300Tdi Timing Belt Tension

[SPendrey]

I doubt there is a "correct" answer to this, as there are so many answers floating around the Internet, but here goes...

Just did the timing belt on my (Disco) 300Tdi, and the tensioner was set to 22Nm as per the Tech Archive article here.

Having done this, I noticed Rave suggests 14-16Nm using a type of torque wrench that I don't have (see pic), and I see @ 6mins 30secs on a video from Rimmer Bros their mechanic says 12Nm.  Another video suggests 15Nm verbally, but reduces to 11Nm in the text/comments.

Is there a consensus on what I should have done?  That said, I'm probably not going to undo everything now!

[Snagger]

Why would you take youtube or retailer advice over the workshop manual figures?  Stick to what's in the manual for tensions, preloads and torque figures - LR did extensive calculation and testing to come up with them, youtubers didn't.

[dailysleaze]

There is conflicting advice from LR hence why people give different values, as it depends on what source they've read.

The TSB that related to the timing belt modification kits in March 1998 says 11Nm, but the 3rd edition Defender 300Tdi workshop manual in May 1999 still says 15Nm for a new belt and 12Nm for used. So who knows. I did 11Nm and it's been fine for 5 years.

Defender Workshop manual 1999

[monkie]

There was also a thread on here recently regarding reusing head bolts for the 200tdi. The defender book said one thing the discovery book said another!

[Kurt]

Used 11nm on mine with no ill  effect. I believe the revision of the torque figure is to stop the belt from pulling the injector pump pulley out of line and causing belt wander.

[SPendrey]

OK, thanks all.  Since I bought 3 timing cover gaskets, I might as well use the last one (yeah, that's right!) correcting the tension.

 

Can I also suggest the Tech Archive article is updated? 🙂

[Snagger]

12 hours ago, Kurt said:

Used 11nm on mine with no ill  effect. I believe the revision of the torque figure is to stop the belt from pulling the injector pump pulley out of line and causing belt wander.

Makes sense.  The extra tension in a running belt would prevent it skipping teeth at that setting anyway.

I wonder if the lowered tension was as a reflection of the belt alignment issues that plagued 300s, the lower tension being considered a way to mitigate a thinned belt to prevent it from snapping?  Mike at Britannica Restorations (Ontario Youtube series) had issues with one that had the belt kit replacement but still had alignment problems from a warped timing case, all started from the injector pump rear bracket alignment.

[Ed Poore]

I wish I hadn't seen this. Just done the timing belt on mine but followed the workshop manual...

[SPendrey]

So you used "14 to 16Nm"?  I used 22Nm, which means I know what I'm doing this weekend, again!

[Ed Poore]

Yep, 15Nm

[Daan]

I pretty much do it on what feels right, but I have done it so many times now that can't care to remember.

What is more important though is how tight you do the cap head bolt that holds the slotted roller; I had this come loose on a few occasions and this is potentially lethal for your engine. I replace this bolt for a longer one (next size up), apply loctite and do it up as tight as I dare. 

 

Daan

[Peaklander]

On 11/29/2018 at 9:08 PM, Daan said:

What is more important though is how tight you do the cap head bolt that holds the slotted roller; I had this come loose on a few occasions and this is potentially lethal for your engine. I replace this bolt for a longer one (next size up), apply loctite and do it up as tight as I dare.

This is exactly where I am - I found, just in time, that this has happened to me during planned maintenance of my belt.

 

I am very confused now, as I thought I had made an error in 2017, in not using a washer at the tensioner roller and also using a short cap head bolt. Now I have discovered the previous parts (that I thought I hadn't kept) and in there is a short bolt and no washer.

So that's two belt fitments that have used this method.

Sourcing what I think are the correct parts including ERR900, I now have a genuine washer that I find locates at the front of the roller, not the back and a long bolt to go with it. The previous assembly is therefore completely different to what these parts would produce, that is a roller supported at the front, rather than at the rear.

 

So I think that I did use the correct parts. Those available on Turner's website are the short cap head (no washer) and not the long flanged bolt with washer. Is there a torque spec. for this small bolt or is it just very tight?

Can anyone help?

Turners can't advise on this (I asked).

[Snagger]

35’lbs rings a bell, but I can’t swear to it.

[smallfry]

Once a timing belt has been run, it requires less tension. The danger with these belts (on all vehicles) is too much tension. Its always tempting to tighten it just a bit more. They do not stretch, they wear material off minimally, off the teeth and back, not the sides like the 300 Tdi does, thats an alignment problem as we all know.  Most vehicles these days have an automatic tensioner, which tensions the belt on fitting, than the retaining bolt can be tightened. I have changed belts that have been quite loose, excessively so sometimes, that have been running like this for some time, so the low figure given would not worry me

Too much tension can cause premature failure by fatigue, and also cause bearing wear in components that they drive.  You can normally tell if a belt is too tight, as they make a strange thrumming noise.

[Maverik]

18 hours ago, Peaklander said:

This is exactly where I am - I found, just in time, that this has happened to me during planned maintenance of my belt.

