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MG MGB Technical - unleaded,how can i tell

ive owned my mgb gt for two weeks now,its a 1977.
i have set the engine up to run pretty decent,but the last owner didnt have a clue as to wether ot runs on unleaded or not,all he could tell me was that it had a recon engine a number of years ago,is there a way of telling,i dont want to use the car in case i damage anything.would putting an additive in anyway make any difference?
a davies

To be sure you would have to remove the head to determine whether or not there are hard exhaust valve inserts fitted and that would seem a pity to have to do. Quite frankly I would be inclined to run the motor on unleaded keeping an eye on the valve clearances because if they were seen to be closing that would indicate valve seat recession. So use the motor as it is without any additive which doesn't do any good anyway and deal with the problem if and when it arises. The worst that can happen is that the valve seats receed and you have to have the head machined and hard inserts fitted. Depending on the use you put the car to it could last for years before you have to do any work on it if ever.
Iain MacKintosh

I think the FBHVC would disagree with the claim that the additives don't do any good, they invested a lot of time and money in testing a number of commercial products on BL engines - http://www.mgb-stuff.org.uk/lead_replacement.htm. Whilst none of them were quite as good as lead, some were better than others, and at the time Castrol Valvemaster was best. The tests were done on new engines, companies like BMW have shown that engines run on leaded for a number of years have enough lead leached into the valves and seats - lead memory effect - to protect the engine for 'its normal service life'. I've been running my unmodified engine at high speeds and long distances since leaded finished using Castrol Valvemaster and have not had any recession. Whether that is down to lead memory effect (I know this head ran on leaded for many years) or the additive I have no way of knowing, but a bottle or so a year is cheap insurance.

As leaded seems have vanished anyway (Bayford Thrust made it available via independents for a number of years) I *would* use an additive on your unknown quantity, but keep an eye on the valve clearances. If they start getting bigger then you are probably getting recession, so a modified head would probably be the way to go. Just what has the seller been running it on since the turn of the century?
PaulH Solihull

Iain, I was interested in your reply for two reasons. The first, that additive "doesn't do any good anyway". I would love not to have to use the stuff. Why do you say what you say?
The second, "keeping an eye on the valve clearances". You obviously mean by observing something without removing the head. Would this be via the tappet clearances reducing, or something else?
Richard Coombs

Yes, as the valve seats is earen away the valve will come up to meet the rocker, causing the gap to reduce. I dont like the additives and only used Valvemaster to stop pinking. Now I have got the engine set so it runs on premium unleaded without. The conbustion chambers were really black and messy last time the head was off, this may have been thje additive as they seem fine now. ( from what is visble via the plug hole.)
Stan Best

With the head removed how would you tell if the seats are hardened? Or would inspecting the guides provide evidence.
c cummins

With the head removed, the presence of hardened valve seats becomes quite apparent. You will see a ring around the exhaust valves that is sunk into the head. This is the seat itself. RAY
rjm RAY

Were valve seat inserts always hardened sufficient for unleaded petrol? I ask because way back in the '60's before unleaded was heard of my '58 ZB Magnette already had valve seat inserts. I know, because one of them dropped out!

Andy
Andrew Dear

Mr Davies,

That unleaded topic is not a rarity on this forum, mainly from european owners. I can't tell for UK 1977 MGB engine, but that year in america they were unleaded type. As unleaded fuel was normal in 70's.

But the basic question is how frequent do you drive your MGB and does your driving is rally type? If you drive normally for less that 6,000 miles/year (10,000 Km) well do not bother as reccession will be minimal and when it will be engine overhaul time, you could replace with proper seats. That advice was given to me from a guy who rebuild engine, and my MGB-GT, TR6 and MGB never had a burnt valves more often than in the brit. cars gold era..

Cheers,

Jean G.
Jean Guy Catford

The clearances get less with seat recession.

As everyone has said, just enjoy driving your car and let time tell.

Peter
P Burgess

Ah yes, clearances reduce with recession, not increase.

I tried the octane boosting Valvemaster but it made no difference to pinking, a case of YMMV.

Early cars did have hardened seats before lead was added, it was a side effect of boosting octane that led (pun not intended) to its lubrication effects being discovered, and inserts were no longer fitted as a matter of course. However that should have been before a 58 Magnette was built, so that could have had them fitted for other reasons like burnt seats.
PaulH Solihull

It is not so much a matter of the seats being "hardened", rather of the material of which they are made; in many cases it happens to be a material which is hardenable or hardened, but not necessarily. Various forms of high nickle or stainless steel were common, which would be OK for low lead, with Stellite(s) being used in HD engines, like diesels, natural gas, or race applications. Nowadays, they are often a powder metal composite. OTOH, I can remember old guys talking about machining the inserts out of water pipe and such! One such old school Mechanic fixed a badly burnt exhaust valve on my father's 1950 Morris Minor by welding the valve and seat up with high carbon music wire, which he tore out of a dead piano. It ran fine under heavy use for several years before it was traded on an Austin A40.

FRM
FR Millmore

This thread was discussed between 30/10/2011 and 31/10/2011

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