I picked up a misfire on my car recently and parked it. Eventually I got around doing a diagnosis with my Autocom CDP+ and the report shows permanent misfire on cylinder number 1.

When I removed the spark plugs I noticed that the electrode on the spark plug was bent but not broken. All others were fine.

Next I proceeded to do a compression test on cylinder 1 and though all the other cylinders were very good, and all roughly equal, cylinder no 1 had no compression.

I inserted a borescope and inspected the inside of the cylinder and there are no visible damage to the piston crown. Unfortunately I could not inspect the cylinder head and valves but I suspect a broken valve or guide. It is worth mentioning that there was no audible noize from the engine aside from rough running after the misfire started.

Has anyone had the same experience and what could be the problem?

I thaink you for listening and assisting

 

What year is your car? Which engine?

Would suspect a valve problem, yes, but at this point if you have no compression, there is no other fix than taking it apart so you will find out when it gets opened up. A complete used engine is usually cheaper/more efficient than repairing these engines, and according to MB the cylinder heads are not to be machined, so if it's just a valve, you would have to replace it and that's it.

 

Hi Joe and thanks for the interesting reply

This car I had new since 2008. It's an M273 engine, spec 961.

I've had many years of auto engineering experiece so if it's a valve job I'm willing to tackle it sometime. Thing is I've googled for a tear down manual and cannot find anything in detail other than hundreds of threads on the silly balance shaft issues all over the world. If there's no damage to the head, which I cannot say, it might just be worth the while to DIY as proper disassembly of the head from the block would be key to not having to machine. However, even if I have to machine the head I have a company that will make me a custom thickness head gasket.

I'm not really keen to change the engine with a used engine as in my experience one never know what's on the inside of such an engine. Back to mine, I see the major area to take care of is to not allow anything touch the cam bearing surfaces as a complete head replacement would be required if that should be damaged.

Any idea where I can get some more information on the disassembly of the engine?

Best regards

 

You say you have many years of auto engineering experience??? Not trying to be rude at all...... but if you are experienced why not do a cylinder leak down test so you can find out the problem. If air comes out the intake, it has an issue with intake valves. If air comes out the exhaust, it has an issue with exhaust valve. If air comes out the crankcase, it is leaking from the piston/rings. If your spark plug had a closed gap, most likely there is something from your intake manifold probably coming apart. The most common problems with the M272 and M273 is the valve guides get loose and cause the valve seats to get damaged or the intake manifold can come apart on the inside and can cause issues like you are having.

 

I did test compression but before I dig deeper and even pull the engine I turned to this forum as there are many helpful people here. Perhaps I did not choose my words properly and aimed to get more information on common failures.

You refer to loose valve guides as being a common problem and this is interesting. What I really would like to know, besides getting a tear down procedure, is why this happens, and what is the result. I have seen speculation that this is common with these engines but I have as yet not seen any website, video or posting with photographic evidence.

The only thing I get on the subject is many "experts" writing that this is a common problem. I would really like to know if there are anyone here who has experienced this problem and can tell us about this.

Incidentally I havce not heard of the intake manifold coming apart causing similar issues. That's interesting Do you care to give me more information on this please? What do I look for in regards to this problem?

Thanks for your input. I appreciate!

 

I guess you read part of what I posted. If you ruled out electrical faults, then you move to hardware. Compression tells you how good of compression the cylinder can hold. Cylinder leak down test can tell you where your problem is. But anyways, the valve guides can come loose causing the valve guide to move side to side making the valve seat oval instead of perfectly round. You mentioned that the spark plug gap was closed? It won't close on its own, I have had many intakes come apart and cause this. Intake manifolds use plastic materials for their moving parts.

 

I read your whole comment. Now read mine. I said the spark plug electrode was bent but not broken. Not closed. It is bent sideways. As for compression and leak down tests, thanks for the lecture. I will remove the intake and inspect through there. Perhaps a piece of plastic went through the intake and bent the plug electrode

 

saskloppers, did you ever figure this problem out? I am having the same problem with my 08 S550. Lower compression on 1 piston, about 105 PSI, all others around 155. Brought it to a shop and they said it needs a head job. I only have 65k miles on it so it seems funny to have such a big internal problem with low mileage. I have an 08 E350 with the M272 engine (which is basically the V6 version of this engine) and it has 145k and is running strong and smooth. I would be interested in your resolution.

 

Hi Hector

I can't believe it's been that long already. I removed both batteries after storing the car and have not been able to take a look. At the moment both my boat and Cobra is parking it in, so I need to make a plan sometime. Did actually arrange with a local shop to take it in and waiting to be advised when they have space. So I've been just too busy to bother.

If you get yours done before I've had a chance, please post a write up. And take photographs. If you could, get the replaced/damaged parts so we can do an analysis on what's the problem.

I'm a retired metallurgy engineer with decades of forensic work in the field so it would me most interesting to see what is found.