 

I am very confused now, as I thought I had made an error in 2017, in not using a washer at the tensioner roller and also using a short cap head bolt. Now I have discovered the previous parts (that I thought I hadn't kept) and in there is a short bolt and no washer.

So that's two belt fitments that have used this method.

Sourcing what I think are the correct parts including ERR900, I now have a genuine washer that I find locates at the front of the roller, not the back and a long bolt to go with it. The previous assembly is therefore completely different to what these parts would produce, that is a roller supported at the front, rather than at the rear.

 

So I think that I did use the correct parts. Those available on Turner's website are the short cap head (no washer) and not the long flanged bolt with washer. Is there a torque spec. for this small bolt or is it just very tight?

Can anyone help?

Turners can't advise on this (I asked).

I believe there are two types of tensioner units, one early type - which is derived from the 200tdi and a later type.

Early type used the long bolt and the stepped washer with the oval cut out - this was very similar to the Discovery 200tdi set-up - picture of tensioner here (this is also whats shown in a lot of the parts manuals) - Tensioner Part number ERR1972 (from some google searches this part number also appears to bring up the later slotted type too which is not helpful.)

300tdi timing belt tensioner - Bing images - notice there is just a hole in the middle of the wheel.

LR then changed to the more commonly seen tensioner - where they effectively moved the clamping mechanism to be integral and to the rear of the tensioner unit. - this just needs a the short hex cap head bolt to work. - Tensioner Part number LHP100860

300tdi timing belt tensioner - Bing images

300tdi timing belt tensioner - Bing images

Both tensioners are interchangeable with any 300tdi.

[Daan]

I have not seen the longer bolt with the slotted washer before. My engine was one of the last build 300 TDIs, and I bought it new. the first time I changed the belt, the tensioner had come loose, hence my precautions.

[Peaklander]

The bolt torque is 45Nm according to my 300TDi overhaul manual, which is also the torque for the idler pulley nut. I think what must have happened in 2017 when I changed the belt for the first time in my ownership, is that I couldn't measure the torque as it's a hard to access cap head. I probably used a standard allen key with a ring spanner to provide some extra turn and maybe got it wrong.

This time I will probably use the long bolt and slotted washer - as then I can use a torque wrench, although I think I now have some long hex mounted on 3/8" drive; I certainly didn't in 2017. I will use threadlock too.

[simonb]

The tensioner with the shoulders was used with the early crank sprocket which like on the 200TDi, had no shoulders. This tensioner had a thick washer behind it and the timing case, and used a long bolt and washer to secure it.

Early in the life of the 300TDi, engines were failing with belts rubbing against the timing cover.

The tensioner was redesigned without shoulders, and the crank sprocket got shoulders added. The washer thick washer behind the tensioner was deleted and a short bolt used to fix it without the front washer. This largerly fixed the problem, although the injection pump bracket was also redesigned and the modified part used on some engines.

No 300Tdis should be using the original parts - they should always have a shoulded crank sprocket and plain tensioner.

Edited April 21, 2023 by simonb

[Peaklander]

I previously used and will continue to use the newer idler and tensioner that don't have shoulders. The crank pulley does have shoulders. I don't think that using the earlier long bolt and front washer at the tensioner will compromise the alignment and will allow me better torque setting.

[Northwards]

It looks like a 300Tdi timing belt change is in my future too. I've seen it done in person before, but not done it myself (and I've watched a few videos).

I think then that I'm quite clear on the whole process, and have all the tooling I'll need - with just one simple exception. How are you guys measuring the 11Nm? All the beam/needle torque wrenches I've seen are hefty 0-250Nm jobs, or really expensive dial type things. The only things I've found that would be close to giving a workable range are from cyclists tool shops. 

Am I missing something obvious? 

I guess you could set a clicky torque wrench to 11Nm and then try and keep the force static once it's clicked, but that seems a bit dodgy - especially when the manuals are being as specific as 11Nm vs 15Nm vs 12Nm - not much room for error in there. I can see that it doesn't need to be that precisely precise, but still I'd like to have a suitable tool to use. 

[Retroanaconda]

I’ve always just used a larger one, it’s seemingly accurate enough for the purpose. Smaller ones are available though:

Amazon link

 

[Northwards]

Thanks Retro, I have a couple of clicky ones in both 3/8 and 1/2” but don’t actually have one of the beam/needle ones at all, so maybe something like that is the answer.

I didn’t think the gauge on the bigger ones would be accurate enough, and would barely register at 11Nm.

[Peaklander]

There was recent discussion in this thread. Some do it by experienced 'feel', others with a suitable torque wrench. I did it with a spring balance, pulling at about 2.5Kg at the end of a measured-length torque wrench that was used just as a bar.

Whatever way you do it, tighten the tensioner bolt properly! 

[Northwards]

Thanks for linking to that - and apologies to all for repeating the question. I did try to do a search or two on the forum but that didn't come up. I think I was focusing on the job - "300 timing belt tensioning" rather than the tool - "beam torque wrench"...

As I haven't done the job 6 to a dozen times I think I'll get the small calibration beam wrench for confidence sake.