timing chain problem - Mercedes-Benz Forum

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post #1 of 5 (permalink) Old 07-22-2006, 07:03 AM Thread Starter
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Exclamation timing chain problem

I have an a class a140 2001 model which the timing chain has snapped ! Could somebody tell me or know the best way to fix,Also would the engine have to be removed to do it ? Also advice on the timing marks .
Have only covered 44k and the mercedes dealer in southampton has not been very helpful !
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post #2 of 5 (permalink) Old 08-11-2006, 05:00 PM
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If the chain has SNAPPED you have done damage to the cylinder head and Valves..One MUST remove the head to inspect for damage....

I Would like to know how/why a chain SNAPPED? Pics?
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post #3 of 5 (permalink) Old 08-12-2006, 11:42 AM Thread Starter
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timing chain nightmare

Thanks for your comments on my timing chain problem which we have found the cause of all the trouble,The chain tensioner had seized which caused the chain to snap! The damage was only one bent valve and the pistons were fine luckily for me .
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post #4 of 5 (permalink) Old 03-22-2009, 02:40 PM
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Hi I have a A140 too with a snapped timing chain. First of all don't be fooled into thinking that one valve has bent. I have all 8 of mine bent (7 are not visible to the naked eye). What happens is the tensioner seizes and then the chain slips one tooth and then this is enough to make all valves make slight contact with the piston. One valve will then make a solid contact with a piston and bend and then embed into the heads side wall. If you (when the head is removed) removed the cam leaving all the valve springs intact you can pour petrol or a thinners down the ports (don't worry about petrol/thinners leaking from port to port as exhaust ports are joined with a small hole) and if petrol/thinners seeps from the valves then there bent. It is not a case of regrinding them as some may tell you. The gas tight seal will never be tight again. make sure you replace the valve guides, washers under spring and valve stem seals as they will be hard an oil persihed.The tensioner can be fixed by unseizing as mentioned in a vice but if it seized once it will under oil pressure seize again. Renew it as you will suffer with snapped chain again. If the old chain is around the lower crank sprocket (unlikely) then you can buy a new chain and join it with a zip tie (cable tie) and feed it on (best done with 5th gear engaged and 1 wheel jacked off the floor) and rotate the offside front wheel backwards. If the chain is slack it will jam up and you will have to start again. The other option is get a long brazing rod (mine was about 3 foot long) about 1mm diameter and lay the chain onto of the rod and balance it so the chain is straight, now aim the chain down in between the tensioner, above the lower groove. It is much easier if you feel until it stops then get a friend to rotate the wheel as mentioned earlier backwards and this will take up the chain. Now it gets a bit tricky, if you have access to a magnetic pickup tool then you can feed it into the side of the lower groove and with a little bit of gentle coaxing hook the end of the new chain. This takes a lot of patience as if you brake or drop any item in the chain cavity, you will have to drop the engine to remove the timing chain cover to be sure of removal of the bits lost. once snared you can gently pull the chain up through the lower tensioner groove and zip tie the 2 ends to prevent loss back down the hole. Once you have refitted the head make sure you have lined up the tensioners lower arm with the locating pin that goes across the hole where the cam cog lays, the tensioner arm has a u shaped molding to accommodate this. Timing marks are on the Crank pulley OIT as Top Dead Centre or TDC and this will align to a molded lip on the side of the Crank case. On the cam just behind the Cog is a mark to denote TDC on the cam, this aligns to the 2 little points onto of the cam bearing journal cap. If your set up straight the cam lobes on cylinder 1 (Nearest the Chain) will be facing upwards. If you have oiled up any moving parts with fresh oil in the head then your ready to rotate the engine 2 or 3 times to make sure your timing marks align. If they didn't your might have started up and smashed the valves again. Lastly the tightening sequence for the headbolts is to confusing to explain but the first stage is 35nm or 26 lb/ft and stage 2 to a further 90 degrees and finaly stage 3 another 90 degrees with an angle gauge. I'm not an expert but this is the method i used renewing all gaskets that need replacing and of course new head bolts too. Good Luck
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post #5 of 5 (permalink) Old 03-23-2009, 01:33 PM
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With the help of one owner I have just added information on the timing chain problem, My cd also has files on the replacement but that is to replace an existing unbroken chain, not one that's already broken. Mercedes-Benz Obviously live in cuckoo cuckoo land because they say the chain will out live the engine, what a pity the engine doesn't out live the car! 40,000 miles that a disgrace to any manufacture a rubber composite belt can be expected to last longer than that.
it's worth noting that both of these cars are A140, early A140 had a problem with the cain tensioner, if you own one it really would pay to get it checked before the problem arises.
What a pity MB didn't instigate a recall, there again they don't consider there are any problems on any of their cars! Non so blind as those who cannot see, or in this case don't want to!

Last edited by lofty; 03-24-2009 at 02:20 AM.
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