[Thistlegreen380SEC]

Greetings members,
I currently own a 380 SEC, totally original.
I wish to keep the original engine block, but was wondering what would be required to transplant the pistons, cam etc from a 420 SEL donor car.
Would I have to bore out the block?
Just curious if anyone has tried this.
Cheers, William

 

[ianrandom]

Hi William.

If you have time to complete your profile, it helps to get answers. People tend to need to know what part of the world or market version & model of your car.

As to your question, I've never heard of this being done but I can see why it would be good to keep matching numbers on the car. Perhaps someone else will have an idea.

 

[bondavi]

The 420 motor has a 92mm bore versus 88mm for the 380, both sharing the same crank stroke.

 

[tusabes]

The cheapest thing to do , assuming you've found a good 420 engine , is to simply swap the 420 long block with your 380. Keep your original 380 stored away if this is a pristine car and you think it may have collector value as numbers matching when it comes time to sell , but in reality these are throwaway cars unless you'rs is mint

 

[Teutone]

Greetings members,
I currently own a 380 SEC, totally original.
I wish to keep the original engine block, but was wondering what would be required to transplant the pistons, cam etc from a 420 SEL donor car.
Would I have to bore out the block?
Just curious if anyone has tried this.
Cheers, William

1. keep at least the original 380 block for matching numbers.

For the Gen I transmission to work with a Gen II engine you would have to adapt the ring gear (different tooth count), plus the crank position sensor that sends the all important signal is different.
A GenI 500 intake with fuel distributor and same sensor set up can be used on the GenII 560 engine. But to make it run right takes quite a bit more.
GenII cars have different transmission housings/ mounting points, crank position sensor etc, so a GenII engine will not just bolt up to your GenI transmission and work.

Easiest and most cost effective would be to find and use a GenI 500 engine instead of the 380. That's pretty much bolt up, plug and play.

Please click "user CP' to complete your profile and check the 'New members welcome, please read....' announcement on top of the W126 page for 'how to.'

 

[Thistlegreen380SEC]

Hey, thanks for the reply.
I am very happy with the performance of the 380 and have done a timing chain rebuild about 10,000 km ago. The motor is about 230,000 km old. Still a lot of life left in her yet.
As always, I wonder about doing performance tweaks, even though I want to keep it totally original. That's why I wondered about the 420 V8, which I think was available in Sweden.
It's good to know that the 500 is basically a bolt in, plug and play operation, I might keep my eye out for one of these and just have it stowed away in the garage.
This 380 SEC is my first M/B, and my first experience of a V8. The body is pretty much corrosion free, having been shedded most of its life by it's one previous owner. I count myself fortunate to have this particular car, which confirms all that is good about the marque and the engineering that has gone into such a gorgeous old girl.
Cheers, William.

 

[Thistlegreen380SEC]

Hiya, Thanks for your reply.
The 420 conversion was basically me fantasicing, 'what would happen if I did this/is that possible'.
Anything is possible, but I may just look out for a 500 engine and do a straight swap somewhere down the road.
I am at an age when I really don't want to meddle too much with the vehicle's originality; once you start changing things, it's hard to go back.
I am extraordinarily happy and proud of what I have. The interior is pretty amazing for a vehicle that is 30 plus years old.
It's funny, you say that these are 'throw-away cars' - I am so sentimentally attached to this beauty, I could never part with it. Sentiment is one of those curious things, some things which are not worth a lot of money are actually almost priceless - this Merc was a gift from my father who is no longer with us. Hence I have to keep it in it's original form, and I have to keep it forever.
Being my first Merc, it is everything I expected from a vehicle builder with such a wonderful heritage.
Cheers, William.

 

[Thistlegreen380SEC]

Hey, thanks for this detailed info. I was reading in the July 2017 edition of Mercedes Enthusiast magazine about the 380 SLC (C107 SLC) and how it had the M116 V8, which was 3.818 cc. I wonder if this was the same engine found in my 380 SEC?
I confess I am a bit of a stickler for details like this - a Merc tragic!
Cheers, William.

 

[Thistlegreen380SEC]

Yeah, I'll definitely complete my profile.
I feel this forum will be a very useful and informative source of info for me in the future. Great to be a part of it!
Cheers, William.

 

[Teutone]

GenI W126 SEC, 380 & 500 build 1981-85, GenII SEC 420, 500 & 560 1986-91
The North America version of the M117 engined GenI 500 usually had a 8:1 compression engine with 184hp.
Higher compression versions for other markets had more power.
A rare M117 GenII M117 560 produced 3oo hp, the US version around 240hp.