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Broken M121.940-help

Posted: Mon 02 Jul, 2018 6:49 pm
by rens1976
Ok. So the little head gasket leak is a corroded water port. There are about 5 that need fixing. The mechanic says he is unsure if the head can be fixed-he’ll wait for the engineer’s diagnosis.
Equally as troubling is that it looks like the engine has been cooked in the past and one of the bores is marked requiring a rebore and oversized pistons. Complicating things is that when a TDC piston 4 sits flush with the top of the block however piston 1 does not. There is a noticeable lip like the piston is sitting too low. My thoughts were bearing or conrod collapsed when she was cooked.
So my questions are
If the head is beyond repair, are there many around and can i put one from a 190 on the 2 litre?

Are there many whole engines around that I could drop in?

Assuming everything in the bottom end is stuffed and I need to do the full rebuild including a timing chain what ball park figure am I looking at spending?

Lastly, is there an alternative?

Appreciate the replys

Re: Broken M121.940-help

Posted: Tue 03 Jul, 2018 12:40 pm
by Bartman4800
Can you post some pictures please? That will make it easier for us to give you some advice. (You need 5 posts minimum)

With the height difference between 2 pistons: if it really is that obvious I am pretty sure there are 2 different pistons in your engine.
Conrods do not collapse from heating up; steel only becomes soft above 800 deg. C
And a worn out bearing shell will not give you more than a 1 mm difference if that.

Sounds like your engine has been messed with in the past. Everything is repairable, but maybe an alternative is the better option.

There are reconditioned cylinder heads for sale, I think an american company does them.

Bart

Re: Broken M121.940-help

Posted: Tue 03 Jul, 2018 5:06 pm
by rens1976
Thanks for the reply Bart.
When I say piston one is not flush, it’s out by about 1mm. My thinking was likely the bearing.
I managed to put a call into Ron (mercmad) who did not have a spare lying round so put me in touch with Chris Stuart who doesn’t have one either. So I think a rebuild is on the cards.
Apparently these are a bit hard to come by :banghead:

Re: Broken M121.940-help

Posted: Tue 03 Jul, 2018 5:39 pm
by Bartman4800
Because these engines are also used in the famous 190 SL, parts are quite available.

http://www.mercedesengineparts.com/epag ... es/200/200

200 euro for a set of pistons is a bargain!

Here is another one:

http://mail.precisionintl.com/engine.as ... 4&EID=2562

A bit of reading:

http://forums.190slgroup.com/archive/in ... -6419.html
https://en.wikipedia.org/wiki/Mercedes-Benz_M121_engine

Re: Broken M121.940-help

Posted: Tue 03 Jul, 2018 7:19 pm
by rens1976
Thanks Bart
That will come in very handy.

Re: Broken M121.940-help

Posted: Wed 04 Jul, 2018 1:10 pm
by CraigB
Just adding some personal experience, albeit landrover, I had head problems and pulled it and thought - bugger, that bore is scoured I didn't think it got that hot. Then started cleaning tops of pistons and spotted that one was different. I had been running the car fine for say 100k kms. Presumably someone ran a hone through it and bunged just the one piston in after a seizure. Very real possibility that your car has had a piston stuck in there with slightly different crown height and could be from anything if it has the right bore. I agree at that price if you can get oversize pistons just go for it. Another possibility that i have used is if all the other pistons check out, you can sleeve just one cylinder and nothing wrong with using a good used piston, hone the lot and put in new rings - but you do need to check out each and every item is in fact ok. But there are options.

Cylinder head though, that can chew up a heap of cash trying to repair a dodgy one and worth putting the word out for a good used one - often heads from europe or countries that can't run water for fear of freezing are better. (ie. always run antifreeze whereas in Oz people get slack over the years and just bung in water.)

Re: Broken M121.940-help

Posted: Wed 04 Jul, 2018 7:21 pm
by rens1976
Thanks Craig
I will try and get a new head. Here are some photos from my old one.
The question I have is that I have found that elusive European head that is immaculate that is purportedly from the same motor.
However the part numbers don't match as you can see in the photos and the temperature sensor hole (I think that is what it is) is pointing in the oposite direction. The water ports and bolt holes look the same.
Does this matter?
For clarification:
The first 3 photos are the head I was thinking of getting and the last 3 are of the current one.
The one I want to buy has part number: 121 016 31 01
My current one has the part number:121 016 28 01
Thanks again for your replies.
Rens

Re: Broken M121.940-help

Posted: Wed 04 Jul, 2018 7:56 pm
by Bartman4800
Above the part number, you see an Eta sign, with 9.0 behind it. This is the compression ratio.
Compare the 2

The outlet for the coolant is a pipe that is screwed into the head. If you are careful you can loosen this and turn this around.

Mercmad might be able to tell you if there are any more differences between the 2 heads.
The one for the 1.9 might have a slightly smaller compression chamber; if you put that on your 2.0 it might even have a larger C.R. (but with modern fuels should pose no problem).

Where is the water damage on your head? The round water holes have steel inserts in them to direct the water. These can be replaced.
Your head might not be that bad. Let Mercmad have a look at it or someone else who knows these.

