Timing Belt tensioners revealed...

chromeBuddha

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In light of recent exciting adventure in wrench turning, I have some questions about the nature of the TB tensioner, its mechanism, etc.

Here we go:
1. Is the cam mechanism in the tensioner such that a 360 turn of the tool will bring the tension back to where you started? Or is it progressive, so the more you turn it clockwise, the more tension it creates?

2. Is there anything that you need to make sure of when initially installing other than the alignment prong being in the slot in the head and the tension being off (ie the holes being to the left near the bottom)?

3. Is it a good idea to recheck the tooth and groove after you have done the manual rotations and, if it has shifted, relieve and re-tension?

Thanks for any insight.
 

GoFaster

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1. Don't turn the center cam 360 degrees and then this is a non-issue. I've never seen anyone even try to pull that stunt - it gets so hard to turn the cam that a normal person will realize that something is wrong and hopefully stop before breaking something. The spring is pinned from rotating inside. Spinning the center cam 360 degrees probably isn't even possible without binding up the spring inside.

2. Having the alignment tang on the backing plate into the proper slot is the big one. The other one is when adjusting it, DON'T turn the tensioner adjustment cam in the wrong direction! The picture in the shop manual shows the way you are supposed to turn it.

3. Yes. The tang will stay in the groove, but rechecking the tension and locking tools after rotating the crankshaft 2 complete revolutions is a good plan. No need to release the tension - just check whether the notch lines up with the projection. If it does, it's fine. If it does not, hold the center cam from rotating with the pin wrench, release the locknut, and do what needs to be done with the pin wrench to make the notch line up, then re-torque the locknut.
 

chromeBuddha

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There is an square cam block that rides on the stud off the engine block. This is what adjusts the tension. I don't think the spring is being wound. It seems like there may be some degrees of rotation beyond the tooth and gap mark where the tension increases, but, if you go much further, it should start to drop off as the square cam rotates.
 

chromeBuddha

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Great! It even points to the reason all the belts are running closer to the engine side of the pulleys.

Is there a way to save this .pdf on this site as well? Good info shouldn't be lost.
 

alphaseinor

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It also explains the increase in mis-aligned tensoners causing damage to the engine.
 

Blackbug1

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Thanks for the link, that is great info. I printed it and put it my 3 ring notebook for my 98 NB TDI. This site is really great and full of knowledge. I have learned so much since I have found it.
 

DeafBug

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That is what you are looking at when the schedule maintainence in your owners manual states "Check timing belt" You not only check the belt but the alignment on the tensioner and adjust if needed. But you only adjust it advance, never retarded. Retarding it can make it loose then engine damage can happen. I always look at the tensioner when doing belts before loosing anything. Many times it is retard.

FYI, in the document on the 4th page, where it shows you "wrong" is retarded. if the tab is on that side anywhere, advance it. If the tab is ont the other side then leave it alone, depending on how soon you are to get your timing belt changed and how far off from where it should be.

Also I want to point out that while the engine is running the tensioner tab moves often, so if you shut the engine off, the tab could be on one side instead of spot on. You need to observe that before deciding if the tensioner needs adjustment. Best observation is to remove the timing belt cover and run the engine. Get the mirror and look, same way you decide on the injection timing. Don't worry if the tensioner doesn't move at all. I see those too.
 

javert

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Actually the best way to check it is to have the engine shut off and slowly bring the flywheel up to Top Dead Center, then check to see if the pointer is in the correct position. Adjust if required. You may need to use a mirror. It can look a bit off if you are not looking at it head on. This is truly the best way to check it. If adjustment is required, adjust and then rotate the engine two full turns and slowly bring back up to Top dead center and then check again. IF you go past TDC then you must go around 2 more times, never turn the engine counter clockwise ! I like to turn the engine by hand until I get close to TDC and then use a screwdriver to slowly in a controlled manner, rotate the flywheel (via the window on the top of the bellhousing) up to TDC. Due to the compression pulses of this engine, getting it right is very very tricky. If you follow the posted tech tip you will be fine.
 

gottdi

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Nice write up. Now I know why my belt runs closer to the engine block. Not much closer but closer none the less. I now have that info in my book. Excellent for all who need to do a TB change. Be sure to give the instructions to whom ever is going to do the TB. Unless of course it's a TB guru who already knows the info. But it would be a good idea to have it on hand anyway so you can follow along. Pretty easy to do and pretty easy to screw it up if you don't follow the directions.
 

chromeBuddha

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Yep, that definitely failed. Where that piece is broken out, there should have been another "finger" pointing down and latching into that small groove at the end of the large slot...so when that broke, it was just like the one to the engine block had broken.
 

