Well I finally got the 420's motor taken apart far enough to see why it would not start... passenger upper guide broken, driver upper guide beginning to come apart, timing chain still intact but quite loose, driver head appears damaged.

The head has four valves that appear collapsed as the rockers were sitting beside the valve springs! Each valve is an exhaust side... so there was no compression on that side when trying to burn fuel. Luckily no parts fell down into the crankcase, everything was sitting up top. Is this motor an interference motor?

So, what should I do in this situation? I could get a 560 or Euro 500 motor for about $1000 to drop in there, but it would still need timing chain done almost certainly. Then on the other hand, if I rebuilt the entire top end on the 420, it would be basically new minus some wear on the bottom end. I don't see why I couldn't get 400-500K from a M116/7 with a rebuilt top end. I'd have Metric probably do the heads.



Thoughts/opinions?

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Yep. it is an interference design. Sounds like classic chain slip due to broken guide getting in the way. Depending on what you want to spend, and if you want the car to stay original, it can be rebuilt. You may have/probably will have damaged piston crowns, and possibly damaged piston bores. A complete tear-down and inspection will be necessary, before you can really determine the cost of the rebuild, unless you just decide to go for broke and do it all. Piston rods are strong enough that probably no damage there, but not impossible. I've seen reports of valve pieces rattling around on top of piston doing all kinds of damage before the engine shut down, so don't be surprised. I have a picture somewhere of a piston with holes knocked in the crown from the same thing... Guess where the pieces end up?

I foriginality is not a concern, I'd recommend a reman exchange from someone like metric motors... Advertised price for a long block is roughly 5grand US...

Good luck!

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RM Smith
1988 560SL

"Where is it again that we are going, and why are we in this handbasket"?

Out of the few hundred we have repaired we have never had a piston problem.

What a waste it would be to replace a whole engine for 4 valves being bent. I have a 420 that has had it happen twice, The last time was 400,000 miles ago. He has 850,000 on it currently, drives close to 100k a year and does the rails every year.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Well I forgot about a yard that has a 140K mi 560 motor for $200 out the door... intake to oil pan. Car has sat for about six years but I'm going to look at it tomorrow. It's cheaper than all the gaskets I need alone.

If it is in good shape, I'll have a new chain rolled into it along with the rails and a tensioner.

From a fiscal stand point it isn't worth the cost to rebuild this 420 motor.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

This sounds like a deal. And you aren't kidding about the gaskets. I added them up and if you can't get a very substantial discount, they're very, very high, a significant fraction of the cost of a rebuilt head!

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86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm

I have an account with a few dealers, so I can get those parts for good prices, but I'm not sure I'd want to rebuild the top end or not. Confidence isn't here for a multicam motor yet. If I can't, then I'd have to pay more for the part to be under warranty (understandable). Not to metion I'm not sure how far gone this M116 motor is currently.

If I get this 560 motor, I'll install new seals all over before tossing it in... front/rear mains, oil pan gasket, and the like.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]