Low oil pressure under braking

[Roger Keys]

Heres an odd one.

Under heavy braking oil pressure drops, basically to zero if its from a high enough speed.

Plenty of oil, including overfilling it.

Checked the dipstick against my other Stag. All ok too.

Is this a known issue, ie cracked pick up pipe etc?

Any ideas? Is there baffling in the sump on these?

[JohnD]

Oil 'slosh' in the sump.

Just like you, under braking inertia seems to force everything forwards (Newton's First Law).
LIke the sixes, a Stag has a reduced hieght front to the sump pan, deepr behind where the oil collects and the oil pump sits.
BUt under braking the oil, which when hot has the consistency of water, will slosh up on the that shallow part, get churned by the crank journals (not a good thing) and leave the pump sucking air.

The solution is baffles in the deep part, around the pump inlet.
A horizontal surface plate, at about the level of the oil when at rest, plus some vertical baffles arund the inlet.
The plate and the baffels should be held no more than a 1/4" (6mm) from the inside of the sump.
Here's a picture of mine on a six.

Also some pics that may be of baffles on a Stag engine.  Looks like a V-engine, might be Ford.   Don't where I got them!  

For mine, I welded tabs to the inside of the sum at tjhe correct level. The surface plate slots into the tabs, which are then bent down towards the sump wall, retaining the plate.  This allows later removal and cleaning of the sum, whereas the other has just tack-welded the surface plate in place!

JOhn

PS, I've since added a lip to the front of the surface plate, to abolish the gap between the that and the shallow front part.
And bend a flange around any holes , so stiffen plate and inhibit slosh through the hole.   J.

[Roger Keys]

Quoted from JohnD

Oil 'slosh' in the sump.

Just like you, under braking inertia seems to force everything forwards (Newton's First Law).
LIke the sixes, a Stag has a reduced hieght front to the sump pan, deepr behind where the oil collects and the oil pump sits.
BUt under braking the oil, which when hot has the consistency of water, will slosh up on the that shallow part, get churned by the crank journals (not a good thing) and leave the pump sucking air.

The solution is baffles in the deep part, around the pump inlet.
A horizontal surface plate, at about the level of the oil when at rest, plus some vertical baffles arund the inlet.
The plate and the baffels should be held no more than a 1/4" (6mm) from the inside of the sump.
Here's a picture of mine on a six.

Also some pics that may be of baffles on a Stag engine.  Looks like a V-engine, might be Ford.   Don't where I got them!  

For mine, I welded tabs to the inside of the sum at tjhe correct level. The surface plate slots into the tabs, which are then bent down towards the sump wall, retaining the plate.  This allows later removal and cleaning of the sum, whereas the other has just tack-welded the surface plate in place!

JOhn

PS, I've since added a lip to the front of the surface plate, to abolish the gap between the that and the shallow front part.
And bend a flange around any holes , so stiffen plate and inhibit slosh through the hole.   J.

Thanks for the info

What leaves me unsure however, is that my other stag doesn't do it at all - no matter how hard i brake.

So something is different between the 2 of them.

Looks like im going to have to have the sump off to investigate

[esxefi]

change the oil pressure switches around and see if it then does it on the other car,one switch might activate at a higher pressure even though they might be the same part no.

[Flying Farmer]

Had the same problem with my Stag engine TR. Ended up cracking 2 main bearing caps after my first ever track day.

Subsequently I have welded a plate across the sump pan at the height of the shallow part of the front of the sump, just leaving a hole for the oil pick up and the dipstick.
This seems to prevent oil surge even under serious track day abuse provided the oil level is kept to the max mark. Have now done all 4 of my Stag engine sumps.

Neil

[Roger Keys]

Quoted from esxefi

change the oil pressure switches around and see if it then does it on the other car,one switch might activate at a higher pressure even though they might be the same part no.

Ive got an oil pressure gauge connected at the moment, on the problematic one. And the other has always had one.

It literally drops to zero if the braking is from a reasonable speed.

