4.5 '117' engine build
 

I will start a new thread for the engine build on my '72 108.
The timing chain broke a year ago and broke the left valve cover and the head. I will need to look for other damage too, but I hope the block is ok.

I recently acquired a complete engine from a '76 450SL.

If the only thing broken on the 108 is the left head, then I may just pull the heads, get new valves, check the guides, and do a valve job. I am sort of thinking of rebuilding the engine, but since I only have so much time I will likely not do that.

Other than obvious replacement parts, is there anything that should be replaced while things are apart?

Are there any upgrades that could be done? I am thinking euro-spec cams would be great. Do the ports have any areas that need porting?

Any other suggestions?
Thanks,

Csaba

The 76 engine you have may be hydraulic cams & lifters so for even burning on both banks you may want to swap both heads if so (or just convert the new head to mechanical by swapping in the old cam, if it's still straight, and the cam towers and ball studs). The heads may be different as far as combustion chamber volume too - may want to measure the volume of them with a syringe and veg oil. Whichever is smaller volume would be a better compression ratio.

The '76 engine will be a K-jet engine so the heads will be different-the fuel injector ports are different and they have air injection ports that you would want to close off. I think the combustion chamber is smaller-they are 45cc. Would be a good time to switch to Megasquirt. I would not touch the bottom end unless you have good reason to. Performance head work would be very expensive and for a low compression engine probably not worth it. These engines have small valves for the displacement so that would limit possible flow increases.
Why don't you just install the '76 engine? You will have the same issues to deal with either way.

If that 76 motor is intact, definitely keep it as-is and just use it. The wiring change over is minor.

Keep the original exhaust manifolds.

-CTH

Hi Tony,

>The '76 engine will be a K-jet engine so the heads will be different-the >fuel injector ports are different

Is there a way to install a D-jet injector into a K-jet head?

>they have air injection ports that you would want to close off.

No A-I on this one, maybe that was California only.

>I think the combustion chamber is smaller-they are 45cc.

Interesting, I thought both had 8:1 CR. At least that is what the 'MB production models' book says, but I've seen a lot of inaccuracies in it.

>Would be a good time to switch to Megasquirt.

One thing at a time! :-) But it's definitely under consideration.
However, since the car is very original, I wonder if it would hurt its value if it had an FI that most MB mechanics would not be able to work on...

>Why don't you just install the '76 engine?

I am definitely considering it, I just thought it may be easier to just swap heads. Plus it would get a valve job.
If there are holes around the timing chain lower down then I may have to!

Do you know if the engine can be removed by itself, or does the tranny have to come out with it?

CTH, thanks for your comments!

Csaba

OK, thanks, I'll check. I assume going hydraulic would be better because of less maintenance.

Csaba

I doubt Megasquirt would affect the value as long as the wiring harness was not cut and everything could be put back to original. D-jet injectors fit in K-jet ports-they just fit differently, the pintle caps need to be changed and some modification would be necessary to the fuel rail and hardware-it's not a direct swap over. The K-jet .985 and .986 use hydraulic cams. Both engines have 8.0:1 cr but the d-jet .981, .982, .983, .984 engines have flat pistons with a negative deck height of around 3.15 to 3.6 mm. The .985 and .986 engines have dished pistons with 0 deck height. From calculations it seems that both engines have 45cc heads. You could use some 3.5 heads and increase your CR.
You can pull the engine without the transmission but putting it back together might be a challenge.

You're better off pulling the transmission with the engine. Also, on the 108, you'll want to take off the hood. I'd also pull all accessories with the engine and swap them all over on your shop/garage floor. For the torque converter bolts, those are probably easier to replace one the "new" engine and transmission are in the car. That way the engine is stationary when you turn the engine over. Just don't forget to put them in before starting the car.

Best Regards,

David

Guys, thanks for the info. Yes, I figured I need to take the hood off, since it won't go vertical.

Csaba

Here is a pic of the engine damage. The camgear actually broke off the cam! Ouch.
I started disassembling things and plan on pulling the heads off before I decided whether to replace entire engine or just the heads.

Csaba
72 280SEL

If your '76 engine is good why mess with tearing down the damaged engine? You will have to take off the timing cover and oil pan to inspect for damage -both difficult with the engine in the car.

I did not know I would have to remove the oil pan. You are right, I better start assessing the condition of the '76 engine.
Thanks,

Csaba

What should I replace on the engine before installing it? Front and rear crank seals, water pump, valve cover gaskets. Anything else? Timing chain? It's tensioners?

Thanks,

Csaba

Yes to timing chain, yes to timing chain tensioner rail. If the timing chain guide rails are plastic, yes; if they're aluminum-backed rubber, no. You may want to check the valve guides, and replace as needed. You should do the valve stem seals "While it's out"

Spare engine test
 

OK, I did a leakdown test on the right side cylinders of the spare engine (the one form a '76 450SL), and they all had ~70% leakdown - ouch. 0% means there is a perfect seal, a used engine usually will have ~10 leakdown. 70% is really bad. I don't know that if I started the engine if the rings would re-seat. I kind of doubt it.

Interestingly I noticed that the engine had new camgears and timing chain.

So now I am considering using just the heads, or maybe just the left side head on the original '72 280SEL engine.
I looked at the injector holes, and they are different. Likely they can be made to work with the right size injector seal. Does anybody know for sure what is needed?
Alternatively, I think a friend has a set of mid 80s 380 heads. Would those work?
Thanks,

Csaba