Author Topic: Tensioning the Timing Belt Correctly (Read 6476 times)

Northboundtrain · « **on:** March 18, 2005, 01:03:47 am »

How do you measure the tension on the timing belt, and what should the tension be? I've always just done it by feel, and it has seemed to work out okay (although, the first belt change I did, I way over tensioned the belt and it made a horrendous squeal). I'd just like to know how to do it correctly. The Bentley Manual shows some kind of tension guage, but I can't seem to find this tool anywhere.

Thanks

Busdriver · « **Reply #1 on:** March 18, 2005, 11:15:27 am »

I just paid a VW dealer $650 to change the belt on my A3 TDI (used, but new to me). The procedure in the Bently looked intimidating, and I didn't want to risk blowing up my Jetta (used, but new to me). But I HAVE (uneventfully) changed the timing belt on a gas VW engine by the very method described above. I was mostly intimidated by the use of the "special VW tension gauge". Now I can buy the tools to lock the injection pump and camshaft for $50 and save myself $600 when the belt needs changing again in 60K miles. Thank's!

Northboundtrain · « **Reply #2 on:** March 18, 2005, 12:16:20 pm »

Thanks, I figured that there was a good rule of thumb for this. Much better than the back-of-till-it-stops-squealing method. :wink:

asau · « **Reply #3 on:** March 18, 2005, 10:09:27 pm »

I tried the fingers at 90 method but it feels really loose to me. Is that how it is really suppose to be? Has anyone used a newer tdi timing belt tensioner tensioner? The newer tdi's timing belt tensioner has a tension guage built into the tensioner, has anyone tried to use one of the newer tensioners on a older model diesel? does it work? would it work?

chrissev · « **Reply #4 on:** March 18, 2005, 10:19:09 pm »

Quote from: "asau"

I tried the fingers at 90 method but it feels really loose to me. Is that how it is really suppose to be? Has anyone used a newer tdi timing belt tensioner tensioner? The newer tdi's timing belt tensioner has a tension guage built into the tensioner, has anyone tried to use one of the newer tensioners on a older model diesel? does it work? would it work?

The belt is not supposed to be tight. You should be able to press it down a bit in the middle between injection pump and cam sprockets. You should be able to twist it almost 90 degrees but not quite. If it is tighter than that, it will put pressure on the injection pump internals and damage them.

fatmobile · « **Reply #5 on:** March 18, 2005, 11:55:26 pm »

I've heard that 90 degrees is for the gas timing belts, which are narrow compared to the diesel timing belt.
45 degrees has worked better for me.
If you set it too loose, it will vibrate between to crank and idler pully when you rev it up.
Set it too tight and it will make lots of belt noise.

GoFaster · « **Reply #6 on:** March 25, 2005, 08:05:18 am »

I wish I'd read this thread a couple hours ago ...

Today's chore was changing the T-belt on my '96 TDI which is supposed to have the automatic tensioner, but I discovered after taking it all apart that the dealer had given me a manual tensioner as a replacement. I read the manual for how to set it, but obviously I don't have special tool number 210, so I just adjusted it so that on the long free run between the crank and the tensioner, I can push it back and forth 1/2" - 3/4" by hand. There's a top idler roller between the pump and cam on a TDI that prevents twisting the belt (or using special tool number 210) from being done there, but I can *barely* push the belt off that roller by fingers if I push really hard.

The engine started and ran fine, and didn't make any strange noises, so I hope it's OK.

By the way, the manual tensioner is steel and has nothing to break inside, but the automatic tensioner is plastic and has all sorts of springs and cams and gizmos inside, so I think maybe the manual tensioner is an upgrade ...

How often are you supposed to check the belt tension with the manual tensioner?

QuickTD · « **Reply #7 on:** March 25, 2005, 08:12:43 am »

Did you replace the tensioner mounting stud in the head as well? The manual tensioner uses a 10mm stud, the automatic one uses a stepped stud - 10mm on the head end 8mm on the outer end. I would worry a bit about it coming loose if you put the manual tensioner on the smaller automatic stud...

I don't think you need to worry much about checking the tension. You might check it after a few thousand miles, after that the belt is seated into the pulleys and won't stretch much more for the life of the belt.

GoFaster · « **Reply #8 on:** March 25, 2005, 12:28:52 pm »

No, didn't replace the stud, because the whole thing happened because the dealer gave me the wrong tensioner. That explains why the torque setting is different. Old automatic tensioner is fubared, and today is a holiday so can't get parts. I'll keep an eye on it.

GoFaster · « **Reply #9 on:** March 28, 2005, 05:25:38 pm »

Update: So far, it's all good.

Drove it 20 km, re-torqued the nut to the specification for the automatic tensioner while the engine was still hot. The manual tensioner had not budged. Then I took another M8 nut and applied loctite and torqued that against the first nut. It's not going anywhere. And I put a paint line across both nuts and the tensioner, so that I can make sure it's not going anywhere at the next oil change interval (about 1500 km away). If it's all good at that point, I'll forget about it.