Aston Martin Vantage 4.3, 2007 Main Bearing math question
Discussion
Hi Guys,
looking for a math pro because I´m desperate figuring out how to measure the correct journal clearance.
The Crankshaft has a diameter of:
61,99 mm
Main bore clearance:
66,03 mm
66,05 mm
66,05 mm
66,06 mm
66,07 mm
There are 4 types of main bearings categorized in color codes, colors could be mixed.
yellow approx. ~2,02 mm
green approx ~2,01 mm
blue approx ~2,00 mm
black approx ~1,99 mm
clearance should be within 0,02 mm ~ 0,04 mm
Thanks to you all
Frank
looking for a math pro because I´m desperate figuring out how to measure the correct journal clearance.
The Crankshaft has a diameter of:
61,99 mm
Main bore clearance:
66,03 mm
66,05 mm
66,05 mm
66,06 mm
66,07 mm
There are 4 types of main bearings categorized in color codes, colors could be mixed.
yellow approx. ~2,02 mm
green approx ~2,01 mm
blue approx ~2,00 mm
black approx ~1,99 mm
clearance should be within 0,02 mm ~ 0,04 mm
Thanks to you all
Frank
From just a quick look at the numbers you supply, from my reading all of your numbers are to 2 decimal places, whereas the chart demands three decimal places to be able to determine the required bearing correctly.
It would appear that all but one of your bearing bores could be out of tolerance, as the chart gives 66.032 as a maximum but you are recording over 66.04 on four of your five dimensions (and, depending on the 3rd decimal place, the other one could also be outside the maximum). The chart also suggests measuring each bore twice at 90 degrees to each other, so I'd expect two dimensions for each bore diameter.
You give only one crankshaft journal diameter, and that also only to 2 decimal places, to which my question is "Really?" All absolutely identical sizes? And the one dimension you give could fit anywhere into the chart between bands 'B' and 'L'.
So from my reading your dimensions are not adequate to use to make a decision. I could, of course, be wrong.
It would appear that all but one of your bearing bores could be out of tolerance, as the chart gives 66.032 as a maximum but you are recording over 66.04 on four of your five dimensions (and, depending on the 3rd decimal place, the other one could also be outside the maximum). The chart also suggests measuring each bore twice at 90 degrees to each other, so I'd expect two dimensions for each bore diameter.
You give only one crankshaft journal diameter, and that also only to 2 decimal places, to which my question is "Really?" All absolutely identical sizes? And the one dimension you give could fit anywhere into the chart between bands 'B' and 'L'.
So from my reading your dimensions are not adequate to use to make a decision. I could, of course, be wrong.
Ah - didn't appreciate you can mix two different bearing thicknesses in one journal - which seems weird to me as you won't get the same clearance all the way round. This also adds an extra dimension to my chart as I assumed you'd use one colour for both shells in a journal, and I need to study yours and think about it. I have to go out to do stuff, so this is a holding post to let you know I've seen your response.
I'll get back to you a little later today with my thoughts, for what they're worth. I'll add this thought, though. All engines have a range of clearances, etc but there is usually an optimum value for performance, life, etc - it could be max allowed clearance, it could be min allowed clearance or it could be nominal (i.e. half way between). Do you know what you're shooting for? As it appears you can play games with the bearings to put the clearance pretty much where you want
I'll get back to you a little later today with my thoughts, for what they're worth. I'll add this thought, though. All engines have a range of clearances, etc but there is usually an optimum value for performance, life, etc - it could be max allowed clearance, it could be min allowed clearance or it could be nominal (i.e. half way between). Do you know what you're shooting for? As it appears you can play games with the bearings to put the clearance pretty much where you want
Right. I've had a closer look at the printed (AML?) chart you provided above giving bearing options for various crank journal and main bearing bores and I now realise that the clearance referred to is the total diametrical clearance and not the radial clearance, so my numbers in my chart were wrong in that my clearances were twice what they should have been. On this basis I've deleted my post with the formulae and my table.
I was also curious, so I've also used the dimensions you gave for the thicknesses of the various grades of bearings and used them to make some calculations at the various limits of the zones in the AML chart. This has led me to believe that the values you give for the bearing thicknesses cannot be correct, as my calculations using them and some values off the chart give some clearances below the stated AML limits (in the text above the chart), and the total range of clearances is smaller than the stated range in the text. I've recorded the points I selected and the corresponding calculated clearances in the table below.
So a lot depends on whether you think the bearing thicknesses you stated are correct and whether the chart you provided showing the appropriate bearing choices for various crank journals and bearing bores is actually a master document that should be adhered to. I've not commented on the figures in your table as, while the maths appears to be correct, the little bit of work I've done casts doubt on the bearing thickness data you've used. I also worry when you use a tilde implying approximate dimensions as well as using two decimal places - I would have thought that precision was required.
