Discussion
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Going by the colour of both the plugs and the black engine oil those are out of something pretty old, carbs not FI and one cylinder is probably running a tad richer or colder than the others. If a compression test is OK I wouldn't lose any sleep over it but I might tweak the idle mixture if it has multiple carbs. Plugs in a modern FI engine tend to be almost white because the mixture spends the majority of its time exactly at stoichiometric.
chard said:
Thank's yes oldish Sunbeam Alpine with twin SU's.
With an engine that old and no doubt experiencing a certain amount of ring blowby, valve and seat wear, carb wear etc it would be unusual to get a perfectly matched set of plug colours anyway. The oil is definitely a bit shagged if that's after only 4k miles though. I suspect your compressions are down a fair bit and carbon is contaminating the oil quite quickly but it'll no doubt soldier on a long time yet. If you aren't already using synthetic or semi-synthetic oils there's no reason to believe they only have a place in modern engines. Over time they can remove sludge and carbon deposits that tend to build up with mineral oil and might extend the old girl's life a fair bit.Impressive analysis from a set of plugs.
Yes compressions are down a bit, oil gets dirty quickly and uses 1/2 pint every 1000 miles or so. I use Halfords 20/50 oil.
At some point I may strip down and refurbish as required but perfomance seems ok. She will sit allday at 80 will still do the ton and gets close to 30 mpg. Only 2000 miles p.a. its not a priority.
I will give it another service and forget about it for another year. Which oil would you recommend?
Yes compressions are down a bit, oil gets dirty quickly and uses 1/2 pint every 1000 miles or so. I use Halfords 20/50 oil.
At some point I may strip down and refurbish as required but perfomance seems ok. She will sit allday at 80 will still do the ton and gets close to 30 mpg. Only 2000 miles p.a. its not a priority.
I will give it another service and forget about it for another year. Which oil would you recommend?
chard said:
Impressive analysis from a set of plugs.
Yes compressions are down a bit, oil gets dirty quickly and uses 1/2 pint every 1000 miles or so. I use Halfords 20/50 oil.
Ha! She's barely run in. Back in about 1979 I set off to make the 155 mile trip from Herts to Derbyshire to rebuild the utterly shagged engine in my 1275 Marina at my uncle's garage. I set off up the M1 with a full sump and a full spare gallon of oil in the boot. After 50 miles of motorway driving with a smokescreen coming out of the back so thick you couldn't actually see if anything was behind you the oil light came on. I pulled over and put half the spare gallon in. Another 50 miles and it needed the remaining half gallon. Going over the Pennines about 10 miles out from Taddington with no oil left the power started dropping so rapidly as she started to seize up I had to keep changing down gear to get up hills until eventually I was crawling up them in 1st and 2nd. Trying to coast downhill to save the engine and let it cool down and crawl uphill as slowly as I could I finally hit the last downhill stretch of about a mile and knew I could coast the rest of the way. My uncle's driveway was so steep however that even in 1st she only made it halfway up on her last dying breath and then gargled to a halt. That's what I call making your destination by the skin of your teeth.Yes compressions are down a bit, oil gets dirty quickly and uses 1/2 pint every 1000 miles or so. I use Halfords 20/50 oil.
chard said:
At some point I may strip down and refurbish as required but perfomance seems ok. She will sit allday at 80 will still do the ton and gets close to 30 mpg. Only 2000 miles p.a. its not a priority.
I will give it another service and forget about it for another year. Which oil would you recommend?
At that sort of annual mileage I suspect it makes little difference. An expensive oil will still go black almost immediately as it removes sludge from inside the engine and unless you keep chucking lots of high detergent oil at it on a regular basis until it's cleaned out which will work out very expensive maybe the cheap 20/50 and change it once a year is the best bet.I will give it another service and forget about it for another year. Which oil would you recommend?
Edited by Pumaracing on Friday 28th October 04:11
chard said:
Impressive analysis from a set of plugs.
I can't quite tell what you had for breakfast yesterday from the plugs but I can tell a lot more than I've already said. I can see you're running unleaded because the plugs are grey whereas leaded usually leaves them digestive biscuit colour. Octane and lead replacement additives usually create a golden brown coating which if you use too much can build up into furry deposits that make the electrodes look like Ewoks.You can even see evidence of the twin carbs. Look at the very end of the plug metal just below the thread. 1 and 4 have dry clean dark black sooty deposits and 2 and 3 have a more shiny finish with more build up. This is because of the firing order and the twin carbs. A firing order of 1,3,4,2 which can be restated as 2,1,3,4 means the inner cylinders fire immediately before the adjacent outer ones. With twin carbs and a siamese manifold this means the inner cylinders have to get the fresh charge up to speed from scratch and then the outer cylinders take advantage of the already flowing intake manifold speed and fill better and burn a bit cleaner. This "charge robbing" which notoriously affects the siamese port Leyland Mini engines makes the inner and outer cylinders operate quite differently. You won't see this variance on the plugs on engines which have either one butterfly per cylinder or a single carb or FI feeding a plenum.
So the plugs and oil colour tell me old engine, quite a lot of ring blowby, carbs not FI, unleaded petrol, dino oilo not synthetic, twin carbs, siamese manifold, probability of octane booster or unleaded replacement additive but used very sparingly, and a small mechanical issue with the cylinder that has the plug on the far right. Probably a slightly recessed valve seat or maybe a piston ring issue, probably a bit lower compression on this cylinder than the other three.
For breakfast you had waffles with Canadian maple syrup flown in specially on your private jet - or maybe just cornflakes and coffee.
I should do this for a living. Oh, actually I do.
MattYorke said:
I'm normally very impressed by Dave's analysis. This time I'm utterly blown away. You guys aren't mates, just doing the above for a wind up are you?
Mates nooooooooooooooooooooooo Dave? Dave who?Hats off he knows his stuff Internal Combustion guru. The cynical amongst us (not me) might suggest he looked at the car(s) in my profile and took an educated guess (smoke and mirrors stuff)
My breakfast however.....................................Damn he got that right as well
The black wet think in the plug is not necessarily oil. It might be unburnt fuel. I mean that some particles aren´t burn. I have seen couple of motors witch has got "wet" plug´s and oil consumption is zero/10 000km.
My street tuned RV8 has sometimes "wet" plug´s also, sometimes it vary between each cylinder. sometimes no 7 and 6 and sometimes 5 and 2 excample.. I understand that is typical if plug gasket is not 100% tight and usually race engine´s make it more than STD street engine.
Sorry my boor English..
My street tuned RV8 has sometimes "wet" plug´s also, sometimes it vary between each cylinder. sometimes no 7 and 6 and sometimes 5 and 2 excample.. I understand that is typical if plug gasket is not 100% tight and usually race engine´s make it more than STD street engine.
Sorry my boor English..
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