Looking forward to hearing from you

Sass

 

Will do. My plan is to run some fuel additives and changes all spark plugs to see if it idles any better. I currently have 2 theories: 1 carbon build up causing valves not to seat well and 2 something from the intake broke off and went down and caused mechanical failure. so for theory 1 the additives may help burn off some carbon. In a month or so i will bring back and have them retest to see if compression changes. Indy tech doesn't seem to think it will hurt the engine as long as compression stays above 100.

Thanks.

 

Hello Hector.

I think you are both on the wrong track and also on the right track. Firstly additives will not help. Then, changing spark plugs might be futile too, but I would remove and check each and everyone carefully anyway. That's how I determined there's something from the intake that has gone through the cylinder, when I noticed a bent electrode. A borescope check showed no other damage though, so it was not significant enough to even mark the piston crown.

Suspecting that something broke on the intake and went through the cylinder I'd give 1st prize. That said, on mine there is physical evidence that foreign matter entered and exited the engine. So my bet is that your shop is on the right track.

Your message prompted me to do the job, probably in the next week. With these engines extreme care must be taken when disassembling and assembling the heads as the camshaft and valve cover forms a unit with the head. It's possible to damage the head/cam when not removing correctly so I'll be making a tool to keep the camshaft and cover in place before removing the head bolts first. A tedious job I would think....

Good luck

 

I got this photo from knowbenz posted on his instagram. Problem is due to plastic bushing worn out on the intake and went through the cylinder and melted and stuck on the valve. This problem often happens on the first or the last engine because plastic bushing in side the ​​ intake manifold easy to get off.

 

Hi Hector

Oh wow! That adds a new dimension to the problem. One that might be easy to resolve

I'll take my borescope and look inside the engine again, this time at the valves. Possibly I could make a tool to break that loose off the seat if that's the case. Might mean turning the engine over by hand though, Nevertheless, even by removing the intake I should be able to reach it. Thanks!

 

One more photo from Benz showed that plastic bushing is melted and stuck on the valve, keep us posted for the finding and results.

 

Looks more and more like what I'm experiencing. Thanx Minh. Will post once I've done a check.

 

Minh, thanks for the reference, this is helpful! Do you know if it was the intake or exhaust valve that had the plastic melted on?

This is exactly what I was expecting may have been the problem. Thats why i was hoping that running it hard with some cleaning additives may burn up the melted plastic, but the additives probably wouldn't make it to the exhaust valve.

 

Usually, admission valves are bigger than exhaust ones so, the sticky one seems to be exhaust.

 

Hector that one is an exhaust valve. The higher temperature of those will melt the plastic more rapidly due to the cooling effect of gasoline. I suggest if you're going to run some solvents use O-Xylene and Toluene but be very careful of the oxygen sensors in the catalytic converters with anything else. I'm going to try and pry most off but need to first remove the intake. I'll remove those silly flaps totally. BMW people has been doing that for ages due to the same problem. Having been in auto engineering it's something we've done repeatedly so I don't see why it won't work on the MB engines. Sure, there's a bit of a torque drop off at low RPM high loads on the dyno but on the plus side, the engines I tested all showed gains on the graphs at high revs. Should you decide to do that, remove the exhaust manifolds and inject solvents into the ports. Try letting those soak as long as possible. Both chemicals have proven to dissolve Polypropylene plastics, which are used in auto parts.

At room temps these are not as effective except over an extended time. If you have the luxury of not having to make use of the car, take your time. This will eventually break down the PP molecules through perserverence. Besides, once running the friction will also burn the plastics off.

Read this article and research if you can.

https://www.researchgate.net/post/Wh...ganic_solvents

 

Plastic melted stuck on the exhaust valves, I think we can remove exhaust manifold in order to access the valve, using metal brush or chemical to get a rid of melted plastic as much as you can, once enginie able to run then it will completely burn the remaining plastic just in few cycles.

Keep us posted about cleaning methodlogy and result.

 

Im sure this is a dumb question, but is there anyway to get this cleaned off without removing the head?

 

NEVER machine a cylinder head that has 'overhead camshafts as that destroys the camshaft bearing alignment. Machining only the cylinder side to remove 'warpage' causes the head to have uneven thickness, and it WILL warp when tightened to the flat block. Refer to the factory specifications for allowable 'warpage.' These heads are quite flexible and use a lot of head bolts to clamp them to the rigid block.
Older Mercedes heads used replaceable cam bearing towers and shims under each tower as required to perfect cam bearing alignment. MANY perfectly usable overhead cam aluminum alloy cylinder heads (and engines) have been destroyed by ignorant 'machinists' removing metal from the engine block side of the heads to correct 'warpage.' That guarantees very rapid engine failure because the camshaft bearings then can have very high radial loads due to the unevenness of the head. This quickly leads to camshaft bearing and shaft wear, galling, seizure, breakage, and engine destroying.
The ONLY WAY to salvage a machined cylinder head is to use bolt the cylinder head to a thick (1" or more") torque plate and align bore the camshaft journal bearings (mounts.) In practice, it is far cheaper to buy a good USED cylinder head than the cost of making a torque plate and align boring the cam bearing mounts.

