420SL Engine Damage - Rebuilding

[JacquiIngram]

My wife purchased an 87 420SL in July with full service history etc. Mileage is 59,000 and at the weekend the timing chain cracked the camshaft casing. While the car is under warranty we are very disappointed with what has happened. We would like any advice as to whether this is a (common) problem. Also what work we should ensure the garage carries out to the engine. For example should all valves be replaced or just those that are bent? Should valve guides be replaced? Should both sides of the engine be rebuilt or if only one side of 'V' has suffered damage is it only necessary to do that side? Someone has suggested that it is possible that once the top of the engine is rebuilt it can then put extra strain on the crankshaft? Please can you offer any help and advice? Thank you.

(Edited by JacquiIngram at 10:22 am on Sep. 28, 2001)


(Edited by JacquiIngram at 10:25 am on Sep. 28, 2001)

 

[Neil Eglintine]

420SL Engine Damage

Ha! Just been reading some stuff on 420 timing chains on the www.mercedesshop.com forum. I have no experience or expertise on this matter, but it appears to be a weakness on this engine.

No doubt our more expert contributors will comment on this.

 

[David Halsey]

420SL Engine Damage

All cars with chains have the ability to break, as do timing belts.
However, with a chain there is an aubible noise when the chain is on its way. They are tensioned by hydraulic means. For a chain to snap at that mileage is extremely rare and suspect.
You should check the history carefully.
As to the work, if only one bank has been damaged then that is all that is needed to be fixed.
Make sure that a new tensioner has been fitted during this repair

 

[Andy]

420SL Engine Damage

Hi ya,

Sorry to hear of your plight and to hear of people giving you such poor information. Whoever suggested that once you have rebuilt the top end this will have a disatorus effect on the crank, obviously does not have a clue. Only if the bottom end ( crankshaft & bearings) is weak or got a problem in the first place could any problem occur.

Any way to the problem at hand. It is unusual for a timing chain to break. Especially a duplex chain as fitted to your 420. I agree with David that usually timing chain problems are usually accompanied with noises.

We have just carried out repairs to a 380v8 where the timing chain has jumped. Before jumping in, remove both rocker covers. Check to see if any of the rocker arms are loose. If even one is loose on each bank. Then both cyl heads will require removal. In our case only one bank required removal. We double checked the other by carrying out a cylinder leakage test.  

The engine will have to removed. Its just easier with an SL, due to the sump being cast in one piece.  Other wise its a problem to remove things like oil pumps to remove the front cover etc. Also the SL does not have an abundance of space. Once the front end of the engine is striped & check all the timing chain gears for wear & the rails. When the cylinder heads are striped it is relatively easy to check for wear in the valve guides. At 60k I don't think the valves guides would be worn.

The repairing garage should ( I would only take your vehicle to somebody with extensive knowledge & tech information, as taking it apart is never a problem. Rebuilding can be) replace all bent valves,valve seals,timing chain & tensionser, all timing chain rails, broken casing. The oil pump should be check for any debris ingress. Although if the timing chain has snapped then there would not of been much time for it to suck up an debris.

Once rebuilt. Check the vehicle runs correctly. Take for a road test. If possible. Be vague about when you are coming to collect. That way when you arrive. The vehicle may be cold. So you can check cold start running as well as hot. Making sure there are no hidden supprisises when you wake up the next morning.

I hope this has been of some help.
If you want me to quote for the work, then contact me directly via my website or the phone number there.

Regards Andy@www.mercedesservicing.com

 

[Andy420sec]

420SL Engine Damage

59,000 miles? The timing chains are virtually bomb proof. I would get a professional to check the car out and see if the mileage is straight.

Naturally, if a dealer sold you a car with an iffy mileage (heaven forbid) then you would be better asking for your money back and starting again.

Having just replaced the camshafts, timing chain and guides on mine I wouldn't bother doing it again...