Oil Pressure

For all TA 21, TB 21, TC 21 and TC 21/100 cars
paddysteel7
Posts: 23
Joined: Wed Aug 27, 2014 1:13 am
Name: Patrick Steel

Oil Pressure

Postby paddysteel7 » Mon Mar 23, 2015 4:55 pm

Does anyone know what is happening with my oil pressure. on startup at tickover around 100 pounds then after 10 minutes it is 15 to 25 pounds at tickover then at 30 minutes down to 0 pounds on tick over at this time can get gauge to move slightly by milking accelerator but will get rattle if not careful. Temp gets to 75 degrees and stays there. It looks like the pressurre relief valve is just a dome and spring. Oil is Halfords Classic and fresh yesterday filled to revised dipstick level.
Thanks
Patrick Steel
Grey Lady, TC108g, TD21 SII, TA 14 Shooting Brake

Peter Martin
Posts: 158
Joined: Tue May 22, 2012 5:26 pm
Name: Peter Martin

Re: Oil Pressure

Postby Peter Martin » Mon Mar 23, 2015 8:47 pm

Assuming it is the TC or the TC108g then the pressure relief valve is removable/dismantable it consists of a plunger (valve),a spring and a domed retainng cap , the valve may not be seating correctly and thus has stuck open causing starvation to the vital parts,on a TD the valve is integrated in a single unit but equally the thing can stick,in either case ,remove and have a look, it happened once on my TE on a very cold morning on the American tour luckily it cured itself. Assuming everything was ok before you changed the oil ,you may be lucky, your description of a rattle and virtually no oil pressure when warm suggests the engine is being seriously starved and the big ends have gone/are going .The 100psi on start up is quite high & this may have pushed the valve wide open allowing some crud under the seat where it has jammed.I would not run the engine until someone who knows what they are doing has a look, it could be very expensive.I have used Halfords classic 20-50 oil for years in my cars with no problems, I do change it annually

paddysteel7
Posts: 23
Joined: Wed Aug 27, 2014 1:13 am
Name: Patrick Steel

Re: Oil Pressure

Postby paddysteel7 » Mon Mar 23, 2015 9:10 pm

Hi Peter I changed oil yesterday. The pressure is on a gradual drop from cold to hot. I removed the relief valve for second time and it looked clean. The valve is just a dome with a shaft that locates in the spring I think this is an early type. I suspect it is the bearings but hoping for less drastic solution.
Patrick Steel
Grey Lady, TC108g, TD21 SII, TA 14 Shooting Brake

RichardWallach
Posts: 343
Joined: Mon May 21, 2012 10:14 am
Name: Richard Wallach
Location: Melbourne, Australia

Re: Oil Pressure

Postby RichardWallach » Tue Mar 24, 2015 7:23 am

Patrick,

I agree with Peter, unless there is a clear issue with the valve, and it does not sound so, then it is a job for the experts. My oil pressure on the TA21 hovers around 50 pounds when cold at idle and then drops away to about 5 pounds when quite hot. Under acceleration it rises to about 35 pounds when hot.

Richard
Melbourne

Peter Martin
Posts: 158
Joined: Tue May 22, 2012 5:26 pm
Name: Peter Martin

Re: Oil Pressure

Postby Peter Martin » Tue Mar 24, 2015 9:56 am

Worth another look at the valve, remove it and examine the surface of the cone/seat, also see if you can feel the surface of the valve seat within the block they should be shiney/smooth,if not a fine screwdriver with a rag may be enough to clean it up.If you have access to one of these clever scopes/cameras that go round corners as used by surgeons etc you may be able get a clear picture of the internals.A mirror and torch may work .I do not know the spring dimensions, might be worth checking with RT in case yours has lost a bit .A quick check for bearing trouble is to empty the sump into a clean container and look for shiney flecks of whitemetal in the oil, 1or2 you are probably ok, lots = big trouble, also feel the internal surface of the sump bottom, it should be smooth and clean not gritty & black.re pressure drop, my TE idles at 75 cold and 15 when really hot, she runs at 55 at 3000rpm hot,a friend with a TC has near identical figures to Richard .

paddysteel7
Posts: 23
Joined: Wed Aug 27, 2014 1:13 am
Name: Patrick Steel

Re: Oil Pressure

Postby paddysteel7 » Wed Mar 25, 2015 4:50 pm

Thanks guys I fear you are right and will have to do something soon but waiting for shells to be restocked by RT.
Patrick Steel
Grey Lady, TC108g, TD21 SII, TA 14 Shooting Brake

RichardWallach
Posts: 343
Joined: Mon May 21, 2012 10:14 am
Name: Richard Wallach
Location: Melbourne, Australia

Re: Oil Pressure

Postby RichardWallach » Wed Mar 25, 2015 9:32 pm

Patrick,

Always worth giving Chris Prince a call. I have found him to be both very knowledgeable and helpful.