TornadoRed

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bulldogger1 said:
Here's my broken tensioner.
Was that the original one in your 2000 MY TDI, or a replacement?
 

bulldogger1

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TornadoRed, that was the original tensioner. The mechanic that did my TB service only replaced the belt. Needless to say the picture shows why you should get the 100k deluxe kits and do it right. If not, you get to tear the motor apart like I did.
 

javert

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Bulldogger1,


Your pic is a classic example of a misinstalled timing belt tensioner. The evidence in the pic clearly shows that the tensioner was hammering on the stops as well as mistracking. I can assure you that this tensioner was not installed correctly and that is what led to its ultimate destruction.
 

chromeBuddha

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By hammering against the stops, you mean it was hitting the end where it looks like there is an indentation in the stop?

If we could look at this with the tensioner installed and properly tensioned, we would see the tang that broke off approximately centered in the slot? And that the normal rigors of use would have it bouncing freely in the middle and rarely, if ever, contacting the stops?

Since the guy that did the TB didn't have the tools (as evidenced by the paint marks we found when we pulled the head), it is likely he jury rigged the tool to set the tension and didn't know about the tooth and groove alignment marks...so may have dastically over or under tensioned.

All the money wasted making MI I, II and III and all we want is a mini spy cam looking at the backside of a tensioner...is it too much to ask?
 

Dieselgeek

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Cause and Effect

chromeBuddha said:
By hammering against the stops, you mean it was hitting the end where it looks like there is an indentation in the stop?

If we could look at this with the tensioner installed and properly tensioned, we would see the tang that broke off approximately centered in the slot? And that the normal rigors of use would have it bouncing freely in the middle and rarely, if ever, contacting the stops?

Since the guy that did the TB didn't have the tools (as evidenced by the paint marks we found when we pulled the head), it is likely he jury rigged the tool to set the tension and didn't know about the tooth and groove alignment marks...so may have dastically over or under tensioned.

All the money wasted making MI I, II and III and all we want is a mini spy cam looking at the backside of a tensioner...is it too much to ask?
A while back I mounted and tensioned the tensioner in a vise and I confirmed that the tang that is "failing" on these tensioners sits in between the two stops in normal operation. The tang never contacts the stops unless some other part in the system slows down or stops turning, however briefly. Once some other shaft slows down stops turning (for whatever reason), the crank pulley keeps pulling on the belt. Since one shaft is frozen, the crank forces the belt to tighten up and the tensioner is required to deflect fully and whips the tang into the stop and breaks it off.

Simple.
 
Last edited:

RabbitGTI

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chromeBuddha said:
Great! It even points to the reason all the belts are running closer to the engine side of the pulleys.
Nice PDF. Ya lost me on the "reason all the belts run closer to the engine side of the pulleys". My B4 has always had the belt run closer to the passenger side of the injection pump pulley. Can you clarify what you meant? Thanks.
 

javert

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chromeBuddha said:
By hammering against the stops, you mean it was hitting the end where it looks like there is an indentation in the stop?

If we could look at this with the tensioner installed and properly tensioned, we would see the tang that broke off approximately centered in the slot? And that the normal rigors of use would have it bouncing freely in the middle and rarely, if ever, contacting the stops?

Since the guy that did the TB didn't have the tools (as evidenced by the paint marks we found when we pulled the head), it is likely he jury rigged the tool to set the tension and didn't know about the tooth and groove alignment marks...so may have dastically over or under tensioned.



Yes to both questions.
 

chromeBuddha

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The pdf indicates that the replacement parts stand the pulley away from the block a shorter distance. What everyone who I have spoken with who has changed a TB recently has said is that the TB runs a mm or so closer to the block on the toothed pulleys than the TB they replaced. I think the pdf addresses this.

RabbitGTI said:
Nice PDF. Ya lost me on the "reason all the belts run closer to the engine side of the pulleys". My B4 has always had the belt run closer to the passenger side of the injection pump pulley. Can you clarify what you meant? Thanks.
 

lostcord

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How does being at Top Dead Center affect the position of the tensioner pointer/tab thing?

Actually the best way to check it is to have the engine shut off and slowly bring the flywheel up to Top Dead Center, then check to see if the pointer is in the correct position.
 

jasonTDI

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lostcord said:
How does being at Top Dead Center affect the position of the tensioner pointer/tab thing?
It dosen't. The tensioner keeps even tension around the whole lap of the belt.
 
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