timing chain tensioner snap ring

[bluedevils]

I received the new M44 update tensioner, and as soon as I open the box, piston popped and I cannot push it back. There is a snap ring on the second grove which prevents piston to compress into the housing unless I push really hard. But it pops back again, doesn't stay compressed. Shell I remove the snap ring? Thx in advance.

[TobyB]

I think you CAN remove the snap ring, but you don't have to-
just jam that puppy in there!

I popped mine loose before installing, and primed it with oil (2002 habit)
and never had any trouble afterwards...

t

[bmwman91]

It is vastly better to install it with it already popped / expanded. Putting it in compressed means that it is waiting for the chain to whip around against the tensioner rail hard enough to release the piston, which can easily definitely damage the chain. Putting it in already expanded is MUCH safer, and is only a little more difficult.

[uturn]

Installing it uncompressed is asking for a stretched chain and premature wear on the chain rail. Install it compressed. With the valve cover off, take your hand and push on the rail to uncompress the tensioner. Oil pressure will adjust the tensioner to the correct length. Read the Bentley manual on E36's for M42/M42 maintenance procedures.

It is vastly better to install it with it already popped / expanded. Putting it in compressed means that it is waiting for the chain to whip around against the tensioner rail hard enough to release the piston, which can easily definitely damage the chain. Putting it in already expanded is MUCH safer, and is only a little more difficult.

[uturn]

Leave the snap ring alone, it what will keep the tensioner compressed when you compress it enough.

[kwill22]

I don't see how installing it uncompressed is hurting anything. We know what the Bentley says. You're only installing it once so where's the stretched chain/premature wear etc coming from?

[nando]

Installing it uncompressed is asking for a stretched chain and premature wear on the chain rail. Install it compressed. With the valve cover off, take your hand and push on the rail to uncompress the tensioner. Oil pressure will adjust the tensioner to the correct length. Read the Bentley manual on E36's for M42/M42 maintenance procedures.

if you can stretch your chain by installing the tensioner uncompressed your chain was fucked already. the whole point of the tensioner is that it pushes on the chain to take up the slack. and you can compress it with your fingers, so what you're saying is you could stretch the chain with your fingers.

[bmwman91]

if you can stretch your chain by installing the tensioner uncompressed your chain was fucked already. the whole point of the tensioner is that it pushes on the chain to take up the slack. and you can compress it with your fingers, so what you're saying is you could stretch the chain with your fingers.

Word.

There has been zero evidence, ever, that the M42 chain stretches over time. The primary failure mode for the chain is that the hardened rollers shatter off, typically from a failed tensioner which allows the chain to slap against the surrounding aluminum castings. Metric Mechanic converts M42's to single-row chains and even then stretch is a non-issue (and it is what I run in my MM engine). Brandon Purcell, owner of probably the foremost M42 info site, measured a 100k+ mile chain versus a new one and they were exactly the same length.

Putting in a new tensioner uncompressed requires MAYBE 50lbs of pushing force, and that is precisely the same force that it is putting on the tensioner rail after it pops free if you put it in compressed. The max force it makes is the combination of the internal spring (~50lb) and whatever the oil pressure adds, and the oil pressure is what provides a majority of the tensioning force (probably > 50lbs).

Don't put a compressed tensioner in folks. The 3-5 seconds of totally unconstrained operation your chain will see as it slaps around are a high risk for breaking rollers and jumping teeth. This is one case where the Bentley manual is wrong.

[Merlin8]

I put mine in uncompressed and there was still a half second of rattle. I believe its due to the oil making its way in. Although I have had my timing components replaced since the plastic wore out and the chain was slapping around on metal runners and a two inch piece of metal broke off.

[bmwman91]

The initial rattle is from the chain whipping around against the tensioner rail & head castings. Eventually it smacks the rail hard enough to release the tensioner piston so that the internal spring and oil pressure build up the required force on the rail.

[uturn]

A fully extended tensioner before you get ready to break it down is 83mm in length. Once it extends that far it locks itself and will only allow 3mm of compression travel. This is why I say do not install it extended. After 3mm it essentially becomes a solid rod as you continue to turn that endcap and force that rail onto the chain. The novice wrencher most likely won't differentiate an extended/fully extended tensioner.

A tensioner with the clip in the last groove is 79mm and allows the piston to travel 13mm when you compress it. This is the "extended" tensioner that everyone alludes to.

