RS, how do you adjust the valves on a Kubota? ...
With your copy of the Workshop Manual for your tractor close at hand ...
Seriously though, it was pretty simple (for my tractor specifically, YMMV)
1. Remove anything that will prevent you from removing the valve cover. In my case it was the muffler/exhuast/tailpipe.
2. Remove the glow plugs (so there is no compression and the engine can easily be turned with a wrench on the bolt head that holds the crankshaft pulley on)
3. Remove the valve cover.
4. Set the engine to Top Dead Center (TDC) on the compression stroke for cylinder no. 1.
So the first thing you have to do is identify which cylinder is no. 1 on your engine. Typically, it's the first cylinder at the front of the engine (but on at least some Yanmar's it's the last cylinder at the rear ... at least according to mechanic friend)
Kubota describes cylinder no. 1 for my tractor being the one closest to the "gear case" in the Workshop Manual. If you aren't a mechanic and real familiar with their terminology that can be a little confusing. When I initially read it, I thought
"Gear case ? ... are they referring to transmission ?" (rear of engine)
Nope ... it's actually a case/housing on the
front of the engine that holds various gears that probably control the timing of the camshaft, injection pump, etc.
There are two TDC's for cylinder no. 1 - one is on the compression stroke and the other is on what Kubota calls the overlap stroke (which I believe is the exhaust stroke) ... so it's possible that the engine can be 360 degrees out of the position you want it in.
On mine, when the engine is at TDC, the TDC alignment mark on the flywheel will be in the
middle of the window (a small 2" hole on the right side of the bell housing, covered with a removable rubber or plastic plug) and both rocker arms for the intake and exhaust valves on cylinder no. 1 will have clearance (ie. both valves are closed)
Once you have no. 1 at TDC, you look in the Workshop Manual and check
the table and see what valves on each cylinder you can check/set with the engine at that position. On my engine it was intake and exhaust valves for cylinder no 1 ... then something like intake on cylinder no. 2, exhaust on cylinder no. 3, ... etc.
After you have all the valves set for that engine position, you rotate the engine 360 degrees and check/set the rest of the valves that you didn't already do.
For my engine, the clearance spec was something like 0.0054 to 0.0073 (?) ... so I used a 0.006 feeler gauge.
On each rocker, there is an adjustment screw (with a locknut) to take up the slack and set the clearance ... you loosen the locknut, place the feeler gauge in between the valve and the rocker and tighten the adjustment screw until there is a
slight resistance or drag on the feeler gauge and then, using the screwdriver to
maintain the position of the adjustment screw, tighten up the locknut.
After you think you have it set pull the feeler gauge out and stick it back in between the valve and the rocker ... it should come out with only a minor amount of drag/resistance ... and go back in with only a very
minor amount of effort, if any at all.
I used a 0.007 feeler gauge blade as a "no-go" check ... IOW, after I adjusted it as above with the 0.006 blade, I would try to insert the 0.007 blade ... which
shouldn't go.
FWIW, when adjusting valves, it's better that they be slightly on the
loose side rather than being too tight (being too tight can cause burnt valves, more common on exhaust valves)
... - or is this a question that if i have to ask I should get a mechanic to do it?
That's hard for me to say with any degree of certainty, without knowing how mechanically-inclined you are.
I will say this though:
Assuming that one has a manual which lays out the procedure, and one can follow written directions, and exercise reasonable care in doing so, it really isn't all that difficult ... or at least it wasn't on my tractor.
Hope this helps.
