rebuilding 930 tensioner

[greyes59]

wanted to know how to rebuild my 930 tensioner.
I have the rebuild kit already

[ajwans]

Do a search on here. I seem to remember John Walker posted a full description of the rebuild. A workshop manual also contains instructions.

andy

[mcaterino]

There used to be a nice write-up online of this, which I can no longer find. There is also a well illustrated procedure in the 70-73 version of the workshop manual, pages E106c-f.

Mike

[ajwans]

John Walker's writeup: Rebuilding tensioners

andy

[ajwans]

I saved the text from an online writeup which disappeared a few years back. Unfortunately I don't have the pictures which accompanied each paragraph.

andy

Originally Posted by http://www.thesey.com/tensioner.html

Porsche 911 timing chain tensioner rebuild

Secure your tensioner in a vice either by the bolt flange or by the webbing

First of all you will need remove the C clip and Spring retainer which is very straight forward. The spring is not strong and easily compressed but the C Clip can fly off at high velocity so either make sure you catch it or wear safety specs. The next step is to remove the oil retaining piston/seal (the seal that keeps the oil INSIDE the tensioner). The manual says to use pliers but it is a very tight fit and you'll need a lot of force. Not mentioned in the manual, but it's pretty obvious, is to loosen the bleed screw allowing air under the piston -it will be a cinch to pull off after. I found two screwdrivers either side to prize the seal off worked better with out mangling the soft alloy ...and the seal comes off thus. Drain out the oil so you can see the top of the plunger and lock ring

The next job is to remove the plunger lock ring. The plunger spring is not very strong and can easily be compressed with hand pressure. However you may find it impossible to compress the plunger enough to remove said lock ring. This is a good thing because the tensioner operates hydraulically and is working as it should. I had to depress the oil control ball inside the plunger with some wire so the plunger could be pressed down -see next image

Depressing the oil control ball though one of the 2 apertures in the plunger. Note: I found 0.6 MIG wire worked well

Now carefully remove the lock ring (Again either make sure you don't send it orbiting across the garage or wear safety specs) With the lock ring unclipped, carefully withdraw the plunger and catch the Ball retainer, ball and the tiny spring. The intermediate piece will probably stay inside the plunger and require some persuading with your piece of wire to drop out.

In order of assembly R - L: the plunger with intermediate piece followed by the ball, spring, ball retainer, plunger spring and spring guide.

A close up of the ball assembly (the bit that prevents your tensioner collapsing) You can see from the size that any small particles of crud or wear could easily affect it working properly.

Here is an intermediate piece from another tensioner I was rebuilding -the seal has seen much better days. This could allow to bypass the ball valve and lead to tensioner collapse. This is the seal that was added when the very early 901 tensioners were updated

A closer view

This is what you'll get in your rebuild kit. Only the plunger, the plunger spring, the oil retaining piston (upper oil seal) and it's spring and keeper you will need to reuse. Throw everything else away to avoid mixing with new parts

I cleaned all the parts in solvent, then washed them all in the kitchen sink with water + detergent, finally blew them out with compressed air. Clean the tensioner body in the same manner.

The upper seal area is polished and should look like this -check it is not pitted like another I was stripping down

When everything is clean the tensioner is ready for reassembling. After advice from Magnus in Sweden (Safe on Pelican board) I machined an M5 bolt to hold the plunger in place whilst fitting the C clip. It was good advice as the clip is tricky even with 2 hands.

It screws into the tensioner body like this and touches only the top bevelled part on the plunger

Now to assemble the plunger -fit the new seal and put the new ball, spring and ball retainer together

On closer inspection the ball retainer had some nasty flash on both sides left on it which I cut off with a sharp blade and then polished it against some steel rather than filing or sanding. My other rebuild kit had the same problem meaning it wouldn't fit into the plunger bore

Put the intermediate piece in seal first and then the ball, spring and retainer. You can check the ball is seated properly visually

I found it easiest to fit the spring into the plunger and then slide the body on horizontally. Push the plunger down and secure with the M5 bolt

Fit new lock ring.

