Adjusting valves questionIt is past time for me to do a valve lash adjustment.

[Jimongee]

It is past time for me to do a valve lash adjustment. I am a former automotive technician so adjusting valves is turnkey for me. However making sure the respective cylinder is at TDC on compression is not as simple as a gas engine [you can feel compression in the spark plug hole if you can't find a clear timing mark on gas engines]. That said my Yanmar shop manual instructs to align the flywheel mark visible thru the starter mount hole or thru an inspection hole on the backside of the trans. That works for cylinder # 1 but then it instructs to rotate the crank 240 degrees and adjust # 3 and again rotate 240 and adjust #2. My question is that due to the critical importance to assure that each valve is fully closed-how can you judge 240 degrees accurately without an index mark? I know I can tell when both valves are fully closed on the low side of the cam lobe, but since holding a valve open [to little lash clearance] for even a nano second at the wrong time will burn it-I would prefer a more accurate and dependable indicator. So we're back to the rotate procedure. Long message, but if anyone has specific hands-on experience with adjusting the lash on this model-I would really appreciate your information. thanks
jim
SV SamiDog
2002 Hunter356

[model 10]

It depends on what RPM you are at for a "nano second"to go by. As an expert mechanic you should be able to tell the flat spot on the cam. Plus you don't need any stinking makers. Rotate the engine in the normal direction and watch the valves.

[a64pilot]

I remove injectors and use a soda straw to determine TDC, although you can watch the valves and likely do just as well, I just want to be precise is all.
My serpentine belt pulley covers my crank pulley and I have not remarked the serpentine pulley yet.

[Lepke]

When rotating and watching the valves, go an 1/8 to 1/4 turn past where the rocker goes slack. I been doing most valves this way since the early 1960s - never burnt a valve. Diesels, gas and radial aircraft engines.
Race shops have degree wheels that go on the crank pulley front. They're marked in single degrees. Normally used for cam timing in racing engines.

[Diesel Bill]

Hate to throw this out as you guys will think it's nuts. Any way here goes.
Pick a cylinder, any cylinder. Rotate in direction engine runs. Watch the rockers. when one valve opens all the way, (full lift of valve off the seat) the other valve is fully seated and can be adjusted. After setting the lash mark the rocker with a yellow crayon. I have never seen a 4 cycle engine where if one valve is wide open the other valve lifter isn't on the cam base circle. This includes full race cams with a lot of valve overlap.

[a64pilot]

There is however usually some overlap which could fool you into thinking it's fully closed when it isn't.
You can just look at valve position and how it lines up with either the intake or exhaust manifold and determine if it's an intake or exhaust valve, then when turning the engine over watch and it's pretty easy to determine compression stroke.
However it's often a bear to turn over a Diesel multiple turns without some form of decompression, one reason why I pull the injectors, plus I take them in to have them "Pop" tested which is cheap but worth doing, also if you pull the injectors once in a blue moon, they don't stick nearly as bad as if it's been years since they have been out.

[four winds]

I agree the Yanmar instructions are hard to comply with.

Some form of watching the valves work fine.

For me the trick is to watch the intake valve. When it closes that cylinder is about to come up on compression. So, the intake closes, that piston begins to rise with a little more rotation. Both valves can be adjusted at that time. The exhaust valve won't start to open until almost a full revolution, after the power stroke.

[Diesel Bill]

The exhaust valve will start opening before the end of the power stroke as the piston approaches BDC

[four winds]

That is correct, Diesel Bill. But not much before it, in order to extract as much power as possible after combustion.

The intake closes somewhere near BDC, then compression, then combustion, and the exhaust opens somewhere near BDC as the piston returns to the bottom.

So, when the intake closes, rotate an additional ~ 100 degrees or so and that's pretty dang close to having the compression well underway. And well before exhaust begins. Both valves fully closed and can be adjusted.

To verify, rotate it through intake closing and exhaust opening and note the amount of rotation. Then run it around again and pick a spot half way through the noted rotation, after the intake closes.

Works well, faster and more certain than other shade tree methods. Just my opinion and experience.

[DougR]

A simple way to do this is to rotate the crankshaft in its normal direction of rotation until any given cylinder is in the valve overlap position, i.e. both valves are moving. The exhaust valve will be closing and the inlet valve will be opening. This will be TDC on the overlap stroke.

Then rotate the crankshaft an additional 360 degrees ( one rotation). Now that cylinder will be at TDC on compression stroke and you can adjust the valves on that cylinder.

DougR

[four winds]

Diesel Bill, just noticed you posted the one valve at a time method above.

Just want to say, I don't think your nuts. That works fine as you posted. Just that for me it's hard to stop at the point of fully open valve, or judge exactly where that is. As you know, a very small amount of valve movement is a considerable amount of rotation. And at the point in the cycle where overlap occurs, if any.

The both valve closed method is the greatest amount of rotation without valve movement. And much easier to hit a sweet spot.

Again just my opinion.

[sailcrazy]

Maybe I'm not understanding what you want to do, but we just had an Onan mechanic (or so he claimed and advertised to be) adjust the valves on our Kuboto-powered Onan genset a few months ago-along with a few other issues we needed help with. I watched closely, so I could do it myself in the future. He turned the engine via a socket on the engine front until the valves were both closed and the gaps on the tappets were visible, and then adjusted both the valves on that cylinder. Then he rotated to the next cylinder and repeated. What I saw was very different from what you're talking about above.....what am I missing?

[Captsteve53]

To make life easy for non mechanics in the past I have placed the engine on TDC #1 using the manufacturers method the filed or center pop a mark on the front crankshaft pulley(then white paint) and on the timing cover (making it easy to access rather than going to the rear of the engine using pins/lights/dowels etc, also then marked the 240 and 240 on the pulley (different marks so there's no confusion), to mark the 240 used a 360 degree protractor, easy and close enough then to rock the crank and check you have it right- just for input

[sandiegoskipper]

Would a dial indicator work, screwed into the injector hole?

[Kita]

Originally Posted by sailcrazy

Maybe I'm not understanding what you want to do, but we just had an Onan mechanic (or so he claimed and advertised to be) adjust the valves on our Kuboto-powered Onan genset a few months ago-along with a few other issues we needed help with. I watched closely, so I could do it myself in the future. He turned the engine via a socket on the engine front until the valves were both closed and the gaps on the tappets were visible, and then adjusted both the valves on that cylinder. Then he rotated to the next cylinder and repeated. What I saw was very different from what you're talking about above.....what am I missing?

I don't think you missed much,he rolled the engine over untill mark on crank lined up for top dead center on number 1 (TDC) & then looked at the valves,when both are closed or have clearance or lash if you may he adjusted that cylinder, then roll the motor over one revolution & adjusted the next one in the firing order sequence no matter how many cylinders..what the others are talking about is if you know what sequence you can jump around and do different cylinders and the reason for that is so that you don't have to roll the motor over over and over for each cylinder. For example on a Volkswagen old Beetle engine you roll the motor over clockwise which is the direction of rotation until number one is at top dead center then you adjust that cylinder then you can roll the motor counterclockwise one half turn or 180 degrees and then do number 2 then a half turn number three and so on it saves you from having to roll the motor over a whole bunch of times and it also saves time