Cambelt fitting

[muley]

Oliver,

I +think+ - and I,m not the expert here - that the 90 deg twist referred to was on the Esprit and that may well have been a longer run than just between our cam pulleys. I set up my Polo (don't laugh) cambelt with a 90 deg twist but that was on the longish run from the crank pulley to the (single) cam pulley.

Have a nice run out - looks like it's going to be a good weekend - shame it's not Goodwood breakfast this Sunday!

Cheers


Jim

[John_W]

Is the `90 degree twist` check applicable on the top belt run between the cam pulleys ?

Oliver,
I'm not sure what you mean by that, but if you can twist the belt by 90 degrees between the top pulleys, then it's much too slack.

I'm still getting 10mm movement at TDC, 7mm at 60 ATDC. I'm not sure why the difference ? Surely the belt can't be unevenly stretched already ? Or is there some science here i don't understand ??

I'm not sure about TDC or 60 deg ATDC positions specifically, however when you turn the crankshaft the force applied will not be even throughout the 360 deg rotation, because you'll have to apply more force when the cylinder is coming up on the compression stroke. There will therefore be more tension in the belt and you won't be able to deflect it as much for any given force applied.

Agreed, you will not be holding any force on the crankshaft while you're testing the belt tension, but the valve gear (springs etc) will be in different configurations at TDC vs 60 deg ATDC, and may well be applying different tensioning forces to the belt. I think it would be best to check the tension at the position recommended in the manual, and forget about other positions.

My old belt was distinctly floppy between the two top pulleys - which I did not think was good. The new one I fitted just by judging the required force and deflection. It's been fine so far.

If the belt is over-tensioned it will whine horribly and accelerate wear.

John

[RayD]

I'm sure you're right John,

I think the thing to remember is to make sure the last thing you did before measuring, is to turn the engine clockwise - rather than get it to 65 degrees and wind it back a bit.

Ray

[Oliver]

Hi guys,

Just driven down the coast and it goes fab (for an NA), but there was a whine present, once warm. I`ve taken the engine mount off again, and i`ill wind it over and slacken off the tensioner a mite, then get it hot and hopefully get rid of the whine. Oh, i hope i can overcome my desire to leave out the rear lower engine mount hex bolt ! Surely three is enough ?!


Oliver

[Oliver]

Hi chaps,

My professional mechanic friend has had a look and his opinion is that the belt tension is correct. (Looks like i got something right). After getting the engine hot and hearing the whine developing, his diagnosis was that the (new) tensioner may be responsible for the noise ! Trouble is, now i`ve loctited the crank pulley bolt in, i can`t remove it! AARGH!

When i removed the tensioner and idler from their boxes and spun them they felt good and smooth, albeit a bit stiffer than the old ones.

I have decided that i will probably replace the engine mount and top cover tomorrow and do some gentle driving and hope the noise goes away.

Presumably the chances of a (new) genuine tensioner being defective are small. Has anyone had reason to doubt the quality of the Beck/Arnley water pump ? Any sagely advice much appreciated!

Oliver

[Oliver]

After being convinced that i have the belt tension set correctly, using a long screwdriver up against my ear as a listening device pressed against the various components, i am now 99% sure that the whine is coming from the water pump. Presumably no one else has had a problem with pattern water pumps ?

Oliver