[Roger Keys]

Quoted from Flying Farmer

Had the same problem with my Stag engine TR. Ended up cracking 2 main bearing caps after my first ever track day.

Subsequently I have welded a plate across the sump pan at the height of the shallow part of the front of the sump, just leaving a hole for the oil pick up and the dipstick.
This seems to prevent oil surge even under serious track day abuse provided the oil level is kept to the max mark. Have now done all 4 of my Stag engine sumps.

Neil

Clearly a good idea. But what im experincing is not normal. This is just having to stop quickly as one ofte does when sharing the roads with muppets.

[Flying Farmer]

Quoted from roger keys

Clearly a good idea. But what im experincing is not normal. This is just having to stop quickly as one ofte does when sharing the roads with muppets.

Don't know what is normal. Since the engine in my TR was my 1st Stag engine I assumed they all do that. Gentle braking on a downhill road would lose the oil pressure if the oil was half way between max and min.

Admittedly the engine in the TR is installed more level than the usual Stag installation which is raised at the front which probably accentuates the oil surge problem. Taking no chances I baffled the sumps of my next 3 engines.
Might be worth checking the dipstick. A very slight bend in the stick can make a couple of pints difference in the oil capacity due to the fact it is entering the sump at a 45 degree angle. On one of my baffled sumps I didn't align the hole in the baffle correctly and had to bend the stick slightly and I was amazed how much difference it made. Had to move the max and min marks by putting it in another engine to establish the proper max oil level.

[kelvin45]

Quoted from Flying Farmer

Had the same problem with my Stag engine TR. Ended up cracking 2 main bearing caps after my first ever track day.

Subsequently I have welded a plate across the sump pan at the height of the shallow part of the front of the sump, just leaving a hole for the oil pick up and the dipstick.
This seems to prevent oil surge even under serious track day abuse provided the oil level is kept to the max mark. Have now done all 4 of my Stag engine sumps.

Neil

Good info Neil. Worth trying

[Roger Keys]

Quoted from Flying Farmer

Don't know what is normal. Since the engine in my TR was my 1st Stag engine I assumed they all do that. Gentle braking on a downhill road would lose the oil pressure if the oil was half way between max and min.

Admittedly the engine in the TR is installed more level than the usual Stag installation which is raised at the front which probably accentuates the oil surge problem. Taking no chances I baffled the sumps of my next 3 engines.
Might be worth checking the dipstick. A very slight bend in the stick can make a couple of pints difference in the oil capacity due to the fact it is entering the sump at a 45 degree angle. On one of my baffled sumps I didn't align the hole in the baffle correctly and had to bend the stick slightly and I was amazed how much difference it made. Had to move the max and min marks by putting it in another engine to establish the proper max oil level.

The dipstick angle theroy might be good. Whos to say there was any level of accuracy on this.?

Anyway, sump removed, baffles installed, pickup tube replace as a precution (sucking in air?) , rod and main bearings replaced (just as well as some down to copper) and reassembled. Ive run it, but not road tested it yet. (many other parts missing)

While i was there i couldn't help myself and had to wash off all the underseal etc around that area. Im pleased with what was underneath. All very original.

[Pete Lewis]

On a refill  i would do a simple dip stick calibration  just check that adding the correct quantities ties up with the marks on the stick,  

pere

[JohnD]

I've recalled that early sixes had a simple sump, as I showed above.
Later, a gauze mesh surface plate was fitted, to a solid steel rim, that would inhibit slosh into the shallow front.

Could it be that the same was doen on Stags?   And you have an early one?

JOhn

[Roger Keys]

Quoted from JohnD

I've recalled that early sixes had a simple sump, as I showed above.
Later, a gauze mesh surface plate was fitted, to a solid steel rim, that would inhibit slosh into the shallow front.

Could it be that the same was doen on Stags?   And you have an early one?

JOhn

Possible. But i cant find any evidence there was a change. And my other one, which doesn't suffer had nothing in the sump either. The reason they are different in behaviour is a bit of a mystery, but on the upside its fixed now

Which is good as in a month it will be on some italian pass!