Running on unleaded

[threelitre]

Hi!

Just a short report on running my A+ engine on unleaded without any additive or LRP stuff.

I have been doing 21k miles since I bought the car and did always use unleaded super or optimax. Ignition could stay as recommended this way. When my brother once filled up with standard unleaded, I noticed that there is no pinking or hot running to be noticed, so the ignition timing would have been fine even for the lower quality stuff.

Since last year (and about 5k miles) life has got even harder for the valve seats - probably - since I use LPG now and did only use about 30 litres of petrol since then. Obviously, being a gas, LPG does not contain any additives to protect the valves.

The car is used daily with a mix of motorway travelling and town driving. Due to the 5speed box the revs are usually kept quite low, although longer journeys around the 4k rpm mark do occur.

As the engine does not have hardened valve seats, the free play of the valves needs to be checked regularly, so that recession can be noticed early. So the valve clearances do get checked at every service now (every 10k kms or 6k miles). On the second service one exhaust valve was found out of the clearance (too small) and reset. Now, after 21k miles, 3 exhaust valves where found to be slightly tight. But compression readings show that no valve leaks yet.

After many predictions the engine would go bang after a short distance, I think now I can feel quite safe about using unleaded, even in my older classics. Although it seems essential to keep control of the valve clearances, probably more so on a 4-speeder used on the motorway a lot.

I will keep watching this - well, next service will be early 2006 I think - and will report if something happens. I do wonder if the recession will gain a little more speed over time or if it will stay more constant. But as long as I get the valve clearance checked regularly, there's still plenty of life left in this head before I need to tackle an unleaded conversion.

Regards,

Alexander

PS: Filling up yesterday: 160 miles for 7 quid

[E_T_V]

Very interesting!

I'd guess the valves will recede at a fairly constant rate until they run out of metal to recede into! perhaps this thread could go in the FAQ attached to the bit about running on unleaded?

Keep us updated and I'd be interested to see how the LPG is plumbed in as I've never seen an A series with LPG

[threelitre]

Keep us updated and I'd be interested to see how the LPG is plumbed in as I've never seen an A series with LPG

Oh, easy: The gas is just entering the inlet before the carb. But I can take some pics and comment on them...

Alexander

[e692wtt]

I seem to recall reading in Car Mechanics magazine that LPG is ok to use in 'Leaded only' engines as it burns at a lower temperature so the point at which significant wear to the exhaust valve seats occurs is reached less often, if at all (usually it is above around 3000rpm with the engine under load and running on petrol, that valve seat erosion occurs). I could be wrong on this though!

When Leaded four star was removed from sale at the end of 1999, Car Mechanics mag suggested that people do exactly as Alexander says, and make regular checks to the valve clearances (but especially the exhaust valves) and see if a problem develops and then only fit a new unleaded head if necessary (why spend money if you don't have to?)...

If valve seat erosion occurs, the valve seat effectively disappears up into the head, as E_T_V says. I'd say that assuming there is no loss of compression the first thing you would notice would be reducing performance as the exhaust valves get partially shrouded by the head and so the engine can't breathe as well as it is meant to. But I would expect burnt out valves, and/or a lack of available valve clearance adjustment, well before this point.

Let us know how this experiment goes, Alexander, and if you could show us some pictures of the LPG Installation that would be very interesting .