Checking and adjusting the tappets or valve lash to those in the US

[Pats-bike]

Have just checked and adjusted the tappets (valve lash) on my LF250 and was glad that I did!
The correct adjustment is as follows:
Inlet 0.08-0.12mm or 0.003-0.005in
Exhaust 0.10-0.14mm or 0.004-0.006in.
As the cam lobes/tappets/rockers wear normally the gap slowly enlarges as the miles are clocked up but out of the four valves (2 per cylinder - inlet and exhaust) all but one had the gap too small which isn't very good for the valve seats. I've only done 4500km since new so hope that I haven't done any lasting damage to the valve seats or valves themselves - I've tried the bike and it pulls okay so I must have got away with it. The job is quite lengthy as there are quite a lot of odd bits to be removed (seat, tank, carb cover, air filter and bits of pipe etc) to simply get at the cylinder heads but it should be within the capabilities of the average mechanical person. When removing the petrol tank the two fuel pipes (main and reserve) will have to be clamped as the on/off valve is not part of the tank. Remove the spark plugs to make turning the engine easier. On the left hand engine cover there is a slotted plug about 30mm in dia which if removed will allow you to use a 17mm socket wrench to turn the engine. For each cylinder turn the engine until the exhaust valve is just closing and the inlet valve is just opening (on the rock) then carefully turn the engine one complete turn further. This allows the tappet adjustment to be made with the cam lobe in the correct place - approximately on the back of each lobe. Each valve has its own round cover set in each rocker cover. When you come to replace the petrol tank do make sure that you don't damage or kink any of the fuel tubing as it could split - happened to me and I lost near a full tank of petrol all over the ground! Hope this helps, Pat

[Rogerborg]

Damn good advice from Pat!

I checked the clearances on my 18 month old 5900km LF250B today, and they were all tight.  The rear exhaust valve had virtually no clearance.  I've adjusted them generously: a sloppy 0.1mm on the inlet and 0.15mm on the exhaust, slightly more than recommended, but it's better to be over than under.  The bike now idles noticeably more easily, and faster too - a good sign when you haven't adjusted anything else.  There's some healthy valve chatter now from cold - it was ominously quiet beforehand.  Read this carefully:

IF YOUR ENGINE IS QUIET WHEN IT'S COLD, THIS IS NOT A GOOD THING!

Performance when cold seems slightly down, but that's also a good thing: the clearances should only shrink (and thus give maximum valve opening) when the engine is hot.  If you've got a quiet, powerful engine from cold, then it's likely cooking its valves when it's hot.

As Pat says, is a fairly big job, with a lot to come off before you can get at the values: several hours done solo, with some fairly tight access issues to deal with.  There's nothing particularly complicated though, and one thing I'd note though is that you can unbolt the fuel valve and remove it along with the tank: no need to clamp anything off.

The tank is a tight fit to get back on though, so I can see that it'd be easy to trap the fuel lines.

Also, I just couldn't see the timing marks on the flywheel, no matter how much light I shone in there.  However, it's not rocket science to find TDC on the compression stroke for each cylinder.  Turn the engine counter-clockwise, watch for the inlet valve opening and closing, then you can just shine a light in the spark plug hole and watch for the piston reaching its highest point.

Something else I noticed was that the rubber inlet manifold (above the carb, under the tank) was already perished and split.  This is on a 18 month old bike!  I glooped it with some silicone sealant, but I'll have to keep an eye on that.  There was also some slight tearing on the rubber at the back of the air cleaner box, which I've also bodged with gloop.

If you've got an LF250 and you're not confident checking the valve clearances yourself, I'd recommend paying someone to do it for you.  It's could end up costing you a lot more later if you don't.