220SE engine smokes cold

[wwheeler]

I have a 220SE motor that was just rebuilt. This is on a W111, but would be similar issues to the 230SL. The engine was completely rebuilt. 2nd oversized pistons, complete valve job, you name it.

It now has about 250 miles on it and runs very well hot and cold. But it has always smoked some when cold and still does. In the beginning, it smoked just a bit even when it was hot. Now that has stopped and burns nothing when hot. So making progress, but I would have thought the cold smoking would gone to just about zero by now. BTW, during the 250 miles, I have regularly varied the speeds and the loads on the motor as you should for a new engine. I have been told that it still needs more miles on the engine for the rings to fully seat and that it should not smoke much at all after that.

I did a compression test early on, not so much for the actual figure, but to see if the figures were consistent which they were. So wondering if there is a part like an exhaust valve seal that typically leaks when cold but not hot. Or do I really need to give it more miles to seat the rings further?

Thank you.
 

[Charles 230SL]

hi Wallace, sounds like you may have a 'jumped' valve seal. I've seen this happen with new valve seals that were installed too loose.
vr, charles

[wwheeler]

So I guess the theory here is that while the engine is cold, the valve stems and guides have more clearance and allow more oil to slip past. Then when it warms up, the gaps close reducing the oil amount that leaks through?

In any case, the seal is not doing its job. Sound right?

[ja17]

What oil are you using?

[Charles 230SL]

yes. that's correct. Recall that valve seals are pressed onto the tops of the valve guides and should be tight enough to prevent them from ‘jumping’ off and riding the valve stem. I’ve seen machine shops rebuild heads and install poorly-fitting (loose) valve seals. The seals stay in place for a short period of time but eventually work themselves off the guide and fail to seal around the valve stem. Lack of an adequate seal around the valve stem permits oil to find its way into the cylinder resulting in blue smoke – typically at start-up and until the guides warm up enough to reduce the amount of oil that gets through.

I wouldn't expect a freshly rebuilt motor (new pistons/rings, new valves, guides and seals) to smoke even when cold. I realize it’s an aggravation but if the blue smoke continues, you might consider removing the rocker cover and taking a look at the valve seals - you'll have to peek between the valve springs but if one has pulled loose, you should be able to see it. 

[wwheeler]

Thanks for the replies. I am using VR1 20W-50 oil. The break in oil I believe was 10w -30 oil, not sure of the brand. I am told that as the rings seat, the cold smoking should minimize. It has minimized when it is hot and has reduced some when cold. Still, I would think by now, the cold smoking should be very little.

I don't have any experience with these engine when rebuilt. But I don't recall any rebuilt engines I have done in the past having this much smoking when cold. That is why I am wondering if there are peculiarities with these six cylinder engines that may cause this.

Thanks.

[Benz Dr.]

Look at the ball studs. If little or no threads are left showing this could be a rocker geometry problem. If wrong, you can wipe out a set of valve guides in quick order. Not nice to discover but it happens. The engine will always smoke once this happens. 

[wwheeler]

The ball studs are new. This was an extensive rebuild. I think I may do a cylinder leak down test. That would at least rule out mechanical issues. Next would be to examine the valve seals.

Thoughts?

[Benz Dr.]

It doesn't matter if the ball studs are new because that's not where the problem will be found if there is one. As you cut the valve seat deeper it makes the valve stem sit higher. In order to obtain a proper rocker to cam lobe clearance, you would have to screw the ball stud in further. Get the ball stud low enough and the valve stems will wipe out the valve guides. This is why I use shims under the cam bearings in all of my rebuilds. One time going through that ordeal was more than enough to convince me to figure out what went wrong. 

Shims raise the camshaft and in turn make you raise the ball stud to find proper adjustment. By raising the ball stud, you improve rocker geometry which makes the rocker push straight down on the valve stem. In severe cases, you can wipe out a set of guides before your engine is warmed up on the first start. Hopefully, this isn't your problem.

[wwheeler]

Thanks for the info. I see what you are talking about. The head had extensive work done and I think the valve seats were replaced as well. I will have to check.  I am planning on examining the the valve seals and I will definitely look at the ball stud threads.

