Author Topic: Wear limit on bores  (Read 2246 times)

carrera

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Wear limit on bores
« on: 01 March 2020, 01:29:26 PM »
Checking to see if I have missed something in WIS.

What is the wear limit on a B2x5 engine

I have seen that a "B" block is stated to be 90.02-90.04mm

How is this to be interpreted ?

90.02 when new, with a wear limit of 90.04, or

90.02-90.04 when new and no defined wear limit.

I have also seen that the piston to bore clearence is stated to be 0.025-0.056.

Those numbers seem to come from Nominal bore - max piston size 90.000-89.975 = 0.025 minimum, or bore size 90.02 - smallest piston size 90.02-89.964 = 0.056 maximum

The logic of those calcs doesn't make a lot of sense to me

Anyone know better ?
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sgould

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Re: Wear limit on bores
« Reply #1 on: 01 March 2020, 03:05:18 PM »
The parts list has 4 pistons listed for the 2.3 engine for 2000-2010  (and 4 different ones for 1998-1999)

There's
Class AB
Class B
Oversize 0.5 mm
Oversize 1.0 mm

No actual dimensions in the parts list.

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sgould

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Re: Wear limit on bores
« Reply #2 on: 01 March 2020, 03:11:57 PM »
The WIS info on bore says...

Standard (A) 90.000 - 90.020

B  90.020 - 90.040

First oversize 90.500 - 90.520

Second oversize 90.100 - 90.020 which must be a typo!! 90.120 surely...
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sgould

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Re: Wear limit on bores
« Reply #3 on: 01 March 2020, 03:21:12 PM »
There's a bit in the WIS under "Engine/Pistons, connecting rods, cylinder bores"  about measuring clearances with the piston in the bore.  There's bits about using a feeler gauge and pulling it out with a spring balance.  I can't get my head a round the maths ata quick read though...
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carrera

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Re: Wear limit on bores
« Reply #4 on: 01 March 2020, 03:40:38 PM »
Cheers :)

I think the bit about using the spring balance is to do with measuring the ring resistance. I saw that a couple of weeks ago and thought, well that's one way to do it.

The problem with WIS is there are so many important bits of information buried away in corners I haven't seen yet :)
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carrera

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Re: Wear limit on bores
« Reply #5 on: 01 March 2020, 06:44:52 PM »
Second oversize 90.100 - 90.020 which must be a typo!! 90.120 surely...

If that's what it says, second oversize should be 91.000 to 91.020

Which leads to an interesting question, that means the oversize dimensions are as for an "A" bore, rather than a B bore

But then I look again and I see that each individual bore has a bore classification, meaning they could be different. What!  Brain fried, why would they do that ??

But still back to the original question, what do the quoted dimensions mean, a range for new, or an absolute new and a wear limit
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sgould

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Re: Wear limit on bores
« Reply #6 on: 01 March 2020, 09:54:18 PM »
The way I read it is that the figures are for completely new.  Back in the day, cheaper car manufacturers like BMC had at least three sizes of piston to fit the bore size that they found after machining. This was to save them changing the worn  cutter as often!  Reading the Saab bit on the piston ring gaps, it says that they should be placed in the bottom of the bore "where the wear is least".  No mention of the amount of wear permissable.
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sgould

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Re: Wear limit on bores
« Reply #7 on: 01 March 2020, 10:11:42 PM »
I can't find anything comparable in the WIS, but there is a bit in the Haynes manual. And, as to be expected, it doesn't always match!

Haynes says that there are five sizes of piston AB, A, C 1 & 2.  With 1 & 2 being the oversize ones.  The size is stamped into the top of the piston and also on the front top corners of the engine block.  It then goes on to say that if the clearance of the piston in the bore is more than the nominal new max size, "the opinion of an engine reconditioner" should be sought as to whether a rebore is required.

So nothing definite...
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carrera

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Re: Wear limit on bores
« Reply #8 on: 01 March 2020, 11:52:44 PM »
It then goes on to say that if the clearance of the piston in the bore is more than the nominal new max size, "the opinion of an engine reconditioner" should be sought as to whether a rebore is required.

I think the Haynes info is comparable, but then ducks the issue by limiting "wear" to the worst stage scenario with new components.

The whole using a feeler gauge and spring scale to match pistons to bores is not an approach I have seen before, nor does the "if it's greater than 0.05, assume the bore is 90.20 and chuck on a value og 0.003mm for wear. My version of WIS and the online version have different specifications too which doesn't help with trying to do the maths to understand the approach.

On the plus side, the piston matching section does talk about a clearance of 0.031 to 0.069mm being acceptable...... which is 0.006 to 0.013 greater than the calculated difference of new components.

Sadly, I am the engine reconditioner, and I don't have an proper opinion yet  :D
9-5 Aero Estates, 2002 Cosmic Blue, 2003 Steel Grey, 2003 Graphite Green, 2004 9-5 Glacier Blue 2.0 saloon, 2004 Nocturne Blue 2.2 diesel estate, 2006 & 2008 Black Aero saloons, 1998 9000 CSE with Aero engine, 9-5 NG Aero XWD Turbo4, 9-5 NG Aero XWD TTiD