are a bit more tricky but not too difficult. Engine cold is how the adjustment should be done. The valve adjustment is there to compensate for the metal expanding with heat.

Find valve lash specs first.
get feeler gauge that will fit where you need and is of the right size.
Loosen the lock nut on the rocker
loosen adjustment screw
tighten adjustment screw until the feeler gauge is just touching both the valve and screw.
remove feeler gauge
tighten lock nut while holding adjustment nut.
recheck with feeler gauge, it should still slide in and out easy just touching both surfaces.

rinse and repeat as needed. Easy peasy.
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