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MG MGB Technical - Petrol and catalytic converters

Hi,
I've been using Shell V-Power (a high-octane) petrol with a lead additive since they stopped using leaded petrol. However, Shell's stopped making it and my mechanic is saying that it doesn't matter.

Well I've been using unleaded petrol for the last 2 months and it seems to work fine except that - I don't know if I am imagining it - it runs a bit rougher AND I seem to smell some fuel (seems like it anyways).

I haven't fitted in a catalytic converter tho. Should I ? What good does it do ?

Thanks in advance. SM


sudhir menon

Hi.

You need to do something to protect the valve seats, or have hardened valve seats fitted.

I think you may be a little confused about catalysts.

A catalytic converter goes in the exhaust to 'clean up' the fumes, I don't think you need one.

There are fuel catalysts on the market (eg Broquet), which go in the fuel tank or pipe and are supposed to protect the valve seats and boost the effective octane a little.
My very limited experience suggests that unleaded can be used safely with a Broquet unit in place, but maybe they would have been OK anyway, or I (Land-Rover SIII) and my friend (Metro) were lucky.

There is LOTS in the archives about this.

Don
Don

Empirical data from here in the US indicates that the lack of lead in petrol is not an issue. I've never had a problem with valve recession, nor have I ever heard of anyone having a problem with valve recession. With all due respect to Don, I don't think you need to do anything right now. Watch your valve clearances -- it they close up, then think about having hardened seats fitted. If they don't, drive and enjoy! But I wouldn't pull the head until there's evidence of a problem....

My 2¢
Rob Edwards

Rob, I had some valve recession on the exhaust valves of my 74. I don't know how many miles were on the engine but two valves were recessed into the combustion chamber 1/16" to 1/8". Maybe it's not common but it does happen.

FWIW, Clifton
Clifton Gordon

Hi Sudir

If you have been using leaded petrol in the past, there will be a certain amount of lead already incorporated into the exhaust valve seats. This will protect you for a while.

How long depends on how far you drive and how hard.

Castrol make a product called Valvemaster, this or similar products may be available. You squirt some in the tank each time you fill up with petrol. This product has been tested, and is known to work. Tin based catylists perhaps may work, but I do know of tests carried out for the New Zealand Automobile Association by Monash University in Australia that showed that the use of a tin based product had no useful effect.

If you do need to remove the head for any reason, its a good time to fit hardened exhaust valve seats. Inlets will be ok.

Cheers Ian F






Ian Fraser

Thanks for the input, Clifton! I guess I can no longer say that I've never heard of anyone having a problem. ;-)

Cheers!
Rob Edwards

Well, I've been using the lead additive (from Shell) now for about 5 years and stopped in Feb this year when they discontinued it. I use the car as an everyday car.

What are the signs of valve recession ?

I'll look for the valve master from Castrol.

Thanks all who responded. I finally know what a bloody catalytic converter does :)
sudhir menon

The main sign of valve recession I experienced was the requirement for frequent valve adjustments. I didn't know what was causing the valve clearances to change until I removed the head. Your symptoms may be different, I think the valve heads were binding intermittently in the recessed seats. The car ran ok and the compression was a little below normal but the readings had about 10-15 lbs. variation in readings.

Clifton
Clifton Gordon

This thread was discussed between 16/04/2005 and 17/04/2005

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