Cam Pre-Tensioners for Timing

[Heiko]

Originally Posted by NewArt

Well, hells bells, I'm impressed! Having just done the aforementioned pumping to set my cam timing, these could have come in handy.
I guess one would need to have a set of old tensioners kicking about and also understand the principle of the platinum-plated Porsche tools to fabricate such an item. Seems pretty straight forward, but did you have access to the genuine tools to see how they were made?

NewArt, I've never had the luxury of touching the 'platinum-plated' Porsche ones... but the Porsche tensioners are adjustable to a steady tension point which basically keeps very steady predefined pressure onto the chain guide. I'm sure you pay $100 per pound of accuracy, but for my wallet and sake of timing adjustment this is better than nothing.
The spring pre-load is still the same as the original pressure, the bolt simply keeps the tensioner from collapsing beyond a certain point... which is what the oil does, basically slows the collapsing process.
I guess one could improve on this version and drill out the hole bigger and instead of having a bolt hold the initial set-point, use a bigger bolt that pushes against the spring to increase the preload.... I guess if someone knew what the preload was from the original Porsche ones, one could preload and measure the distance the bolt would have to compress the spring to achieve that same pressure... wouldn't be so hard.
Once the process is complete, you pop them out and replace them with the real ones (yes and don't forget to pump them in oil before inserting them).

[jaykay]

Nice Heiko! Seems you have invented a tool! How did you ascertain the set points if the springs just collapse that readily? I suppose that each tensioner has a specific length fully extended/free under its spring load.

Not ever having done this, I just have to wonder if the official Porsche tool(s) actually compensates for slack tensioners???

[Heiko]

The 9599 tool from Porsche seems to have the same part number stamped on each of the three tools
which raises a flag to me regarding setting proper tension on the pads during timing adjustment.
When you order part 000 721 959 90 from Porsche it says three required (1 tool per bag)
BTW - I wonder if it costs so much as its name starts with Porsche 959_

For instance we know the spring load on the standard tensioners for bank 1 and bank 2 are similar
and the IMS spring tensioner (middle one) has much less tension on the spring.... I'll try to
measure the pressure today if I get a chance. But the manual says to insert the 9599 tool into
each of the tensioner holes and then adjust the pre-tension force (there is a little stem that
appears at the end of the nut when proper tension is achieved) (see pic below)

So if each of the three pre-tensioners are the same, and each is adjusted to the same pre-load
point then the pre-load force must be the same on each; and since we know the springs aren't
the same strength on the stock 3 tensioners, I'm lead to believe that this 9599 tool does nothing
else then keep enough additional pressure on the tensioner pads to minimize slack/movement
during timing adjustment, as otherwise each of the 3 tools would be different!

I suppose I could drop a second spring inside the bigger spring already in the tensioner and use the
bolt to compress the inside spring which would add tension, instead of restricting travel.... but for the
sake of getting the timing right, I think key is to adjust based on little to no slack (which the stock
tensioner limits under pressure and oil flow)

BTW Just out of curiosity I checked the pressure on the 14yr old vs new tensioners
The preload readings I got on stock OLD tensioners (no oil) - travel limit on each ~22mm
IMS Tensioner top 8.6 lbs to bottom 14.2 lbs
Bank 2 Tensioner top 17.4 lbs to bottom 40.9 lbs
Bank 1 Tensioner top 17.2 lbs to bottom 39.9 lbs

The preload readings I got on the NEW tensioners (no oil) - travel limit on each ~21mm
IMS Tensioner top 11.2 lbs to bottom 17.8 lbs
Bank 2 Tensioner top 21.1 lbs to bottom 46.0 lbs
Bank 1 Tensioner top 21.0 lbs to bottom 46.0 lbs

[Gelbster]

Heiko -thank you for sharing your good work on alternatives to buying 3 x Porsche 9599 timing chain pretensioner tools.
Your comparison of the new/old tensioners indicate a 12%+/- deficiency in the old ones. I presume this is potentially significant in terms of an increasing probability of camshaft deviation with more future miles on the old tensioners.
Does anyone know the official wear/performance standards for the old tensioners?
If the old tensioners usually need to be replaced at say 80k-100,000 miles, then your re-purpose/modification of the old tensioners is a brilliant use of a worn out part. I can't even find a price for the 9599 pretensioner tool-even if I did want to buy them!
Interestingly, Porsche switched to a compressed air-operated tool for chain tensioning on their current V8 engines. The generic version of that tool is available for about $70 but I found no evidence it was interchangable with 9599.
Thanks again for sharing Heiko.

[Brad Roberts]

I appreciate all the hard work and effort that went into these (I know what it takes)

But...

Why??

We've built a LOT of engines.. (with zero cam timing issues) and NEVER used the factory tools or any special modified tensioner??

We thread them in until the chain stops moving (which means your against the pad)

Typically this is 2-3 complete turns. Unless your tensioners are sitting for 6months?? I've rarely had them bleed down unless we tried to bleed them down.

Am I missing something??

[Heiko]

You're not missing anything. I simply had some decent tensioners to chop up and figured instead of tossing them I'd try to make something useful out of them. Mostly though it started as curiosity of what would be different using preloaded stock tensioners for the timing setup vs some tensioners with an adjustable preload like the porsche ones, which of course got me thinking, why, what's the difference etc. anyhow these things worked well but I also agree that I've had great results with just using the primed stock ones :-)
H

Originally Posted by Brad Roberts

I appreciate all the hard work and effort that went into these (I know what it takes)

But...

Why??

We've built a LOT of engines.. (with zero cam timing issues) and NEVER used the factory tools or any special modified tensioner??

We thread them in until the chain stops moving (which means your against the pad)

Typically this is 2-3 complete turns. Unless your tensioners are sitting for 6months?? I've rarely had them bleed down unless we tried to bleed them down.

Am I missing something??

[Gelbster]

Brad's contribution to the discussion is useful to someone like me ,doing an M96 rebuild for the first time. There is no single definitive source of info to take you through the rebuild process other than the Porsche Workshop manual. That is littered with very expensive special tools and it seems foolish to ignore these instructions as an M96 noob .
"We've built a LOT of engines.. (with zero cam timing issues) and NEVER used the factory tools" What ,not even a cam position holding tool?Impressive.
I just wish Jake Raby would publish his book ! "The M96 Definitive Guide ".
That would be invaluable.