aaron3

I recently had the dreaded toothed belt warning occur. I pulled the right belt cover and checked the tension on the belt (which I had just checked a month before) and found it to be fine, all marks line up, belt looks good.

I grounded the sensor and ran the car for 5 minutes. The light did not appear. Therefore, I can deduce that the warning brain and the wiring to the sensor is ok. The problem lies in the connection at the sensor or the wiring into the tensioner.

Here's the question: I can't tell how the wiring is connected on the idler roller with only one belt cover off. Do I have to remove the center cover too? What all has to be removed to remove the center cover?

Any ideas, photos, etc are very appreciated. Thanks.

John Speake

Mark,
The wiring is taken through the cover, and the wire clips onto a tag on the tensioner arm. The arm is mounted on plastic bushes so it doesn't ground the connection. The ground is through a rather tenuous path of washer, spring, pin etc. See the excellent diagram on Tobny's website

http://members.rennlist.com/v1uhoh/timing.htm

Also, see his other page on setting the tension.

SteveG

On the diagram, Isn't "positive lead" incorrect? That is a brown (ground) wire, is it not? Other than this, we are indebted to Tony for that diagram.

aaron3

Ok, I took everything apart and found that the contact bridge that runs from the spring on the tensioner to the tensioner arm is BROKEN !!!

Here's the next questions:

1. The contact bridge looks like copper (??). Is this possible? Can you solder copper?
2. Doesn't the thrust pin continuously push into the tensioner pulley and provide the ground circuit also? If this is the case why am I still getting the light?
3. Does anyone know if I can replace the contact bridge only? Does the tensioner have to come out to do this?

Any help is again appreciated.

John Speake

1) Copper or maybe phosfor bronze ? Both are solderable, but solder isn't strong enough for those conditions.
2) the tensioner arm is insulated from ground on its pivot bushes, the ground is made through the pin to the body of the tensioner. But only to the contact bridge if there is enough pressure between the parts. It's crude, but works quite well.
3) You will have to remove the tensioner, this is possible without taking all the covers off, but you have to be very careful to get the gasket to the block prorperly in place, and also the pin located into both the tensioner and the pivot arm when you put it back. All the tensioner bolts are accessable outside the covers.

aaron3

John,

Thanks for all the advise and the help.

1. If I remove the tensioner, do I run the risk that the belt will loosen too much and the cam sprockets will move?

2. I'm still not sure I understand the electrical circuit that is formed by the tensioner, etc. Last night, when I had it all apart I measured the continuity from the 'tab' on the tensioner arm to the broken contact bridge. I was expecting 'no continuity' but instead there was continuity. I don't understand how this can be since the tensioner arm is physically isolated from the block and the 'tab' is not connected to the contact bridge due to the break. I reasoned that the continuity was due to the tensioner pin making contact with the tensioner arm. Is this true? My question is why doesn't this pin to arm contact occur under ordinary circumstances (i.e why did I get the TB light with good belt tension?)

John Speake

hi Mark,
1) When I did this on my 16v car (to replace a split boot that the OPC missed) I locked the cams in place with a spanner on the end nuts. Yes, the belt goes very loose, and you need to take care, but if you get it one tooth out on re-assembly, it is easy enough to slacken it all off and reset the belt.

It may be that you have so much apart already that doing it the proper way would be too much extra work.

2) I hadn't really thought about this before, but you are correct, there are two possible ground paths. one through the arm/pin, and the other through the spring washer, contact bridge.

Having said that, the path via the end of the pin to the arm is a point contact, and steel to steel, subject to rusting. The contact through the spring washer and contact bridge has a larger contact area, although there are disimilar metals in contact. As I said before, not a brilliant design !

When I re-assembled mine, I cleaned all the contact areas, and then applied contact grease to try and stop corrosion.

Garth S

For a little security, use a light spring clamp or tie-wrap to secure the TB to the cam gears before releasing the tension: this is also a useful 'third hand' trick when installing a TB.
The 'electrical' circuit of the tensioner is dead simple: From the center cover tab, continuity is maintained through the wire pig-tail to the tensioner/carrier arm. The carrier arm is insulated from the block by the two plastic bushings on the pivot stud/bolt. The arm continues to provide a ground path to the piston rod - to the tensioner body - to the block which is grounded! As the pivot points of the push rod are lubed, and do not provide reliable continuity , an 'earth' path is provided from the carrier arm to the insulated piston rod by a copper strap, or a braided wire.
When at adequate tension, the continuity to ground/earth is maintained. When tension falls below ~3.0, the spring seperates the piston rod from one, or both of its cups - breaking continuity = alarm.
The spring remains isolated electrically, for it remains in contact with the tensioner body and carrier arm at all times when installed with a TB in place, regardless of how loose it may be.

Bill Ball

The tensioner carrier arm contact point with the end of the tensioner pin is inconsequential. The ground path is via the tensioner body.

John Speake

QUOTE
The tensioner carrier arm contact point with the end of the tensioner pin is inconsequential. The ground path is via the tensioner body.
__________________
Bill
>>>>>>>>>
hi Bill,
We never said the final ground to chassis was through anything else other than the tensioner body - we are talking about the other parts of the circuit.

Bill Ball

Maybe I misundestood. I thought there was some reference to cleaning the contact point between the pin and the carrier arm. That does nothing. As long as the wire from the arm to the pin is intact (it is the main weak point), no other points of contact with the carrier arm matter. Sorry if I misread. Carry on.

John Speake

OK Bill,
I see that what I wrote could be mis interpreted as cleaning the pin to arm contact, rather than the contact bridge to spring etc ....... I meant the latter of course

Sorry for any confusion !

Regards

Garth S

Mark,
Have we thoroughly confused you??

If you want a quick fix - that may last for 5-10 years - you can solder a braided wire 'bridge' across the break of the copper strap. If you can get enough working room, do it in place (without tensioner removal). Buff the copper strap ends clean, wrap and apply the heat!

aaron3

Hey you guys. Thanks for all of the dialogue, advice, etc. I really, really appreciate it.

I think I will try the braided wire bridge trick. It really only needs to work until I do the next T-Belt change, which based on time, may be next spring. At that time the tensioner will be rebuilt and I can replace the bridge. I'll let you know how it goes. I'll try to take some photos.

majhopper

I just discovered that I do not have a bridge, but a custom built wire with ring terminals at each end.

I am confused as to what exactly the bridge is supposed to do, other than provide a path to ground. Am I running a risk of catastrophic failure by leaving the wire in place?