Boris Spasov

Hello colleagues, I have a case study and I am asking for help... It is about Audi A4 B9 2017 3.0tdi 272hp. I decided to service the engine properly, camshafts, chains, connecting rods and main bearings all OEM plus new bolts. There was no problem with all the parts except the main bearings and this is where the need for help comes in. No one knows which bearings to order, no one knows what color the car left the factory, some say they measure the shaft, others say they measure the bearings, others say they measure the clearance between the shaft and the bearing, and now once a week we can't order these bearings. What I found out is that they originally come in 4 colors and opposite each one there are dimensions but are they mm or clearance. No one tells or knows what we should look at, what we should measure and how and how to navigate which bearings to order. ... Please advise and help thanks Good night

LightningTruck

It's up to your engine builder as to what bearing clearances are appropriate for the application and oil being used.
After grinding and polishing the crankshaft, professional engine builders measure with micrometers to check clearance on every bearing journal. He will tell you what bearing size to order based on the measurement. A cut crank is usually 0.010" undersize on my side of the pond.
The factory wants very tight clearance on a new engine for use with very low viscosity oil. The factory may use a slightly tighter or looser bearing shell to obtain a precise clearance number for each bearing journal. Color would be a quick way for a factory worker to identify the bearing shell clearance.
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Home mechanics use Plastigage to check clearances.
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Years ago on a Corvette engine I found just a couple bearing shells marked "STD 0.001" meaning they were standard size plus 0.001" to get the desired precise clearance while being assembled at the factory. I had that crank checked by the machine shop. They inspected/measured and said it didn't need to be cut, just polished. Told me to order standard size bearings "STD" and use 10w-30 oil. I used Plastigage to verify each bearing clearance was within spec during assembly.
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142 guy

Do you have the factory service manual for the car? I don't have a TDI service manual; but, the service manual for the TFSI engine does not provide bearing dimensions. It provides guidance on how to determine what bearings were originally installed in terms of the identification letter and the color code and shows where the identification letters are stamped on the block and the crankshaft end. There is no indication as to what the dimensions of the bearing shells are and which bearing might be tighter / looser.

The service manual provides a specification for the allowable radial clearance on the crankshaft bearings. This clearance is to be measured using a Plastigauge. The presumption appears to be that if the clearance is out of spec you reinstall new bearing of the original spec and measure the clearance and hope that it is returned to spec. The service manual provides no guidance on what to do if the crankshaft is worn and you want to grind it and install bearings of a smaller diameter because there are no bearing dimensions in the service manual. The service manual does not even describe how you replace a crankshaft, i.e. match up the crankshaft journal diameters with the bearing color. Perhaps the journals are all one size and the bearing colors are to accommodate differences in the outer diameter of the connecting rod and the journals?

I would be inclined to check the clearances with Plastigauge and if the clearances are within spec leave it alone.

silver03gt

Was the crank cut and polished? Unfortunately the only other thing you can do is order one set of each color bearing and Plastiguage each rod. They all are not necessarily going to be the same color so you will need to check each one.

SMac770

When asking about parts at this level, you have to be specifically clear about which engine you're talking about. That means the engine code, anything less accurate is open to getting things wrong. Is this a CRTC or CSWB 3.0 TDI? Or is this a DCPC or DCPE 3.0 TDI? MY17 and 272 metric hp, I'd guess CRTC. But we shouldn't be guessing.

Running as if it was CRTC: https://www.ilcats.ru/audi/?function...57&language=en
You see there's red, yellow, and blue bearing shells. Specification value is shown there.

I don't have a workshop manual for CRTC, but I imagine it would say the same thing the prior era 3.0 TDI said. The correct bearing shell colors are marked on the block and on the crankshaft. Four shells, four letters of R (red), G (yellow), or B (blue). Is yellow spelled with a G in German?

The crank provides the lower colors (the ones that sit in the retaining frame). We see this crank with GGGG (so all yellow) stamped on the end: https://www.oemvwshop.com/059105019b...shaft-p502738/
The block provides the upper colors (the ones that sit in the block). Supposedly they are along the edge of the block opposite the side with the round spring thing. But don't find any pics that clearly show the letter markings.

But are those references valid for a used block and crank? No idea. You'd have to validate it using the Plastigauge process that others have pointed out. The radial clearance spec is in the workshop manual.

142 guy

That link at least provides some useful information because it looks like for the mains red is the smallest diameter with yellow and blue being the next sizes up. That suggests that if your block comes marked with red and you need to resurface the crank then you probably need to find an aftermarket supplier of bearings who specify the bearing ID because there are no OEM bearings smaller than red. The color system appears to be purely for precision setting of the clearances on the initial build with the information stamped on the block if you ever want to do an exact replacement. I know Honda uses a similar system on the C32B engine; but, as I recall the service manual at least provides the diameters for the shells so that you might be able to do a re sizing.

The Audi TFSI service manual tells you how to check the bearing clearances. However, if your clearances are out you are left in a 'now what' limbo.