Chain tensioner M117

[Niclas]

While cleaning my chain tensioners inside the little piston ring came out in tree pieces (two big and one small one).
How is it suppossed to be?
Can I buy just the piston ring? If some has the MB number it would be great because my dealer is useless finding what I want...

Otherwise,
would it work with just the two big parts or can it couse teh camshaft chain to jump or something. The piston seems to fit with a microscopical clearance, can it really be any oil flow there even whithout the piston ring?!?

/Niclas

[Big_Richard]

.

[13B]

I think he's talking about the rubber O-ring on the piston in the chain tensioner.

If you run the engine with a non-functional chain tensioner you risk the chain jumping teeth on the camshafts, Nic.

I.

[WGB]

The 117 tensioner is not usually serviced and is not particularly expensive to purchase new.

In a M117 motor it is absolutely critical to holding the chain in place and preventing major catastrophe as it has no ratchet action and relies on internal friction when at rest or on startup  and oil pressure when running to tension the chain.

At the risk of being blunt I would put your present tensioner in the bin and purchase the correct new one - there are two, one with air pump and one without - before your motor has to go in the bin.

Bill

[TJ 450]

Yes, I don't think M117 chain tensioners are something to play with. They are a disposable item.
Like Bill stated, you don't want bent valves and all the rest of it.

Tim

[Niclas]

Yepp I think it's on its way to the bin, I'll go to the dealer today.

Thanks guys!

/Niclas

[WGB]

They are not very expensive for a genuine Febi (Ferdinand Bilstein) one from a non-dealer but two or three time the price from a dealer in Australia.


Bill

[Niclas]

I went to my Mercedes dealer yesterday and found out that the thing I thought was a piston ring was actually a VERY brittle rubber ring...
I also found out that most of the little parts in there is sold as separate items and I also got to know that a complete one was 360 Euro and the parts I needed costed about 10 Euro.
I'll put it back anyway. There was nothing stuck in there, and there is a test method described in the Service Manual Library how to make sure it works. Also I relized that there is a spring inside the tensioner which I think gives some basic force.

/Niclas

[WGB]

I see AutohausAZ sell the airpump one for US$120.

My Euro non-airpump model cost about AUD$180 - 3 years ago in Australia at M-B Spares and the dealers wanted AUD$400.

I would ask one of the non-genuine parts suppliers how much a Febi one costs.

Bill

[s class]

Just a few months ago I got a non-air injection 4.5 Febi tensioner for ZAR 1000 (about $140).  From an altenative parts supplier. 

[TJ 450]

Have you determined the extent of chain stretch?

Tim

[Niclas]

Not yet, do I have to fire it up to determine the chain stretch or does the spring make anough force.
Why is it both oil pressure AND a spring anyway?

/Niclas

[13B]

The spring keeps the chain barely taught enough for the few seconds from when you turn on the engine and the oel pressure builds up to take over by pressurising the chain tensioner.

Without the spring, the chain would be very floppy and be very noisy.

I.

[WGB]

Not yet, do I have to fire it up to determine the chain stretch or does the spring make anough force.
Why is it both oil pressure AND a spring anyway?

/Niclas

Chain stretch can be determined by putting the RH cam on its timing mark by rotating the engine clockwise (with a 27mm socket on the crankshaft nut and the sparkplugs removed) and reading where the timing pointer is on the crankshaft pulley.

It is measured in degrees after top dead centre and here is a pictorial that shows the timing marks before going onto changing the chain and sliders.

117 timing chain replacement

Please don't scrimp on the tensioner or you will be potentially consigning your car to an early grave.

Bill