4 replies to this topic

[paulrockliffe]

Hello,

Is it possible to tell if a head has been modified for unleaded operation without messing about with the engine?

I ask because I've just used the engine identification chart thingy and realised my head *should* be leaded. I don't know if the head has been changed, or modified to take unleaded, so was hoping to be able to tell.

Would running unleaded on a leaded engine cause anyother problems other than premature wear of the valve guides? Do I just need some lead additive stuff for the engine, or should I get the head sorted, if it's leaded?

Cheers.

[Big_Adam]

Short answer.

No.

Long Answer.

No. You have to take the head off.

[Sprocket]

There is a subtle indiator

If the oil gallery plug in the thermostat end of the head is a pop rivot, chances are its unleaded, if it is a brass plug, its leaded.

This is considered a rule of thumb and by no means infalable

[998dave]

sprocket - he asked if it was modified.

I'd say the only way to tell is to look.

Or run it with unleaded till it gives up, and then change it?
The wear rate will be about the only noticeable factor I believe.

Has the head ever been off the engine?

Dave

[Dan]

premature wear of the valve guides?

It's got nothing to do with the guides. It's the valve seats that wear. They keep receding into the head until the engine simply stops working. The valve seats will have a lead memory from all the years of leaded petrol being used on them. This is just a thin smear of lead coating the seats. It gets removed rapidly by machining or hand lapping of the valves, using Redex or other additive engine or fuel cleaners, using modern high performance unleaded fuels with detergents built in or a thorough de-coking, or it gets worn away more slowly by simply using unleaded fuel and driving the car. Once the lead memory has gone there is less than 10,000 miles useful life left in a leaded engine using unleaded fuel. Then the head will need rebuilding. You need to use either an additive in the tank with unleaded or simply keep using leaded fuel if you can find any. Don't use LRP though, it's terrible. You may get advance warning of trouble if the valve clearance is rapidly closing up and needs constant adjustment but all this would tell you is that the lead memory is gone and the valves are rapidly receding.

Edited by Dan, 21 December 2007 - 06:02 PM.