Rebores on the 4.6L?
Posted: Sat Jan 22, 2022 9:12 am
Reading the specs on the 4.6L, it appears that even a tiny bit of wear means you need a rebore?
From a factory size of 94mm, you get a limit of 0.015mm of wear (a bit over half a thou). Then you can go to a B size piston at 94.016mm.
Another 0.015mm on a 'B' size bore and it's time for new sleeves or a rebore?
I don't quite get why bore wear of only 0.03mm (1 thou) means you need to chomp 20 thou out to fit +20 pistons and rings? I haven't seen +10 pistons anywhere.
Are the cylinder bore wear limits really that tight?
Are there 'real world' bore wear limits? Does loss of compression and blowby and skirt wear get exponentially worse as bore wear and ring gap increases?
Is there sufficient material in the liners for a 0.5mm rebore?
Is another option to keep your pistons, assuming they're not worn out and replace the liners? I think this gets a lot more expensive if fitting top hat liners and needs all the machining work too.
EDIT: After a careful measure with a bore gauge, all my bores are slightly over size and over oval. Not by a lot, the worst being cylinder 8 which is 94.11mm side to side and 94.08mm longways. So as I have B pistons, 0.08mm over size, side to side and 0.05mm over size long ways. Ovality is 0.03mm so double the spec.
Best is 94.04mm by 94.03mm which is very close to spec.
I don't have a calibrated gauge to check my bore gauge on, just a digital caliper. But I did compare with the bottom of the bores and these are 94.01mm so I think my measurements are close.
From a factory size of 94mm, you get a limit of 0.015mm of wear (a bit over half a thou). Then you can go to a B size piston at 94.016mm.
Another 0.015mm on a 'B' size bore and it's time for new sleeves or a rebore?
I don't quite get why bore wear of only 0.03mm (1 thou) means you need to chomp 20 thou out to fit +20 pistons and rings? I haven't seen +10 pistons anywhere.
Are the cylinder bore wear limits really that tight?
Are there 'real world' bore wear limits? Does loss of compression and blowby and skirt wear get exponentially worse as bore wear and ring gap increases?
Is there sufficient material in the liners for a 0.5mm rebore?
Is another option to keep your pistons, assuming they're not worn out and replace the liners? I think this gets a lot more expensive if fitting top hat liners and needs all the machining work too.
EDIT: After a careful measure with a bore gauge, all my bores are slightly over size and over oval. Not by a lot, the worst being cylinder 8 which is 94.11mm side to side and 94.08mm longways. So as I have B pistons, 0.08mm over size, side to side and 0.05mm over size long ways. Ovality is 0.03mm so double the spec.
Best is 94.04mm by 94.03mm which is very close to spec.
I don't have a calibrated gauge to check my bore gauge on, just a digital caliper. But I did compare with the bottom of the bores and these are 94.01mm so I think my measurements are close.