If the chain breaks the upper left guide and the pieces fall into the chain and it jumps timing you could have at min 4 bent valves and at worse , a completely destroyed motor ive seen in myself , broken valve head punched a hole in the side of the cylinder, or broken camshafts

I am wondering about extracting the pins the secure the guides.

I read somewhere that the threaded holes in the pins match the valve cover bolts - any truth to that?

Anybody know the specs on the valve cover bolts if so?

And stop it with the horror stories of broken guides and bent valves! I'm paranoid enough as it is...

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1988 420SEL

The thread in the pins is metric. I extract them with a bolt from home depot/socket/nut. If something goes wrong with the thread you dont ruin your valve cover bolt.


W126 service manual:
https://www.startekinfo.com/StarTek/outside/12253/?requestedDocId=12253

Exactly: plan is to drive to Home Depot and take out a valve cover bolt (inside, so it doesn't drip oil on the Home Depot parking lot and, more importantly, down the side of the engine!) and go inside to buy matching bolts in various lengths.

That is, if the valve cover bolt is the right size.

If it isn't, I'll be standing in the driveway wondering whether to reassemble the car or call a friend for a ride to go get the right size.

Thanks!

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1988 420SEL

Oh yeah, thanks for the link to the W126 service manual. I could never make the flash version work for me so I got the CDs of that and took out all the PDFs and combined them them by section.

Is there a page ref for the specs on those threads?

And if anybody wants the PDFs, let me know and I can send them along.

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1988 420SEL

You can use a bolt and washer with nut to remove rail pins , thread size is 6x1mm, use about a 30-40 mm fully threaded bolt and find a spacer so the pin can be pulled thru , a guide dowel can work , or buy a aftermarket pin tool (press tool) you can find on e bay, you can find the chain guide there too that attaches around the right head sprocket that allows you to roll in the chain

Thanks for the specs! Beats the hell out of taking to all apart to find out, then having to go shopping for the bolt.

Much appreciated.

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1988 420SEL

So the chain looks fine - maybe new. I'm going to check it for a master link. Just because of the age issue though I want to change the guides and oilers.

But it isn't obvious to me how to get those guides out without removing the sprocket wheel.

Maybe tensioner out, then tensioner guide, then the other guide?

But then what about the driver's side?

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1988 420SEL

I recently did a 560sl motor and I couldn't get the upper guides out easily but I thought I could get the guides out, ended up removing the gear, after you loosen the 24mm nut you can use a rubber hammer to tap it off, and you can heat it up and it will also slide off hot , after retorque to 45lbs ft of torque

Yeah so, I can say definitely that on this engine you need to take the sprocket off to get the guides out. But I didn't do it.

It was easy enough to pull the pins on the guide using a Home Deport sourced M6 w/ some washers as spacers but as I was fooling around doing this, the chain got so slack that I just plain chickened out! I was convinced that it was slack enough to fall off the crank shaft sprocket, leaving me pickled. So, while I could / should have gone ahead and pulled the sprocket off and pulled the guide out but instead I put it back together and had a looked at the relative positions of the TDC on the sprocket versus TDC on the pulley on the front of the engine.

Yeah. Should have done that first, right?

Anyway, TDC on the camshaft sprocket corresponds to 8-10 degrees ATDC on that pulley.

So am I jumping too far to a conclusion here thinking this indicates a pretty well stretched chain? And that I should just face the facts of life here and replace the whole thing - chain, tensioner, sprockets as well as guides?

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1988 420SEL

5-6 degrees is iffy, 8-10 is time for a chain, etc. strongly suggest do not start it again as that's the greatest stress on the chain.

I just did my wagon 104 engine with 210,000 miles ex roadside assistance car , and my chain was stretched 12 degrees, after replacement got back low end torque and pulls strong in every gear starting at 3500 rpm instead of 4000 rpm

So I got it mostly apart here, and everything was going well until...

Tensioner guide pivot. There's a hex-headed plug there - right where it should be for the guide to pivot on - there's no pin in there.

In order to see in there I'm going to have to pull out the radiator, which I do not want to do.

Can someone please explain to me what is in that hole and how to get it - and the tensioner guide - out of there?

Thanks in advance.

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1988 420SEL

This is not what I was expecting!

How does that thing come out, and then go back in?

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1988 420SEL

Panic first! ..that's my motto.

Once I chilled out a little I figured out that the tensioner guide pivots on a hollow pin that is kept in place by the short hex-headed bolt. An M6 bolt threaded into a piece of tubing made a nice soft extractor. Pin is now out and back in, locating the shiny new guide!

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1988 420SEL