I remember the engine builder mentioning cam bearing tower shims, but I think they were talking about that to compensate for the change in head thickness.

Thanks.

[wwheeler]

I finally got the valve cover off to take a look. I now have close to 400 miles on the engine and it still smokes only when cold and none when warm. Same amount of smoke when cold and hasn't changed either way. Attached are the pics of the ball studs. I was surprised they were so far down and I seem to remember on my 280SE engine that there was more of a space between the hex and the base. The part numbers are different between the two engines though. Dan was concerned that the geometry was off and now I am wondering the same thing. The valve seats were NOT replaced and was mistaken about that.

The other area I was going to look at was the valve stem seals and see if they had slipped and moved up. I am leaning (hoping really) toward this as being the issue. I just cannot imagine an engine with 400+ miles on it should still be smoking at all. The break in process should be mostly done by now I would think. Looking for the seal, I honestly cannot see a thing between the double springs.
Am I missing something?

The engine runs so well and it is frustrating that I have this relatively minor problem. Thanks for the help.

Wallace

[Benz Dr.]

I never feel comfortable unless I can see some threads showing on the ball stud. Those are pretty low actually.

[wwheeler]

How low can you go? Well not much lower and why I posted the pics. So what would be the recommend course of action? I know you would have to pull the head to replace the guides, but any other tests before that? I guess shimming the cam at this point would be futile if that is indeed the issue?

I still cling to hope that it may be the seals and a less costly and less involved operation. It seemed to smoke upon initial start up on a test stand. I should have done something then but was convinced it would “break in”. It has lessened quite a bit since then and only when cold. So it has improved, not gotten worse.

I am thinking that it may be best to replace the seals and see if that helps. If so, maybe I can shim the towers later. Is that possible with out removing the head?

So is it agreed that assuming everything else is correct in this engine, that it should not still smoke after 400 miles?

[Charles 230SL]

no, the engine shouldn't smoke at cold start-up. I'd rule out the valve seals before thinking about pulling the head.  I know it's hard on the back but you might try using a small (dental-type) mirror and a flashlight and try seeing between those springs on each valve. It only takes one loose intake seal to cause smoke.

If the valve seats weren't replaced then its possible the old seats were ground too deep. If the shop mentioned cam tower shims, I wonder if they themselves were concerned the valve seats had been cut too deep.

[wwheeler]

Good thoughts and I will try the mirror. I will have to confirm the use of cam tower shims and will do that.

I was also thinking about the shim piece that sits on top of the valve. I do not show that I replaced those and according to EPC, the standard is 4.5mm (180 053 19 52). I show that there are 3.5 and 2.5 mm shims and are available. If I used a thinner shim piece, wouldn't that effectively rotate the rocker arm back closer to normal geometry and also gain some height and the ball adjuster.

The shims aren't cheap, but if that will help the situation, I am ready to do that. I realize that if there is some damage done to the guides, this will not fix the problem but rather just prevent it from getting worse. Any thoughts on this?

I am thinking I might go ahead and replace the seals. Which method is preferred to keep the valves seated- the string in the combustion chamber trick or using air pressure via spark plug hole. I have an air compressor and a leak down tester. Both which should work for the cylinder pressurized method.

[Charles 230SL]

..If I used a thinner shim piece, wouldn't that effectively rotate the rocker arm back closer to normal geometry and also gain some height and the ball adjuster.

Yes. I would think reducing the shims to 3.5mm would be enough to get back to normal rocker geometry - I've never had to do this. hopefully Benz Dr can offer some insight.

..Which method is preferred to keep the valves seated- the string in the combustion chamber trick or using air pressure via spark plug hole.

I prefer using an air compressor to hold the valve shut, but have in the past just raised the piston to tdc - just remember it only takes a few degrees to drop the valve (I've done that too)

[wwheeler]

When you say it only takes a few degrees to drop the valve - you mean degrees of crankshaft rotation? I plan on putting the piston at TDC when doing this and hopefully would prevent the valve from dropping in case of PSI loss in the cylinder. What that do the trick?

Thanks!

[Charles 230SL]

Yes, degrees of crankshaft rotation.
Not the end of the world if you do drop the valve into the cylinder, it just takes some finesse to fish that valve stem back up through the guide.