AFN, AHU, 1Z , ABL big end failure.

powermandan

Well-known member
Joined
Apr 5, 2021
Location
Worcester UK
TDI
ABL, AHU, AFN
Bit of story, I rebuilt a AFN engine and sprayed the block etc.

The First thing that happened was the BV43 Turbo self destructed and snapped the shaft on the way to the tuners...

At the time I put it down to poor tuning (was surging badly) and maybe the oil feed, it had a dark side style universal oil feed. But when you consider the cross sectional area of the aftermarket feed Vs stock feed. The new part was actually smaller. So I replaced the turbo and increased the oil feed to 3/4 inch which is much bigger than stock and changed the oil etc.

Then on its next run out lasting around 1 hour, driving up and down hill doing some tuning runs.

It spun a big end bearing on number 1 which was completely destroyed and deposited in the sump.

So I'm rebuilding it again. Im unsure what caused the orginal failure.

Unfortunately I didn't have a dedicated oil gauge, so the next build will have one.

It was fairly obvious that there was swarf going round the system from the condition of the other bearings. The mains had a few scratches in them and one of the other big ends was down to copper. So maybe the turbo failing introduced swarf that ultimately finished of the engine. Or maybe it was oil starvation that destroyed the turbo and big ends.


So I'm doing my best to cover all the bases on this rebuild.

One of the things I'm conserned about is that, because the block was in bits for so long, flash rust had appeared on the flange where the oil pump bolts too. I didn't think too much about it on the first build. But as there is no gasket between the oil pump and flange, it now conserns me that maybe this is causing oil leakage and dropping the pressure significantly.

I'm considering using some RTV on the flange although no one seems to quote pressure ratings.

Opinions thoughts/ advice?
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
In my experiance with aftermarket oil feed lines I find that the banjo end is much smaller of a area to take oil from the OEM banjo bolt. Solution is to use a small dremel and make it larger!
But you clearly have.... had a oil pressure issue. You may be right about the flash rust. When I hear that I cringe. Engine builds are supposed to be surgically clean. Still it could have been the turbo oil fees issue robbing oil pressure.
Most turbos now days have oil metering built in. Bit many in the past and still to this day need the right amount by adding a metering orifice and dialing the oil pressure in. I'm not exactly fimilure with that turbo but it could have been the 3/4 line making things worse.
Oil pressure needs to be taken at the turbo oil feed line and also at the pressure transducer location at the filter to the crank!
Food for thought.
 

Mozambiquer

Vendor , w/Business number
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
2004 VW Touareg V10 TDI, 2012 Audi Q7 V6 TDI, 1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI, 2005 VW Passat wagon TDI X3, 2001 VW golf TDI, 1980 VW rabbit pickup,
Don't put rtv on that flange! If there's rust, clean it up, but rtv in places like that will get into the oil pump and pull system and cause more problems than you're trying to fix.
It's also a very good idea to have an oil pressure gauge.
 

powermandan

Well-known member
Joined
Apr 5, 2021
Location
Worcester UK
TDI
ABL, AHU, AFN
Thanks for the replys.

I won't use RTV, I was on the fence about it really.

Its such a shame I didn't have the gauge in the first place.

Anyone got any rough pressures I should expect on the oil filter housing?
 

powermandan

Well-known member
Joined
Apr 5, 2021
Location
Worcester UK
TDI
ABL, AHU, AFN
So, put it all back together today. Seems to be running well.

So have oil gauge on the housing now.

When cold I had 72.5psi at idle

When boiling hot I had 14.5 psi at idle at about 58psi over 4K

The 14.5 does consern me because I have seen people say 20psi at idle. However there are no manufactures specs for idle.

The only thing I can find is an ALH engine which is similar i guess which says 2.5 bar at 2000rpm minimum. Which I'm pretty sure I had.

When I rebuilt I clearanced all the bearings and they were all within spec. And fitted a new pump. Although as far as I can see there was nothing wrong with old pump.

Also it's a Chinese gauge so....

Thoughts?
 

powermandan

Well-known member
Joined
Apr 5, 2021
Location
Worcester UK
TDI
ABL, AHU, AFN
Bit of an update for anyone interested

I think I've sorted problem. The engine in question is fitted to a T4 transporter. Which did not come with TDI as standard. It's a pretty common conversion to swap in an AHU/AFN. But you have to transfer quite a lot of bits off the the original TD block onto the TDI block to make it fit. One thing being the TD oil filter/cooler housing.

When I was transferring the bits, I did not notice there was a restrictor fitted to the AFN housing. Which I did not transfer to the TD housing that is currently fitted.

That restrictor limits oil flow to the head thereby increasing flow and pressure to the mains. My observation at this point was I was getting about 1.5 bar of oil pressure at 2000rpm where the book called for 2.5bar

In the mean time, I took the sump off again, and found a few copper chips, obviously very conserning. So I checked all the rod bearings which were ok. I did check one main, which was also perfect and came to the conclusion that the chips may have come from the turbo. So I put the sump back together and then I ended up destroying another CHRA inspecting it. Which annoyingly was also fine.

I kinda wish I had checked all the mains in retrospect. To put my mind at rest. But from my first blow up. I know the mains are the last thing to go. So makes me feel a bit better. I'm currently of the opinion that the the chips I found were hiding in the block and somehow avoided being washed out when cleaning and have been washed down with the engine running.


So I have fitted the aformentioned restrictor that now and it has bumped up my oil pressure at the housing about 1 bar. Which brings it into spec with what the bentley says.

Picking the bones of the orginal failure:

I'm fairly sure the original failure was due to poor tuning and all my own doing, I was on my way to tuners to get it sorted. Prior to the drive to the tuners I had been annoyed by all the coal i was rolling , so I detuned the pump voltage map, i.e the ECU thought it was injecting 20mg/stroke but it was only injecting 10mg/stroke. What I didn't factor in was the ecu was still trying to get the turbo to boost based on the 20mg/s . Which meant my turbo was stalling/surging constantly on the 50mile trip. This then lead to the turbo shaft snapping.

I then made another stupid decision to limp it 3-4 miles. Although the oil pressure light didt come on at the time. testing today has revealed that the dash doesn't alarm until your past 2000RPM. Which I probably wasn't reaching as I was busy limping it along without and boost. So based on the amount of oil in the intercooler. I was starving the engine.

Fast forward 3 weeks, I change the turbo/ switch to smaller nozzels (orig .260) now .216 and the mapping and promptly decide to go do some power runs up and down the mother of all hills near to me, where tbh it was running really well, After about the 4th run the bearing spun and I think i had just finished what I started 3 weeks earlier and I limped it off the motorway.

So fingers crossed I've sorted it all now.
 
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