Bart

Re: Broken M121.940-help

Posted: Wed 04 Jul, 2018 9:12 pm
by rens1976
Thanks Bart. I did not know the compression was the other number. So obvious now! The old and the one I want to buy are both the same compression ratio so that’s a start. Will give mercmad a bell tomorrow. Although when I spoke to him yesterday, he did seem to think the head could be interchangeable now that I think about it but will clarify.

Re: Broken M121.940-help

Posted: Wed 04 Jul, 2018 10:52 pm
by CraigB
I wonder if someone more skilled than me can look up the part number on the epc. It would be nice to know why the different part no. - could be something simple and also often i think the epc will show superseded part numbers - ie. could show that one of those numbers is the new part number and therefore tell you it will fit.

Re: Broken M121.940-help

Posted: Wed 04 Jul, 2018 11:22 pm
by rens1976
CraigB wrote:
Wed 04 Jul, 2018 10:52 pm
I wonder if someone more skilled than me can look up the part number on the epc. It would be nice to know why the different part no. - could be something simple and also often i think the epc will show superseded part numbers - ie. could show that one of those numbers is the new part number and therefore tell you it will fit.
A great idea. I may mention it to Mercmad when I give him a buzz tomorrow (Surely he'd be all over it).

Re: Broken M121.940-help

Posted: Thu 05 Jul, 2018 10:18 am
by rens1976
Ok. A quick call to Mercmad this morning and it looks like the heads are interchangeable. Just waiting on one last lead here in Australia and if it comes up short I’ll buy the European head.
I’ll keep you posted with the rebuild.

Re: Broken M121.940-help

Posted: Thu 05 Jul, 2018 11:10 am
by Bartman4800
Just be careful Rens. Because a head looks shiny does not mean it is serviceable. Are all the metal insert present I mentioned earlier?
Is it crack free? etc. etc.

I would not give up on your own head first if I was you...


Bart

Re: Broken M121.940-help

Posted: Thu 05 Jul, 2018 2:45 pm
by rens1976
Bartman4800 wrote:
Thu 05 Jul, 2018 11:10 am
Just be careful Rens. Because a head looks shiny does not mean it is serviceable. Are all the metal insert present I mentioned earlier?
Is it crack free? etc. etc.

I would not give up on your own head first if I was you...


Bart
Hi Bart
I looked at my old one and I can only see one of these metal inserts and it is pretty well stuck in the head.
How many are there and are they available do you know?
I’ve looked in my workshop manual and can not find a reference to them.

Re: Broken M121.940-help

Posted: Thu 05 Jul, 2018 3:14 pm
by Bartman4800
With the pictures of the new head as a reference, It looks like you need 6 off.

Mercmad mentioned this years ago, ask him.
A engine rebuilder should be able to get them.

Items 6,7 8 and 9 in this view (for a 190SL, which should be similar)

https://www.niemoeller.de/en/190SL/190SL/B040/2/

If you give us your VIN number, people here can find out exactly which ones.

Bart

Re: Broken M121.940-help

Posted: Thu 05 Jul, 2018 7:37 pm
by rens1976
Thanks for your efforts there Bart. I definitely only have one of those in my cylinder head. The other has gone-I assume corroded away or removed by one of the previous owners when changing the head gasket. So I must get another.


Today the engine came out and will be sent to the machine shop tomorrow. Looks like it will get 40 thou (1mm) over sized pistons-giving me a massive 124 cubic inches.

Re: Broken M121.940-help

Posted: Fri 06 Jul, 2018 10:34 am
by Bartman4800
Just one more thing Rens:

Measure the overall height of the cylinder head. Your book should say what the stock height is.
Max. material removal is 1 mm.

I would replace all water diffusers if I was you. Chances are that they are half rotten, or the holes have become larger due to corrosion.
They are fairly cheap.

Bart

Re: Broken M121.940-help

Posted: Wed 11 Jul, 2018 9:01 am
by rens1976
OK. The engineers had a look at the cylinder head and in their opinion I should find an alternative.
Whilst the old one can be saved, the internal corrosion looks to be the killer with significant thinning of the alloy. So rather then be back at the machine shop again when those bits decide to let go, I've opted to buy what appears to be a very good one from Europe. UPS can deliver in under 5 days, so I've gone with that option. It should be at my front door on Monday.

Re: Broken M121.940-help

Posted: Wed 11 Jul, 2018 3:19 pm
by CraigB
Well done - if it is a really good head maybe you can scan it and then 3D print some new ones!

Re: Broken M121.940-help

Posted: Wed 11 Jul, 2018 7:00 pm
by rens1976
CraigB wrote:
Wed 11 Jul, 2018 3:19 pm
Well done - if it is a really good head maybe you can scan it and then 3D print some new ones!
I wonder what that whole process would cost?
I get the impression there are not a lot of 200's around in Aus so it may be a loss making exercise.

Re: Broken M121.940-help

Posted: Thu 12 Jul, 2018 11:02 am
by Bartman4800
I have been thinking about a head for my 220Sb engine.