 

Hi @saskloppers, did you success to get the rid of melted plastic stuck on exhaust valve?

let us know result and methodology for this problem.

 

Hi Minh and thanks for tagging me.

No I have not attempted at all. Was going to but since the Covid-19 lockdown here we're working around the clock to keep everyone safe unfortunately.

Regarding the question of getting the plastic off without removing the head I have thought about the possibility of another solution and one which I will attempt before doing much work.

I am contemplating removing the exhaust manifold and using a small gas torch through the ports. This will heat up the exhaust valves, and if I can do this sufficiently the molecular structure of the plastic can be weakened as it softens. By doing that, and turning the engine over for a while before the temperature drops this might clear all the plastic off.

By repeating this process and taking care not to heat the cylinder head too much in theory a good result can be achieved eventually. This might clear the valve and seat sufficiently to allow proper seating. Even if the seating is less than desirable but there is still enough to control the compression/ignition process, once this is achieved it might be worthwhile running the engine for a while at idle to get the desired heat into the combustion chamber and expelling the debris. Then when the engine is cooled down, another test will show if the seats/valves have suffered any burning.

At least that way there's a chance of removing the debris and restoring without removing the head. And furthermore, should there be an indication of a lower compression with a leakdown test, but the indication is slight, it is also possible to reface the seats with metal polish and a drill. That will entail removing the camshafts. Something I don't have a problem to do. At least this will save a lot of effort and possible cylinderhead warpage by inproper removal.

Note that I have restored a burnt valve on my BMW M3 GTR, also a V8, in this manner. However I did not use valve grinding compound as it is too abrasive and you don't want that **** in the combustion chamber. I used a metal polishing paste called Autosol. And a bit of patience. However this engine is even today still running strong.

Maybe something to consider?

Stay healthy!

Sass

PS, if you attempt to do this, remove the spark plug and ensure the exhaust valves are in a slightly open position. You'll need the heat to flow around the circumference of the valve head. Too large opening and some areas won't be heated properly. I recommend opening a maximum of 1/8 inch

 

Hi Sass,

Definitely we shouldn't open cylinders head cover for this issue because too much work and we might get the same results more easier. Open cylinder head cover just help to identify problems, however it's not necessary for this case.

i think your solution will work, just a small piece of plastic melted and stuck on the exhaust valve then therefore as soon as exhaust manifold open then you can see what you need to do because access to the melted plastic stuck on the valve perhaps will not hard at all, even you can find a suitable tools to pry it off and it will burn completely when the engine able to fire.

i also interested in the modi you might perform on intake manifold such as get a rid of flap...it will help to avoid plastic drop into combustion chamber but also avoid vacuum leak because I encountered the car random misfire when idle due to vacuum leak due to rubber seal aged on these two flap rod.

 

Hi Minh

See on Amazon if you can get a small handheld gas burner with a flexible nozzle. For all the effort it's definitely worth a try. As for overheating the aluminium I may be overly cautious here as the head, with all the heat cycles that has gone through it, especially around the exhaust ports would have hardened properly so the chances of ruining something there is minimal. Yet it pays to be cautious.

As for removing the flaps it's fairly simple. But care must be taken not to ruin the intake. What I did is the shaft apertures that runs through the intake on the BMW and which connects to to the flaps had individual holes, which I closed up using JB Weld. (My favourite for automotive repair work). You want to make sure there is no bleed-through from other intake runners that will mess with the air fuel ratio. So close those up.

Replace the end seals or simply close them up. The arms on the vacuum actuators will have to be removed but ensure the electronics controlling the actuators remain plugged in. You want to fool the ECU into thinking that the actuators are still operative, else the car will give a MIL and possibly go into limp mode.

If you're lucky and there's no leak down once the job is done that means there's no burnt valve or seat surface. If there is, then you can remove the valve springs and retainers on the exhaust valves and proceed with the resurfacing of those. For that you will need something that can reach the seat. Apply the compound in a manner that is workable.

AND TAKE CARE WHEN REMOVING THE VALVE RETAINERS! You do not want the valve to drop onto the piston, thus you will have to rotate the engine beforehand to get the piston as close as possible to the top to prevent this from happening. I use an old spark plug that I modded with an air connector which I plug into the spark plug after inserting it in the aperture and tightening it. Make sure you have a decent compressor handy to ensure the pressure keeps the valve closed whilst removing the retainers.

Once completed and assembled I would rinse the combustion chamber out with a decent solvent to get rid of as much as possible of the compound before doing the test and inserting a spark plug to run the engine. I used Wurth brake cleaner. Worked well.

Ensure you do a leakdown test again and then assemble everything and start. If I am on the mark with my assumption the engine will be running sweet. With the flaps removed the intake sound might be a little bit different. Don't let that bother you.

Enjoy the Easter

Sass