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DB18 Spark Plugs

grahamemmett
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DB18 Spark Plugs

Post by grahamemmett »

What is everybody using in their post war DB18s?
I always used NGK B6ES but in an attempt to cure a persistent oiling up problem changed to Champion N14-Y.
It’s not made any difference and the new plugs have gained a hard coating underneath all the oily soot.
865ABF29-E192-47D2-B9C4-41D750B331E5.jpeg
No idea why the photo has appeared twice!
I also get an awful lot of oil around the plugs. I’ve just replaced the rocker cover gasket to see if that’s the problem, but here is a photo if anybody has an idea I’d be grateful.
865ABF29-E192-47D2-B9C4-41D750B331E5.jpeg
B90558AF-B22F-416D-B0BC-21539A54DD71.jpeg
Graham Emmett ¦ DLOC Chairman ¦ chair@dloc.co.uk ¦ 07967 109160
Northwich, Cheshire
DB18 1949 LCV522 (Yes that one with the P100s)

Marcel Renshaw
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Re: DB18 Spark Plugs

Post by Marcel Renshaw »

NGK for me and not had any issues.

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marchesmark
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Re: DB18 Spark Plugs

Post by marchesmark »

Graham,

Is it all plugs or only 1 or 2? Are they oiled up or sooted up? Does the car run well otherwise, or is it misfiring or running rough?

Mark

grahamemmett
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Re: DB18 Spark Plugs

Post by grahamemmett »

Hi Mark
They are all sooted up.
I have found that there is a great deal of oil going from the rocker cover breather into the air silencer as there is no deflector or gauze in the way, just a clear pipe. I have temporarily disconnected the breather pipe and added a couple of foot to it to direct it out of the bottom of the car and when we can get out I will see if that is an answer to the problem.
I started to get the problem last summer and came back from Peebles on 5 cylinders as number 2 was completely oiled up. That horrible streak of oil in the photo is from no 2 but I hope a new rocker cover gasket just fitted will stop that.
Otherwise it runs well for a period then no. 2 or no. 3 will get oiled up and not fire, clean them up and I'm back on six.
The engine has only done maybe 15-20 thousand miles and I have 135-145 psi on each cylinder so I'm sure (well, fingers crossed) it's not internal.

Not sure if that's any clearer.
Graham Emmett ¦ DLOC Chairman ¦ chair@dloc.co.uk ¦ 07967 109160
Northwich, Cheshire
DB18 1949 LCV522 (Yes that one with the P100s)

Mark Bullen
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Re: DB18 Spark Plugs

Post by Mark Bullen »

Is it possible it's running too rich? I had a problem with the float bowl being perforated and overflowing but this also meant excess fuel in the carburettor. Also number 3 cylinder is closest to the carburettor and would likely show the problem first as less distance for the fuel to travel. Maybe try a Gunson colourtune in different cylinders. There are some good spark plug charts online which can help with reading faults showing on plugs.
Also could the inlet valve seals, shaft clearance or not shutting off fully be allowing excessive oil in. I think you can check for valves with a compression tester but can't remember how.
In theory the spark plugs should be gas tight so drawing in oil would seem strange, unless there is a higher vacuum under the piston down stroke than pressure in the upstroke. However there are probably much more experienced mechanics than I who might refute this.
Would be very interested in what you find as I too have a DB18.

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marchesmark
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Re: DB18 Spark Plugs

Post by marchesmark »

Hi Graham,

Still a bit confused! You say it is both sooted up and No 2 is oiled. Normally the former is caused by too much fuel, the latter by excess oil in the cylinder. This is likely to be a fuel or ignition problem though, and the normal rule of thumb says if you definitely think it is one, it is actually the other. Here's my thoughts, this is how I would approach it if it were my car:

- all sooted up: as Mark B says, that could be an indication it is running rich. A telltale sign of that is an excessively black exhaust pipe.
- fuel: check carb: dirt in jet, needle worn, butterfly not closing properly etc. Check air filter: blocked/dirty.
- ign: check condition of spark at each cylinder. If weak, work back down HT lines, dist cap, rotor arm and king lead, then onto the coil. If you are getting weak sparks in each cylinder,the fuel/air mix won't burn properly causing sooting up.

- just one/two plugs oiled up.
- fuel: unlikely to be a fuel issue if all other plugs fine.
- ign: either spark plug, dist cap or HT lead. You have changed the plugs, so I would suspect the lead. Check the spark, and/or just replace the lead. Check for tracking in the dist cap, change it if possible.

If this all seems fine, then oil is getting onto the plugs somehow. Check compression, if OK then piston rings fine. Could either be oil being drawn in via valve stems (but that normally shows as blue smoke on start up) or possibly the head gasket gone between the cylinder and an oilway.

