Hi, So I did a leak down test on the head of my W115 and 5 out of the valve's failed and held no liquid.... so since I've never done this job before, and I haven't done this type of thing for a long time now... do I need to replace the valve seats or valve seals?? I have a box of new valve seals.... they are rubber sort of things with a spring stretched around them, so new valve seals or seats to make the leak down test a success....

Thanks J

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1975 240D W115 version 3 (Australian car )

Valve seals have no effect on a leakdown test. Changing them will not change the leakdown test results. I am not sure we are communicating or understanding well.

yea....... I meant these New valve stem seals on the Mercedes-Benz OM615 engine | Flickr - Photo Sharing!
valve stem seals.... I have a new box of them...... so what does the leak down test tell me I have to replace then?

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1975 240D W115 version 3 (Australian car )

Please describe the procedure you used in more detail.

Is the engine assembled? In the car? Is the camshaft installed? Have the valves been adjusted? What liquid did you use? What were the results you were expecting?

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James Marriott
2003 Buick Regal
1983 300D (228k, frau Auto)
1996 Suburban K2500 (192k, 6.5 turbo diesel/4WD towmaster 10,000)
www.engineeringworks.biz
1987 300SDL junker 170k
1982 300SD junker, 265k

I am assuming you filled the Intake and Exhaust ports with some sort of fluid to see if there was a leak.

If you did this with the Head laying on the side Fluid can also leak out of the Valve Stem Seals.

But, what you are really looking for is to see if Fluid is leaking past the Valve Faces/seats. If Fluid leaks out fast there you need to do a Head Job that requires removing all of the Valves; seeing if the Valves and Valve guides can be reused and grinding the Valves and seats back to the Manuals specifications.

One Question is what did you use as the Fluid for the test?
Next is what type of trouble were you having to begin with?

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84 300D, 82 Volvo 244Gl Diesel

I used kerosene...
I was using it to get some of the soot out, so I also decided to do a leak down test with some....

the car was almost impossible to start and when I finally did with lots of cranking some push starting there was a massive miss fire and if you didn't hold down the throttle almost full it would just stall.

when I did the leak down test 5 of the 8 valves didn't hold and kerosene (don't worry I made sure that the cam lobes were fully closed for that pair and not even slightly open as to let the fluid through) just started coming through the intake/exhaust manifold holes in the head, only the intake and exhaust valves for the first cylinder held fluid.

Also is it OK to scrape some of the soot off the pistons with say a hacksaw blade or a flat screw driver?

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1975 240D W115 version 3 (Australian car )

Normally, a "leak down test" involves blowing air into a cylinder that is at top dead center with both valves closed. Where the air escapes and the volume of escaping air helps diagnose the problem. ie leaky valve, rings or head gasket will let the air escape via a different route.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

How do you know there was clearance between the rocker and the cam lobe for the valve to be able to close fully?

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James Marriott
2003 Buick Regal
1983 300D (228k, frau Auto)
1996 Suburban K2500 (192k, 6.5 turbo diesel/4WD towmaster 10,000)
www.engineeringworks.biz
1987 300SDL junker 170k
1982 300SD junker, 265k

there was that slight play

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1975 240D W115 version 3 (Australian car )

Sounds like the head needs a valve job. Be very careful who you let do it. It is pretty simple but getting harder to get done properly even here in north america.

So do I buy valve seats and take them and the head to the workshop?

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1975 240D W115 version 3 (Australian car )

Just take the head. The existing seats will be ground. They may determine some valves and guides may need changed as well. Get a price estimate from them.

Valve jobs used to be cheap here. Perhaps they still are where you live. You could ask any local repair shop that services mercedes where they send their mercedes cylinder heads for reconditioning and the average charge they pay. That increases the chance the place you take the head will do the job properly.

Before taking the head in open some valves and look to see if there is a lot of carbon buildup on the seats and valve faces. Carbon alone in large amounts could stop the valves from sealing.

Do not spend more money than the car is worth. Old mercedes repair shops used to do the valve jobs themselves years ago.

Is there anyway to reduce the amount of carbon build up? and if I scrape it all away including the pistons.... and do the head job will the smoke produced be less?

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1975 240D W115 version 3 (Australian car )

You can scrape the Carbon off but as long as the Compression is not good the Carbon will be back. In fact a good running Diesel Engine has some Carbon Build up.

If you can still View those Online Mercedes Service Manuals what to check for the Valve/Head job is there.

One of the issues is that if the Valve Guides are badly worn when the install the Piolt to Grind or Cut the Valve Seates (to make them round again) the Valve Seats will not be cut or ground accurately.
Even if you replace the Valve Seats with New Valve Seats they are supposed to be ground or cut so they are centered on the Valve Guides.

If Valves are not worn too much on their stems and there is enough meat left on the Valve Faces they can also be reused.

Note: The Exhaust Valve Stems are partly Tubular and filled with A Chemical that is OK as long as it is not exposed to the Air. If you cut or crack one the Chemical ignites/explodes.
The purpose of the Chemical is to aid in the heat transfer and keep the Exhause Valves cooler.

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84 300D, 82 Volvo 244Gl Diesel

Putting new Piston Rings in an Engine holds in more combustion pressure. Doing a Head/Valve Job also holds in more combustion pressure.

The problem with doine only one is that the pressure goes up and that pressure wants to go out of the part that you did not fix.

They were speaking of Gasoline Engines but, back in the old days they used to say that if you only a Valve/head job that the combustion pressure goes up and trys to get past the Piston Rings and that it would cause more blow-by.

I do not know if that will happen on Diesel Engines as I have never seen just a Head Job done on a Diesel Engine where I got to see the Follow up results of it.

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84 300D, 82 Volvo 244Gl Diesel