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MG Midget and Sprite Technical - Unleaded

Hi all,

Sorry if this sounds a stupid question but I've just acquired a 74 midget 1275 with a replacement silver seal engine. Can I run it on unleaded or do I need an additive?

Is there any way to find out from the engine number?

Thanks in advance
A Murray

Just run the car and if, over a period of time, you lose tappet clearance on the ex valves remove the head and have inserts fitted and maybe recon the rest of the head.

Peter
Peter Burgess Tuning

What Peter says.

A lot of cars will have been fitted with replacement unleaded heads over the years, but there's no way of telling without dismantling.
Dave O'Neill 2

Thanks chaps, much appreciated.
A Murray

This is unleaded, -- right?


Lawrence Slater

It's quite likely the valve seats will have retained quite a lot of lead from the leaded petrol it used to run on. If the engine has been dormant for much of the time since unleaded was phased out you shouldn't have anything to worry about. If you reckon on running it for perhaps 3,000 miles per year it will probably outlive me.

BTW, was this the Green one I saw with a "for sale" sign on the main road out of Wilmslow?

BTW, there is a very active local branch of MASC who meet at the Kilton pub on the A50 running North out of Knutsford on the second wednesday of each month. You are most welcome. Ask for Neil (our leader) or me.
Don't park in the hotel carpark, use the other one accessed down the little lane that runs off the main road.

Rob
Rob aka MG Moneypit

Only until the valves are lapped in again I'm told Rob.

But I'm testing this out on my spare sprite engine at the moment. I've put back a standard 1275 leaded head. It's never seen unleaded until now. The valves needed coarse and fine paste to get a good seal. Only done about 500 miles since it's been on, but so far so good.


So how about my picture? Is that an insert? it looks like it to me.
Lawrence Slater

Lawrence, you are right. It will not survive the valve lapping.

Rob
Rob aka MG Moneypit

Can you do a sharper pic Lawrence?

http://www.roadmachine.fi/redline/redline/tech/MIRA%20Red%20Line%20Test%20Results.pdf

I couldn't get the link to display so maybe cop and paste?

Peter
Peter Burgess Tuning

Hi Peter.
I Can't get a better pic unless I take the head off again. Doesn't the red arrow suggest an insert? And why else unless for unleaded? Well that's my thinking anyway.

Not sure I understand the data in that pdf. Could you summarise?

Whoops, forgot pic. See next post.
Lawrence Slater

Base of insert marked by red arrow?


Lawrence Slater

I think the link is saying even with redline additive the valves are going up in the head, esp ex valves, but it isn't self explanatory is it?

I don't quite see the point of lapping and just running it when you could have had the head inserted for leadfree when it was off?

Your pic doesnt really look like inserts to me, sometimes the throat is machined/cast like the pic. I cannot see the telltale line in the chamber delineating an insert. Hence asking for higher quality pic. Your pic also looks like the seat is recessing so even if insert maybe CI repair one.

Peter
Peter Burgess Tuning

Inserts are well worth the relatively mnor expense if you already have the head off. Not just for unleaded, but becuase they also protect the head. My experience:
About 1/3 into a 400 mile trip with our was-trusty (till one of the boys killed it) family BMC1300, we were climbing a long hill ( about 2 miles long) passing everything in sight (it was fiddled with of course) when the distinct symptoms of an exhaust valve just starting to go occurred by the time we got to the top (this is also when I found it need to go a shade cooler in plug heat range).

Having commitmments the next day, I kept going, and by the time I got home it was well and truly 3 cylinders.
I removed the head that night (I was younger and had energy then!) to examine the damage, saw they telltale giant vee burnt out of the valve and expected the head to be cracked across the seat as often happens in the case of a severely burnt valve. Consoled myself thinking at least I had a spare head!

However, when I had rebuilt and tweaked the engine, with the unleaded change here on the horizon, I had fitted unleaded seats to the exhausts, and closer examination revealed no damage at all to the head thanks to the insert. Dropped in a new valve gave it a 10 second lap and it was perfect.

So I've been a fan of hardened inserts ever since.
Paul Walbran

Hi Peter/Paul,
The picture is of the head on my '73 Midget (The one I bought for scrap/spares but put back on the road instead). I had the head off for a blown hg. Pulled the valves out to give the head a clean up, and took that picture. I Couldn't tell if it was unleaded, and the seller didn't know if it was or not.

Money. That's why I didn't have inserts fitted when I had the head off. I don't want to spend more than I can sell the car for. The future buyer can do it. The engine runs well (now I've done the hg), and as the hg was only 10 quid from sussex, I haven't got much to lose. If the valves start to recess, I'll know by the gaps closing.

The OTHER head I'm referring to, is the head on my SPRITE spare engine. Just rebuilt this engine(new rings/shells), and put a standard leaded head back on it. Again, didn't want to spend money on it, as I intend to sell the engine, when I rebuild my OTHER spare engine, which will have an unleaded bigger valve head on it. (Probably the one supplied by Peter B :). ).

Meanwhile, both leaded head engines are doing well so far. The Midget engine was the one that did 388 miles the other day, a lot of which was at 70/80mph. In a month or so, I'll pull the rocker cover and check the gaps. It's an experiment, and isn't costing me much to do it.

I'm not the only one to do this 'experiment' btw.
http://www.minifinity.com/forum/viewtopic.php?f=22&t=45273
Lawrence Slater

Hi Lawrence
The thing about unleaded is that wear increases exponentially with RPM. Drivers who spend most of their time below 3000 RPM won't notice much difference.

My main comment about fitting unleaded seats was that there are other benefits to having them fitted. I've seen so many heads crack under badly burnt valves that to find an easy survivor was a real plus.

As to your photo, sometimes the way the seats were machined into cast iron heads ends up looking exactly like inserts. I have to say that there are some heads that the only way I can distinguish it is to drag a file across the seat. Which only happens when the seat is a bit ratty, why waste a good one!
Paul Walbran

Ok, thanks Paul.
I'd better keep the revs down then, until I sell the Midget, and take the spare engine back out of my sprite.
Lawrence Slater

Oh no, not another experiment!
Dave O'Neill 2

Well it gets boring just driving them. lol.

But, no, not really. If the valves recess before I sell the Midget and the spare engine, then I'll get hardened seats. If not, I won't, and the buyer can do it.
Lawrence Slater

reminds me

I started out lapping my valves on the MG Metro head when I did all the seals and gaskets at the time I had the engine out to sort the clutch issues

Then remembered the potential 'taking away the lead layer' thing and stopped on number one

I will pop the rocker cover off this weekend and check to see if I have had any recession

If so it seems Peter will be getting another head to lavish love upon

fingers crossed...



not Peter's obviously

;-)
Bill sdgpM

This thread was discussed between 24/06/2015 and 26/06/2015

MG Midget and Sprite Technical index

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