Low oil pressure 803cc

[pde2000]

I've just been getting back into running my 4door series 2 deluxe and am looking at ways to get the oil pressure back up. There is no knocking, and with new oil and putting back in an old tecalemit filter instead of the new one i have been using the pressure from cold is back up to 40psi idle and 60psi on the move. In the old days it would drop down to 20psi at lowest when warm but it's now dropping to about 10psi. With the new filter and old oil the warm idle was roughly zero.

Is there any point in screwing in a blocking obstruction into the orifice of the new filter and bunging the whole filtration route to get a bit more pressure? The bypass filtration is practically worthless anyway. I seem to remember grinding in an exhaust valve and failing to thoroughly wash the head after, so a bit of corundum could have got into the engine (long time ago).

regards, paul

[liammonty]

It sounds as though you've got wear in the bearings, so I can't see any harm in blocking off the filter to see if it helps a little, although you do have some oil pressure with the correct filter. The 803 does have a notoriously weak bottom end, so it sounds as though you've done well to keep it running so long (certainly better than I did with mine...). I think it's generally a case of when the bottom end fails, rather than if. I've heard tales of them requiring new cranks at 20,000 miles when new.

[pde2000]

Thanks for the prompt reply Liam. The car had done 40,000 when i got it, but the original owner had been meticulous with servicing and kept a full record. It was one of the attractions of the car, having such a comprehensive folder of paperwork - every detail of its history right down to the bonnet release and jacking point tickets. Sadly my lack of knowledge and skill meant that most repairs made lead to disaster so its remarkable that the old thing still works as well as it does, and i will never again venture onto a motorway .

I want to avoid going back into the engine if possible, as its a bit beyond me. After a decoke and then long drive on the motorway up to manchester i had to have the piston rings replaced, and the exhaust valves, as it lost all compression. The original diff had been run dry before i got it, and i replaced it with a 4.2 rather than try to replace the crown and pinion. The cars been standing mostly for the last 18 years since having kids.

regards, paul

[pde2000]

Well, just gone on a run with the new (8 years old) filter plugged and the results are exactly the same as with the tecalemit. I have a theory that the 803 filter was a marketing trick; pay for regular replacements but they don't really do anything. Looking on the A30 site; http://forum.austina30a35ownersclub.co. ... 51&start=0 it seems that folk there have come to the same conclusion; don't replace your old filter, the lower pressure from a new one with just wear out the bearings.

[liammonty]

So if there is no increase in oil pressure when blocking the filter off totally compared with running the correct fliter, I'd be inclined to fit the new filter, together with one of the restrictors that are available through Declan's friend. I think that even bypass filtration would be better than none, and the poor little 803 needs all the help it can get!

I agree with your sentiments about the motorway - that's where my '54 SII engine died (conveniently just before Trowell Services on the M1). I couldn't bring myself to repair the 803 engine, and replaced it with a S/H 948. I loved the car after that - it totally transformed it and made it so much more usable. Hopefully you won't get to that stage, but if you do, a straight engine swap would be more straightforward (and cheaper) than a rebuild.

[Declan_Burns]

I have a few restrictors for the 803 cc on stock.
Regards
Declan

[myoldjalopy]

An 803cc engine (and gearbox?) with a 4.2 diff? Doesn't that make acceleration rather sluggish?

[liammonty]

An 803cc engine (and gearbox?) with a 4.2 diff? Doesn't that make acceleration rather sluggish?

That's a good point. I was thinking the same - I'd be surprised if it can maintain speed in top on the flat. The diff change may have affected oil pressure at a given speed, as the revs will be so much lower than with the 5.375:1 ratio. Not sure if the diff was replaced before the oil pressure drop though?

[smithskids]

How about the oil pressure relief v/v?

[pde2000]

The pressure gets up to 60psi when cold, so the relief valve is working ok. The 4.2 does require dropping down to third on some hills, but most can be happily done at 30mph in top gear. The original tires are at least an inch bigger diameter than the new ones (I kept the original spare tire, that came with the car when it was new) so the old diff was over-revving really. The first run out after replacing the diff got up to national speed limit but resulted in burning an exhaust valve, and as i said the head didn't get a thorough washing after the grinding in. I could go back to the original diff, but the wear is rather bad (whiney).

Pressure with the blocked filter is the same as with an original one, which is what leads me to believe the originals are dummy. The sales brochure for the series II claims the filter is full flow.

[pde2000]

Oh and talking about motorways; I drove up to Chester after changing the oil in the gearbox (stupidly i put some stp additive in) and the noise got progressively worse. On the M1 home the noise suddenly stopped, and then a horrible banging started, as the prop ripped the back off of the gearbox. I think that was the last time the AA took me home. So the gearbox got replaced, and when that started popping out in second, it got replaced with a recon, so there's a spare in the shed.

The sliding joint at the end, where the prop attaches had dried up because the stp had blocked the narrow feed hole.

[oliver90owner]

The pressure gets up to 60psi when cold, so the relief valve is working ok. 

