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Fuel pump fibre spacer - purpose?


Sparky_Spit
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What is the purpose of the 1/4" thick fibre fuel pump spacer used on later FM 1500 engines?  Is it for preventing heat transfer from the block to the pump body, or to space out the later type pump as the lever would have too great a stroke and be at risk of diaphragm damage?

I ask as I have 2 pumps (an original AC type which I've re-furbed and a good quality generic replacement one) and 2 engines (a 1296 FD and a 1500 FM) which have been swapped around a couple of times over a period of a year or so, and I want to make sure I'm not doing any damage to either pump or cam lobe by not using the spacer. Both engine's cam lobes look okay, but I just want to check what is correct and why. Thanks in advance.

Actually, thinking about it, is there any difference in the distance from the camshaft's centre axis and the outer face of the fuel pump mounting flange on the outside of the block with respect to FD and FM engines? 

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20 minutes ago, Sparky_Spit said:

What is the purpose of the 1/4" thick fibre fuel pump spacer used on later FM 1500 engines?  Is it for preventing heat transfer from the block to the pump body, or to space out the later type pump as the lever would have too great a stroke and be at risk of diaphragm damage?

I suspect that its primary purpose is to reduce heat transfer from the block, but to be effective it has to be very thick, and as a result the lever on the pump had to change so that it would reach the camshaft lobe, hence the later style of pump must always be used with the spacer and the early style pump must be used without the spacer.

 

The flange position wrt the camshaft should be identical on FH and FM engines.

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55 minutes ago, Mjit said:

...and the 'needs spacer' type will fit and work without the spacer.  For a few hundred miles.  Before the pump arm fractures, at night, on the A41, and falls in to the sump.

😢

That's okay then... I live nowhere near the A41....😉

Yes, I can see how that happens. After trial fitting a pump to an FM block this morning, with the sump off and a camshaft fitted,  the difference in lever action and the amount of throw is significant.

Thanks for all the replies everyone

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