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JohnD

Lead-free valve recession

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You may have noticed, if you frequent American classic car boards, that they deny that valve recession due to the loss of lead in fuel is a problem, and even say that UK concern is an obsession.

A recent discusison on The Triumph Experience turned up this paper: https://archive.epa.gov/international/air/web/pdf/vsr-finaldraft.pdf     It's from the US Environmental Protection Agency, a branch of government, and the Partnership for Clean Fuels and Vehicles, a branch of the United Nations.   The paper seems to  discount valve seat recession due to lead free fuel, finding "virtually no evidence of excessive valve wear has been found in vehicle or engine operation in normal everyday use".   However, it concerns itself mainly with modern vehicles, but goes on to admit that, "Some auto enthusiasts own vintage or antique vehicles. These vehicles are unlikely to be operated under conditions that would induce excessive valve seat wear, so operating them with unleaded gasoline is generally not a problem if the octane rating is sufficient."

The US claim that they haven't seen recession is impressive, but I would still urge that anyone who uses their classic under other conditions, motorways, competition and if the valveseats are ever lapped-in, should beware!

John

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I've been running the Spitfire 1500 without additive on lead free (usually super) fuel since 2014, that includes 2x10CR and 1xRBRR as well as plenty of other usage. No signs of valve recession so far. I figure that once the recession starts I'll have saved more than the cost of the head re-work by not putting additives in.

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The FBHVC vsr tests ran a small engine at high rpm and wot for several hours. The test bore little resemblance to road driving, where wot is used maybe 5 % of the time. To me the american exeperience rings true. I ran the s/c TR6 for 25000 miles with no additive, and no vsr, and hardly ever exceeding 3000 rpm.

Microwelding is heat related. Ex gas temperature rises with rpm but also depends upon throttle opening, load:

image.png.cabedc516d87e818ff8d9c4adf57fc96.png

So part-load and middling rpm reduces temperatures of the ex gas appreciably.

Peter

.

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PP = Leaded Petrol? B20 - biodiesel, E20 - 20% ethanol, but T20?   All more or less the same.

And, I believe that your engine is turbo-charged, Peter, so a hotter burn than usual?

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3 hours ago, JohnD said:

PP = Leaded Petrol? B20 - biodiesel, E20 - 20% ethanol, but T20?   All more or less the same.

And, I believe that your engine is turbo-charged, Peter, so a hotter burn than usual?

Hi John, Supercharged with a rather poor Wade blower that heats the mixture to around 40-60C.  Result: very smoothe combustion, runs like it has a couple of extra cylinders. No sign of vsr. That extra 60C adds to combustion temp, and the extra boost adds more gas. On the other hand the rpm are rather low. Around here I hardly ever drop out of o/d top and just poke the throttle to climb the hills. Peter

 

 

 

 

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PeterC - is seat recession a result of micro-welding then? I didn't realise that.

I've been running my Spitfire on unleaded (97 or 98 RON) and its exhaust valve seats had some very clear and consistent damage which maybe looked like microwelding. See pic below. I hadn't noticed any recession when checking valve clearances though. 

My pal uses a Midget (A-series) as daily transport and must cover 20k or so a year, up and down the country. He was sceptical about VSR until about 2 years ago when his exhaust valve clearances abruptly started shrinking every time he checked them. His conclusion was that lead-memory was real and he had eventually used it all up. 

So I don't think VSR is imaginary but whether it's a problem will depend on your mileage... 

DSC_5501.JPG

Edited by PeteStupps
typo

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Exactly that.  And it doesn't happen much if you are just pottering about - needs sustained highish rpm under load (ie motorway work).  A series was reckoned to be one of the worst affected.  Mk 1 TRiumph 6s also seem to get affected - though it could just be the people I know and how they use their cars.....

Mk 2 6 seem less affected - maybe.  At least I did a good 15k with mine (which would have included plenty of open road work at speed) and the seats were fine when the head was removed for other reasons.  They did have plenty of lead memory though.

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