Oil pump size

[Derek Sheldon]

Can somebody please advise the standard bore of the oil pump and the recommended size to upgrade.
Many thanks

[Paul Cooper]

Derek,
I seem to remember boring mine out by 1/16in. Note that it’s not a case of over boring on the current bore centre line but offsetting the pump body in the lathe by a further 1/16in to increase the pumps volume.
There are more details in most of the old A7 tuning books etc.
Hope this helps.

[Chris KC]

I believe a standard A7 pump is 1" bore and if it's in good condition there is no reason to overbore it, assuming a standard engine lubrication set-up. If your engine is pressure fed the pump configuration will depend to some extent on how it is set up.

As Paul says, it is not the diameter but the offset or eccentricity which increases output. Merely increasing bore diameter will only remove wear. My engine runs fine with a 20 thou increase in offset - but that's my engine and may not read across to front feed arrangements.

[Derek Sheldon]

Thanks Paul.
There is an Australian chap who needs to know the standard size as he is not sure if it’s been done previously. The

[Tony Betts]

as KC says a good standard pump doent need oversizing.

but after 90+ years thats not always the easiest thing to find.

the pressure fed ulster engine, in my supersports is on a standard size pump. it produces 45lbs cold and 25lbs hot on tick over. ive never had a problem with lack of oil.

when i get time, i put together O/S pumps. i leave the machining to a friends machine shop. as his lathes are more accurate than mine. the pumps are machined 1/32 O/S offset.

i think 1/16 will break through the bolt hole.

tony

[Derek Sheldon]

Thanks for your help chaps.