Morris Minor Owners Club

What's involved in converting to unleaded?
What parts required and where is best place to buy them?
Is it worth doing or is it better to fit some other engine? (1300)

Some would say just "filling it with unleaded", textbook answer is a 'new' (exchange) cylinder head fitted with hardened exhaust valve seats - about £150

Aye - unless doing massive mileage don't bother. Just run it on unleaded, and open up the exhaust valve gaps to 15 thou - and keep an eye on them every 3000 miles or so.

The head on my Midget 1098 was quite tired, and though one day I intend to get it converted (and overhauled fully) I can't afford it at the moment. So I dug out my spare unleaded 998 Mini head and dropped it on. The inlet valves are smaller and with the Midget having the 12G295 head the Mini chambers aren't as good for performance, but it gave me a perfectly good head with unleaded seats without breaking the bank

The Minor 1098 has the same shape chambers as the 998 Mini, but with slightly larger inlet valves and a smaller volume. So you might lose a little on gas flow, but gain a bit on compression ratio. The biggest thing you'd gain is an unleaded head cheap off a Mini forum or Feebay, instead of having your 12G202 Minor head converted at a much higher price

For an unleaded conversion, new guides, new or reconned valves, and a light skim to top and bottom faces to clean them up you're probably looking around £200, if you'd prefer not to go the Mini route.

As I said, £140 exchange

bigginger wrote:As I said, £140 exchange

Where's that from? The £200 I'm going on is what it would cost to have my own head done, and even if an exchange was possible (I haven't found anyone who keeps 295 heads gathering dust) I can't see it being any cheaper. £140/£150 for a full sorting out would make me somewhat happier as and when I get the job done!

Though for a standard 1098 Minor lump, that's still £140 compared to 20 quid for an unleaded Mini head in good nick...

From a large retailer that (as usual, as a Mod) I'm not allowed to name. It's for a standard head though

The unleaded Mini head can be used - but there will be some loss of performance. Of course - an unleaded head from a 1275 engine makes an excellent upgrade - with extra power too! The head is 12 G940 - but not all are unleaded - you really need to see the exhaust valve inserts to know for sure. The exhaust valve swould need to be sunk into the head by 40 thou - perhaps not so easy with hardened seats fitted - or little 'pockets' can be machined (hand ground with stones in leccy drill) into the top of the block under the exhaust valves. This takes about 1 hour (mostly sealing up the block to keep the junk out) - and is a very worthwhile conversion!
But really - for ordinary Minor pottering about - just run the engine on unleaded - it will be fine - and the worst that happens is that the valve gaps slowly close up, in which case - just adjust them open again!

hi i agree with bigginger was going to have my 1380 head fitted with unleaded seats cost me £150 but head no good
if you are after a cheap allturntive look on ebay for late metro -mini ones which are unleaded ok some do not come with buypass hose no problem not useing this. if you are luky you could pick one up .which i just did for £45 unleaded mini one with buypass hose you would use 1275 head on 1098 or you can change the hole engine to 1275will fit on your standed box but make shore its unleaded first
if it was me i would look out for either in the mean time just use unleaded it could run for meny meny month-years i did this on a 1275 ital engine meny years a go for 2years no problem neil

I have to agree with BMC, I have run many old cars on unleaded that were nit converted and have never had a problem.

If the worst happens all you have to do is convert at no more cost than if you had done it earlier.

I wouldn't spend the time and money untill it needed it because it probably never will.

Unless you do many long journeys.

On the later metro and mini engines I am sure the engine number on the little tin plate was a give away as to wether unleaded or not.

I think but would ask somebody to remind me if wrong that after the 99 or 12 at the start of the engine number if the next digit was an H it was unleaded.

Dont take that as gospel till somebody else confirms it, that bit of info was a long way back in my memory and covered in much junk.

