[chuckspeed]

On the lead question:

Two components come into play. The short answer? Replace the seats.

The long answer? Well...

When we burned lead as an antiknock compound, the compound would precipitate (drop out) on the exhaust seat. To prevent a build-up from causing exhaust valve failure, manufacturers bega to design in valve rotation to literally 'grind' the deposits down.

This works really well forleaded fuels, but in the absence of them, the valve literally 'grinds' itself into the seat - a phenomenon known as valve recession. Hardened seats eliminate this.

The reason some folks have not had trouble with their motors is the lead from many years of use bonds to the exhaust seat and forms a 'cushion' which saves the seat - temporarily. The 'cushion' is only good for about 15-20K miles - there's no guarantee how long it will last, but it 'fools' some folks into thinking there's no need for hard seats.

 

[chuckspeed]

I've used CD-2 as a lead substitute in several motors over the years with no ill effects. I've not used it for long periods, so I can't comment on the long haul. A substitute is better than nothing, tho...Run the substitute until you start to have problems (if any) and then do the permanent fix.

That's how I ran Maggie the Opel until #2 rod bearing spun. After that, she got hard seats alla way 'round.

One other thought - this came from the engine guys @ McLaren a few years back...

Supposedly AV gas still has a sizeable amount of lead in it. When McLaren was developing the GNX, they had trouble with burned exhaust valves. As a stopgap 'till everything was all sorted out, they got a five-gallon can of AV blue (i think) and ran it thru the motor. Enough lead plated out on the seats to last the equivalent of 30K miles wikth no ill effect.

Just a thought,

Chuck.

 

[chuckspeed]

AV gas = aviation fuel. It's formualted to an entirely different standard than pump fuel, and available in much higher octane ratings than we get o the street.

The high octane ratings are not needed for normal (less than 10:1) compression ratios, but the lead content is relatively high - even compared to the old 'ethyl' days.

I'm a fan of automotive history, BTW - It's how I know a little about a buncha stuff. That -- and workng in the center of the automotive universe provides an interesting perspective. Biggest internal combustion motor I've been near was a 3000 HP V-16 turbodiesel in Heavy Engine Test at Detroit Diesel. Bigger than a GT, that motor was - made BIIG noises!

 

[chuckspeed]

Kristy-

Like the plate.

Run the additive until you need the seats; then drop the $$. it may be a 1000 miles; it may be 30K miles. Remember, the mech is in it to make $$, so you will always NEED it.

You'll know it's time when:

It starts to run rough; and

it's traced to low compression inna cylinder.

#3 seems to be the lean one; I'd expect that to drop first.