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Old 09-19-2002, 01:21 AM
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Join Date: Sep 2002
Location: Mancos, CO
Posts: 11
Question Timing chain broke. Interference engine in '86 420SEL????

I am looking at an '86 420SEL. It's timing chain broke (go figure has 240k on it). I am assuming this is an interference engine (valves hit pistons), but would like to know for sure. Also would like to know a ball park figure of how much rebuilding the engine would be if I do everything myself (excluding machine work). I would appreciate a quick response to my question, as the car is up for auction in 2 days. Thanks for your help.

Dave Henneman
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Old 09-19-2002, 08:22 AM
engatwork's Avatar
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 11,967
It is (was?) an interference engine.
Not having rebuilt one of the V8's I would throw out a figure of a couple grand to rebuild it if you do the majority of the work yourself and use a reputable machine shop. It will obviously be based on how many pistons/valves and rotating parts you will have to purchase. Maybe someone that has recently gone through one of these can provide a more accurate number.
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Old 09-19-2002, 10:15 AM
Posts: n/a
You really have to look inside the engine to come up with a close estimate. My mechanic friend had a 420 sel that the timing chain broke on and one cylinder wall was damaged when a piston shattered when the chain broke requiring a new silicone sleeve. This can push the price upward. Other than that, it was the normal parts and over 50 hours labor. While you are at it, change the valve stem seals at that mileage and have the heads checked for valve guide wear etc . When he was done with the repairs the bill to customer was about $3500 US
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Old 09-19-2002, 10:24 AM
blackmercedes's Avatar
Just a guy
Join Date: Dec 2000
Location: St. Albert, Alberta, Canada
Posts: 3,492
Not many people repair the M116 4.2L V-8 if they let the chain break. Rebuilding and parts costs are far too high. Unless very little damage was done, you're probably looking at a very big bill.

If you want a really inexpensive (relatively) solution, shop for a used engine. This is risky, as the engine's history may be questionable.

The next alternative is a rebuilt "crate" motor. This is probably the most common way to solve the problem. MB sells engines that are rebuilt, but so do others. Metric is just one that advertises in the Star. I have no expertise in these services, but a search will probably bring back lots of threads.

You might be able to buy a "new" engine from MB. This is going to be the most expensive route, if available. Not many go this direction given the low value of the rolling 420SEL chassis.
John Shellenberg
1998 C230 "Black Betty" 240K
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Old 11-11-2007, 05:14 PM
R.O.M.O.A.S's Avatar
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Join Date: Nov 2007
Posts: 9
I am doing mine right now and for some reason I lost the intake valves only on the drivers side head.
I am replacing all the guides in the cover because that is what failed and caused the damage I do my own machine work. I have so far $800.00 in it and that's all the guides a complete engine gaskets set to reseal the engine I surfaced the head and did the valve guides replaced the 4 intake valves all other is in great shape. I am servicing the pass head to do. I feel heads on these should be done in a set.
but I did allot of shopping around as well I feel the trick is if your not sure what to do ask a pro a mess up after doing all this work if done wrong will most likely coast twice as much if not right or destroy the engine.
my input.
1987 420 sel
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