Morris Minor Owners Club

Down the pub I was told by a mechanical engineer whom I respect, that once an old engine is carboned up you don't really need to use lead replacement in the fuel - does anyone have views on this or is it a question of better be safe than sorry and keep on using the replacement fluid?

"Carboned up" is not really a technical term. The correct expression is "Lead memory". Search on here or Google it and I'm sure you'll find many threads on the subject......

I've always chosen the safe side,my personal choice is my peace of mind.I would change if I knew for certain my head was suitable.I know there are strong feelings but its a personal choice and I see the extra few pence as worthwhile.

There is absolutely NO need to use any 'snake oil' fluids........the engine will run for many many many many thousands of miles without any worries. But - do check the valve gaps, and set the exhausts to 15 thou (inlets 12 thou) - and check/reset them every 3000 miles. Only caveat is if doing many many hard motorway miles - and then you should really fit an unleaded head (and still set gaps as earlier!). No need for this to be expensive - the 998 Mini head is supposedly 'unleaded' in all later engines and entirely suitable for 948 engines and cheap as chips to buy. And 1098 engines can either use that same head with slight loss of power (but actually it may give better economy) - or upgrade to an unleaded 12G940 head from a 1275 engine. And obviously - any 1275 can simply use the unleaded head from a later engine.

Many thanks

told you

Not so easy to source unleaded heads for the 803, but I suspect the low compression ratio means not much chance of any damage, and my car is treated fairly gently anyway. So Roy are those clearances for hot or cold?

The Mini 998 head is perfect - but maybe not that common where you are. I agree - your low comp etc - I think you are safe! Cold clearances - although not sure it makes much difference.

Greetings,

What is the part number for the later unleaded 998 mini heads?

TIA,

Not so sure of a part number, but my old 1989 F Metro ran on unleaded petrol. So anything off a later 1.0L Mini or A series 1.0L Metro should be unleaded.

Hi again,

I seem to have answered my own question - from the minimania web site it would seem that the unleaded 998 mini head is the CAM4180. The only downside to using I can see is that the nominal combustion chamber volume is very slightly larger than the original Minor one, which will give a slight reduction in compression ratio. A skim off the head might well remedy this if felt necessary.

Someone else came up with that idea today too - but I have never heard it before. Would be interesting to measure the chamber volume to confirm - but my money will be on 24.8 cc.

The minimania site quotes the chamber volume in the CAM4180 head at 25.5 cc, as opposed to the 2A629 head (which they suggest is the 948 Minor version) at 24.5 cc.

The difference is small, expecially when you factor in the volume which is in effect added to the combustion chamber by the thickness of the head gasket and also the unswept volume at TDC (depending how far below the block surface the piston stops), but there will nonetheless be a (small) reduction in compression ratio.

I suspect .020" skimmed off the head would more or less compensate for it.

Regards,

I just doubt the figure......the mania site is not exactly famous for correct advice.......quite the opposite....... But if doing any skimming - may as well take 60 off and get a half decent CR!

mickeytwonames wrote:Down the pub I was told by a mechanical engineer whom I respect, that once an old engine is carboned up you don't really need to use lead replacement in the fuel - does anyone have views on this or is it a question of better be safe than sorry and keep on using the replacement fluid?

Mick, I took BMC s advice and set the valves to 12 and 15 thou.
I also have an unconverted head and add "snake oil" to the tune of 1ml per litre of petrol.(pennies)
Like Lambretta lad I figure that it may be better to be safe than sorry, not least because before I purchased my motor I dont know if it was decoked,truth is although the owner said it had a standard leaded head he also didnt believe in lead additives.
When I bought it it ran over, but the new rocker settings and numerous new small bits, points etc stopped that.
Or it could have been the lead additive?
Fact is if you add snake oil it wont matter, but you may get an urge to eat live mice

hi
you pays your money you takes your choice ,fair play to you

Don't bother with the snake oil..... Do check/reset the valve gaps every 3000 miles - which could be once per year for many of us...

or once every 10 weeks

If after the first 10 weeks the gaps haven't changed significantly, you can safely stretch it out to every 5000 miles......

ta roy