After having experienced timing-chain guide disintegration, Is it possible, short of pulling the heads, to determine if valve & piston interference (and any resultant damage) has occurred? (I'm trying to decide if replacing the chain and guides is worth the time and effort.)


The engine still cranks (slowly and reluctantly). This is with a '91 420SEL with 130,000 miles on it.

Thanks.
-Brett

You can bring the engine to TDC on #1 and see if the marks on the cam tower and thrust washer align. That will tell you if the chain jumped - the marks will be 'way off. Look at closely at the rocker arms with the cam lobe up and you may see that the exhaust valves are not closing all the way. If either is the case, you have bent valves and the head needs to come off.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Thanks for the tips.

I'm pretty sure I know what a "cam tower" is, but what is the "thrust washer"? I set the engine at #1TDC and looked for anything on the camshaft that might be a timing indicator. I did notice some "ears" pretty much in the middle of the length of the shaft, which didn't seem to serve a mechanical function. If these are any indicator, they are not synchronized.


Assuming the exhaust valves are the rear valves on each cylinder (is that correct?) I did find that the engine has some closure issues. On cylinders 5 and 8, with lobes pointing up, I could stack up feeler gauges to 1/4 of an inch and easily slide them under the cams.

So, assuming that this indicates bent valves (safe assumption right?) what other damage may have occurred? Is it a matter of replacing valves, timing chain and guides (along with related gaskets and seals)? Or is there likely to be more than that? Do pistons and/or cylinders typically suffer damage in these situations?

-Brett

The thrust washer goes between the sprocket and the tower. It has a notch that should line up with the line on the top of the cam tower. Lining it up is sort of a moot point, since you have bent valves.

On the 380 and 420 that I have repaired, no damage was done to the pistons. But you won't know until you get your head off.

You have the rest basically right. You need to replace the three rails in the heads, the plastic bits in the cam oilers, the timing chain, and the tensioner. As I recall the machine shop bill for the head was about $500, but they were able to supply four used exhaust valves. I think that the other parts and gaskets were about $350. I also dropped the pan and cleaned out some plastic pieces.

The alternative is a used head, but that is a crapshoot. All that is guaranteed is that it is "rebuildable." A used engine is another alternative. Make sure the cams are good, as they are expensive, and you would have to do the rockers as well.

The job is a lot of work, but nothing complicated. I think that the book for R/R one head is 17.5 hours. Be sure you have #1 at TDC before you unhook the chain, and good luck.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Thanks Chuck.

I'm thinking now that this car will become a parts donor for my others (current and future).

-Brett

i had the same issue what i did was use the spring compressor for removing the rocker arms and removed the spark plugs used compressed air in to the plug holes and found 4 bent valves in the drivers side head i removed bolth and rebuild them my self compleat i have a machine shop so no big deal.
i lost guide rails as well so took it all apart and did them to a little time consuming for never working on this kind of car befor.
i purchased a mitchel on line for the tech manuals i have found other then torq spek's the rest was usless to me it did not show timing marks at all as to the relatchion to what marks wher on the cam bearings and did not state that the small v in the washer behind the cam gear was a timing mark so i called MBI in portland OR. and they told me this.
nice people there.
i am having a delema as to the vacuum lines on the engine now as to wher they go right now and trying to find a diagram for it .
as to your idea of parting the car out it is you choice it depends on what you have in it.
i got mine from craigs list in portland OR. for $500.00 and towed it home because of the chain i got a total of $550.00 in new parts and my labor i got the car for my wife a sound car other than the issues above it is cherry so i decided to fix it.
i guess you have to look at the investment you will have in it when finished and what you can get for it after. i feel they are worth it and planning on getting another one. they are not that bad to work on kinda fun from other cars. but plan on buying some special tools you will need and get them don't try to micky mouse tools to work you will total head bolts like i did a few bucks for the offset wrenches are worth it. and take you time dont rush. if you build your own heads change the valve guides as well at least for the bent valves a must easy to do and cheep i would do bolth heads as well this way you know what you have and do all the rails even for the oil pump chain.
after all this i bet you will find that you will keep the car good luck if i can help just pm me i will do my best to awnsew any questions you might have.
i will be done with mine in 2 more days pending vacuum diagram if i can find hope this helps you.

1987 420 SEL V-8 Gas. black

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1987 420 sel