Drive-belt tension gauge

[helen&tony]

Hi
Hopefully, i'm going to have a lash at a few mechanical jobs next month, and I've collected the spares. Cambelt is first job, and I'm in 2 minds as to whether to purchase a tension gauge, as various natterings with members here off - site confirm it's O.K. to let the belt tension itself during the assembly procedure using the tensioner before locking it off, BUT...being a pernickety being, I see the quoted pressure against the drive belt, and can't help but wonder....mmmm...dilemna
Cheers
Helen

[widdowson2008]

Just my take on the issue – others may disagree.

My first thoughts are 'Why change something that works?'
When we changed spenners head, we put a new cam belt on. The spring was checked and was within specification so we re-used it. Almost a year to the day since we did it, and still running fine. So the arrangement seems fine after doing a total of some 100000 miles.

I think the deflection stated in the manual is for checking the belt, not for tensioning it.

The geometry of the cam belt arrangement is such that the spring will tension the belt correctly if the manual procedure is followed.

The important thing to ensure correct tension is to check the spring ‘free length’ (63mm).
If that is outside the parameters stated in the manual, then it will not produce the correct belt tension, resulting in a slack belt.

Another thing to consider.
If you suggest replacing the spring with some mechanical device (bolt for example), it would mean modifying the set up. Not sure how you would do this.

[Simon Jones]

On my previous Bongo, I changed the cambelt, tensioner bearing & spring, as well as the water pump while I had it all apart. It won't add a great deal to the cost or time, but it's much easier to do on your terms rather than when it decides to start to fail.

Likewise, on a V6 it's worth changing the camshaft & crankshaft oil seals at the same time as they are likely to leak as they get older. Having said that, on a V6 it is quite unusual to change the hydraulic tensioner, but that's partly due to their reliability & the £200+ price tag.

[widdowson2008]

On my previous Bongo, I changed the cambelt, tensioner bearing & spring, as well as the water pump while I had it all apart. It won't add a great deal to the cost or time, but it's much easier to do on your terms rather than when it decides to start to fail.

Likewise, on a V6 it's worth changing the camshaft & crankshaft oil seals at the same time as they are likely to leak as they get older. Having said that, on a V6 it is quite unusual to change the hydraulic tensioner, but that's partly due to their reliability & the £200+ price tag.

Hi Simon
I don't think the query is WHAT components to change. My understanding is that Helen is looking at an alternative to the Mazda tensioner spring device.

[helen&tony]

Hi Steve
Yes...I remember what we discussed, and I agree with doing it without the gauge, but you know me by now.... I'm just wondering how to check that tension....I'm one of those pernickety so-and-so's who check TDC with a dial gauge when timing a re-build!
Cheers
Helen

[widdowson2008]

Hi Helen
I probably misunderstood your reasons. (again )
I got the feeling that you were looking at devising some sort of fixed mechanical tensioner, similar to those used on the alternator and air con drive belts which rely entirely on friction on the 'V' setion of the belt. The friction causes wear over time and this is why they need to be adjusted from time to time. Changed spenners 'V' belts the other day and was not too surprised to find evidence of breakdown. (cracks on the inner faces).
The camshaft belt being 'toothed' doesn't stretch as such, but the teeth do wear over time.
If you take a look at the cambelt tensioner, it is designed (via the spring) to keep the belt at a constant tension, which I don't think could be achieved with a fixed tensioning system. (could it?)
Sorry if I mis-uderstood.


...and yep - I know you.

[teenmal]

Hi Helen
I probably misunderstood your reasons. (again )
I got the feeling that you were looking at devising some sort of fixed mechanical tensioner, similar to those used on the alternator and air con drive belts which rely entirely on friction on the 'V' setion of the belt. The friction causes wear over time and this is why they need to be adjusted from time to time. Changed spenners 'V' belts the other day and was not too surprised to find evidence of breakdown. (cracks on the inner faces).
The camshaft belt being 'toothed' doesn't stretch as such, but the teeth do wear over time.
If you take a look at the cambelt tensioner, it is designed (via the spring) to keep the belt at a constant tension, which I don't think could be achieved with a fixed tensioning system. (could it?)Sorry if I mis-uderstood.


...and yep - I know you.

Loosen the tensioner lock bolt to apply tension to
the belt. Do not apply tension other than that of the
tensioner spring. Tighten the tensioner lock bolt. Be sure the
tensioner does not move together with the bolt
rotation.
The tentioner is fixed not floating with the spring like a jockey pulley

[widdowson2008]

Hi Helen
I probably misunderstood your reasons. (again )
I got the feeling that you were looking at devising some sort of fixed mechanical tensioner, similar to those used on the alternator and air con drive belts which rely entirely on friction on the 'V' setion of the belt. The friction causes wear over time and this is why they need to be adjusted from time to time. Changed spenners 'V' belts the other day and was not too surprised to find evidence of breakdown. (cracks on the inner faces).
The camshaft belt being 'toothed' doesn't stretch as such, but the teeth do wear over time.
If you take a look at the cambelt tensioner, it is designed (via the spring) to keep the belt at a constant tension, which I don't think could be achieved with a fixed tensioning system. (could it?)Sorry if I mis-uderstood.


...and yep - I know you.

Loosen the tensioner lock bolt to apply tension to
the belt. Do not apply tension other than that of the
tensioner spring. Tighten the tensioner lock bolt. Be sure the
tensioner does not move together with the bolt
rotation.
The tentioner is fixed not floating with the spring like a jockey pulley

Yer right. So the timing belt IS effectively fixed. and there was me thinking it was a floater.

[helen&tony]

Hi Steve...
I don't know who's misunderstanding the most, as I have been getting VERY confused lately...most of my thinking has to be before noon, when brain slows
The tension is set using the spring,after which it's locked,as Teenmal says, but I see that once locked, Mazda say to check it....BUT...if they have designed the system to tension accurately enough BEFORE lock-down, I am just wondering why they say check?....really, if it's locked, I feel that it should be loosened off and re-tensioned at a given service interval, unless a degree of stretch is accounted for in the initial sequence....
Cheers
Helen

[teenmal]

Hi Steve...
I don't know who's misunderstanding the most, as I have been getting VERY confused lately...most of my thinking has to be before noon, when brain slows
The tension is set using the spring,after which it's locked,as Teenmal says, but I see that once locked,say to ch Mazda eck it....BUT...if they have designed the system to tension accurately enough BEFORE lock-down, I am just wondering why they say check?....really, if it's locked, I feel that it should be loosened off and re-tensioned at a given service interval, unless a degree of stretch is accounted for in the initial sequence....
Cheers
Helen

This is the reason that you recheck it.Tighten the tensioner lock bolt. Be sure the
tensioner does not move together with the bolt