Lotus Elan

Is this oil pump ok?

PostPost by: richardl46 » Mon Jun 03, 2019 7:29 pm

My 1972 +2 came with the oil pump on the right fitted. I think the relief valve has been sealed with resin to prevent it moving. Is this a high pressure pump and could it be one reason (apart from the sump being over-tightened) why the engine leaked so badly?

On the left is a spare pump that came with the car and appears to be new. One question would be why the sprung plunger is projecting instead of being retained by a staked retainer. I assume the plunger is pushed in and retained when fitting the pump.

I don't want a high pressure pump and would like to think the new pump on the left is ok to use.

Thanks, Richard
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PostPost by: nmauduit » Mon Jun 03, 2019 8:43 pm

even at a higher high pressure the relief valve should be operating, otherwise you'll end up with too high pressure at high revs... which could explain oil seeping wherever the weak(s) points may happen to be. Your gauge would tell you if oil pressure rises too much.
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PostPost by: promotor » Mon Jun 03, 2019 9:08 pm

The valve in the picture (the one that looks like it has a very basic mesh on it) is an oil filter by-pass valve and it allows un-filtered oil to still get to the engine if the oil filter becomes a restriction or is completely blocked.

Usually performance oil pumps aren't supplied with this by-pass valve installed - it is blanked with a plug - as the cars usually aren't doing high mileage and therefore don't need to have this safety valve as filters are likely to be changed after only a few thousand miles and are unlikely to become blocked.

The pump with the protruding aluminium tube is suggesting that a high pressure spring is fitted as some uprating kits come with that as part of the kit - it's just an easier way of retaining the spring without having to "stake" the retainer in place (and possibly get hit in the eye while trying to hold everything in place under spring tension!!).
In the gallery underneath this aluminium tube is where the pressure relief valve (ie not the by-pass valve) sits. That valve should just drop out in the pump on the left when turned upside down.
The spring underneath the aluminium tube may or may not be a high pressure one - you would have to measure its rate if you wanted to be sure if it is or isn't before fitting it.
Last edited by promotor on Tue Jun 04, 2019 6:53 am, edited 1 time in total.
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PostPost by: 2cams70 » Tue Jun 04, 2019 12:47 am

Both these pumps appear to have been modified. The left one has an aluminium spacer installed to increase the relief valve spring tension and hence the oil pressure. The right one has the oil filter bypass valve blocked up with something (looks like epoxy in the picture). The right one could possibly have a high rate relief valve spring fitted too to increase oil pressure. The spring would need to be removed and inspected to determine exactly as it's not possible to tell from the picture. Increasing the pressure can be achieved by either installing a spacer together with the existing spring or installing a replacement spring of higher rate.
Suggest you buy a new complete pump as both of these appear to have been bodged somewhat and they aren't that expensive. NOS Ford pumps are the best if you can get hold of one. If you must you could probably use the LHS one without the spacer together with the spring retainer from the RHS one. You would still need to confirm it had a standard spring however.

Don't be surprised though if the oil leaks remain after replacement as oil pressure only acts directly at the bearings. It doesn't act on the seals or gaskets directly.
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PostPost by: richardl46 » Tue Jun 04, 2019 3:28 pm

Thanks for the replies. Records with the car show a new oil pump being bought from Paul Matty in 2008 and I assumed that was the new one on the left. I'm not keen to use anything that may have been messed about with on a rebuilt engine so will get a new standard pump ordered.

Regards, Richard
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PostPost by: denicholls2 » Thu Jun 06, 2019 12:56 pm

"High" pressure on a Twincam is not that high. Cold oil pressure on a healthy engine at idle is about 40-45 psi. My Renault Europa under the same conditions is 80+, so I would not worry much about "high pressure".

When I was a kid rebuilding a BMW 1600-2, we put the crank sprocket on backwards because it looks funny the right way. This somehow caused the relief plunger to stick. Its high pressure symptom was blowing the filter gasket almost immediately. Until you're at that point I would not have much concern about high pressure.

Higher pressure will cause a bit more squirting where the oil can get out of its passages, but I agree it is unlikely to be the cause of leaks unless they're at the oil pressure sensor or similar.
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PostPost by: 2cams70 » Fri Jun 07, 2019 3:17 am

I forgot to add to this - if you buy a new pump, especially a NOS one make sure the PRV is free before installing it. Make sure you can lift it off it's seat with a screwdriver. It's common for the PRV to rust in place during long term storage under less than ideal conditions.
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PostPost by: oldelanman » Fri Jun 07, 2019 7:36 am

2cams70 wrote:I forgot to add to this - if you buy a new pump, especially a NOS one make sure the PRV is free before installing it. Make sure you can lift it off it's seat with a screwdriver. It's common for the PRV to rust in place during long term storage under less than ideal conditions.


Very good advice.
Can also happen when an engine is not run for a long period.........

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