Engine Oils, a question for the PetroChemists amongst us

[andrewh]

I have a Aston Martin DB5 which has an engine professionally rebuilt by RS Williams who is perhaps the best Aston DB engine builder anywhere in the world. The car is filled with Mobil 1 which is a synthetic oil and after 1500 miles the oil is golden brown. It is uprated to 4.2 litres and has upjetted SUs.

I have just changed the oil on my 3.8 E type at 550 miles. The engine was built by myself, uses no oil and runs very well indeed, however the oil was absolutely black as was the filter. I am running Morris low detergent 20/50.
It has had gasflowing carried out , bigger inlet valves, Rob Beere reprofiled my cams and next size jets fitted, UO from memory?

I realise that oils remove hydro carbons from the engine and suspend them in the oil . All well and good, but wonder why the DB5 engine is a) running synthetic oil prescribed by one of the best engine builder out there, and b) why we don't seem to prescribe that on the E type and given that both engines are very very similar in basic design and are of the same era. I do recall Richard Williams mentioning something about special piston rings that he uses that increase torque, but that was many years ago and I cannot remember the exact detail.

Finally, my 3.8 MAY be running a bit rich as I get quite a lot of soot ( not oil ) around the exhaust tails. As I have been running it in I have not been opening it up hard and as she is upjetted do we think she maybe getting a bit coked up?

Anyway, I am sure there are easy answers to these questions which have just been milling around in the grey matter for a few days.

[christopher storey]

Andrew : I know that my views are not shared by everyone on this forum, but I regard UO as too rich by a very large margin, and I believe this will be the cause of your trouble. It is noteworthy that Jaguar ( and of course SU ) used UM as standard on all 3 carburetter applications for road cars throughout the life of the 3 carburetter engines, whether in 3.4 ( XK150S ) , 3.8 ( XK150S and 3.8 E and Mark 10 ) , or 4.2 ( E and Mark 10 ) sizes. I realise that different filtration may have some ( although I suspect not a huge ) justification for a change, but given the research that Jaguar always did into engine performance, I put a lot of weight behind their views

[Heuer]

UO needles will be too rich on an engine with standard filtration and even a car with an ITG or K&N filter only needs UE. My car is fitted with UO needles but that was done by Andrew Turvey of CMC when they had the car on a rolling road and associated telemetry.

[andrewh]

interesting. Ok. I followed a engine set up suggested by Harry and the car is fabulous.

I need to look into this then as I don't want to bore wash the engine. So is it the collective view that the black oil is rich mixture related not to do with the oils being used? I will talk with Rob Beere next week to get his opinion

So if I converted to an ITG filter which look not too bad in my opinion, presumably I then need to get a catch tank?

Anyway, I hope I can garner a few more opinions before dropping the jets back down again.

[Mark Gordon]

I have over 3000 miles since my engine rebuild, using Castrol GTX 5W30. No discernible oil burn (some minor leaks :( ) and the oil has just a slight brown tinge to it. I go along with the opinion that the black oil is due to rich carbs and not the oil itself.

[PeterCrespin]

The black is carbon
The carbon has come from somewhere
Black oil after only 300 miles is astonishing unless poured into a filthy engine
Your engine was presumably put together clean
Therefore the carbon has not come from the engine
The only other sources is.....?

Problem solved

[Heuer]

....... a disintegrating ITG foam filter?

[ralphr1780]

...I would (re)check the valves!

[adam]

Hi I use Castrol XL 20/50 hardly any change in colour between changes.

Adam

[andrewh]

Ok, well the engine runs beautifully. There is nothing the matter with the valves from the way she runs. It does seem likely it's too rich. I need to remind myself of the jets I bought from Burlen and go back a size. It was 600 miles Peter not 300 but the same applies I am sure. I may have used some graphite aeembly grease on the mains to protect them until pressure built but cannot now recall. On previous engine builds this has had the blackening effect on the oil. Of course it would help if I could recall!

I will report back when I have checked a few things Thanks as always.

[christopher storey]

Andrew : the needles are fairly cheap - IIRC about ?7 each . I would start by putting in the standard needle which is UM and see whether it feels OK . One of the problems which surrounds this issue is the illusion that richer : more power. It is true that XK engines by and large require a richer than stoichiometric ideal mixture, and those who work on the American system suggest that 12.5 : 1 is about right. I use an EGA analyser and work on the basis that with standard needles a fast idle mixture of about 4.5 to 5% CO gives the best results, which tends to correspond with the American view

Incidentally, if you used Graphogen for assembly ( wonderful stuff ) then it probably accounts for the colour

[andrewh]

Ah yes Graphogen, could not recall the name, pale yellow tube. I always do use this and therefore I probably did on the E type as I would have been really keen to protect the bottom end. I had flirted on another engine with red assembly lube and can't remember which I used. Marvellous thing age!
I welcome your advice and data and will take it on board. In years gone by you could tell a good mixture from the charcoal colour of the tailpipes browning slightly after a good thrash, but modern fuels don't burn the same.

Edit.

As a matter of interest does a 400cc larger 4.2 use the same carbs exactly and needles as a 3.8?

[christopher storey]

Andrew : yes, as I set out above, all 3 engine sizes with straight port heads used the same UM needle and springs

[andrewh]

Andrew : yes, as I set out above, all 3 engine sizes with straight port heads used the same UM needle and springs

I would have thought that there would have been a need for bigger jetting to cope with the increased cubic capacity, are the jets different then if the needles are the same?

I spoke with Rob Beere and he thought that the UO needles in MY engine with its various mods would be fine but perhaps a better air filter system would be good. He suggested going back to a UM and seeing how it runs. It would be pretty immediately obvious if it was not getting enough fuel. As for a bit of black soot around the exhaust tailpipes his view was they are all like that and they want a bit more fuel than other engines to run right. He saw no harm in running it on the UOs.

