belt tension gauge vs belt deflection

[codgerdave]

Hi all,

I have a 1989 BJ73 (JDM RHD), on which I will shortly be replacing the water pump (the gasket is leaking, and it seems like a good idea to replace the pump while I'm at it). I'm not very experienced, but I have the shop manuals and it doesn't seem like a very complicated job...

A question, before I start, however:
When replacing the drive belt, the service manuals give different procedures according to the provenance of the vehicle. E.g.:

[Canada] Using a belt tension gauge, check the drive belt tension (Nippondenso BTC-20 or Borroughs No. BT-3373F)
Drive belt tension:
New belt: 145 +/- 25 lb
Old belt: 100 +/- 20 lb
[...]
[Others] Check the drive belt deflection by pressing on the belt at the points indicated in the figure with 10 kg of pressure.
Drive belt deflection:
Single belt type
New belt 8-12 mm
Used belt 11-16 mm
Double belt type
New belt 12-15 mm
Used belt 14-20 mm

Now, notwithstanding the fact that the FSM omits said diagram, what's going on here? My BJ73 is a Japanese import, so I assume the instructions for [Others] hold. What's the difference between the two sets of procedures? Must I go out and buy a belt tension gauge? How exactly does one apply 10 kg of pressure to a belt? By eyeballing it? While I'm in there, I'll replace the power-steering and AC pump drive belts too - do the same instructions hold?

Anything else that I should know about that comes to mind, feel free!


Cheers, and thanks for such a great resource.
Dave

 

[roscoFJ73]

Hi all,

I have a 1989 BJ73 (JDM RHD), on which I will shortly be replacing the water pump (the gasket is leaking, and it seems like a good idea to replace the pump while I'm at it). I'm not very experienced, but I have the shop manuals and it doesn't seem like a very complicated job...

A question, before I start, however:
When replacing the drive belt, the service manuals give different procedures according to the provenance of the vehicle. E.g.:

[Canada] Using a belt tension gauge, check the drive belt tension (Nippondenso BTC-20 or Borroughs No. BT-3373F)
Drive belt tension:
New belt: 145 +/- 25 lb
Old belt: 100 +/- 20 lb
[...]
[Others] Check the drive belt deflection by pressing on the belt at the points indicated in the figure with 10 kg of pressure.
Drive belt deflection:
Single belt type
New belt 8-12 mm
Used belt 11-16 mm
Double belt type
New belt 12-15 mm
Used belt 14-20 mm

Now, notwithstanding the fact that the FSM omits said diagram, what's going on here? My BJ73 is a Japanese import, so I assume the instructions for [Others] hold. What's the difference between the two sets of procedures? Must I go out and buy a belt tension gauge? How exactly does one apply 10 kg of pressure to a belt? By eyeballing it? While I'm in there, I'll replace the power-steering and AC pump drive belts too - do the same instructions hold?

Anything else that I should know about that comes to mind, feel free!


Cheers, and thanks for such a great resource.
Dave

You can apply 10kgs of pressure(or tension in this case) using fishing scales or there are devices out there ready made for it.
I guess most of us do it by trial and error and I have never used any type of gauge to adjust belt tension.
Usually loose belts jump around a lot when idling but dont always slip.
In some vehicles its crucial to be close to spec or the bearings/bushes will chew out.
Landcruisers are a little less fragile but I still wouldnt want to over do it
Once the belt has gone flat between pulleys,the adjusting bolt/nut will go tight. Give a it another turn or 2 and check again after a few hundred klms.Belts always need to be retensioned from new.
Usually the adjusting mechanism will start to deform if you have too much tension in a belt

 

[rstl99]

WHen I was a young lad someone advised me to adjust a belt by leaving about an inch of slack when pressing down on it. I've got the one on my 3B engine adjusted this way, but when the engine idles it vibrates (doesn't jump or slip, but I can see lateral movement on the part that goes down from alternator to crank), so I may need to snug it up more I suppose.

 

[codgerdave]

Excellent. That's exactly the kind of advice I was hoping for.

Cheers
Dave

 

[83bj60]

As rstl99 said, it's better to be a bit slack and not slipping (you'll know by the squeal) than too tight (you'll know when the water pump bearing burns out)