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MG MGB Technical - 3-Brg B cyl. wall thickness.

Hi all,
I have a 3 Brg engine that is getting a 1950 bore.
Is there a difference in cyl. wall thickness against the 5-Brg block?
Dirk
Dirk Van Ussel

Hi Dirk I cannot give you a definitive answer, but if I was going to 1950 I would be using liners.

Colin
Colin Parkinson

If you are spending your money on a 1950, I'd be going for a 5 bearing block
willy
William Revit

Dirk-
Either sonic testing or X-raying of the engine block in order to determine cylinder wall thickness prior to boring is advisable. Note that when sonic testing the probe measures only the thickness of the surface that it is sitting on. For example, if a cylinder has a sleeve (liner) in it, the sonic tester will only measure the thickness of the sleeve (liner). It will not tell you how much parent block material is still present beyond the sleeve (liner). The absolute minimum cylinder wall thickness after boring should be considered to be 0.100" (2.54mm). Even so, a certain amount of cylinder wall flexure is to be expected. Sleeves (liners) can be obtained for the BMC B-Series engine from County (County Part # CL1950). These have a wall thickness of 0.130" (3.302mm), are 6.060" (153.924mm) long, and have an external diameter of 3.380" (85.852mm), making them appropriate for engines in the 1869cc-to-1948cc category. Sleeves (liners) have the additional advantage of being made of either spun cast iron or spun cast Ductile (Nodular) iron, either of which is of better quality than the 'engine block-type' cast gray iron. Their advantage is their better wear characteristics due to greater hardness combined with a high graphite content, as well as superior rigidity that facilitates oil control, which are the reasons that Peter Burgess uses them in every large-displacement engine that he builds! Spun cast Ductile (Nodular) iron is three times stronger and marginally harder than spun cast iron, making it the preferred choice for Big Bore engines. If the sleeves (liners) are shrink-fitted into place, then the heat distribution should be as good as that of a normal cylinder of equal wall thickness.
Stephen Strange

Thks all, and Stephen. Didn't know that nudular cast iron is best.Was going to liner he block anyway.
I suppose the basic casting is the same for both engines.
Dirk Van Ussel

I can't understand why you would spend up on a 3 bearing block when you could be doing a 5 bearing version
William Revit

3-bearing blocks used to be popular for racing, due to lower friction on the main bearings.
Dave O'Neill 2

William:I like the mechanical rev counter,I have a steel crank and the block will be used for a Twin cam,with the alu sump.
Dirk Van Ussel

Fair enough Dirk, if you're happy, that's all that matters---sounds like an interesting engine build,
willy

Dave, I've heard that before but really I think it was just a case of there only being 3 bearing engines when the 1800 was first introduced----My personal choice would be / is a 5 bearing block/crank but in Dirk's case where he already has the 3 bearing bug and the parts ready to go there is no other choice
William Revit

This thread was discussed between 18/02/2018 and 21/02/2018

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