Captain_Slow

The car isn't going anywhere until spring and I've wanted to replace the oil in the tensioner with something more viscous to reduce the chance of leaking. I had an unopened bottle of Lucas Hub Oil I planned to put in a leaking hub on a Unimog. Talk of using a viscous engine oil treatment product in the belt tensioner (de-tensioner) gave me an idea for how to put this Lucas stuff to work.



This stuff is extremely viscous at sub-freezing temperatures. I had to use a heat gun to get it to flow (or plan on returning a few days later to check on it...it flows much faster if you aren't watching it).



After 24 hours the level in the funnel hadn't changed noticeably...out came the heat gun. On a warm day it would flow much better without help.



Clean hub oil going in, dirty old engine oil coming out. I was surprised to see very dirty oil coming out. How much work is this oil doing? The outflow tube leads to a pan below.

The plan is to continue adding hub oil until it flows clear from the outlet side.

Adk46

Interesting idea. OK for the school of thought that the oil is there just for heat transfer. Up for debate for those who believe the oil also provides for (or at least allows) damping to stop the belt from flapping about.

The "dirt" in the oil is presumably wear particles from the washers. Maybe they do move around to provide damping.

I guess I don't have to worry about leaks in my Unimog hubs, not for a few months.

SteveG

There is no dampening effect.

Captain_Slow

Today's balmy 60F high temperature enhanced the flow. The surface of the new oil is in the funnel stem, just below the cone of the funnel. Oil coming out is amber with traces of the dirty oil. Based on how little dirty oil is in the pan on the floor it doesn't appear that the new oil is dense enough to sink to the bottom of the chamber and displace all of the old oil. So it seems there's no way to really change the oil without removing the tensioner.

Mrmerlin

FWIW on filling the tensioner,
I like to use the visene bottle with the tip drilled out so the fluid will flow.
The tip fits into the fill hole once the bleeders are removed.

The reason to use this is so you dont use a device that can force oil into the tensioner ,
if you use an oil pump can for example,
I did once, and it blew the inner C clip off the rubber bellows and then the oil flowed out of the piston /bellow area,
This required removal of the tensioner to refit the clip.

This gravity idea looks like it will work.
and since no pressure is used it should not cause any other issues.
My only concern is that you will be having parts that have oil in them that have to be cleaned or thrown away.
I think the visesne bottle is the best for this job.

NOTE I like to use the STP oil in the tensioner as it is thicker and appears to not leak out as fast as either of the oils that have been specified by Porsche.
I use dreibond or Honda bond on the tensioner gasket this also assists in making the seal last longer

Captain_Slow

The Lucas hub oil is very viscus. It would probably work better using Stan's method, but the thought of trying to fill the tiny eye drop bottle seemed like another potential mess. I tried a syringe (the kind used to inject medicine into a toddler's mouth). It looked like it would work fine, but the Lucas oil wouldn't flow fast enough, causing the air in the clear tube to compress, then when removing the syringe most of new oil was forced back out as the air expanded. Messy. So, I went with the gravity method. I'll stick the fill and drain tubes in an empty engine oil bottle and let gravity do most of the cleaning.



30F warmer yesterday and this is the result.



Outflow on right is almost clear. But has all the dirty oil been flushed? The fittings are up high. If the new oil is less dense than the old oil then only oil near the fittings got flushed.



Not much oil in the pan. Near the rear the cleaner fresh oil is visible. What's the oil capacity of the tensioner? How much of the volume is occupied by piston and washers?

Captain_Slow

All of my questions were answered at Theo Jenniskens' site. The interior volume does appear to be largely occupied by the piston, rod, and washers. Theo has compiled Porsche technical bulletin information and some info from Wally at 928 Specialists. These references indicate the oil, passages, and washers provide damping action. During my next timing belt job I'll rebuild the tensioner and might use Mobil 1 15-W50. I'm sure a lot of debate has already occupied many folks for hours.

http://jenniskens.livedsl.nl/technic...4/mytip416.htm

rjtw

skpyle

Sorry guys, I am sticking with Stan on this one. Thicker oil takes longer to leak out of the tensioner...

