can someone tell me the correct spacing between the centre bores on a 1380?
Correct Space Between 2&3 On Offset Bored 1380?
Started by
cradley-heathen
, Apr 25 2012 09:57 PM
6 replies to this topic
#1
cradley-heathen
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Metro-Man
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Posted 25 April 2012 - 09:57 PM
#2
Cooperman
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Uncle Cooperman, Voted Mr TMF 2011
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Posted 25 April 2012 - 10:44 PM
Offset 1 & 2 cylinder centres 0.015" towards the front and 3 & 4 cylinders 0.015" towards the rear.
#3
cradley-heathen
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Posted 26 April 2012 - 05:20 PM
sorry maybe i should have been more clear, what i want to know is, when examining a block that has supposedly been offset bored, how big should the gap between 2&3 be, so i can determine if it has been bored correctly or not
#4
Cooperman
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Uncle Cooperman, Voted Mr TMF 2011
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Posted 26 April 2012 - 06:12 PM
sorry maybe i should have been more clear, what i want to know is, when examining a block that has supposedly been offset bored, how big should the gap between 2&3 be, so i can determine if it has been bored correctly or not
Ah, I don't know the answer to that. However, if I have a few days I could work it out by measuring the cyl 2 to 3 spacing on a standard 1275 block, which I have somewhere in my storeroom, subtracting the difference in diameter with the 73.5 mm bore, then adding 0.030", the resulting dimension being the nominal gap. If you want me to do this just let me know and I'll do it on Monday.
#5
cradley-heathen
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Posted 26 April 2012 - 07:40 PM
cooperman, you are a legend, if you could do that, i would be extremely greatfull!
#6
Cooperman
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Uncle Cooperman, Voted Mr TMF 2011
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Posted 26 April 2012 - 09:42 PM
cooperman, you are a legend, if you could do that, i would be extremely greatfull!
I'll do that on Monday and post it on here as soon as I can.
It should be possible to tell from a photo, but I suspect you want an actual dimension.
#7
Cooperman
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Uncle Cooperman, Voted Mr TMF 2011
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Posted 27 April 2012 - 02:51 PM
Just been out to the workshop and measured a standard bore 1275 A+ block.
The cylinder centres between 2 & 3 are, as close as I can measure, 3.015".
This gives a distance between cylinder walls of 3.015 - 2.76 = 0.255"
A 73.5 mm bore diameter for 1380 = 2.893" which reduces the land by 2.893 - 2.76 = 0.133"
So, without offsetting this would leave 0.255 - 0.133 = 0.122"
With 0.015" offset in either direction this increases the land by 0.015 x 2 = 0.030
So, for a 1380 offset by that amount the land will be 0.122 + 0.030 = 0.152"
With my measuring tolerances would say that it's been correctly offset if the land is between 0.145" to 0.155"
No wonder there can be head gasket issues with those big bore engines!
The cylinder centres between 2 & 3 are, as close as I can measure, 3.015".
This gives a distance between cylinder walls of 3.015 - 2.76 = 0.255"
A 73.5 mm bore diameter for 1380 = 2.893" which reduces the land by 2.893 - 2.76 = 0.133"
So, without offsetting this would leave 0.255 - 0.133 = 0.122"
With 0.015" offset in either direction this increases the land by 0.015 x 2 = 0.030
So, for a 1380 offset by that amount the land will be 0.122 + 0.030 = 0.152"
With my measuring tolerances would say that it's been correctly offset if the land is between 0.145" to 0.155"
No wonder there can be head gasket issues with those big bore engines!
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