Citroen XM Forum

Will, this is daft.
What you've said means that the belt can start life with limited side-contact, and therefore limited grip, and accelerated wear.
Then "I'm sure that once the belt wears and drops below the outer circumference of the pulley, the angle of v is irrelevant, as the belt has already worn to whatever angle the pulley is."
This means that the belt is slackening as it wears down, which we know just aggravates the situation.

For minimum wear - and maximum grip - the belt must match the vee for width, height and angle. Anything else just compromises power transfer and service life.

Come on guys!

You have a knack of mis-contsruing what is said.

A belt supplier will supply a correctly profiled belt, but once it has worn down into the v, it has to have adopted the angle of the metal pulley. As we know they continue to wear rapidly at that point, even though they have the profile of the v. The one thing that has changed is that the belt is down below the circumferance of the pulley.

Contact area cannot be that critical to power transmission as a solid belt would transmit higher power compared to a toothed belt if that were the case and it doesn't.
Pressure on the contact area is probably the largest factor but then i would guess so is heat, as the belt heats beyond its operating temperature the belts ability to transmit power decreases.
I would guess if the belt and pulley were matched exactly the heat generated by excess friction as the belt enters and exits the pulley would lead to overheating and rapid destruction.

I think the fact is the gearing of the pump drive due to low drive speed of the camshaft are running the v belt setup at the limits of what it can cope with, if things are not perfect rapid destruction of the belt ensues. Citroen knew this which is why they were forced to increase driven pulley size as a bodge, modified cars with the later 100mm pump pulley probably are not running a large margin between fluid volume required and generated at idle which is why they didn't go any larger with the pulley.

D

I still think that if your car is eating belts (any sort) there has to be an issue Dean surely and is playing with other types and designs not just circumventing the problem? Regards, Matthew T.

Yes you are right Matthew, however, i have rebuilt a spare FDV and fitted that, and stripped, cleaned and re-calibrated my Pressure reg, checked all pipes for restrictions and reassembled so there is nothing else i can do/

D

Good bit of info here:
http://info.gates.com/rs/gatescorp/imag ... e-0314.pdf
http://vulcan-grip.com/pages/belt-slippage-basics

I don't really believe that this is primarily caused by bad design. There were many (100,000?) PRV engined XMs made, and there seem to have been very few that need the belt replacing every week.

I think that it is likely that one or more of your pulleys is worn (due to previous prolonged running with a loose belt) so that the effective contact area with a new belt is at the wrong angle. My dad was an auto-electrician, and this was an uncommon but known problem with the fan-belts on some models of vehicle. Usually the owner would come in complaining that no matter how tight the belt was adjusted, it still squealed.

I think that it is likely that one or more of your pulleys is worn (due to previous prolonged running with a loose belt) so that the effective contact area with a new belt is at the wrong angle.

The final answer - probably. As Chris mentioned, this is basic stuff.

Only 30 miles today but so far so good, the belt is holding up fine with no chirping or slip evident.

D

That's sounding positive. Hope that hasn't just jinxed it....