Yanmar 2gm20 valve clearance issue

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Oldyanmarguy

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Sep 17, 2017
16
Springer 45 Camden
Hello, new user here.
I have been trying to set my valves on my 2gm20 with the spec of 0.20mm / 0.008

I turn the crank to the tdc mark for each cylinder and set, then full turn the crank back to same tdc mark and check, but then if i full turn again back to same tdc mark the clearance is then closed tight and then another full turn and the clearance is correct !

Is this my lack of knowledge about the camshaft lobes or is it something else ?
Does the timimg operate on a double rotation of the crank ?
Any advice would be great, especially as i may be fitting a new cylinder head soon.
 
RoyS

RoyS

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Jun 3, 2012
1,742
Hunter 33 Steamboat Wharf, Hull, MA
You have figured this out. The cam shaft rotates once every two crank revolutions.
 
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O

Oldyanmarguy

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Sep 17, 2017
16
Springer 45 Camden
Hello and thanks for the replies. So as long as i set the clearances with the correct tdc marks on the flywheel then im doing this the right way ?

Yes i have a manual, it has been extremely useful, thanks.
 
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Ken13559

Ken13559

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Oct 29, 2005
2,356
Hunter Marine 326 303 Singapore
At the correct tdc mark both intake and exhaust tappets will be loose or have gap.
If one is tight and the other is loose then you're on wrong mark.
 
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mz4wheeler

mz4wheeler

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Mar 11, 2015
357
Hunter 33.5 Tacoma, WA
In theory, over the years, the valve clearance becomes tighter, right? Or, is it a combination of valve further seating into the head (becomes tighter) and top of valve wearing against camshaft (becomes looser)?
 
Charles Erwin

Charles Erwin

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Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
The camshaft pushes on the lifter, which pushes on the push rod, which pushes on the rocker arm which pushes on valve stem (actually a cover.) There would be 5 places wear occurs if you include the valve seat in these overhead valve motors. Valve to rocker arm clearance changes as these things wear.

However, valve spring pressure on Yanmars are pretty low so it is unlikely you will wear much at the lifter/cam interface. (I am doing one right now that got water in the oil. The ensuing corrosion caused high friction in the lifter bores which lead to considerable cam lobe and lifter wear.)

But the entire design includes pretty large contact areas and relatively low spring pressures so things do not wear much and valve lash adjustments do not need to be done all that often. The main culprit is valve seat wear and that will reduce the stem to rocker clearance. So mostly these clearances should get tighter.

Charles
 
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Ken13559

Ken13559

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Oct 29, 2005
2,356
Hunter Marine 326 303 Singapore
How tight/loose is the right gap? That's the question I often ask myself when I adjust the tappet/valves. So not knowing that answer, should I err on side of tight or loose on feeler gauge?
 
Jim 5757

Jim 5757

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Jun 19, 2004
365
Island Packet IP 32 99 Forked River, NJ
From my experience too tight is worse. When engine heats up clearance gets smaller. Too tight and you may burn valves.
 
Charles Erwin

Charles Erwin

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Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Ken

You can obtain 'go no go' feeler gauges. The blade tip is .008 and the rest of the blade is is .009. The idea is if both parts slide in it is too loose, if neither part goes it is too tight, and if the tip goes and rest does not it is just right. Or you can use a standard .008, tighten the jamb nut, then check it with a .009. Too tight means the valve opens too soon, too far, and closes too late. That means exhaust valve/seat can get toasted, and possibly a collision between valve and the piston top. Too loose and the opposite happens - usually no physical damage but no good for motor performance. Set the clearance motor cold.

Charles
 
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Jim 5757

Jim 5757

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Jun 19, 2004
365
Island Packet IP 32 99 Forked River, NJ
+1 on Ken's post! I worked on the old air-cooled VW's for years. Valve clearance on those buggers was critical and had to be done often. Unless you have the 'feel' of what's correct, using the feeler gauge .009" is way too tight to fit, and .007" is way too loose. Then the .008" will be juust right:clap:
 
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Ken13559

Ken13559

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Oct 29, 2005
2,356
Hunter Marine 326 303 Singapore
Jim/Charles, thanks for the idea. I don't have a .007 nor .009 gauge or perhaps I should add-on other sizes to make up the size. I'll also look for the .008/.009 go-no-go feeler gauge. They do sell it right? 'cos its the first time I heard of this type of feeler gauge. :)
Thank you.
 
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Oldyanmarguy

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Sep 17, 2017
16
Springer 45 Camden
Im using .008 which i had confirmed today by a professional yanmar mechanic. I have had to buy another cylinder head, luckily its in good condition and way better than mine. Trouble is it does not have the pre combustion chambers, i have removed my old injector heat shields but the lower nozzle part is well and truly siezed in. Its going to be hard work getting them out, will try a socket placed in and tapping with a hammer, carefully !
 
Charles Erwin

Charles Erwin

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Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Oldyanmarguy said:
Im using .008 which i had confirmed today by a professional yanmar mechanic. I have had to buy another cylinder head, luckily its in good condition and way better than mine. Trouble is it does not have the pre combustion chambers, i have removed my old injector heat shields but the lower nozzle part is well and truly siezed in. Its going to be hard work getting them out, will try a socket placed in and tapping with a hammer, carefully !
Click to expand
If you read the Yanmar manual you just reach in with a hooked tool and they slide right out. I can say with complete confidence that the book is quite wrong.

The tapping method probably won't work either but it might if the tapper is a BFH - means one with considerable mass. Not unusual that removal needs a hydraulic press. Be careful because the pre combustion chambers are in the injector bores which are sloped relative to the head surface. Rig some support so as to be sure you push or tap dead straight along the theoretical axis of the injector bore - else you risk damage.

When you replace the chamber be sure all the parts are included in the stack. Use nickle anti seize on both halves - aluminum and copper versions don't work. Above all make sure to use the o-rings where the injector joins the head to keep moisture out of the bore.

Charles
 
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Oldyanmarguy

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Sep 17, 2017
16
Springer 45 Camden
Well i have fitted my new cylinder head, valves lapped and checked, exhaust port checked. New gasket and all torqued properly in spec with yanmar manual. New injector heat shield washers, insulators and o rings. Injectors pop checked, only visually whilst standing at safe distance ! The engine now starts way better with no oil in exhaust but i still have a small issue with unburnt fuel. I have checked fuel delivery and timing so now it has to be the injectors.

I am considering taking the injectors apart and carefully cleaning them myself or i will have to take them to an injector shop, which will not be that simple as i am currently travelling on the boat.

I have tried to open the injectors before but will need to lock them in a vice if I want to suceed.

Considering all of the above, i cannot see what else it could be other than faulty / partially clogged injectors ?
 
Charles Erwin

Charles Erwin

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Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Overfueling - unburned fuel - results in black and sooty exhaust at start up and when opening the throttle. There will be some especially when the motor is cold but if this symptom is persistent it is commonly an injector that leaks. These injectors open at no less than 2350 psi. No drip at any value below that. A capable injector shop will test and repair for about 50% of new injector price. As to what else it might be there are a few other things (including old or dirty fuel) but why not rule out an injector leak first.

Charles
 
jviss

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
My experience has been that if you can identify the tractor that the engine goes in, you can buy new injectors from an agricultural diesel supply house for much less than an injector shop charges to repair or rebuild them. I don't know if this scheme works with Yanmar, but it certainly does in the case of the Universal M25. New injectors from MarineDieselDirect via the Universal P/N: $365. Called around for a rebuild, $180. Bought new, from an agricultural supply place: $83.

Do some research and you can save big money. Same with glow plugs, $65 v. $6.
 
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