Piston ring scuffing

[Dave Mann]

I finally stripped the engine removed from the car because of high oil consumption both leaking and burning, the leak was from the paper joint at the front right hand corner where the joint had become hard and a small piece had disappeared. The burning was as a result of extreme wear of the piston ring grooves and piston rings the corners of which were as sharp as razor blades a sure indication of ring scuffing. I've only seen one other example of ring scuffing on two 7000 BHP engines on a Royal Navy ship. The question is why, we know why the ship suffered from ring scuffing but I've never come across it on a Seven engine, could it be from running on E10 petrol which this car has run on since E10 became available?

[Alan]

I remember discussions about ring wear when E10 first appeared. I’ve not seen or heard anything recently.

[Dave Mann]

Further inspection of the engine reveals the top ring gap has opened from 0.006” to o.050” and the top ring vertical rattle in it's groove of 0.015” hence the oil consumption of a pint in 50 miles while the cylinder bores have little wear with some of the machining marks being visible after 22300 miles. I suspect the materials of piston and rings may be wanting. This is the last engine to be rebuilt whilst one car has an engine rebuilt in 1985 has done 53300 miles and consumes a pint of oil in 700 miles.

[Parazine]

The phenomenon is known in the trade as "pumping oil". On the downstroke, oil floods into the oversize ring gap from below, on the changeover, the oil passes behind the ring and on the upstroke, the oil is transferred to a space directly connected to the combustion chamber.

Was it present/more pronounced on the top compression ring/gap? If so, I would suspect an over-rich mixture. Excess petrol will wash the lubricant out of the top ring area. What sort of carburettor are you using? What make of piston are you using? Are the gaps in the pistons worn or is it just the rings?
Short runs with a lot of use of the choke will also show this problem.

I've seen this symptom on Seven pistons before, the rings sometimes worn to half thickness and the edges like razor blades. Sometimes, just the ring is worn, sometimes the ring and the gap in the piston are equally worn. May indicate some materials failure in the rings....

It's very unlikely E10 is responsible; we've been using 5% ethanol fuel for some years and remember Cleveland Discol?   Ethanol = Ethyl Alcohol, i.e. the stuff we consumed in vast quantities on a Saturday evening in the past.       The same stuff Distillers Co. sold to Cleveland Petroleum Products Co. to make their blended fuel.

Nothing new in E10, except possibly, the quantity.


  427px-Im196204Aus-Cleveland.jpg (Size: 141.83 KB / Downloads: 352)

File:  https://www.gracesguide.co.uk/File:Im196...veland.jpg , downloaded 22/01/2025 22:00

[John Cornforth]

Hi

At about 10 mins 30 sec into this video about an AC 2 litre, there is a historic claim that Cleveland Discol contained 15% alcohol.

https://www.youtube.com/watch?v=OfU_NHFjnkI

[Dave Mann]

It has a 22FZB carburettor and this car has a engine heater which is used in winter so the choke is rarely if ever used. Around town it does 36mpg and on a run 50mpg. Both the top ring and it's groove are worn giving a 0.015” vertical play of the ring. I paid a visit to the Anson Museum on the volunteer day when there was a dozen or so ex Mirrlees and ERF members present and all they could suggest was lack of air filter or dirty oil but the car has an air filter and 1000 mile oil changes. One bright spark asked if they were Chinese pistons and rings something I'm becoming suspicious of, the pistons have a cast name Nownl. I do recall when I last had a block bored by by Cotterell Engineering they recommended using slipper pistons, what did they know?
I'm old enough to remember Cleveland Discol and now doubt that E10 is the cause particularly as there are a number of owners using it and nobody has reported this problem.

[Ruairidh Dunford]

If it helps, Dave.

We have also used E10 in all the cars since at least 2018, with no discernible ill-effect.

[Speedex750]

My experience of big industrial diesels is that the running in of new rings to honed bores is vital to avoid scuffing. The engine has to be run under load to press the ring onto the bore. Unless a newly rebuilt A7 engine is just allowed to tick over for a while, on the floor before installation perhaps, it's hard to imagine how you can drive it without putting it under load?

New rings and rehoned bores (a flap wheel will do the trick) should fix it.

Dave

[Ivor Hawkins]

I agree with Dave, get that engine under load…pussyfooting around, has, in my experience, led to a weak, wheezy engine.

Get out there and drive it is the answer!

[Nick Turley]

Every time