I am therefore beginning to think I must have used the Graphogen in the build for the oil to be black. I will see how I get along with the new oil and may drop down to UEs.

I would say that it is not immediately obvious if the mixture is too rich as its not piling out black soot and the exhaust is very clean

[jag68]

Andrew

The UO needle is quite rich - too rich in my opinion to use on a street car - Jaguar recommending it for racing. It's not the next step from a UM. The richness range from UM is (richness increasing) UB UE UU UX UP UL UO. The UU needle is 3.6% richer, and the UO is 6.1% (figures from WINSU site). I have similar mods on my engine, as yours, and run it at sea level. I used the UU needle when competing with the car, and switch back to the UM needle when cruising for the economy. Switching needles is simple when you install to the same depth. All these needles have virtually the same profile in the idle positions so you don't need to retune the car every time you switch The tuning procedures at idle from the manual are for setting jet height, and once done needle profile takes over at higher rpm's The XK engine definitely like it rich for more power, and richer helps a bit if you have detonation problems.

I'm curious - how does your car idle with the bigger cams? Do you notice it's a bit rougher than when it was stock at 750 rpm idle? I went over to Webers in late 2013 and found it idles much better.

Terry Sturgeon

[KingRichard]

Hi,

I am still working on this matter. I now have UM back in after had UB. I also have laying around UE but not used them, as I think they are too rich. I found UB to be on the rich side. UM I have put deeper in for about 0.3 mm to make them a little richer.

I have standard 9:1 4.2 engine.

I aim for 13.6 AF/R at idle. Cruising about 14 to 14.5 AF/R and full throttle at 12.5 AF/R.

Richard

It is true that XK engines by and large require a richer than stoichiometric ideal mixture, and those who work on the American system suggest that 12.5 : 1 is about right. I use an EGA analyser and work on the basis that with standard needles a fast idle mixture of about 4.5 to 5% CO gives the best results, which tends to correspond with the American view.

[andrewh]

Andrew

The UO needle is quite rich - too rich in my opinion to use on a street car - Jaguar recommending it for racing. It's not the next step from a UM. The richness range from UM is (richness increasing) UB UE UU UX UP UL UO. The UU needle is 3.6% richer, and the UO is 6.1% (figures from WINSU site). I have similar mods on my engine, as yours, and run it at sea level. I used the UU needle when competing with the car, and switch back to the UM needle when cruising for the economy. Switching needles is simple when you install to the same depth. All these needles have virtually the same profile in the idle positions so you don't need to retune the car every time you switch The tuning procedures at idle from the manual are for setting jet height, and once done needle profile takes over at higher rpm's The XK engine definitely like it rich for more power, and richer helps a bit if you have detonation problems.

I'm curious - how does your car idle with the bigger cams? Do you notice it's a bit rougher than when it was stock at 750 rpm idle? I went over to Webers in late 2013 and found it idles much better.

Terry Sturgeon

Terry, great Intel in your post. Thank you. Is there a tip to getting the height of the needles spot on? Obviously measuring them but...?
My cams are the originals reprofiled by RB for SUs. There has been no obvious effect on the smooth idle, but remember I built this car from a wreck so did not experience it before. The engine has bags of torque and feels extremely quick. I have kept it below 2500 with the odd blip to 3000. It feels at 3000 to be dipping in torque a bit which is perhaps the restrictive original air cleaner or maybe tightness in the engine. This is where it's gets a dilemma . Should I change from the standard inlet and exhaust and maximise the engine mods or stick with the programme. What I would say is the car is calling for wellie...it's just asking for it...it wants to go!

Reference idle she is set up to idle about 950 and is smooth.

[andrewh]

Hi,

I am still working on this matter. I now have UM back in after had UB. I also have laying around UE but not used them, as I think they are too rich. I found UB to be on the rich side. UM I have put deeper in for about 0.3 mm to make them a little richer.

I have standard 9:1 4.2 engine.

I aim for 13.6 AF/R at idle. Cruising about 14 to 14.5 AF/R and full throttle at 12.5 AF/R.

Richard

It is true that XK engines by and large require a richer than stoichiometric ideal mixture, and those who work on the American system suggest that 12.5 : 1 is about right. I use an EGA analyser and work on the basis that with standard needles a fast idle mixture of about 4.5 to 5% CO gives the best results, which tends to correspond with the American view.

Ok. Thanks for this info Richard. Is your engine standard?

[mooney1el]

Since y'all are comparing SU needles, I trust you have seen this interactive site. You can put in any needle designation and compare it to any others in the vast library.

http://www.mintylamb.co.uk/suneedle/




Richard

[PeterCrespin]

Your engine contains a huge amount of oil.

You wiped Graphite-loaded lubricant on a few surfaces

A full tube is probably around 50 ml and let's say you used 1/2

The rebuilt engine will have taken 8.5L divided by 25 mL = 340

So your Graphogen was at a near homoeopathic 340:1 dilution

Whatever darkening it caused will have happened in the first minute

So the oil would look as black the first time you checked the dipstick as it did at 600 miles if Graphogen was the cause.

You see where I'm coming from with your 'black oil' @600 miles being due to Graphogen. BTW if you have done 600 miles and only occasionally blipped to 3000 rpm you are in danger of glazing the bores/rings if you haven't already done so. Feeling as if it is running into a torque hole at 3000 rpm is consistent with choking on a very rich mixture. Not saying that's what's going on as I haven't driven the car, but by now you definitely need to give it serious bursts of hard work once fully warmed-up. I wouldn't dream of further mods until you've got the car where it goes like stink and you can wring its neck every time if you so wish.