Adjusting Valve Clearances on a Diesel Engine

[Dockhead]

I have never adjusted valve clearances on a diesel engine -- can anyone give any hints? I've done it a million times on petrol engines. 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?

[Fiveslide]

http://www.hoyetractor.com/valve-set.htm

A service manual will have a procedure, probably more complicated than in the link above, but that is what it boils down to, finding that "middle position" they reference for each cylinder and adjusting the valve to specs. Removing something or otherwise relieving compression will make it easier on you rather than turning it by hand through all the compression strokes.

This is a critical part of your engines health and overall life and should be done more than most people do it. I think most engine makers recomend it at first oil change and every 1000 hours. Its also relatively easy and there is no reason it should have to be done by a professional.

Certainly something you can handle, Mr. Dockhead. I do think I would want to consult my engines service manual rather than just wing it.

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[Dockhead]

Originally Posted by Fiveslide

Easiest way to set the valves on your Yanmar

A service manual will have a procedure, probably more complicated than in the link above, but that is what it boils down to, finding that "middle position" they reference for each cylinder and adjusting the valve to specs. Removing something or otherwise relieving compression will make it easier on you rather than turning it by hand through all the compression strokes.

This is a critical part of your engines health and overall life and should be done more than most people do it. I think most engine makers recomend it at first oil change and every 1000 hours. Its also relatively easy and there is no reason it should have to be done by a professional.

Certainly something you can handle, Mr. Dockhead. I do think I would want to consult my engines service manual rather than just wing it.

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My manual says "this procedure requires special knowledge; refer to your Yanmar dealer"!

I've done it a million times on petrol engines and understand the principles fine -- I just need to know how people relieve the compression (or whether they do so), and what you use for a timing mark.

[Sailmonkey]

On out little Kubota, I don't relieve the compression, I do however zip tie the fuel stop lever into the off position. For timing, find the timing marks, watch for TDC on a particular cylinder and shove feeler blades between the rocker and valve. Easy

[Fiveslide]

Originally Posted by Dockhead

My manual says "this procedure requires special knowledge; refer to your Yanmar dealer"!

That's just... crazy. This is the service manual, not the owner's manual stating this?

It's probably a straight forward procedure, the "knowledge" of which should in no way be considered special.

I'm really interested in seeing this procedure now and why they print that only Yanmar dealers are capable of doing it.

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[Fiveslide]

I found a pdf of the service manual. I will pm you the link or the file if you like. On pade 31 of the pdf in section 3-3 of the manual it tells you how to adjust the valves during an overhaul. I don't see how it could be any different with a complete engine other than the compression issue.

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[perchance]

If you divide 720 degrees by the number of cylliders it will give you the number of degrees you need to rotate the engine to bring the next cylinder to TDC. Check for valve rock on the cylinder to ensure it is at TDC.

[HappyMdRSailor]

DH,

Same exact thing as your petrol engine...

For simplicity, the max gap should be constant until the lifter starts up on the ramp profile of the cam lobe... That being said... You can adjust each valve without figuring out where your particular cylinder is in the cycle... If you watch for max lift of a valve and turn the crank 90 degrees... You are then on the 180 position away from the cam lobe...

Obviously it would be easier to do both valves on a cylinder in the same crank position.... Find compression TDC by watching the valves... It should be no problem bumping the starter, and using a spanner to get your positions...

[sailorchic34]

Originally Posted by HappyMdRSailor

If you watch for max lift of a valve and turn the crank 90 degrees... You are then on the 180 position away from the cam lobe...

Ah, It's the other way, 90 degrees on the crank is 45 degrees on the cam. Cams are half the rpm of the crank on 4 stroke engines.

I too adjust valves one at a time as its quite easy to just watch and see when the valve is closed. I just bump the starter a time or two as needed and go thru the valves. Normally you can do 2 or 3 valves at a time, just not on the same cylinder.

No mystery to it. Gee my dad taught me this when I was 12. I'll sometimes verify that the clearance is not too tight or loose by using one size up and down on the feeler gauges. If in question, its better to be 0.001 loose.

[delmarrey]

On yanmars the front balance wheel has a mark for the #1 cyl and a pointer that should be visible.

With the valve cover off and the mark lined up the front valves should be loose. If not then rotate the motor 360 and check again. Once establishing TDC you can place marks on the balance wheel at 90, 180, and 270 degrees.

Once you have adjusted the #1 cyl you can rotate the motor 270 degrees and check for another pair of loose valves and adjust that cyl. Repeat!

I'm in P.I. right now and don't have access to the manual for the gap but if you can get the instructions from a manual (above) then do so. Valve adjusts are critical on motors.

[Cheechako]

I've not found the need to relieve compression. You can turn them very slowly to where you need to be. IF I remember right watch for the exhaust valve to be depressed and back up and before the intake goes down. There's your adjustment spot. Someone please refine this for me...with more detail...

[HappyMdRSailor]

Originally Posted by sailorchic34

Ah, It's the other way, 90 degrees on the crank is 45 degrees on the cam. Cams are half the rpm of the crank on 4 stroke engines.

Hee Hee!!!

Brain... Pffffft...

[four winds]

Originally Posted by Cheechako

I've not found the need to relieve compression. You can turn them very slowly to where you need to be. IF I remember right watch for the exhaust valve to be depressed and back up and before the intake goes down. There's your adjustment spot. Someone please refine this for me...with more detail...

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.

[Blue Stocking]

Depending on your firing order, e.g. 1-4-2-3-, there is a formula that will tell you e.g., that when the intake valve is closed (TBC) on #1, the exhaust will be closed on another cylinder. There is a constant number to add to whichever valve you are working on, to find the other one ready to set. I know that on certain firing order 6 cylinder engines, you add 9 to whichever # valve you are setting, and it gives you the next open valve.

Found it zyra.me.uk has firing orders.

[mtarcher]

I concur with FourWinds...I adjust the valves on my 3GM at .008in on a cold engine. If I remember right, the tech who helped me the 1st time said that the intake value needed to be most accurate, while the exhaust could be "fudged" to .001in over (loose) if needed.