Couple of other thoughts:

- oil in the breather. This should not be happening and may be the cause of it all, although I would expect all 6 to be oiled up (not sooted up). You could try putting a small fuel filter (disposable paper type) in the line between rocker cover and air silencer, this should catch the oil and give you an indication of what the problem is. Normally the engine would burn the small amount of oil being passed from rocker cover to carb quite easily. Too much oil here can be caused by too much in the sump. I have also heard of the sump getting pressurised due to weak piston rings, but if your compression tests are ok this should not be happening.

Rocker cover gasket: almost certainly not the cause of the problem. It will allow oil to flow down and reach the outside of the plug as you have seen, but the plug will be gas tight - it won't be drawing in oil unless it is also exhausting fuel/air mix on the compression stroke, and exhaust fumes on the exhaust stroke. Either way it would be running very rough and you would know about it.

At least you have plenty of time to work on it!

Mark

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Re: DB18 Spark Plugs

Post by Stan Thomas »

Hi Graham,

It would appear you have two problems (well three - if you include it being a Daimler!)

Firstly, check the crankcase ventilation system and the breathers etc. as you should not get oil in the vicinity of the air cleaner as the connection to the rocker cover is only intended to cope with ventilating the rocker chamber.

Next, it would appear you are running rich on the lower register of throttle opening. first check is to top up the dashpot (*) then run the engine until fully warmed up, then wack the accelorator open - you should not get any black smoke from the exhaust - unless your running rich.

That done, raise the dashpot piston at tick-over by a very small amount (there should be a plunger for doing this under the carb body). The revs should rise, then fall back to the same level.

Next, check the air cleaner, for if my aged memory serves me correctly, it is one of those oiled gauze type - which have a propensity to eventually choke up. You car ressurect this type of air cleaner by cutting off the end to remove the wire gauze to wash it in petrol or whatever - then soldering it all back together.

Remove the air cleaner and do the "dashpot raising" test. If you have a vacuum guage, set the mixture and tick over to obtain the highest reading at the slowest R.P.M. - then re-attach the air cleaner to see if the reading alters (secret tip - upon final adjustment of the carb - any carb - finally very slightly richen the mixture - but only very slightly mind).

Going further into the carb settings, make sure the shoulder on the taper needle is flush with the dashpot piston as some people lower the needle thinking it will improve MPG. Check the float height by insering a 7/16 bar under the float lever which should just close the float needle onto its seat. With the dashpot removed, check the petrol level in the main jet is (about) one milimetre below - but "wet" the jet with a small amount of petrol as a dry jet will cause a miniscus and give a faulse reading. Check the taper needle against the S.U recommendation - you might even need a weaker needle.

Use only thin oil in the dashpot. The heavier the oil, the slower the dashpot piston rises upon acceleration - creating a greater venturi over the main jet - which will cause a rich mixture. (thats why you get a flat-spot upon acceleration with an S.U. carb when the dashpot needs topping up - the piston rises too quickly resulting in an ultra-weak mixture).

If all else fails, Ebay are doing some special advertising rates this week.

Let us know how you get on.

Stan.

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Re: DB18 Spark Plugs

Post by grahamemmett »

As always, the depth of knowledge and readiness to share expertise on the forum always astounds me!
Although I'm sorely tempted by the eBay £1 insertion fee offer mentioned by Stan I'd probably not get enough for it to cover even that charge!
That means I need to set out a structured plan of investigation and remedy from all the points above and work through methodically. It's just a blasted nuisance that it's hard to take it for a proper run (but I will).

Just a couple of points:
The air cleaner isn't really - it's an air silencer and I suspect that as Stan says it's full of dirty gauze inside. Right now laying on its side on my garage floor and it's leaking dirty oil. I might get a temporary modern one from Car Builder Solutions for now.
Because it's full of oil I suspect I'm getting lots through the breather pipe so the line filter is an easy fix. I picked up a couple last year for a quid a piece.
And that makes me wonder why I'm having lots of oil blown down there. When I took the rocker cover off, everything really is well soaked in oil so the oil feed to the shaft must be very good. The compression test seems good so I'm hoping there's no piston blow-by and pressure in the crankcase.
So I will go step by step and keep you up to date.
Thanks all for your input.
Graham Emmett ¦ DLOC Chairman ¦ chair@dloc.co.uk ¦ 07967 109160
Northwich, Cheshire
DB18 1949 LCV522 (Yes that one with the P100s)

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marchesmark
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Re: DB18 Spark Plugs

Post by marchesmark »

Graham,

Fingers crossed for you that you make some progress, but if the ebay option starts to appeal, will you give me first refusal??!!

Mark

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Re: DB18 Spark Plugs

Post by Stan Thomas »

hi Mark,
Sounds like your suggesting we start our own Club "D"bay!

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