Not an engine number 'anorak' - but pretty sure 940 heads with bypass connections are NOT unleaded. That doesn't mean all heads with bypass are unleaded - only the later ones. For me - it has never been a problem on Minor or Mini to run on plain old unleaded fuel - and NO additives !

My dad's found a firm locally that quoted slightly under £100 to fit hardened exhaust seats and valves and grind them in (standard 1098 head). I do lots of fast motorway driving so for me I think a conversion is worthwhile.

Could be Alex - although I highly recommend the 12G940 head on a 1098 engine!

my 2 pennorth is similar to most - if your engine is running ok, then run on unleaded.
The cost of a fully approved fuel additive is cheaper than a head cheaper than converting the head (unless you know you're going to do more than 40,000 miles....)
You may want to modify the timing a bit if you get pinking, but some of the additives include an octane booster anyway, so that negates the issue of a very small change to the timing.

If you plan to do the head anyway, then run on unleaded until the valves/seats are knackered. If this never happens you've been lucky and saved some money - if you do need a recon head later on, you've delayed having to spend a lot of £££'s

bmcecosse wrote:Could be Alex - although I highly recommend the 12G940 head on a 1098 engine!

I still say it's not that suitable. Aside from either shrouding the exhaust valves in the head or less so in the block (which also means taking chunks out a perfectly good and not made any more block), the ports are just too big for a normal 1098. Yes, I'm sure an improvement is seen in the performance after fitting, but that might have more to do with 21cc chambers in place of 26 (or is it 28 like on the Midget?).

Granted 940 heads are a lot more common and so cheaper than an unleaded conversion 295, but that doesn't seem the best reason to fit one to a small bore engine if looking for performance!

The 970 and 1071 S engines (I know - bigger bores and short stroke) had the S head with even bigger valves - and the same camshaft timing as the 1098 engine - and they went very well indeed. Believe me - the 940 head on a 1098 goes like the clappers, at all engine speeds - not just when revving hard -I've had mine on there for over two years now. It's a favourite mod for the 998 Mini lads too - easiest/best value improvement you can make to a standard A series engine. But get the standard one - not the larger inlet valve MG head. Yes - the head is 21.4cc chamber and therefore does increase the comp ratio nicely - without need for any head skimming. Just sink the exhaust valves into the head by 40 thou, and use with 1275 head gasket and rocker gear. A 1.5" carb on an MG metro alloy manifold is desireable to get the best from the head - it will run with a standard carb - but the carb is bound to run out of breath at higher revs !

Why not the big valve head? Are the vales a little too big for small bore engines?

Well - it would work fine of course if you want max power - but for general use without other engine mods the smaller (33/29) head will be fine.

bmcecosse wrote:The 970 and 1071 S engines (I know - bigger bores and short stroke) had the S head with even bigger valves - and the same camshaft timing as the 1098 engine - and they went very well indeed.

They were built to an ever so slightly different design brief though, and the 970 wasn't exactly known for its good road manners!

I can see the appeal of throwing a 940 on, I just don't believe it's the best way to go. Cheapest, most convenient, most suitable on a silly peaky race engine to go with the other silly peaky mods yes, but for a road going small bore I think the best option is a small bore head. Maybe an expensive, skimmed, cleaned up and generally worked over small bore head, but a small bore head nonetheless.

Or get a 295 with hardened seats and a skim and throw it on. Not cheap, but plenty good enough to give a 1098 a bit more go IMO

I have to say I've not noticed any real power loss in the Midget after sticking a bog standard unleaded 998 Mini head on - But then the old 295 was quite tired and the rest of the engine is exhausted.

Why not the big valve head?

The MG metro one with the larger valves is not unleaded and the later MG head that is unleaded uses smaller valves so I assume the room for fitting the unleaded exhaust seats is probably a bit too close for comfort.
As a matter of interest always check the level of the valves in a replacement head, the Midget engine I have in bits at the moment has the exhaust valves a good 10 thou + lower in the head than the inlets so I am having the whole head done.