Based on the piston wear marks, this tensioner operated in the 75mm range.

[kwill22]

I don't understand what you're trying to say. The very first time I installed a new tensioner I put it in and pushed it on the inside to make sure installing it extended didn't jam the tensioner and no problems. Never heard of anyone having an issues installing it extended.

[bmwman91]

Interesting. I see what you mean now, thanks for the details. So popping it open to 79mm is not a problem, but if one were to pop it past that to 83mm then they are going to have an issue? Whenever I install one I have always popped it and then made sure that it travels smoothly by hand-squeezing it. I assume that if it was opened to 83mm, screwing the cap back on would probably feel very tight before it makes it to the fully-seated position since it would be stuck open?

How does one get it to pop out to 83mm? I can't recall ever getting it to open that far. If you do pop it that far, how do you put it back to the right length?

I think that you may have also offered one of the only explanations that I can think of for why the idler sprocket boss breaks off of the timing case.

[bmwman91]

OK, this has been bugging me all day. I got home from work and pulled my tensioner piston.

When I removed it, it measured 85.20mm.

I was able to compress it by hand down to ~69mm. There is indeed a bump/detent about 3-5mm in where the snap ring moves past something, but it is pretty easy to push past it with just one finger/hand squeezing it.

Now, if you pull a used one out of a car, it WILL feel super duper stiff after compressing it a few millimeters. That's because it is full of oil and you have to force it out through the gaps since there is a ball check valve in there. I had to pump it a few times by hand to get it to compress down all the way.

How hard it is to install is dependent on engine position. I was messing around, and when you go to install it you will need to compress it by anywhere from 5mm to 12mm to get the cap threads to the head. If you find that the piston needs to be compressed a ton, run the starter for a fraction of a second to spin the cams and put a little slack into the chain.

I also had a *sproing* moment lol. When I was messing with the tensioner, it popped apart and shot the small end across my driveway into the dirt. It wasn't damaged and the little ball check bits were still in the right place, and the 2 springs were still in the body of the tensioner. I'm not missing anything, right? So I cleaned it up and put it back together. Anyone think that it is a bad idea? I might just order a new one for peace of mind.

[uturn]

A few months ago I installed a fully extended tensioner on a 318ic and was able to seat the endcap. I was not able to move the rail when I pushed on it and the chain tension was ridiculous. More than what I had seen on my 318is, my E30M30 and the few M5x's I have worked on. The endcap was very tight going in which kinda raised a flag. Maybe the motor only having 150k miles has something to do with it, newer rails? Stopped work, then did it according to the Bentley, no issues with the car. Don't recall why I attempted to install it extended that day.

Did some more experimenting.
Starting with a compressed tensioner - 68mm
The initial push on the pistion will get it to expand all the way to 83mm.
tapping the back of the tensioner with a hammer will get it to come apart so you can begen the process of compressing it back to 68mm.


**I attempted to just open it to 79mm but was unable to do so, every attempt from 68mm had it going to the full 83mm length.

**I attempted to get the tensioner to expand from 79mm to 83mm but was unable to do so by rapping on it with a hammer. This refutes my note in the picture, in the previous post about installing it at 79mm.

**With the tensioner in the vise I expanded the tensioner, I had the full range of travel and was able to move the piston freely from 68mm up to 82mm and go from 82mm back to 68mm. Once expanded to 83mm the clip set and then I was only able to compress it back to 80mm.


Because it locks once fully extended it has to be broken down in order to reassemble and compress it. On reassembly, center the protruding clip as you dog down on the vice/C-clamp and the piston will go in. The clip will catch at the 79mm mark and if you back out on the vise it will hold together. Continue to compress it and the clip will catch again at 68mm.


If installed according to the Bentley, you get the full travel of the piston with it locking only after it hits full expansion. I would assume if you get to full expansion then some/all your timing components are worn. Installing it fully extended only gives you 3mm of adjustment but if that's where it currently needs to be then it's not an issue because it's doing it's job taking up the slack. I just don't see running it at the upper limit when you have a nice meaty range in the middle.


In a few months I'm going to reseal my 318is and install new stock timing components I've been collecting(I have that leak at the block and timing cover). I will confirm exactly how far the tensioner expands when installed in the motor. The wear on the tensioner piston has me assuming 75mm but it'll need confirmation.