charger belt thrown off causing damage

[rwilsonrs4]

Well, while out for a spin , things escalated rather quickly at 8000 rpm resulting in the front of the engine block receiving damage which will be tricky to fix , ,it all started while carrying out an Italian tune at over 8000 then it stood on its nose then the battery light came on, so i instantly knew the belt had been thrown off , the engine run fine as the charger has a bypass so runs normally , so got it the couple of miles home on battery power , then opened the bonnet and discovered not good signs , the belt was gone and the idler pulley was lying against the cooling fan and a big chunk missing from the front of the block where the idler pulley bolted onto ....so mucho worko needed to repair this problem but a plan has been found
Originally the plan was to Tig weld up the damage then machine it and rethread it to original dimensions but 3 issues were possible , the block is 17% silicon alloy and may be difficult to weld , and welding is rarely as strong as the original and may also cause localised stress and distorion ,but...., the original bearing was a single row deep groove normal bearing but on investigation of part numbers the bearing fitted was not up to the demands regarding load , heat and rpm, so . after some research and discussion with SKF ....the new plan is for a new bearing carrier to be made to house 2 deep groove bearings , which will be higher speed rated , higher temp rated , better grease and higher tolerance for expansion, and will halve the load on each .
There is still 15 mm of thread in the block so a threaded mandril will be made to screw in then the damaged part will be milled down to allow for the extra bearing width and to ensure pulley alignment and then the original billet pulley will be machined to a press fit on the new housing to the correct alignment , this will ensure a better lifespan than the roughly 15000 miles the original one lasted , all going to plan will be done in a couple of weeks

[Ellis]

"It never rains but it pours" as they say.

Sounds like you've got it well under control. Get it done during the winter period.

[R1RS4]

Sorry to hear mate, not good

How the hell did that break off ?

Do you have any pics?

Cheers R

[rwilsonrs4]

well not really any pics of it as you can barely make out where its is , but its in at my pals machinist/ engine repair workshop ,getting the whole front off for access to get the repair done , , i think the reason for the failure was the securing bolt came loose which allowed the pulley to move a bit which stressed the bearing too much which overheated it and the bearing race cage failed which caused the inner race to shoot sideways and jam in the outer race which stopped the idler pulley and the belt then jolted the pulley and snapped the piece off the block , thats the theory anyway , but a new design has been devised ..after much research and discussion with SKF bearings they had a suggestion ..
2 bearings of a different spec will be fitted to a custom machined hub my pal will do on his hub which will half the load on the bearings as they will spin at near 20 000 rpm due to pulley size /engine rpm , so a plan is afoot for that , the original bearing was a normal spec deep groove single race bearing , the new paired bearings will be better sealed , higher temp rated grease and a higher tolerance to allow for expansion
the original billet anodised pulley will be machined out and pressed onto the new bearing hub for correct alignment so the whole assembly should be good for the forseeable future
EDIT , couple of pics from today , not the best quality , the phone doesnt take close ups it seems lol , not my pics as i,m offshore just now , more to follow hopefully better focus

[S4Player]

I threw a belt a ridiculous speed when we fit done the pes conversion all those years ago. Shat myself is the best way to put it

[rwilsonrs4]

YEP mine is the PES one too but with the modified pulley with the channelled belt run to prevent belt throw , but it has a basic bearing taking some severe abuse it seems ,

[22B]

Oh dear Roy, that's not so good but it sounds like you have got things well in hand already. We'll need to meet up for a blether sometime....

[R1RS4]

Thanks for the pics, yes can see it now

Any damage to the engine pulley?

Sounds like a good fix, the guys at SKF sound very helpful too,

Mine has eaten a couple of belts, which turned out to be a faulty tensioner, lucky no damage though

Richard at TTS has done endless testing with the bearings in their kit, so important getting the spec right due to the loadings

Hope your back on the road soon

Good luck mate

[5681]

Hope you get on back on the road soon sorry to hear about it

[rwilsonrs4]

well it will be 2 weeks before i see if its good again , but the plan we have should work out, i have FB contact with the guys so will get updates when things progress ,
No damage to any other pulleys which is good , there is a bit of play on the alternator belt idler pulley so that will be replaced too as the charger uses that original set up , just an extension of it really
its a strange one with the charger idler pulley bearing, when i saw this i immediately thought that bearing is too small , why is a bigger bearing not in there , but its about the same size as the tensioner pulley bearing , maybe a touch smaller , once investigations were done a bigger bearing can handle more load but the rpm capability is nowhere near high enough due to the bearing speed in distance travelled per min , , you would think ,well a bigger bearing has more balls in it and is bigger so can handle the load , but the speed is too high so it would fail even quicker than a small one , this bearing is 12mm ID 12 mm wide and 37mm OD in diameter , looking at idler pulleys for Aux drive belts , most have small bearings , which makes sense really for the engineering reasons .

[R1RS4]

Hi mate,

Had a chance to look through my pulley set up this morning, thought you might find this interesting

TTS do not use the standard idle pulley mounting point probably for fear of what's happened to yours, so they have a better system buy mounting a seperate plate

I have photographed this from my info

Cheers
R

[rwilsonrs4]

looks like a better idea for sure , bearings look about the same size as mine , , i,ll see how this progresses , maybe TTS could supply this for me the belt is wider than mine , but dont see it being an issue , but the left hand bolt as you look at looks like it is mounted into bolt hole which has broken on mine so not ideal for the plan, depends on what they get done to it also the TTS has a different pulley on the tensioner and the idler is removed , quite different really .

[R1RS4]

Yes the belt has been upgraded to an 8 rib versus Audi 6 rib, the engine pulley is lightened and balanced

The idler is still there it's under the plate with the yellow dot

Like you say, see how they get on with the plan, and it gets resolved mate

Just gives you a different idea going forward

Richard at TTS is a good guy, and very knowledgeable with our cars

[MartayMcFly]

Bloody chargers and their belts!

[rwilsonrs4]

another pic from today , not much more done yet as the machining work is getting planned and sorted , i see from the pic there are 2 pulleys in the bracket , but the original one which is down to the left in the pic has been remove as i suppose its not needed , you can see the bolt hole where the original idler was fitted ,but with the new routing of belts is not required for the TTS set up