Big end bearing and piston ring sizes?

[ianmway]

Hello All,

I'm going to replace the con rods on my Audi 1.8T BAM engine with some uprated ones, at the same time I'm going to re-hone the cylinders and replace the piston rings and con rod big end bearings.

Looking at the photos of when I last had the engine apart the cylinders are glazed, so really need the glaze taken off nothing more.

Looking at the available rings & bearings they come standard or different over sizes, bearings 0.25 – 0.50 mm and rings 0.01 – 1.00 mm.

There is nothing wrong with the engine with 122K miles on it; any ideas if I should buy the standard size or oversized?

I’m thinking the re-honing might require a slightly bigger piston ring and the con rod big end bearings leave as standard as I have no plans to regrind the crank as the job will be done with the engine in situ?

Thanks

[Crafty_]

If you have the crank journals grond you'd need oversize bearings, if you don't you need standard size.

Likewise, you only need oversize rings if you have the block bored. Honing should not take a significant amount of materal off the bores.

[ianmway]

Cool,

Thanks for the response.

[Boosted LS1]

If you bought oversized rings you'd have to file them to the correct installed end gaps. ok if you're seeking perfection. If there's nothing wrong with the bores or current rings then there's no need to change them. If you prefer new rings then have the bores honed, you'll be able to use new standard sized rings.

[ianmway]

Hello All,

VAG 1.8T BAM engine.

I’m in the process of ordering the extra parts to fit the Maxspeeding rods that have now arrived.

https://www.maxpeedingrods.co.uk/product/for-vw-go...

I’ve ordered all the required parts except the big end bearings, there is a bewildering array to choose from with a wide price range £25 - £150, there are 4 KS options alone?

I’m looking for some future proofing as I might go for a big turbo next year, so would be looking at something suitable for 400HP+.

Any recommendations/ideas?

Thanks

[bucksmanuk]

There is considerable BS about engine bearings. OEM are good enough for most applications including hard core motorsport.

The problem is getting hold of the actual OEM bearings as they have lots of lovely lead in them. Some aftermarket ones have no lead in them at all, and are an aluminium tin matrix. They have exactly the same part number on them though. So you think you are getting the same bearing. One little snippet gleaned from working on the floor below the engineers in one of the largest engine bearing manufacturers in the world.

Mondeo shells found their way into an F1 engine. They had the part number stamping process removed from the production routine so the F1 engine manufacturer had no idea they were using normal Mondeo Zetec shells! This was done after it was found that it didn’t really matter what they made them out of, and there are loads of different whitemetals out there as possibilities, they were all scrap after a race.

Get the clearances right on build. Bearing clearance is the biggest single factor that controls all the others on fluid film bearing performance. Mike Neale goes into this topic in some depth here:-https://www.amazon.co.uk/Tribology-Handbook-Michael-J-Neale/dp/0750611987
Decent chap too….

Followed by surface finish of the crank as well as the running surface of the bearing shell itself. There was some excellent research by Ford on this topic.

Don’t thrash it when it’s cold.

Use the proper oil and change it a lot more regularly. Forget this 12,000 mile nonsense… its usually dirt that kills the bearings - IF you have the clearance right to begin with.

[Evoluzione]

bucksmanuk said:

There is considerable BS about engine bearings. OEM are good enough for most applications including hard core motorsport.

The problem is getting hold of the actual OEM bearings as they have lots of lovely lead in them. Some aftermarket ones have no lead in them at all, and are an aluminium tin matrix. They have exactly the same part number on them though. So you think you are getting the same bearing. One little snippet gleaned from working on the floor below the engineers in one of the largest engine bearing manufacturers in the world.

Mondeo shells found their way into an F1 engine. They had the part number stamping process removed from the production routine so the F1 engine manufacturer had no idea they were using normal Mondeo Zetec shells! This was done after it was found that it didn’t really matter what they made them out of, and there are loads of different whitemetals out there as possibilities, they were all scrap after a race.

Get the clearances right on build. Bearing clearance is the biggest single factor that controls all the others on fluid film bearing performance. Mike Neale goes into this topic in some depth here:-https://www.amazon.co.uk/Tribology-Handbook-Michael-J-Neale/dp/0750611987
Decent chap too….

Followed by surface finish of the crank as well as the running surface of the bearing shell itself. There was some excellent research by Ford on this topic.

Don’t thrash it when it’s cold.

Use the proper oil and change it a lot more regularly. Forget this 12,000 mile nonsense… its usually dirt that kills the bearings - IF you have the clearance right to begin with.

That's pretty sound advice, but you miss two things. A lot of OEM bearings come in different sizes and aftermarket do not, they simply supply the thinnest they can safely get away with. Engines don't seize, they just have lower OP.

I don't think dirt kills bearings in modern engines, it's usually lack of oil (pressure).

[ianmway]

Thanks all.

After some adivce & experince postings from one of the Audi forums I've ordered the ALC bearings;

https://www.ebay.co.uk/itm/ACL-CONROD-BEARINGS-STA...

[HJG]

bucksmanuk said:

The problem is getting hold of the actual OEM bearings as they have lots of lovely lead in them. Some aftermarket ones have no lead in them at all, and are an aluminium tin matrix. They have exactly the same part number on them though. So you think you are getting the same bearing.

OEM bearings have been lead-free in most instances for around ten years now. In fact it is the aftermarket/ motorsport applications that only use lead nowadays. it's all to do with leglislation.
I believe motorcycles are still allowed to use lead in their bearings.

Most big end bearings are steel backed with a copper alloy lining and a semi-sacrificial overlay on top (but not lead!).

[99hjhm]

Bearing wise the ACL bearings are excellent. Never used the Maxspeeding rods, but if they have no markings between the cap and rod, mark them somehow as getting one wrong is almost guaranteed to lead to engine failure.

Rehoning the bores shouldn’t remove anymore than a couple of tenths of a thousandth of an inch. If just using a golf ball/grape hone your not going to remove any material unless you get very carried away. So standard rings should be fine. .1mm rings would leave you over .3mm to file off the ring in a std bore, not worth the effort trying unless you have the right gear it’s easy to damage a ring or get the gap very off square.

[ianmway]

Cheers, gone for NE standard size rings.