Mains & Big end radial oil clearance

[dtauwel]

Hi all... My post is merely to try to settle a dispute that includes a 2.0 TSI chain drive (Gen2) engine on an Audi A4 B8 2012 model. Where it get's tricky, frustrating and anoying is with only 0.013mm difference and 90 degrees swing...

I'm gonna try to keep it short but detailed. Just a quick history... I am a petrol & diesel qualified technician with experience on VW and Audi vehicles mostly and I own a independant workshop that I boldly started just over a year ago when a nice workshop opened just opposite a Goldwagen branch.

In November 2020 a friend who only works on Mercedez brought his friend with the Audi to me with a knocking noise in thr engine when revving up the engine. A common fault on these CDH engines is piston seizure. No worries. With assistance from a reputable engineering company, the engine was reconditioned and the client was back to his normal driving routine in no time.

8500kms later and he is back with a knocking noise again... Initialy I thought it might have overheated as I found a leak on the coolant reservoir right away... But no. After stripping the engine. To my surprise, Big end bearing on cyl 4 seized up, luckily, it dit not spin in the housing so the conrod is undamaged.

Here's where it gets tricky. The engineering company sent the foreman to investigate and they claim lack of lubrication due to insuficient oil in the engine. This was not the case as just over 4.2 liters of oil was drained from the engine. I checked the complete oil circuit for blockages and foreign matter, but nothing, squeeky clean....

What I did find was that the main bearing oil clearance measured 0.038mm with plasti gauge... And I know for a fact that these engines must not exceed 0.030mm. Here's where it gets tricky... According to VW operation manuals the clearance must be measured by tightning the bearing cap bolts to the specified torque only and NOT with a further 90 degree turn as is done when doing final assembly of the engine. This is where the engineering foreman disagrees and thus starting the dispute.

If I do it like always while working at VW (at 60nm torque only) clearance measures 0.038mm
If I do it like the engineering preffers (60nm + 90 degrees) clearance measures 0.025mm which is then in specified range.

What is of great concern and here's where it all falls appart... This is the 3rd vehicle in a 6 month period that has returned after engine recon by us via the same engineering company. I know. Sad but true. However the the other 2 vehicles had other underlying conditions as well and was handled accordingly. So I never even thought of actually looking into this issue...

So the question is, do I measure with or without the additional 90 degree turn...

Sent from my S62 Pro using Tapatalk

[MacMan]

Hi all... My post is merely to try to settle a dispute that includes a 2.0 TSI chain drive (Gen2) engine on an Audi A4 B8 2012 model. Where it get's tricky, frustrating and anoying is with only 0.013mm difference and 90 degrees swing...

I'm gonna try to keep it short but detailed. Just a quick history... I am a petrol & diesel qualified technician with experience on VW and Audi vehicles mostly and I own a independant workshop that I boldly started just over a year ago when a nice workshop opened just opposite a Goldwagen branch.

In November 2020 a friend who only works on Mercedez brought his friend with the Audi to me with a knocking noise in thr engine when revving up the engine. A common fault on these CDH engines is piston seizure. No worries. With assistance from a reputable engineering company, the engine was reconditioned and the client was back to his normal driving routine in no time.

8500kms later and he is back with a knocking noise again... Initialy I thought it might have overheated as I found a leak on the coolant reservoir right away... But no. After stripping the engine. To my surprise, Big end bearing on cyl 4 seized up, luckily, it dit not spin in the housing so the conrod is undamaged.

Here's where it gets tricky. The engineering company sent the foreman to investigate and they claim lack of lubrication due to insuficient oil in the engine. This was not the case as just over 4.2 liters of oil was drained from the engine. I checked the complete oil circuit for blockages and foreign matter, but nothing, squeeky clean....

What I did find was that the main bearing oil clearance measured 0.038mm with plasti gauge... And I know for a fact that these engines must not exceed 0.030mm. Here's where it gets tricky... According to VW operation manuals the clearance must be measured by tightning the bearing cap bolts to the specified torque only and NOT with a further 90 degree turn as is done when doing final assembly of the engine. This is where the engineering foreman disagrees and thus starting the dispute.

If I do it like always while working at VW (at 60nm torque only) clearance measures 0.038mm
If I do it like the engineering preffers (60nm + 90 degrees) clearance measures 0.025mm which is then in specified range.

What is of great concern and here's where it all falls appart... This is the 3rd vehicle in a 6 month period that has returned after engine recon by us via the same engineering company. I know. Sad but true. However the the other 2 vehicles had other underlying conditions as well and was handled accordingly. So I never even thought of actually looking into this issue...

So the question is, do I measure with or without the additional 90 degree turn...

Sent from my S62 Pro using Tapatalk

I've always followed the workshop manual to the letter, and never had any issues. I mean VW / Audi designed the engine, including its tolerances, so they would know the correct way to check the tolerances.

It also makes sense to check tolerances without the angle tighten (stretch / yield), otherwise it would mean buying 2 new sets of bolts for everything you need to check the clearance on. 1 set to check the clearances, and another set to fit the crank / rods after checking the clearances, because you really shouldn't re-use stretch / torque-to-yield bolts, especially not on big ends and mains.

And if the engineering shop is adamant that they include the angle tighten, then are they using new bolts every time they do this? I highly doubt it, so the measurements are not going to be accurate anyway.

You mention you checked the clearance on the mains, but the issue was on a big-end.

Did you check the clearance on the big-ends?

- Oil threads and contact surface
- Use old bolt for measuring radial clearance
- 45Nm
- New: 0.02mm - 0.06mm
- Wear limit: 0.09mm

And while the mains (measured correctly) are slightly out of the new spec range (0.017mm - 0.037mm), they are still within the wear limit of 0.15mm.