Richard
Melbourne

Ernest Taylor
Posts: 6
Joined: Mon May 28, 2012 6:58 pm
Name: Ernest H Taylor

Re: Oil Pressure

Postby Ernest Taylor » Sat Mar 28, 2015 8:37 pm

The three litre engine was different from others of the same era in that it used a light oil (SAE20) and employed low oil pressures. Perhaps it is worthwhile quoting from the Alvis Three Litre Manual of Instructions for the TA to TC21/100 models

Oil pressure. The oil pressure varies with engine speed from 2 to 40 lbs. per square inch when the engine is warm. A spring loaded oil pressure relief valve allows oil from the main gallery to pass directly back into the sump when the oil pressure rises above the recommended figure.”

Oil Relief Valve. ….Invariably the cause of a drop in oil pressure is due to a foreign body becoming lodged on the oil valve seating. To overcome this matter the engine should be allowed to idle with the relief valve removed so that the oil flow will remove whatever foreign body is present. When the engine has run for a sufficient time to flush the seating, etc. (about 15 seconds), the oil pressure relief valve, spring and dome nut can be refitted.”

The pressure relief valve is there to limit the pressure to 40 psi. Idling when cold gives a pressure somewhat higher that the 2 to 4 psi quoted above but this falls when the engine warms up.

Before doing anything drastic to the engine, check that the oil pressure gauge is reading correctly throughout its range by comparison with another one known to be reliable. I found this to be the cause of apparently low oil pressure on my TC21/100 – the gauge worked but no longer read correctly.

Nigel Griffiths
Posts: 7
Joined: Mon Jun 10, 2013 3:03 pm
Name: Nigel Griffiths

Re: Oil Pressure

Postby Nigel Griffiths » Wed Sep 16, 2015 9:10 am

Ernest
Most helpful reading your reply on the oil pressure gauge. My oil pressure reading on my TC21/100 is cold up to about 70lbs on start up than quickly settles at about 50lbs. Then when the engine has been running for about 40 minutes I seem to achieve the 'desired' 25lbs at about 40 to 45 mph. But if i keep running at about 60 mph, the pressure increases to 30-35lbs then after a while drops off to 25lbs again even at 60mph. But after reducing speed the oil pressure comes back up to about 25lbs. There is no knocking from the engine except on cold start up when you get a 'tick knock' which I have put to down poor lubrication of the distributor dog arm. This goes on the 3rd or 4th turn of the engine.
Complaining to several friends with better mechanical prowess than mine, have suggested the gauge may not be reading correctly given its age. And when I changed the oil a few weeks ago, I was surprised to find what looked like the remains of a piece of cork. No doubt a foreign body in the system.
Best wishes
Nigel

Ernest Taylor
Posts: 6
Joined: Mon May 28, 2012 6:58 pm
Name: Ernest H Taylor

Re: Oil Pressure

Postby Ernest Taylor » Fri Sep 18, 2015 11:03 pm

Responding to the above post by Nigel, 70 psi when starting from cold is too high and could cause damage, which is why Alvis provided a pressure relief valve to limit the pressure to 40 psi. Assuming you are using the appropriate grade of oil, the explanation for the high pressure when starting from cold could be:
• Pressure relief valve plunger is gummed up and stuck closed. The remedy is to remove and clean.
• Spring holding down the pressure relief valve is stronger than the original or has been packed out with washers or a spacer to “improve” oil pressure. Under the domed nut there should be nothing but the spring and the plunger. If the spring has not been packed out, it might not be original so I would replace it with a genuine one.
• Defective gauge. If you are confident that the pressure relief valve works and has the correct spring, disconnect the gauge at the union between the small bore copper pipe and the flexible hose to the engine and connect another gauge to the flexible hose – the connection is generic so almost all makes of gauges produced before about 1970/75 should fit and there are plenty of these around. Compare pressures on starting from cold. Take care – don’t assume the test gauge reads correctly unless it has also been checked!
The drop in oil pressure you noticed between the two sequences of driving at 60 mph may simply be a consequence of the oil in the sump being hotter on the second occasion. I assume the water temperature remained constant but even so, the temperature of the oil in the sump is not the same as the water temperature: the water has a controlled cooling system, the oil does not.


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