My '91 350's motor is making some noise from the upper chain guide area. It is an intermittent plinking sound, which is worse when the motor is cold. You can hear it in this video.

We took the valve cover off and found that the upper chain guide can move side to side quite a bit.

From this:



To this:




Is this normal? Should the guide be able to move, and where should it sit? Also, how tight should the chain be in the area pictured with the engine off? Should I be able to wiggle it just a bit by hand?

Thanks,

-Jason

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

I do not believe the chaing guide/guard is supposed to move at all. When I got my car mine was loose and making noise. I tightened it up and no more noise from there. But, I have an older vehicle with a different engine.

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84 300D, 82 Volvo 244Gl Diesel

Its been a few years since I have been in that part of the engine, but I don't remember the upper guide moving at all.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

You can definitely hear the guide moving in your video. It's easy to reach, so I suggest you change it before doing serious damage to the chain - assuming there is not too much chain stretch, which would require a new chain as well.

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Don't Chrome them; polish them

Well the motor only has 50,000 miles on it, and the chain didn't seem to have any damage at all. So replace just the guide? There's nothing on the pins that hold it in that wear?

-Jason

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

bump...

Is it possible that sound could be coming from the vacuum pump?

We checked the chain stretch last night and it's only got 1* of stretch.

-J

plinking? sounds like injectors? did you take a steth to it yet? try cracking injectors one at a time.

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1995 E420 Schwarz
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#1991 300D Nearly Perfect
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#1995 E320 Touring
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Ya, we used a steth and the sound seemed to be coming from the block, between the IP and the cam. But we didn't listen to the vac pump at the time.

The only thing that keeps the guide from moving is the width of the guide between the bosses at the lower pin. I've got two apart, seems like about 1/8" clearance or less.

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Gone to the dark side

- Jeff

So does that mean the guide is the worn part probably? I just gave it a listen with a 'scope again and the tappity sound is coming from about the middle of the guide area, not the vacuum pump.

Is there anything else I should check? Is there a way to test the tensioner? Can you just remove it without disturbing the chain?

-Jason

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

The tensioner is on the passenger side of the engine, forward of the turbo, about a 25mm (not sure of the size) hex. Remove the large hex nut (not the smaller one sticking out of it) and the tensioner will come out. It should have a spring inside, I have not disassembled one, but I've removed a couple and I bought a new one for when I replace the chain. It can be removed without disturbing the chain or timing provided the engine is not turned/run/cranked with the tensioner removed, I'd expect there is a chance of the chain jumping timing without it.

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Gone to the dark side

- Jeff

I don't know. IIRC the guide is plastic. That's odd sound for an oscillating piece of plastic to make. I'd pull the belt and check each pulley. In fact, start the engine cold without the belt and run it just long enough to confirm that there is or isn't that sound.

There's nothing to keep the guide in one position except the links wearing a rut in the lower pad.

If you don't mind a mess, start the engine with the valve cover off and see if the guide moves. It should be safe to hold the guide at one extreme with a stick with the engine running.

Maybe simpler is to see if the sound is louder with the oil filler cap off. If not, it's not coming from the timing chain cavity.

Sixto
87 300D

Ok, thanks for the tips. I did notice the sound happens more when the front of the engine is higher. The belt needs replaced anyway, so I'll give that a try. It's just kind of annoying because it's so intermittent. I did make another video, if I have time tomorrow I'll upload it with better sound quality. We did run the engine with the valve cover off, but it didn't make the sound at that time.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

We pulled the tensioner out, emptied and refilled the oil, but it didn't make a change in the tappity sound. With the unit empty, how much force should you need to push the shaft in? It took some force to push it, and it took quite a bit more once we had refilled it.

-J