Beware the dreaded oil pump key failure - Part 2

[DMitch16]

It's not often that you get to replace a balance shaft and oil pump drive key on a B6 and less frequently do you get to change it twice on the same car!

Mine failed originally at 148,000 which was fairly remarkable as I do 20K a year and push the old girl hard every now and then but there was no engine damage other than that. A lot fail much earlier and some are driven on causing more damage or engine fatality so I was lucky. The job was fairly detailed but straight forward as I have done my fair share of mechanics learning from a very young age and I have accumulated the right tools over the years. I was pleased when it was done and everything worked fine. BUT...I chose a cheaper balance shaft solution than KMB opting for a private engineer who was remanufacturing original balance shafts (77mm key) in his workshop. His method was to tap a hard hexagonal insert into the shaft and supply a harder 77mm key. It was half the price of KMB although I thought it would last much, much longer, than it has, sadly not. It failed again on Wednesday night whilst spanking her up a long shallow hill at 4500 revs (9000 balance shaft revs). Again I pulled over and stopped within 30 seconds and it may have saved her all over again! It really was penny wise and pound foolish as now I have to spend another £215 for the KMB remanufactured shaft and longer key plus fit it all over again. Bang goes my Bilstein Pro Kit!

I have removed the balance unit and will split it open tomorrow to see what's wrong once more. Early indications are that either the harder Allen drive key has broken at the balance shaft end or the harder hexagonal insert has been wrecked by the harder Allen key vibrating in the hole destroying the insert. There are small specks of metal in the oil but it seems to be in the pre enginrmfilter areas and should flush filter already All the gearing is fine, the pump fine and all generally looks OK but the shafts will rotate but the key does not.

I was thinking of documenting the balance shaft change and taking some pictures for reference if anyone is interested?

[Gazwould]

Yes an ultimate guide please .

Of course there are ostriches that do not think they will join the 77mm club !

KMB did warn me he supplies also because of failed other engineering solutions to the problem .

As we now know you must increase the contact length /surface area as oem 77mm has only 15mm , common rail oem 100mm 35 mm and KMB 100mm will have 38-40 mm .

The other way is this..



How much contact length did your 77mm solution have ?

As there is more contact lenght to be had over 15mm as the oem balancer shaft keyway doesn't start till a little way in as seen on the left oem , right is regenerated with 100mm key .

[zollaf]

amazing really. hundreds of years ago engineers found a great way to transmit drive through a shaft was to bolt it all together so it doesnt rattle itself away. idiots at vw ..

[DMitch16]

I was right with the pre diagnosis and the KMB shaft is ordered plus a new set of bolts for £17 (the VW parts guy had 7 listed for my car - told him I had taken 8 off!! ETKA apparently does not include the pump mount bolt that either goes through the pump into the crank carrier or its counterpart opposite). I had documented the first failure (repair instructions available on other forums) but had little imagery to compliment them. I'm not very confident with video so it will be more of an illustrated guide. Might get one of my youngsters to help me with it as I have already got to the half way point and will have to do a walk through of what I have done so far with reference pictures.

It seems so much easier doing it the second time! Still messy as there is a lot of oil that is captured by the balancer unit and retained in the pump and I am on my drive because the garage is full of crap. When finished I will change oil filters every week (400 miles) for the next few weeks to eliminate any residual metal fragments in the pre filter channels (it's a couple of quid a filter so I have got 3 more). Should be OK after that as the failure was instant and not gradual disintegration so most of the fragments dropped straight down into the sump, which I will clean thoroughly, away from the take up pipe. Will fit a magnetic sump plug as well for additional protection.

[DMitch16]

Just split the balancer unit - interesting findings this time with the non KMB "remanufacture".

Definitely one for you Gazwould!!

The key is an original part supplied with the exchange shaft. Part 03G115281F which has other markings of 42/14 WAR V100. The hexagonal insert machined into the shaft has a contact surface of LESS than 1cm with the remaining void circular from either drilling out the material to match the length of the key or because the remaining depth was already worn (unlikely with a 77mm key). The contact surface of the oil pump drive is nearly 4cm so 4 times what the shaft contact area is with the other end of the key. There is still slight silvering on the edges of the key after 40k which is possibly due to the vibration that would no doubt occur because of the tiny contact area at the other end especially as the insert had worn internally just like the original shaft key hole but imo much FASTER.

So beware - Do not go for the cheap exchange shafts unless the seller can confirm 100mm key and ALL the shaft key hole depth to be proper surface contact with the key as otherwise they are actually WORSE than the original s h i t e!

I'll try to get some pics up.

Edit: There were 2 hexagonal inserts with the inner one stainless steel and the outer one high tensile T10 steel. The key is harder than stainless steel so destroyed the inner insert pretty rapidly leaving a drive contact length on the key of only 8mm. The outer T10 insert however is harder than the key so destroyed the key rounding it off due to the small contact length. This occurred in less than 18 months!! The KMB shafts are superb with the longer key going deep into the new hex hole in the balance shaft and with a very precise fit almost tight without being so.