M88 chain tensioner.

ron · Post by **ron** » Sat Oct 18, 2014 2:49 pm

Ref. #18 (M88 part) and #26 (S38).#18 is NLA. Has anyone tried modifying #26 to fit a single chain engine?

One of the guys in UK had the head gasket go. So, whilst the head was off, it seemed logical to do the chain etc. The engine has done 70,000 odd miles and the tensioners are well worn so he desperately needs #18.

Any advice/solutions etc.?

TIA

http://www.realoem.com/bmw/showparts.do ... g=11&fg=25

Brucey · Post by **Brucey** » Sat Oct 18, 2014 3:07 pm

#18 listed here;

https://partsale.eu/spare-parts/view/BM ... 42-2114356

-which may or may not mean that there is one to be bought.

On reflection #26 probably can't be made to fit because it is paired with #23 which requires a pivot above the tensioner piston. I don't think an M88 cylinder head has provision for such a pivot.

cheers

GazM3 · Post by **GazM3** » Sat Oct 18, 2014 9:36 pm

Ron doesn't the "upgraded" one from the e36 m3 Evo fit straight in

brickwhite · Post by **brickwhite** » Sun Oct 19, 2014 4:13 am

posted here:

http://www.bigcoupe.com/phpBB2/viewtopi ... c&start=30

with no real solution.

David Muench · Post by **David Muench** » Sun Oct 19, 2014 6:33 pm

Hi Ron

Just had the full timing chain, guides and tensioner assy renewed by Munich Legends and according to my parts invoice list they have used item No 26, part No 11311309945 and mine is a single chain.

rmorin1249 · Post by **rmorin1249** » Mon Oct 20, 2014 12:27 am

David Muench wrote:Hi Ron

Just had the full timing chain, guides and tensioner assy renewed by Munich Legends and according to my parts invoice list they have used item No 26, part No 11311309945 and mine is a single chain.

Interesting. I have discussed this issue with several very experienced BMW mechanics who are knowledgeable about the M88 engine. They all said the single vs. double timing chain issue is far from clear. None were convinced that a car with a single timing chain that is properly maintained and driven within the recommended engine RPMs is any more likely for failure than one with a double timing chain.

Brucey · Post by **Brucey** » Mon Oct 20, 2014 9:49 am

David Muench wrote:Hi Ron

Just had the full timing chain, guides and tensioner assy renewed by Munich Legends and according to my parts invoice list they have used item No 26, part No 11311309945 and mine is a single chain.

I can't see how they could have made that work properly unless they also managed to fit the matching upper section somehow...?

cheers

David Muench · Post by **David Muench** » Mon Oct 20, 2014 6:08 pm

According to my parts list invoice they used # 23, M3 chain slipper part number 11311317335.

Brucey · Post by **Brucey** » Mon Oct 20, 2014 8:41 pm

I found this photo of an M88/3 cylinder head that is also fitted with the two-piece tension slipper;

and you can see that there is a boss in the cylinder head that fits the pivot bolt for the upper section.

I am not sure that all M88/3 cylinder heads have the correct boss in them to allow the fitment of this piece. There appears to be two different part numbers for the head itself; one runs to 1987 and the other to 1989. The latter appears to be backwardly compatible with the former which is now NLA.

There is only one lower timing case and head gasket part number for M88/3 on E24.

So it is possible that later versions of the M88/3 cylinder head had the fittings for the two piece slipper even if they were not all fitted with it initially. Perhaps others could examine their engines for the presence of the correct boss/bolt-hole for the upper pivot?

cheers

TBM · Post by **TBM** » Mon Oct 20, 2014 10:50 pm

Real OEM shows that part as fitting E24, e28, e30 e34...

TBM · Post by **TBM** » Mon Oct 20, 2014 11:00 pm

rmorin1249 wrote:
David Muench wrote:Hi Ron

Just had the full timing chain, guides and tensioner assy renewed by Munich Legends and according to my parts invoice list they have used item No 26, part No 11311309945 and mine is a single chain.
Interesting. I have discussed this issue with several very experienced BMW mechanics who are knowledgeable about the M88 engine. They all said the single vs. double timing chain issue is far from clear. None were convinced that a car with a single timing chain that is properly maintained and driven within the recommended engine RPMs is any more likely for failure than one with a double timing chain.

That is the point exactly. Most people are too cheap or don't want the hassle of dealing with a job of this caliber. Add to the fact that this is a car that will see more revs and harder running than a passenger car will sometimes result in failures that are perceived to be a weakness. I have a feeling that the single chain was put in there as a low drag design from racing. Since in racing an engine tear down is common, then there is no worries.

A double chain is probably more robust since the stretch is different on two chains. If one breaks the other one survives? I'm not an expert but that seems logical.

Brucey · Post by **Brucey** » Tue Oct 21, 2014 10:15 am

the M30 had a double chain for many years and they changed it for a single one, with no ill effect.

The loads on the chain at high rpm are in good part inertially generated, i.e. they are to do with the weight of the chain. So are the losses.

[If this seems intuitively hard to grasp, figure this; if you have a 6cyl cam in a head you can turn it (or a pair together) by hand quite easily, although it might be a bit lumpy. Above a certain speed (which isn't that high) the inertia of the cam carries it through the lumpy bits and this means that the fluctuations in torque required to drive the cam are also somewhat reduced. In fact the cam drive torque falls to something close to the mean value which is only a few kg of chain tension (which is going to be roughly in proportion to the static spring load of the tensioner). This 'driving' contribution to the chain tension stays more or less constant with speed. Meantime at high speeds the inertial forces are considerably in excess of this; in fact they are in proportion to the weight of the chain plus they increase with the square of the speed. These loadings can easily be the greater part in some systems and a double chain doesn't really help at all.]

Chain designs vary of course, however, a double row chain is about twice the weight of a single row one but may only be half as strong again. The reason for this is that unless the side plates are made a lot thicker on the links which are joined with three side plates will only be half as strong again as those on a single row chain (which has two side plates on every link).

This early M30 chain

has slightly thicker centre side plates but they are not twice as thick so the chain probably isn't twice as strong, despite being twice as heavy.

The peak loads on the chain probably occur when the chain flaps about. There are always resonance effects (and these are often worse in DOHC engines than in SOHC ones) plus the tensioner on the M88 engine is fed with pressurised oil (I believe) which means that whilst it may have an inadequate tension on start up (no oil at all...), it may also be excessive at some (probably middling) rpms if it is to be adequate at the highest rpms.

It is a complicated business, and resonances can catch even the best manufacturers out sometimes; if 'motorway cruising speed' in a particular market happens to correspond with a resonance rpm, there can be an unusually high number of failed engines in that market.

cheers