dr bob

Mark, It probably is electrical. That's the darn tension monitoring system for you. Belt loose or flapping, there's an electrical connection that opens and turns the light on. Pull the wire and that same circuit is opened and, miracle!!!, the light comes on. Stop the flapping by adding oil to the tensioner. Verify the correct assembly of the tensioner and the spring and contacts in the switch. When you get the belt on and the tension set, but before you button all the covers on, test the tesnion monitoring circuit with an ohm meter. If you have an open circuit to ground from the pigtail, the switch is not assembled correctly. If it's closed to ground it's OK to assemble, and you know it's working. All before the covers go on, imagine that.

For those playing along at home, in a racing 928 like Mark's, that would be a red one with his name on it, it's actually better to run races without oil in the tensioner. The extra motion allowed on the belt frees up horsepower as it extends and stretches. That warning from the tensioner monitoring system means nothing more than there must be something wrong. It couldn't be the undampened tensioner, not in a red 928 race car. Think of it as hillbilly 'variable valve timing', without that annoying expense of complications around a hydraulic actuator. The valves time themselves!

Bill Ball

ROFLMAO

ew928

Doc Bob.
Will putting Amsoil in the tensioner help dampen the Timing Belt Warning light?

okbarnett

First of all, Im surprised you havent had to replace the water pump in 3 yrs.
Second, These cars are 20 yrs old. I dont see anybody rebuilding the tensioner. I always R&R the thing every time I change the water pump and belts.
The first time I checked it, it was completely siezed . If its not moving freely, its not going to matter if it has oil or not.
After you put it back togather you can (clean),and check the electrical mechanism that the sensor wire is connected to and make sure it is working properly. After that you can eliminate the tensioner giving a false reading and worry about the belt being too loose.

mark kibort

Oh brother! Its funny that something so critical has lasted 10 years of hard racing.

Look, ive had oil in the tensioner, infact, after the rebuid, I even bought a new seal and filled it up with swepco green 75-90weight just for you . the darn light came on as it always did. eventually, most all the oil leaked out the shaft seal. now, it probably has about half the oil as normal, but before the holbert engine had no oil, it all had leaked out the gasket seal. tension is always good, and you are dreaming if you think the oil can have any effect of damping. there is about 50 washers, that are so close together, and a substantial gap around the diameter to the housing. its basically like a direct connect. scots was all siezed up. we fixed that, lubed it up and its running dry as well.

Now, if someone wants to hook some highspeed cameras to the timing belt, they are welcome to conduct the test on my car. but, until then, no one really knows for sure what is going on.

as far as the electrical sytem, it didnt work, even when I got the car. belt tension is fine and that has no bearing on oil in the tensioner or not. the oil is for heat transfer and lubrication for adjustment, and not much more. because of that, i dont beat on the engine until it is fully heat soaked, so that tension is corrrect.

docmirror

The failure mode of our belts is almost always shearing the teeth off the belt surface. That's because the teeth are what carry the torque of the cam, oil pump, WP, tensioner, and rollers. The belt material will last a long time regardless of thickness.

The belt was upgrade to the HTD rounded tooth in mid production. This makes perfect sense because it's harder for a stress crack to start or propagate on a rounded surface. Works for rubber and metal. After that, we got the double nub belt which has a compression groove in the tooth of the belt. All advances in the design of the TB.

The tensioner is not a rebounding device so much as it is a heat growth expansion device. Yes, it does some rebound control from off to on throttle and on to off, it's mainly there to allow the engine to grow when it heats. Which means it's critical to measure the tension according to the book, as temp will give different readings. If you want to verify this, look at the values when setting the valve lash on each side of the engine. The left and right banks are different. The belt does almost no stretching, even the Conti belt despite the thickness should not do any stretching at all.

Adding thickness of the belt is not always the right answer. The belt has to make a lot of inside and some outside radius turns, and adding thickness can potentially add to surface distortion due to the changes in the radius stretching on the inside particularly. Think of what the inside of the belt where the teeth are when the belt goes over the water pump and the tensioner roller. They are stretched a bit, and more thickness, means a bit more stretching, something we want to minimize. However, I've always had excellent luck with Gates belts. I think they are the best made for most all applications.

soontobered84

+1

mark kibort

Exactly! well said! +1

mk

dr bob

To correct your misconception of whethere there is damping available in the tensioner: There is. WHEN THERE IS OIL IN THE TENSIONER, there's a check valve that allows oil to flow freely into the cavity under the piston, but closes to limit flow going out. Result is that the piston can extend easily as the belt gets loose, but is harder to compress when tension increases. To my knowledge and experience, this is a dampener. Perhaps your definitions are different?

Why did the oil leak out of the shaft seal? This failure is common if the tensioner is filled using too much pressure, AND ESPECIALLY IF FILLING THROUGH THE WRONG PORT, since that will fill the top cavity before the bottom, and the check valve prevents flow that way.

The electrical-- You know for a fact that the sensor switch did not function from the time you obtained the car. You've replaced the belt a couple times now, including moving the tensioner and switch unit from the old engine to the new stroker engine, and moving that new engine from the oldcar to the new one. Can I suppose that it never crossed your mind at any of those times to peek at the switch/spring/contacts at the end of the tensioner plunger and see what might be wrong? What might be causing the "!!Check Toothed Belt!!" warning message to shout at you in bright red? If the temp gauge went to full hot, or the oil pressure dropped and the warning lights came on, would you continue driving until you saw steam or heard the rod bearings rattling? "I don't know why the car blew up, dad. I was driving it the way I always do, with the all the warning lights on, then BOOM clank clank clank... It shouldn't have broken. After all, I've RACED it for years with those warning lights on, and racing is the only true test of durability." Does this sound as brilliant to other folks as it does to me?

soontobered84

docmirror

That stack of washers in the tensioner(note that it's not called a dampener, although it does some of that too) is called a 'belden stack'. It's also used in aircraft steering gear where shimmy is a problem. It only works correctly when filled with fluid. Yes, the fluid acts as a damper, just as it does in a shock absorber, same concept.

The tensioner allows the engine to grow when it gets hot. It also takes up some of the vibration between on and off throttle, that's why it's filled with oil. It'll work without the oil but it's not doing as much damping of the vibration.

So the take-away from this is that a 'timing belt' warning will be activated with, or without oil if the "tension" of the belt is too low. However, having no oil in the tensioner will usually not trigger a timing belt warning because the periods(if any) that the belt may be under-tensioned is too short for the circuit to capture. I'm guessing that the switch contact must be continuously made for a period of time before the warning is displayed. As has been said, there is a 3 minute delay such that the engine will warm and grow before the warning circuit is activated.

I just did the tensioner in my 2 VW Golf cars, and they use a spiral wound spring for tension control and a fluid filled puck with I'm guess some kind of flag baffle in it for damping. The Chrysler 4 jug uses the same, and the Nissan small 4 uses a similar system. The pre-load is set with a lock/jam nut on the hub of the tensioner and an Allen bolt to get the setting right. Ferrari uses an eccentric roller that has no damping control at all. It is set for the life of the belt, and seems to work ok. I do not rev my Ferrari hard when it isn't fully warm for this reason.

ROG100

After Jim Bailey enlightened me I call it a de-tensioner.

PorKen

I've used Continental and Flennor belts. Fuhgeddaboudit.



The 'Kibort factor' is the reason self-adjusting tensioner/dampers were invented.

ROG100

Flennor is Gates

docmirror

Gates makes OEM for many brand names. Napa brand is Gates. Like I said, good stuff.