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Hi there, I am currently looking into purchasing some ACL rod and main bearings for a 4g63 build, it gives me the option of standard or .25mm oversized. What would the reason to be to choose the .25mm oversized and are they recommended? Will be boring to 86mm, using standard length 150mm pistons and a standard 88mm stroke crank.

Cheers!

The .25mm and .50mm bearings are used if you have machined down your crank (as a repair for example).

They are not to be confused with the 0.025mm (also known as the H-001) or the HX-STD which are used to adjust the oil clearance in some case.

Here's a link to ACL Catalog that explain the various bearing sizing to adjust clearance.

https://www.aclraceseries.com/images/catalog.pdf

Check on page 6 and 7 for the info!

Hope it helps,

Frank

I once bought all sorts of bearings available on the market (OEM all sizes, ACL, King, Taiho) and tried them all on the same crankshaft. All aftermarket bearings gave me excessive oil clearances as well as most OEM ones. I had chosen the oem bearing that gave me the least oil claerance and have been using it ever since... With a little file work it gives me 0.05 mm oil clearance which is right on the money for performance 4g63...

As Frank said - BTW, it's undersized ;-)

Until you actually measure the journals, you won't know whether you need a regrind or what size will be required if the journals are OK.

Note, Georg is a very experienced builder and while the very thought of filing a shell sends shivers up my back - it reduces the crush and increased the chance of a spun bearing - it works for him, and I expect he's willing to take the risk of a bearing failure. It's definitely not something for an inexperienced person to try.

Using the file usually removes 0.01-0.02 mm maximum. Never had a single failure on performance engines because of it...

Hopefully it stays that way :-)

As I said, you're very experienced, but the OP is far from that, asking these questions.

Rather than 'a file', have you considered slipping the shell half into an old cap you won't be re-using, to support it and give more control, and 'sanding' on a sheet of W&D paper on a surface plate, or thick section of plate glass, for flatness?

Well, the technic I'm using was shown to me by very old mechanic way before i started to learn principles of managing the bearings and what is right or wrong for them. It works very well and i never actually thought about anything else in this department... As you well know if something works automotive guys tend to stick to it)) I'm no different))

Ahhh okay I see, so once my crankshaft arrives I should measure all the journals and select a bearing size from there? Should i do the same for big end bearings?

cheers

Absolutely

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