I asked around, the scanning was gonna cost a couple of grand, but that includes the transfer from the point cloud to a useful format for a 3D CAD program.

I work with SolidWorks 3D CAD on a daily basis, we can generate an IGES file that a machinist (not an Engineer - don't get me started) can use to program his 5-axis mill.

New scanners are getting cheaper and cheaper, in 5 years the scanning can probably done for under 500 aud.


Bart

Re: Broken M121.940-help

Posted: Thu 12 Jul, 2018 8:40 pm
by Aegean
Variations in part numbers are often as a result of different compression ratios. The following table applies to 190SL engines, but I dare say the 121.940 probably followed the same rules.

190sl Casting numbers

121.921

121 010 38 20 Most common
121 010 34 20 7.5:1
121 010 25 20 c.1955 8.6:1
121 016 11 01 Factory replacement engine

121.928

121 010 61 20 8.7:1
121 016 16 01 8.7:1
121 016 26 01 9.0:1

Re: Broken M121.940-help

Posted: Thu 12 Jul, 2018 8:43 pm
by Aegean
rens1976 wrote:
Wed 11 Jul, 2018 9:01 am
OK. The engineers had a look at the cylinder head and in their opinion I should find an alternative.
Whilst the old one can be saved, the internal corrosion looks to be the killer with significant thinning of the alloy. So rather then be back at the machine shop again when those bits decide to let go, I've opted to buy what appears to be a very good one from Europe. UPS can deliver in under 5 days, so I've gone with that option. It should be at my front door on Monday.
Ask the supplier to have the head checked for softness. There is a simple ball test that can be done. If it is soft, it is worthless.

Re: Broken M121.940-help

Posted: Mon 16 Jul, 2018 6:51 pm
by rens1976
Ok. The head arrived from the Germany today and looks a treat. It even had the little fluid direction things inside. Looks like it came from the factory last week. I'll take it to the engineer's tomorrow for their assessment.

Re: Broken M121.940-help

Posted: Mon 16 Jul, 2018 8:17 pm
by Bartman4800
Sorry to be a nag, but please stop using the word "Engineer" when you actually mean a machinist.

An engineer is a person who went through University and got a degree in Engineering, be it Mechanical, Electrical, Chemical, Avionics, Mechatronics etc.

I know in Oz and other English speaking countries the word has not any more value than a plumber.
But believe me that the ones who can rightfully hold the title have studied long and hard to do so.


Rant over ... :snooty: :happy3:

Bart

Re: Broken M121.940-help

Posted: Tue 17 Jul, 2018 7:28 am
by rens1976
Bartman4800 wrote:
Mon 16 Jul, 2018 8:17 pm
Sorry to be a nag, but please stop using the word "Engineer" when you actually mean a machinist.

An engineer is a person who went through University and got a degree in Engineering, be it Mechanical, Electrical, Chemical, Avionics, Mechatronics etc.

I know in Oz and other English speaking countries the word has not any more value than a plumber.
But believe me that the ones who can rightfully hold the title have studied long and hard to do so.


Rant over ... :snooty: :happy3:

Bart
Yes, I do use the term inappropriately :Doh: . I was in fact referring to the machinist. Will not make that mistake again.
I have the same issue with the the term 'Doctor' when it is used by someone with an undergraduate degree practicing medicine or dentistry. The term should be reserved only for those with a PhD, but that's another story.

Re: Broken M121.940-help

Posted: Tue 17 Jul, 2018 7:24 pm
by rens1976
The machinists has the head and liked what he saw, so hopefully this space will be filled soon enough.
80F5B615-0122-4BFA-B663-F2F625B2F639.jpeg

Re: Broken M121.940-help

Posted: Wed 18 Jul, 2018 10:54 am
by Bartman4800
A great opportunity for the pressure washer?

Also, you have a lot better access to your carburetors.
You can get foaming carburetor cleaner that you can use on the inside and outside https://www.ebay.com.au/i/321876391811?chn=ps
I have good results with that. It will make the carbs come up as brand new, and will increase performance and idling.

I see you have 2 carbs, that looks like a 190 SL setup? Or did the sedan come with that as well?

Also: check your clutch throw out bearing, now you have access (and the rest of the clutch)

Bart

Re: Broken M121.940-help

Posted: Wed 18 Jul, 2018 7:25 pm
by rens1976
Bartman4800 wrote:
Wed 18 Jul, 2018 10:54 am
A great opportunity for the pressure washer?

Also, you have a lot better access to your carburetors.
You can get foaming carburetor cleaner that you can use on the inside and outside https://www.ebay.com.au/i/321876391811?chn=ps
I have good results with that. It will make the carbs come up as brand new, and will increase performance and idling.

I see you have 2 carbs, that looks like a 190 SL setup? Or did the sedan come with that as well?

Also: check your clutch throw out bearing, now you have access (and the rest of the clutch)

Bart
Thanks for the link Bart
I'll get some of that.
I have a new throw out bearing and the clutch is fine.
In the second series of the w110 the engine had the bore increased from 85 to 87 mm, giving it the 200 rather than 190 badge and was fitted with twin carburetors (the 190c had a single carburettor). They are Solex carbs.