Captain_Slow

There will never be complete consensus. I think the Lucas Hub Oil is more viscous than the STP product Stan recommends. The bore passage for the compressed oil (details at the Jenniskens site) is narrow...not good for high viscosity. Here's a short video I made after warming everything up a bit with a heat gun. Granted, the oil will flow much better when warmed by the engine and probably work fine, then not leak out when the car is parked.

FredR

The stock tensioner is way smarter than many folks seem to understand. When studying the later model design I concluded that it has in fact three distinct functions:
1. To initially pre-tension the belt by manual adjustment.
2. To automatically compensate for engine thermal growth by reducing the static belt tension
3. To dampen to some extent the dynamic belt tension pulsations.

The interesting question that I have never seen addressed is what happened to convince Porsche that they needed to modify the original design concept as they did in 1983 noting that Porsche successfully took out patents for both designs. I initially wondered if it had to do with the introduction of the 32 valve models but as I am aware that did not happen until 1985 MY. Thus one is left to presume that something happened to convince Porsche that what they had was not sufficient for the need. Maybe it was connected with the development of higher power models like the Euro S and the associated changes to the cam profiles? Doubtless Porsche did not do anything without good reason.

The original tensioner design seems to rely on the Belleville pack being sat in an oil bath to provide some damping whereas the later models appear to induce a flow through the annulus in the body thus the check valve built into the piston. As to whether using STP in the later model tensioners is a good thing makes for an interesting discussion point. Just getting the stuff into the tensioner body is really difficult even at 25C ambients. Whether it is a good idea or not I am still on the fence with this one. I figured that it might be a good idea in hot climates like mine where everything probably runs that bit hotter but in reality I have no quantitative means to determine such.. I will probably pull the tensioner to replace the boot next year unless I see signs of distress when I do my next annual inspection and maintenance activity starting in a few days time. At such time I will try to make an assessment as to whether the STP is beneficial difficult as such will likely be.

Hilton

I used a mityvac and a canister to pull vacuum on the top nipple, with a hose from the bottle of oil to the bottom nipple. Pull some vacuum, then wait until oil is visible coming out of the top nipple (I used clear pvc tube). Easy!

Captain_Slow

Last night I thought of doing the same - but pulling vacuum on the lower nipple. Hilton, your way is better to remove all the air.

skpyle

That is awesome! I am very much stealing your method, Hilton.

Mrmerlin

remember that the inner edge of the rubber boot is only held in place a C clip, the open end should face up when the boot is installed.

NOTE if using the suction method you could unwittingly cause the clip to slide off the boot inside, though I have never proven this .
and you might not see this till the engine has been run to temp, then a small leak from the lower edge of the piston to boot area could be seen.

I know for a fact that by using a pressure type oil can you can pressurize the tensioner body enough to make the C clip come off the boot,
and with it pressurized the oil will flow out of the boot piston area.
Yes I did this so I know it can happen and its a PITB to take the belt back off to, clean up all of the spilled oil

This is why I suggest to use the small visene bottle,
it will make some pressure but not like a hand pump oil can, so you wont be able to unseat the C clip,
and it will easily fit into the tensioner fill area after all of the other parts have been assembled.


I have not checked recently but from my last bottle of Lucas oil treatment a few years ago,
I thought it was not as thick as the STP oil treatment is.

I have not ever had any issues using the STP to refill the tensioner ,
One thing I did notice is that when rechecking the level after the engine has been in use and has been refilled with the STP,
the oil is still usually close to full.

I would estimate over the years I have replaced about 40 to 50 timing belts on different year 928s ,
and most if not all have had leaking tensioners with atleast half of them being empty.

Most owners wont recognize the oil leaking out as it can look like an oil pan gasket leak.