The problem is trying to measure both changes in geometry (failing WP bearings, oil-pump sprocket coming off, failing belt, broken cam nose, etc) or tensioner failures (broken spring, failed fastener) with a single alarm. The PKT uses a NTN auto-tensioner, which automatically takes up any slack in the belt, for any reason-- including expansion with temperature which changes the belt path length by a few mm.

So the amount of rod extension, by itself, tells you nothing-- it could be near its extension limit because the heads were shaved and the engine is cold, or because the engine is warm and something is failing.
Similarly, belt tension doesn't mean anything-- if the WP pulley is falling off, for example, the auto-tensioner will happily take up any belt slack and maintain tension as long as it can.

I think the reason that other cars don't provide a warning is that it is really hard to do with an auto-tensioner. Neither belt tension or rod extension provides a useful picture.

The Porsche tensioner is fundamentally different in this respect. It is a manual adjustment, with temperature compensation. So, once adjusted properly, the belt tension is constant over the temperature range, unless the belt geometry somehow changes. So a tension monitor, however "primitive" it might seem, actually does mean something.

 

Why not make a metal bracket that mounts to the center cover. The metal bracket can be made to fit over outside the waterpump (of course on the side opposite where the belt runs). Kind of like a U bent piece of spring steel over the pulley channel.. Once the pulley starts to move/wobble, it will contact that bracket grounding out the circuit you set up.. Would be cool to use the existing warning system, but I believe that one triggers when ground is broken, and this one would have an open connection until the pulley "grounds" out the circuit..

Anyway..just some random thoughts...

 

Please remember that the current Stock system DOES NOT measure Over Pressure and that is what causes (IMO) most of the failures (broken parts) resulting in drastic under pressure and then the Light comes on.

Wouldn't Kens solution of isolating the Audi tensioner be just as affective in doing this too, it seems to me that you are asking for an under/over pressure solution?

That would be great but more involved, don't we just want to mimic stock?

Thanks, and keep it coming,

Dave

 

I think what Ken proposes makes sense - it tells you when the adjuster has run out of adjustment range.

I'd also like to have a secondary system monitoring the belt for: 1) excessive flap in the long section after the crank drive (e.g. maybe the adjuster siezes up) and also for lateral track &/or swarf on the side of the belt (e.g. something is out of alignment or the belt is just getting chewed up). I think the tracking is harder to pin down a location for...

I'm thinking a U shaped no contact optical system around the belt - fixed on/through the T-belt cover. Trigger the same warning from any of these sources.


Alan

 

A wide roller/ball bearing running on the back of the belt, mounted on a pivoting, spring-loaded arm (or mounted on a cylinder with an internal spring, if that is easier to mount). The spring loading pushes the belt an eighth of an inch or so, which doesn't increase the tension. When the belt loses tension, the spring loading moves the pivoting arm, triggering a microswitch, turning on the belt tension warning. Be nice to get rid of the stock three-minute delay, though.

 

A couple of points:

First, I think this conversation illustrates the clear superiority of PKT system over the stock tensioner system.

Second, inability to meaningfully repurpose the warning light of the inferior system is not a good reason to not use the superior system that doesn't have the slow failure modes that the original system's warning light tries to detect.

Third, I think that activating the warning light based on extension is a good idea, as long as the trigger points are set such that the light doesn't trigger in normal operating conditions.

Fourth, while we can dream up all sorts of instrumentation systems, such as optical detection of missing belt teeth, the system has to be simple and cost effective for the it to be actually useful to the community.

 

I wasn't planning on counting the teeth... great idea!

I do think optical could be pretty simple, self contained & well out of the way... Someone should make one!

A DIY version would not be quick - or cheap - or easy... nor likely very well calibrated to its purpose - a bit difficult to test its operation & effectiveness.

Might be a good 3D printer project though... Here's what I came up with a while back - just an idea - nothing since.

Alan

 

Look'n good Alan!

In the mean time ... I'm going to try Kens idea and isolate the PKT as he describes and connect it to the factory Warning light and see what happens. Can't hurt anything, if I get a lot of false warnings I'll just re-ground as it is now.

So what is the "best" mechanical fastener for me to use to keep the Tensioner bolts from coming lose as I will be using Nylon washers?

Thanks all,

Dave

 

Even if I built this thing - I'd still do that too. I'd use mica not nylon for the washers - long history of its use as an insulator under compression & high heat.

BTW the shown diagram boxes the belt on all 4 sides, but since flap movement pretty much has to be ~symmetical this could probably be simplified to a 3 side system (track to both sides and flap only on the gravity assisted side).

Note this is shown in proximity to the belt for representation purposes - but it can actualy be expanded to be as far away from the belt as you have room for in the application both in X & Y. In practice we are limited by the space inside the covers and other stuff encroaching

Alan

 

Will belt dust triger the system?

 

Mica, OK need to start looking for some, also what is your thoughts on the Heat Shrink tubing for the Bolt shafts?

I will also use some Blue Loctite, still seeking suggestions on the locking Fasteners.

Thank you all,

Dave

 

I think HD heat shrink or just some kind of thin wall plastic tube section is fine - its really just a spacer - shouldn't be under any stress really once installed. Once everything is locked into place it almost doesn't even need to be there any more - so not very critical IMO.

Alan

 

Coolant pressure would piggy back the existing coolant temp light - the smaller terminal on the temp gauge sensor.

Studs are not welded. They are just screwed in and held by loctite. (Plated studs may have to be special ordered.)


True. Even if the impeller stopped moving, the system would still be under pressure, so it wouldn't work here.

A pressure switch would be a good indicator of a catastrophic loss of coolant - a quick search finds it is used on race cars for that.

 

With just an LED source I think it would be difficult to keep the beam tight enough that it would - unless there was an ungodly amount - in which case it would probably be a good thing.

Alan

 

Just like the Stock Warning Light would not show the WP not moving, hence shredded belts


Ken have you tried to do this yet, isolate and connect it like you show?

I was looking at the Stage 8 stuff, but don't see one that would work for this application on these bolts I may be missing how they work?

I guess I could just drill and wire them?

Thoughts?

Thanks!

Dave