Irrelevant. The oil pump is positive displacement and oil direction will be detrmined by viscosity of the oil. As the viscosity lowers, any quantity of oil bypassing the PRV, while closed, will increase and the losses from the bearings, back to the sump, will also increase. So a leaky PRV will likely only show up as the oil gets thinner.

[pde2000]

Oh I see, sorry i didn't understand that the relief valve could be leaky too. So the solution is a new valve part?

The incident of the exhaust valve happened nearly 20 years ago, but i am fairly certain that there was a drop in pressure as a result, and guessed at the time that i had scored the main bearings, sufficiently to allow warm oil to escape too easily. Every time i tinkered something went wrong. Should have handed the car over to a pro when i first got it. I did get Eddie Pepper, from the essex branch, to weld up the sills for me. He was old then, so i don't suppose he is still with us.

[liammonty]

It's definitely a bypass filter - see below taken from the WS manual. I'd be amazed if BMC got away with fitting dummy filters! I think it's just that, with the correct sized orifice (!), only a small amount of oil is bypassed, meaning that the pressure drop is imperceptible on the gauge.

IMG_3633.JPG (30.05 KiB) Viewed 3753 times

Regarding the pressure relief valve, it should just be a case of taking it out and checking there's no crud in it preventing it from sealing properly. Once that's checked, I'd put the new filter with one of the (very cheap) restrictors in place, and enjoy it, and try not to worry! As before, if it comes to replacing the engine in the future, good second-hand 948s can be picked up pretty cheap, as everybody seems to want 1098s. the 948 is a lovely sweet engine though.

Regarding the gearbox, that's unfortunate. The box in my SII died too, but that was the 1st motion shaft bearing that collapsed and destroyed the front of the casing! Happy days.

[pde2000]

download/file.php?mode=view&id=1089

This is a photo of the sales brochure for the series II. It states "full flow renewable external oil filter"

I'm not a very trusting sort of person (fingers burnt iykwim)

[pde2000]

download/file.php?mode=view&id=1090

Here's the original Dunlop 5.00-14 next to a new radial, it's about an inch taller. I presume that's why the wheel arches are bigger.

[liammonty]

Thanks for the image of the sales brochure - can only conclude that the marketing bods at BMC got it wrong, as to the best of my knowledge, all 803 engines had the by-pass filters, without the additional pipe work you see on the later engines with full flow filters. I know that the 803 was kept in production up until the early sixties, reserved for disabled peoples' cars in place of the 948 (as if being disabled wasn't bad enough...) but always thought those had the old bypass system too, though I haven't seen one of those cars.

I don't think the high wheel arches were related to the high profile of the crossplies, as later on, I believe even higher profile tyres were fitted to the 1000 models with the 'fuller' later type rear wings (5.20 14). They do fill the arches better than the later optional 145 80 14 radials though!

[pde2000]

Took out the prv and it seems in good nick, with a broad shiny ring where it mates, and smooth. A pig to put back, and the pressure seemed better after, but once the oil got hot it was back down to 20psi on the run, and less than 10 at idle. The engine definitely sounds much happier with higher pressure, and pulls really well. With the higher ratio diff i can easily maintain 30mph in 3rd on a hill, but with the old diff the engine was really thrashing to do that; 3rd and 4th are too far apart.

[Nickol]

Reading with great interest. My Austin side valve 800ccn engine does not have a replaceable oil filter ( it does not have a water pump either ). Inside the sump is a gauze filter which should be cleaned out at intervals. I did this last year but the filter was quite clean. To do so of course, you have to take the sump off and there was more grunge stuck to that than in the filter.
Oil pressure is steady at 30 (the gauge only reads up to 40 anyway) other than at idle when it Drops to about 15 to 20.

[liammonty]

Took out the prv and it seems in good nick, with a broad shiny ring where it mates, and smooth. A pig to put back, and the pressure seemed better after, but once the oil got hot it was back down to 20psi on the run, and less than 10 at idle. The engine definitely sounds much happier with higher pressure, and pulls really well. With the higher ratio diff i can easily maintain 30mph in 3rd on a hill, but with the old diff the engine was really thrashing to do that; 3rd and 4th are too far apart.

It sounds rather like the bottom end is worn - I guess your hypothesis regarding the exhaust valve could be part of it, but don't feel too bad - the 803 engine is known for its weak bottom end. I would just keep running it until it starts making untoward noises (which may be a while if you're lucky) - at that point you can consider what to do. When I changed my engine for the 948, I mated it to a 948 box, which overcomes the issue you mention about the ridiculous gap between 3rd and 4th gears on the original box. It's relatively straightforward to mate the long (non-remote) 803 gear lever to the 948 box - not so easy (although possible) to do the same with a 1098 box. The 948 engine can of course be mated straight to the existing gearbox, as the clutch and flywheel are the same.

Just a thought - what grade of oil are you using? You haven't changed it recently for a lower viscosity have you? Presume it's 20W50? That could have an impact on oil pressure.