Adjusting Valve Clearances on a Diesel Engine

[Kenomac]

When you get it figured out, can you fly down here and show me how to do ours?

[Blue Stocking]

Originally Posted by four winds

Again, the other way around. When the intake closes a new charge is present and the piston is about to to rise and compress the charge. On two closed valves.

Just after intake closing then is a good spot to do both valves.

[Hudson Force]

I have the 4JH3E Yanmar,- similar, but naturally aspirated. I adjust with a gap of 0.008 inches or 0.2 +/- 0.05mm. I find little difficulty hand turning my engine through compression strokes, but I reduce my task by adjusting valves as they rise to TDC as opposed to in line sequence. In order to organize my work I check off the completed adjustment of each of the eight valves on a simple diagram.

[Cheechako]

Originally Posted by four winds

Again, the other way around. When the intake closes a new charge is present and the piston is about to to rise and compress the charge. On two closed valves.

Just after intake closing then is a good spot to do both valves.

ahh .. been awhile! :>)
I was thinking, after exhaust, there is a wider "flat" spot on the cam then between intake and exhaust...

[four winds]

Originally Posted by Cheechako

ahh .. been awhile! :>)
I was thinking, after exhaust, there is a wider "flat" spot on the cam then between intake and exhaust...

I think this is correct. And why this method can be a problem on hot rod car engines with more radical valve timing.

Not a problem on my Yanmar cam. Just be careful to rotate just past intake closing.

[sy_gilana]

This is how I do it.
1 Make sure engine is cold.
2 find the firing order, and choose to look at the rockers on the first cyl, lets call it "1"
3 rotate the engine with a ratchet socket wrench on the pulley nut
4 observe the movement of the rockers, you are looking for the point of Lash, or Valve overlap, this is where the exhaust is closing and the inlet is opening at the same time, its the only point where both rockers are tight, no rattle. Now turn the engine 360 degrees, and both rockers will be loose-ish.
5 Choose 3 feeler gauges, the datum and one up and one down.
6 check existing clearance before loosening the locknut, by checking that the one-down blade goes easily, the one up blade does not go, and the mid one fits just.
7 if it needs adjustment, slack the locknut and rotate the screw to achieve the right fit, then while holding the screwdriver to prevent the screw moving, tighten the nut.

now move to cyl 2 and repeat....

[Ex-Calif]

Originally Posted by Cheechako

ahh .. been awhile! :>)
I was thinking, after exhaust, there is a wider "flat" spot on the cam then between intake and exhaust...

Originally Posted by four winds

I think this is correct. And why this method can be a problem on hot rod car engines with more radical valve timing.

Not a problem on my Yanmar cam. Just be careful to rotate just past intake closing.

Not sure why everyone has an aversion reading the manual for their engine instead of getting guesses from here - LOL.

The exhaust and intake strokes may overlap. In fact they probably do - RTFM.

I don't know what you mean by a wider flat spot - there is only one cam lobe per valve. The known position with both valves closed is the top of the compression stroke but this is probably not where your manual wants you to adjust the valve clearance.

Both valves are closed from just before BDC on intake until just before BDC on power stroke - almost one revolution.

The reason many manuals want you to locate a particular stroke is they may also be instruction you to check for valve lash - Valve lash is an indication of cam lobe wear.

e.g. after adjusting to a .020 valve clearance the manual will tell you that this intake valve should start opening at X deg before TDC - if it is late, it is because the cam lobe is worn. It should close Y deg before after BDC if it is early it is because cam lobe is worn.

Clearly if the intake valve opens late and closes early, you get less fuel/air charge.

BTW - Remove the injectors when doing a valve clearance adjustment - If you adjust valves at 1,000 hours isn't it time to take a look at your injectors?

Also be very careful using the starter to "bump" the engine. On a gasoline engine you remove the coil wire - On a diesel engine it could start!

Valve adjustment time is the time to do a full service on the engine - fluids, injector inspection, filters etc.

No need to take a short cut by not removing the injectors here.

PS - I haven't seen one for small diesels but you can buy a tool. It is a pointer that screws into the port. As the piston comes up and contacts it, it deflects to a card pointer. You rotate the engine back and forth to find TDC on cylinder 1 - half way between two known deflections. There is a degree wheel you then attach to the flywheel so you can measure the crank angle.

[sailorchic34]

I should note that my engine has a V-drive, so the crank faces the stern and only accessible via a crawl down the lazerette, once everything in the lazerette is on deck. I call that boat yoga pose, Sideways stretching cat, BTW.

So being blonde, I just use the starter to bump the engine (with the engine stop pulled). Which is a whole lot less messing about when you have the joy that is a V-drive.

