Jump to content
  • When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Timing Chain Tensioner Piston

Go to solution Solved by TobyB,

Recommended Posts

The timing chain tensioner piston (11311744347) appears to be NLA, at least from the several sources I checked.  Anyone have an extra new one (see Classified WTB)?

Might my old one (X # of miles; probably a lot) be OK to use in my rebuild as long as it's been soaked for hours and the ball rattles?



Link to comment
Share on other sites

The old piston was soaked, cleaned, and dried.  The ball rattles freely and seats well when air is passed through it in on one direction but not in the other direction.  This vintage piston has been paroled and is free to continue doing its job.

Thanks, guys.


Link to comment
Share on other sites

I would rather keep it intact. Only failure related to tensioner piston I have seen is that the parts separated and the smaller ones fell down the pan. That was race engine. I would think they stay better together if not separated before. I don't think you would find anything that interesting inside 😉


Oh, I forgot, actually not the only one. I had one of the tabs holding the slider part brake off. That may have been related to that I was avoiding the first kind of failure and had tack welded the parts together. It broke beside the tack.

Edited by Tommy

Racing is Life - everything before and after is just waiting!

Link to comment
Share on other sites

Thanks, Tommy.  


3 questions have presented themselves during this Great Tensioner Piston Adventure, the answers to each of which will help me understand the mechanics of TC tension better. 


...and I know how this is going to sound...


1.  Sucking and blowing at the notched end:  This piston allows air flow in one direction and not in the other direction.

    Sucking and blowing at the spring end:  No air flow in either direction. 

   (i) Are these proper functions?


2.  (ii) Mechanically, in which direction does oil flow "through" the piston (if it does at all)? 

     (iii) Is there any oil pressure on either end of the piston? 

     (iv) How does the small oil reservoir dat the end of the piston play its part?





Link to comment
Share on other sites

  • Solution

1 yes.


2 in the direction that the ball lets it.


iii nope


iiii it supplies oil to the piston.


The way the thing works:  Oil's supplied by the reservoir. 

The timing chain slaps the piston back against spring pressure,

pumping out a bit of air.

The one- way valve lets oil in, but not back out.  Air can leak out

(around the internal piston fit?  Via a small relief groove?  I've never looked,

and different BMW tensioners are slightly different)

so oil replaces the air.

Eventually, the piston is full of oil, and the spring convinces it over

time to stay out against the chain tensioner, keeping the tensioner tight.

If it overtightens (thermal differential, e.g.) the pressure in the piston goes

way up, and oil is slowly bled off.

If it's loose, the chain slap against the tensioner spring and the

normal action of a 4- cylinder engine's camshaft lets

the piston move, and pump itself up a bit.


The piston's just a biased damper- since there isn't always tension

against the slack side of the chain, it's designed to work its way to 

about spring tightness, and then sit there.  If there's constant pressure against

it (you slowly roll the motor over in reverse for a couple of minutes)

it will eventually collapse.  But once the motor's running, it'll slowly pump

itself back into place- often, with a lot of noise that didn't seem to 

bother the BMW engineers in the slightest.


It's kind of elegant.




Edited by TobyB
  • Like 1

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

Link to comment
Share on other sites

I believe the name "tensioner" is a misnomer because it can't possible apply any appreciable tension on the chain.  It only keeps the chain from flopping (from the slack) in the non-driven side.

  • Like 2

A radiator shop is a good place to take a leak.


I have no idea what I'm doing but I know I'm really good at it.

Link to comment
Share on other sites

To make it simple, the spring provides tension to the chain, not much of it but just enough and the piston acts as a damper. Oil is needed for the damper so air should be bled out by pumping it few times after assembly.

Racing is Life - everything before and after is just waiting!

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • BMW Neue Klasse - a birth of a Sports Sedan

    BMW Neue Klasse - a birth of a Sports Sedan

    Unveiling of the Neue Klasse Unveiled in 1961, BMW 1500 sedan was a revolutionary concept at the outset of the '60s. No tail fins or chrome fountains. Instead, what you got was understated and elegant, in a modern sense, exciting to drive as nearly any sports car, and yet still comfortable for four.   The elegant little sedan was an instant sensation. In the 1500, BMW not only found the long-term solution to its dire business straits but, more importantly, created an entirely new
    History of the BMW 2002 and the 02 Series

    History of the BMW 2002 and the 02 Series

    In 1966, BMW was practically unknown in the US unless you were a touring motorcycle enthusiast or had seen an Isetta given away on a quiz show.  BMW’s sales in the US that year were just 1253 cars.  Then BMW 1600-2 came to America’s shores, tripling US sales to 4564 the following year, boosted by favorable articles in the Buff Books. Car and Driver called it “the best $2500 sedan anywhere.”  Road & Track’s road test was equally enthusiastic.  Then, BMW took a cue from American manufacturers,
    The BMW 2002 Production Run

    The BMW 2002 Production Run

    BMW 02 series are like the original Volkswagen Beetles in one way (besides both being German classic cars)—throughout their long production, they all essentially look alike—at least to the uninitiated:  small, boxy, rear-wheel drive, two-door sedan.  Aficionados know better.   Not only were there three other body styles—none, unfortunately, exported to the US—but there were some significant visual and mechanical changes over their eleven-year production run.   I’ve extracted t
  • Upcoming Events

  • Supporting Vendors

  • Create New...