Oil pump relief spring

[fool73]

During my (as yet fruitless) search for a "correct" oil pump relief spring (in order to reduce my oil pressure), I have come across a few things which have cast some confusion over the issue and made me wonder what the spring I am looking for is actually like.

This picture shows a spring with the coils open along the entire length

http://www.stagbytriumph.co.uk/parts/stag/1974/02/02-08.pdf

and this article mentions that "later" springs are a terrible design, being partly coil-bound

http://www.tscusa.org/tech/oil_pressure_and_oil_pumps.asp

The above two imply that an original correct spring will be open along it's entire length.

I'm not sure how authoritative the following article is, but it mentions the spring being 1 5/8 inches long, with half being sprung

http://www.stag.org.uk/technical/page0021.htm

The following discussion shows two springs of different length, both having half the length open-coiled, but with the shorter one being correct

http://www.stag.org.uk/forum/showthread.php?10483-oil-pressure/page2

So, in order to reduce my oil pressure, should I be looking for a fully open-coil spring as shown on the first link, or a half-open-coil spring, but with shorter length than mine ?

[flying farmer]

Picture of the county spring and the original spring together in post 353 of Flying farmers new project The county spring is the longer one, but both designs are similar.

Neil

[Mike Stevens]

Here's a picture of an original ('old') and replacement PRV spring ('new')! Sadly, I didn't put a rule in the picture to give scale!



Cheers,
Mike.

[fool73]

Here's a picture of an original ('old') and replacement PRV spring ('new')! Sadly, I didn't put a rule in the picture to give scale!



Cheers,
Mike.

Thanks for the pictures chaps. Unfortunately that adds another possibility, i.e a long open-coil spring being a new one. Mike, where did you get your "new" spring ? and was it long ago ?

[Mike Stevens]

The 'new' spring came in a replacement pump I fitted in about 1989 ish! In this case 'new' is relative. I kept the old pump and extracted the spring when I rebuilt the engine in 2012.

You can see they are different diameters as well as length/profile.

Cheers,
Mike.

[wilf]

Umm - I might hear screams of "you bodging g*t" after saying this, but why can you not just cut down the "new" spring a touch at a time until, you get the max pressure you want?

[V Mad]

Umm - I might hear screams of "you bodging g*t" after saying this, but why can you not just cut down the "new" spring a touch at a time until, you get the max pressure you want?

So long as you cut from the closed coils end then you dont increase the spring rate.

[fool73]

why can you not just cut down the "new" spring a touch at a time?

Two reasons really
1. I have no idea how much to cut off. It sounds like it is a job to get out and I may have to do it lots of times to get it right (and don't want to go too far)
2. I would rather keep the original in case when the engine gets a bit worn I want to put it back in.

Thanks vmad at least I now know which end I would have to cut if I did go that way.

[V Mad]

I took a tip from Neil; I welded a half washer to the outside end of the plug so it can be easily removed with pump still fitted to the engine. Then you can pop out the spring to adjust the length until you get it right. And you can always try adding washers if you cut too much off.

[fool73]

I took a tip from Neil; I welded a half washer to the outside end of the plug so it can be easily removed with pump still fitted to the engine. Then you can pop out the spring to adjust the length until you get it right. And you can always try adding washers if you cut too much off.

Thanks. I've seen that tip but unfortunately have no access to welding gear. I wonder how deep it is. Could I drill a hole in it and use a self tapping screw ?

[V Mad]

You must know someone local who could weld it? Or send it to me with the half washer

[Ian Durrant]

I wouldnt worry about keeping the spring intact. Once the engine gets worn then the pressure will drop and fitting a stronger spring won't make any difference. if the spring is limiting it to say 40 psi then it opens at 40 psi. If the pressure is lower than 40 psi then a spring that opens at 50 or 60 psi won't open either. The spring limits the peak pressure and connot compensate for low pressure.

[fool73]

I wouldnt worry about keeping the spring intact. Once the engine gets worn then the pressure will drop and fitting a stronger spring won't make any difference. if the spring is limiting it to say 40 psi then it opens at 40 psi. If the pressure is lower than 40 psi then a spring that opens at 50 or 60 psi won't open either. The spring limits the peak pressure and connot compensate for low pressure.

Duh. It's obvious really when someone explains it you you like that. Thanks. I would still worry about cutting too much off though. I suppose one coil at a time should be plenty.

You must know someone local who could weld it? Or send it to me with the half washer

Thanks. I wonder if araldyte would be strong enough !

[V Mad]

Duh.
Thanks. I wonder if araldyte would be strong enough !

It doesnt take much to pull out the end cap; Araldyte should work if you degrease carefully first.

[fool73]

It doesnt take much to pull out the end cap; Araldyte should work if you degrease carefully first.

I guess I could even do it in-situ to save the hassle of getting it out the first time. Although I would have to be careful not to araldyte the end cap into the pump. That would not be funny.

Actually, that has got me thinking, I wonder if a valve lapping stick would have enough suction to pull it out ?