Luckily like horse shoes, hand gernades and atomic bombs, you only need to be close on the actual location of the cam. 10 or even 45 degrees on the crank at or before tdc on the power stroke is fine. 30 degrees on the crank is only 15 degrees on the cam, and both valves will be closed well before TDC. If your at TDC and both valves are opposite, one open and one closed, your on the start of the intake stroke and not at TDC of the power stroke.

It's safer to do at TDC for sure, but 45 degrees before or 20 degrees after (on the crank) and your still good, that is both valves will be closed completely.

[svlamorocha]

Originally Posted by Dockhead

But on a diesel you can't just pop the spark plugs out to relieve the compression, and you've got no distributor to use to check the crank position. How do you do it? Do you pop the injectors out? My engine (Yanmar 4JH3HTE) has no glow plugs. Do you look at the timing marks on the flywheel for crank position? Is there a step-by-step guide anywhere?

You made me realize that I lost my notes from when I took a course with Larry Berlin at Mack Boring class, which helped me do this job twice in my 3YM20. Here is some blurb that was posted in the Catalina 42 forum that is said to come from Larry Berlin and sounds similar to what I remember except that it is fo ra 4-cylinder engine.:

4JH2E Valve Adjustment Procedure in Archive-Engine-generator-diesel-ob-hoist Forum

I hope this helps for your 4JH.

In all Yanmars you started at TDC compression if cylinder closest to flywheel, which may or may not be #1 depending on the model.

The only thing that is missing here is the little table that shows you the sequence depending on the number of cylinders. There were three ways of finding the points where to stop turning to adjust the first set of valves. One was based on looking at marks in the flywheel, another one based on the midpoint of the range in which the valves are closed (adjust that valve) and another one looking at the "overlap" of valves (adjust valves un cylinder X when cylinder Y is in overlap). Hopefully someone can shed light as to whether those three recipes always give you the same result. Or maybe the right recipe depended on the # of cylinders, which would made sense. All that said, I do recall it was quite obvious what to do once you turned the engine a couple of times.

Do not worry about decompression. A socket with a bar on the flywheel nut will do if you go slow.

[Maine Sail]

Originally Posted by HappyMdRSailor

It should be no problem bumping the starter, and using a spanner to get your positions...

That is exactly what I do only I use a simple spring loaded remote start button.. Pull engine stop, Bump, bump, bump, breaker bar for fine adjustment.. Still hate valve adjustments more because they are tedious....

[four winds]

Ex-Calif, no problem using the service manual method to me. I do.

I was just describing a method that works for almost any engine when no manual is available. As long as the clearance is known. And it's a simple way to verify adjustment is needed.

I also use this method when assembling an engine to get it close enough to safely rotate the engine when using a solid lifter cam. Later, the degree wheel is used to verify specs or wear.

[Ex-Calif]

Originally Posted by four winds

Ex-Calif, no problem using the service manual method to me. I do.

I was just describing a method that works for almost any engine when no manual is available. As long as the clearance is known. And it's a simple way to verify adjustment is needed.

I also use this method when assembling an engine to get it close enough to safely rotate the engine when using a solid lifter cam. Later, the degree wheel is used to verify specs or wear.

Of course I am being pedantic (maybe precise?) - I rarely (never?) check valve lash - especially on a young engine but it is the "proper" thing to do.

In reality I follow the power stroke - If I fire 1, 3, 2, 4 - I just find compression stroke for #1. Do both valves (remembering intake and exhaust will likely have different clearances) - # 3 is next on power stroke, then 2 then 4.

With a socket/breaker bar on the crank pulley you can easily turn the engine slowly and you can feel when it goes over TDC.

No need to remember a sequnce of intake and exhaust valve opening. I don't know who would teach that method in an engine class - Mr. Cunfewzhu?

Cheers

[four winds]

Confusion not intended. Fair enough.

I'll resume my no posting/ read only status.

[Ex-Calif]

Originally Posted by four winds

Confusion not intended. Fair enough.

I'll resume my no posting/ read only status.

I sincerely hope I am not putting you off - Your inputs are just as valid as anyone else!

If there weren't different opinions every thread would have only one reply - LOL!

And I am wrong a lot! But always open to learn (I hope)

Cheers!

[delmarrey]

Heck, in my old gear jam'n days we use to put clips over the rocker squirter hole and adjust them with the motor running. But I guess on a boat one could get sucked up in a moving part as cramped as some boat motors are. Or oil would be running off the back, with the angle of some motors.

Anyway, cams now days are computer ground for special applications, like torque or RPMs so having the lobe at the right angle when adjusting could be important. That's why I would stick with the manufactures recommendations rather then a farmers guess.