8 replies to this topic

[Miniownertobe]

I’ve just bought my first mini and have fallen in love with it. It’s a 1979 1000 and in pretty original condition. The lady who sold it to be inherited it and never used it so when I asked about unleaded vs leaded ( additive ) she doesn’t know. I’ve checked all the service records and can’t see if it has ( or could even be ) converted to use unleaded.

So I’ve filled unleaded in to get home but will this hurt the engine and do I need to use a lead additive and if so what time / how much.

Thanks for everyones help and advice so far.

[nicklouse]

at that age it will need a lead additive. unless it has had exhaust seats changed. which is a head off job to see.

 

no you will not have damaged it by using unleaded to drive home. prolonged use and very high revs can speed up valve seat regression but it will still take a long time.

 

if you are going to overhaul the engine then that would be the time to check/fit the hardened seats.

[Miniownertobe]

Great thanks for the advice

[unburntfuelinthemorning]

Some useful information about lead additives:

 

http://fbhvc.co.uk/l...nd-fuels/fuels/

[Spider]

This sometimes seems to be one of those polarizing topics.

 

I'm no chemist, however, what I've generally noticed is if the car is going to be driven around in a sedate way then it's likely you won't need to do anything when using unleaded fuels. If it's going to be run at higher speeds (generally 3000 RPM and over) for periods and / or high loads (eg, tall final drives) then there maybe issues with valve seat recession. Not really clear cut.

 

The advice I generally like to offer is similar to that of Nick's above. I don't feel it worthwhile to remove the head if only for the fitting of hardened seats, just use a reliable additive. If however at some point, the head is coming off for some other reason, then have it converted.

 

Just coming back the " not necessary / very necessary " debate, I'll point out that in their wisdom, Rover considered it necessary to fit hardened seats in production of the A Series Engine.

 

 

Some good A Series specific info;-

 

"What was the test?

 

CAST-IRON A-series engines (as used in Austin A30s and Minis and Metros) are acknowledged to be among the most vulnerable power units for valve seat recession when using unleaded fuel - and that is why they were chosen for the test. A special batch of cast-iron cylinder heads without hardened inserts was donated by Rover. The engine was run with a new cylinder head fitted for each test, for 50 hours at 3, 800rpm on two-thirds load, 30.8bhp (23kW), with valve-seat recession checked and tappet clearances adjusted every 10 hours; then it was run on full load, 48.3bhp (36kW), at 5, 500rpm for 20 hours, checking and adjusting every five hours. The test was certainly severe, with 1.19mm recession occurring on untreated unleaded fuel, leaving the cylinder head unusable. A test using leaded fuel, however, showed negligible valve seat recession; to pass, a fuel treatment was permitted to show a maximum 0.3mm valve seat recession over the whole test, or 0.13mm during the first 50 hours.

But while the FBHVC and Mira have taken all precautions to ensure their findings are fair and representative, the use of bathtub-type A-series cylinder heads creates some variables that might have escaped consideration.

Heat build-up around the exhaust valves of different engines will depend on the port, valve and guide design and this will affect the level of valve seat recession. In addition, the cast iron used in cylinder heads differs in hardness. David Thirlby, editor of the Vintage Sports Car Club's Bulletin, points out that if the hardness of the tested Rover cylinder heads had been published, it would have provided at least a base line for different owners' clubs seeking to conduct further research. "

 

from here;-   http://www.mgb-stuff...replacement.htm

[ACDodd]

Just to add fitting exhaust valve seat inserts is a good time to overhaul the head. Doing so will restore some of the lost 'Pep' that your engine will have suffered due to worn valves and seats. For the sake of £300 or so plus fitting, you get protection and more performance!

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Edited by ACDodd, 30 September 2018 - 09:22 AM.

[absx2]

This sometimes seems to be one of those polarizing topics.

 

I'm no chemist, however, what I've generally noticed is if the car is going to be driven around in a sedate way then it's likely you won't need to do anything when using unleaded fuels. If it's going to be run at higher speeds (generally 3000 RPM and over) for periods and / or high loads (eg, tall final drives) then there maybe issues with valve seat recession. Not really clear cut.

 

 

 

Moke spider summed it up perfectly as usual and there is a term called lead memory where the lead that has been deposited over the couple of decades or more gives some protection for a while after switching to unleaded. So if its going to be used at around town speeds or short trips covering a couple of thousand miles a year its unlikely that you will ever need to touch it before they ban petrol anyway 

I have used my daily on whatever supermarket unleaded is the cheapest for over a decade with no ill effects including an 4 hour each way motorway stint once a year. 

BUT that is with its original engine with 70.000 miles on the clock that has never had work done to it.

If the motor has had a valve job at some time in its life then its going to eat away the seats much quicker so an unleaded head would be a good idea if you plan on using the dual carriageway daily.

Having worked on minis for 40 years, strangely I used to get more issues with burnt out valves before unleaded fuel even existed. It seemed a regular occurrence that someone would pitch up with a their motor chuffing due to part of an exhaust valve being eaten away.

 

Don`t get me wrong hardened unleaded seats with hardend valves are the way to go but sometimes it not always the number one thing to do on the list of jobs that come with mini ownership..

[leyland73]

For a low mileage car, used for 2-3000 miles per year, the cost of machining a cylinder head for hardened valve seats just isn’t economical compared to a couple of bottles of lead additive. I use millers which also prevents ethanol problems.

If a head needs to come off for another reason eg, porting and polishing work makes sense to upgrade at this point.

[cal844]

I got a fully rebuilt unleaded converted head on eBay(it even came with a new head gasket, rocker shaft etc)

It ran for 1500 miles before we removed the engine due to crunching second gear and poor compression ( rich fuelling and general wear).

I generally advise to convert if you want it to have good performance

Edited by cal844, 30 September 2018 - 07:20 PM.