I'm not being critical and am just offering my interpretation and opinion, either of which could be well off the mark. At the end of the day it's your car.
edited to add updated table
I was also curious, so I've also used the dimensions you gave for the thicknesses of the various grades of bearings and used them to make some calculations at the various limits of the zones in the AML chart. This has led me to believe that the values you give for the bearing thicknesses cannot be correct, as my calculations using them and some values off the chart give some clearances below the stated AML limits (in the text above the chart), and the total range of clearances is smaller than the stated range in the text. I've recorded the points I selected and the corresponding calculated clearances in the table below.
So a lot depends on whether you think the bearing thicknesses you stated are correct and whether the chart you provided showing the appropriate bearing choices for various crank journals and bearing bores is actually a master document that should be adhered to. I've not commented on the figures in your table as, while the maths appears to be correct, the little bit of work I've done casts doubt on the bearing thickness data you've used. I also worry when you use a tilde implying approximate dimensions as well as using two decimal places - I would have thought that precision was required.
I'm not being critical and am just offering my interpretation and opinion, either of which could be well off the mark. At the end of the day it's your car.
edited to add updated table
Edited by LTP on Tuesday 5th April 18:02
One more thought on that (AML?) chart you supplied that gives the various bearing combinations to suit journal and bearing bore sizes.
The text states that the clearance should be no less than 0.022 mm and not greater than 0.040 mm, a range of 0.018 mm. However, if you look at the chart and check the values of, say, a min and max crank journal for any one bearing bore and bearing size combination, you'll see that the range is only 0.006 mm before the chart recommends changing to a different bearing combination. This means that, despite a declared range of acceptable clearances of 0.018 mm the chart is managing the range of recommended clearances to one third of that - 0.006 mm.
Unfortunately, because we don't know the various bearing thicknesses that the chart uses, we cannot derive what the recommended running clearance range that the chart uses is.
My summary of my last few posts? If you take that printed chart as gospel then:
typo fixed
The text states that the clearance should be no less than 0.022 mm and not greater than 0.040 mm, a range of 0.018 mm. However, if you look at the chart and check the values of, say, a min and max crank journal for any one bearing bore and bearing size combination, you'll see that the range is only 0.006 mm before the chart recommends changing to a different bearing combination. This means that, despite a declared range of acceptable clearances of 0.018 mm the chart is managing the range of recommended clearances to one third of that - 0.006 mm.
Unfortunately, because we don't know the various bearing thicknesses that the chart uses, we cannot derive what the recommended running clearance range that the chart uses is.
My summary of my last few posts? If you take that printed chart as gospel then:
- I don't believe the thickness values you give for the various bearing identification colours are correct
- The chart implies you need to manage the clearances to within a range of 0.006 mm
- You are not measuring the components accurately enough to make a decision
- I don't believe you can use your numbers to decide what bearings to use in your engine build
typo fixed
Edited by LTP on Wednesday 6th April 10:25
yes, you are right, I have to redo the measuring and keep an eye on the third number after the dot. Unfortunately it seems that I´m very close to the edge, so there is no much options left. Don´t know why, but the crankshaft, is at the end of the AML table, that troubles me. When the crankshaft was in place with the original main journals, it had too much clearance in my opinion, I was able to move the crankshaft up and down, at least I could feel that there was some kind of space. The engine had only 50K Miles on the speedo. Thanks for diggin so deep into my problem and I realy appriciate it. Your thoughts are allways welcome, it make me think, if I did everything right and this is the main point to proceed in the right way.
Edited by paralis on Thursday 7th April 02:42
I assume the bearing thickness from the chart is the same like I have measured. I ordered every possible bearing that was available from AM and measured it.
" Unfortunately, because we don't know the various bearing thicknesses that the chart uses, we cannot derive what the recommended running clearance range that the chart uses is."
The crazy thing, I also have black main journals which are not in the AML table !
" Unfortunately, because we don't know the various bearing thicknesses that the chart uses, we cannot derive what the recommended running clearance range that the chart uses is."
The crazy thing, I also have black main journals which are not in the AML table !
paralis said:
I assume the bearing thickness from the chart is the same like I have measured. I ordered every possible bearing that was available from AM and measured it.
You can't assume that because I used your bearing dimensions, along with the dimensions of crank and bearing bore off the AML chart axes, and some combinations gave clearances that were below the stated minimum of 0.022 mm - I showed these in red in my post above. The last thing you can do with an engine build is to make assumptions.paralis said:
The crazy thing, I also have black main journals which are not in the AML table !
Yes, I saw that. The AML chart also seems to have a bearing that is marked "Blue/green", which looks like to be the thinnest available. I can offer no opinion as to why that should be, unless they have changed the "Blue/green" to "Black" to avoid confusion with "Blue" and "Green" in combination, as in your post the "Black" is also the thinnest bearing. This is just my guess; the reality could be entirely different.If I were in your position I would re-measure both components (crank and block) using equipment capable of resolving to +/- 0.001 mm and then just use the chart to select the appropriate bearings. But from your initial numbers and assuming your measuring technique is accurate it looks like your block is out of spec.
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