It's a good idea to fit the bleed screw then fill with oil. You will want enough oil so that when the plunger is fully depressed it is still submerged in oil and no air can enter. Use the wire to press the ball and squirt the plunger up and down until all the air has been expelled. As a test the tensioner will be rock solid with the wire removed. It won't budge at all. 1/4 inch socket is to prevent sore fingers from bleeding process.

then onto the oil retaining piston (or upper oil seal) There are new seals in the kit for this but I will think twice about replacing the internal one again as it's a proper sod to extract. I ended up burning it out as there was no way I could remove it without damaging the alloy. It's not that easy to fit the new one either. External seal is a cinch

loosen the bleed screw and with your tensioner at +- 20 deg from vertical push the seal down as far as it goes. oil and air will squirt out of the bleed hole. Nip up the screw with a 10mm spanner when the piston is at the bottom.
Note: The instructions refer to gauge tool P214V which locates the piston at the correct height. I haven't found any reference to the tool on the www. Haynes instructions are to press to the bottom and comparing the position of 2 other tensioners, the factory position is not far off. However the mention of the tool indicates that there should be a small reservoir of oil above the plunger

Note to self: when I rebuild the second tensioner use a receptacle to catch oil over flow

Fit new spring in place

Finally fit retainer and lock ring

You'll need to compress the plunger in a vice so you can fit it back in your engine. If you don't have the Porsche tool handy you can use a pair of cable ties. Although you will have to use considerable force to compress the tensioner, remember it's only the force of the main spring that extends the plunger back to it's orgiinal postion. The tiny spring under the ball compresses, allowing rapid flow of oil through the valve and the plunger almost snaps back to postion. Cable ties will be more that adequate to hold your tensioner while you fit it in positon.

Part# of rebuild kit. About 40 quid for 2 inc. delivery from Sutton OPC

For comparison here is the very early tensioner side by side with the later 901 type. Notice the plunger is longer as is the spring, the lower spring guide is plastic, the intermediate piece has no seal, the ball retainer is plastic without a spring to maintain it's interface with the valve hole. There is no upper piston/oil retaining seal.

Close up of the early assembly

Close up of the underside of the ball retainer. As the plunger is compressed by the chains the oil is forced up these 4 holes and compresses the ball against hole in the intermediate piece forming a valve. The only way for the oil to go is out the relief bores in the side of the plunger which is a very small clearance

early tensioner body

A tensioner internals comparison view

A different perspective of the components of the later type of oil control valve

for comparison here are the internals of the later 930 (not carrera) tensioners against the 901. The ball retainer is made from alloy an not plastic. Not sure if the seal colour has any relevance -the new seals in my kit are black

There are some very subtle visual differences that I can see -whether these are an improved design I can't answer. A slight bevelling on the lower spring guides (top is 930)

Later 930 type body. I've just cleaned it hence the poly bag

Out of interest I put the early type tensioner back together and bled it, which was a bit awkward as there is no spring under the ball, but once the air was expelled the tensioner was rock hard. There is about 3mm of play or back lash which maybe caused by the lack of spring under the ball. The plunger needs to move slightly to create the flow of oil needed to push the ball into position and arrest the oil flow. It's easy to see how this design would create problems as the engine got older. When the engine was new and the chains were nice and tight the plunger would be further down it's bore. As the new chains wore and became longer the plunger would have to extend to take up the slack. This could allow air into the system if there wasn't sufficient oil, although the funnel design looks as if the engineers expected the tensioner body to collect oil from splash. I can see fitting would be a problem also as you couldn't just compress this type in a vice as the oil inside would dribble out. When you released the plunger to tension your chains, air would enter unless you knew to ensure there was enough of an oil reservoir to prevent this.

[greyes59]

Wow! thanks for the useful info.
You see the late style oil tensioner system is so expensive to retrofit so I wanted to rebuild some 930 tensioners I had.
I was able to buy a rebuild kit from Zims so that is cheaper than buying a new 930 tensioner .
carefully rebuilt 930 tensioner plus safety collar is a cheaper alternative perhaps

[jtsilverfox]

Hi guys,
Anyone have any clever (or even not-so-clever) ideas on how the heck to reinstall the c-clip (lock ring) that holds down the piston in the tensioner. I've been trying various things but I just can't get in there to get it started - let alone work it back in. I'm using my homemade tensioner tool 'P214' to hold the piston down, and it's in the way (see photo). But even then, I don't seem to be able to get down in there with any of my needle nose pliers, and/or screwdrivers, to get it back in.
thanks,
cheers,
jt

[jtsilverfox]

Just a brief update: I tried squeezing & clamping the clip with some small vicegrips -- and ended up with a permanent egg-shaped clip...
Went to the local hardware store to see if I'd get lucky -- on finding a replacement, but of course they didn't have anything like that.
However, they did have some internal retaining clips - which had not occurred to me before. (duh!) Got a 5/8" OD one (11/16" measured), and it's trivial to put in with the c-clip pliers! It's a lot thinner than the original ring, but it fits nicely in the grove and seems firm & snug. And it's not like it's ever going to have any pressure on it - only when the tensioner is fully extended, but that should be never. And I'm putting safety collars on them, so that should never happen... Right?