M70 Timing Chain Tensioner Replacement

[Sniff38]

I recently discovered a slow oil leak coming from my timing chain tensioner ('92 850i). Surprisingly there isn't much written on the subject, but I did come across a few helpful sites. I just ordered all the replacement bits (#17, 19, 20, 21, and 24 in photo at http://www.realoem.com/bmw/enUS/show...diagId=11_4904 ) and have a couple of questions.

1) How do you ensure the slotted piston (#16) properly engages the chain tensioner (#12)? Will it be obvious? Is it all by feel?

2) I've read after reinstalling the tensioner you have to prime it with oil since some leaked out during the removal. What is the easiest way to disable the ignition so I can crank the car without it firing? Pull the leads off both ignition coils? How long do you need to crank the engine to get oil up there?

The job seems pretty straight forward, but any useful tips from someone who has "been there, done that" would be greatly appreciated.

Sean

[dragon850]

All you really need #20 but new parts are always good. Piston is installed by feel twisting it slowly you will feel it engage. Make sure you pay attention to the orientation of the spring. Since you purchased a new #21 you wanna make sure you set it to the same position as the old one(mark position before undoing). When unbolting keep in mind spring is under tension if you are not holding it in it will fly far far away!

[TxGR8White]

No need to "prime" anything, just make sure your oil level in the pan is okay.

[Sniff38]

I finally got around to replacing my timing chain tensioner. It took me about an hour, but I was very methodical. The job was fairly straightforward, however getting the black plastic cap (#24) off was a bit of a bear. I ended up breaking little pieces of it off with a long set of needle-nose pliers until I was able to back it out. The cap has 4 plastic "barbs" inside that are essentially one-way. The cap is easy to slip on, but pulling it off is a different story. Sort of like those Chinese New Year finger toys you may have played with as a kid . . . you easily insert a finger into each end of the tube, but when you try to pull them out, you can't.

I was worried about setting the piston (#16) correctly. It has that fork on the end that has to engage the timing chain tensioner (#12) just so. If it's not oriented properly it won't work. I marked "North Up" with a permanent marker on the piston so I was reasonably sure I was inserting it the proper way. Compressing the spring (#17) while trying to thread the sleeve (#21) was a bit of a challenge, but all I can say is be patient. I had my 19mm deep socket on the end of the sleeve and eventually felt the threads engage.

Anyway when I started the car up I heard no unusual noises, so I must have done it all right. Thanks for those who chimed in.

Sean

[Cup1d]

Does #24 unscrew or does it just slide off? I have the same leak. Thinking of sealing 21/20 with "The Right Stuff Gasket Maker". Thanks.

[Cup1d]

Does #24 unscrew or does it just slide off? I have the same leak. Thinking of sealing 21/20 with "The Right Stuff Gasket Maker". Thanks.

Never mind. Went back and read this post again. That *did* suck. Ended up prying with a screwdriver and pulling with needle nose at the same time to get that darn thing off. *sigh*

[Sniff38]

Yep, that black plastic cap (#24) is a "one-use" item. With so little space to work in, I don't know how you could get it off without destroying it.

Sean

[PabloRock]

Just did this a couple of months ago. I just ripped mine off with pliers. Luckily they are readily available and only a few bucks. Still haven't put mine back. Want to triple check for leaks.

[Restor8orman]

I'm busy refurbishing the timing chain tensioner (1990 E32 750iL) but when disassembling it there was no ball bearing present (part #19). As it can only run along the inside of the spring, what does it do? Did all you chaps carrying out the refurb of your tensioners find a ball bearing present?

[BMSman]

There is no ball bearing. #19 is an o ring

[Restor8orman]

Certainly on realoem.com for a 1990 750iL m70 engine right hand drive, #19 is a 5mm dia. ball bearing. BMW part no. 07119986250

[cartoonz]

I'm not sure that it really matters... yes, there is a 5mm ball indicated on the earlier parts diagrams but not on the later ones..
BUT... the part #'s for the other parts (piston, bushing, spring, etc.) are the same
So if you didn't find a ball, don't sweat it.

[Restor8orman]

Thanks, due to the location of the ball within the spring I thought it's only use was to keep the spring from gumming up with old oil, but it's relief to know that it's been omitted on later models. I've order the ball along with the Aluminium washer and the O-ring so I'll incorporate it.