oil pump county v holborn eaton

[stagmuffin]

i know this has been covered before thought id post a pic for those who may need it,just finishing a build and changing over the springs in the oil pressure relief valve.the new county spring as on the right in this picture is approximately 5.65mm longer than the free length of the old h/eaton pump spring pictured on the left and this would account for the higher oil pressures before relief operates .and because of the potential for damage as a result of this the springs have been swapped.found the old unit hard to dissasemble so dropped in a bowl of boiling water this was soon overcome and they seperated easily.hope this info can help someone
DSC00244 (600 x 450).jpg

[dasadrew]

Just to add some more info to this, these are some of the bits posted earlier on a different thread:

My measurements:

HOLBOURN EATON pump:
- free spring length = 43.65 mm
- wire diameter = 1.3 mm
- winding is anti-clockwise

COUNTY pump:
- free spring length = 48 mm
- wire diameter = 1.55 mm
- winding is clockwise

I've been doing some measuring and calculating, the summary is:

Peter from LD Parts tried out an old original EATON pump and he noted that 3.5kg led to 3/8" deflection.

This equates to 35N and 9.5mm, which gives a spring constant of about 3.7 N/mm

I just measured my EATON spring and plugged the length, wire diameter, spring diameter etc., into a spring constant calculator and it turned out that the calculated spring constant is.... 3.7 N/mm !!

I measured the COUNTY spring, which has a different free length, different number of free coils, different wire diameter and it calculated to be 5.3 N/mm.

So the COUNTY spring is over 40% stronger than the original spec.

Looking at the geometry of the relief valve, when it moves about 8.5mm the holes start to bleed off pressure. The holes are fully exposed when the plunger has travelled about 12.5mm

Based on the surface area of the plunger calculated from its 14.2mm diameter, and the correct weaker spring with 3.7N/mm spring constant, 8.5mm deflection would be achieved with a force of 31.5N, or in other words, a pressure on the plunger of 0.199 N/mm².

Full opening of the relief valve is at 12.5mm travel = 46.25N = 0.292 N/mm².

In £.s.d., the correct oil relief valve should start to open at about 30 psi and be fully open at 42 psi.

The stronger County pump valve would start opening at about 42 psi and be fully open at 60 psi.

All of the above calculations seem more or less consistent with the different running reports knocking about, bearing in mind that the oil pressure gauges are notoriously inaccurate.

Drew

[Ian Durrant]

I saw this before Drew, Personally I wouldn't be worried about oil pressure of 60 psi. What bothers me is that using the county pump I have broken two oil pressure gauges because occasionally when starting from cold the oil pressure shoots up to well over 100 psi. A couple of others have reported the same on here. This suggests maybe the relief valve is binding which I am sure I have read elsewhere was the reason hobourn eaton redesigned the spring at one point. I haven't been able to find out any more than that though.

[dasadrew]

... This suggests maybe the relief valve is binding.................

Seems consistent with the other finding I made on my County pump:

............The County plunger is very rough. It is dimensionally correct but mine had notches and burrs which would make it stick in the sleeve. Therefore I will swap over my original plunger too........

[Ian Durrant]

Ah, I don't recall that part. I have been on the lookout for an original pump so hopefully when I find one I can do the same.

Thanks for that Drew.

[marlbstag]

Hi Ian, TD FITCHETTS advert in triumph World shows sevice exchange oil pumps, not sure if they are BL UNITS, £27. Martin.

[Ian Durrant]

Hi Ian, TD FITCHETTS advert in triumph World shows sevice exchange oil pumps, not sure if they are BL UNITS, £27. Martin.

Thanks Martin . When I get to the mechanical stuff in the summer I'll give them a call. I have been keeping an eye on ebay for an original to cannibalise for the spring (and now plunger).

[confrench]

Hi Martin.I have one from TD Fitchett & it is a Holborn Eaton unit.Con French

[STAG1973]

Glad you got it apart ok i see what you mean about the springs and why they need to be swapped over.

Cheers
Adrian