leaded/unleaded

Speedy · #1 29-03-10, 01:49

I am guessing that vehicles were running on leaded fuel back when they were introduced and put into service, but now what is being done as civilian owners of these vet vehicles?

is everyone just running unleaded or is a substitute/conditioner available that everyone is using?

more then likely a simple answer to this question, but thought I would ask since I am not sure.

Lang · #2 29-03-10, 03:59

Michael,

I did quite a lot of research on this for our club a few years ago and the conclusions I reached were:

The original leaded fuel definitely contained products (not only lead) that "cushioned" and lubricated the stems of the valves.

Long term use of unleaded fuel and continuous high speed running sped up valve recession ie wear. Catastrophic failure was not a feature of any of the studies I looked at.

The generally higher octane of modern unleaded fuel has compensated somewhat for the loss of lead with its slower burn rate and avoidance of detonation or pinging on the longevity of the valves.

Quite a number of early 40's and 50's vehicles had hardened valve seats and unleaded fuel is not a factor. You can also get hardened replacement valve seats for almost any type of older engine.

Upper cylinder/lead replacement does an excellent job in covering all the lost benefits of lead.

Bottom line was, with the number of miles and slower speeds 99.9% of our old vehicles travel at it does not matter a damn if you replace the lead or not.

To be fully happy use lead replacement but the chances of you being much better off (with our type of vehicle, not high performance classic cars) than non users is slight.

Lang

Phil Waterman · #3 29-03-10, 19:44

Michael- You ask a very good question about valves and lead or lead substitute and Lang I think hit the nail on the head. It depends on how hard the engine is run.

My experience is limited to this issue as it impacts Chevy CMPs. I've been driving my HUP since 1980 that's 30 years and the engine has never been apart and the head has never been off. No problems and I have not used the lead additive. With the HUP you do not run it at full throttle very much of the time.

But with my C60S I did have valve wear problems with valve recession, actually meaning that the valves had to be readjusted about every 2 years (2000 miles) as the clearance would gradually disappear. When clearance goes to 0 the end is quick see http://www.canadianmilitarypattern.c...edvalve6x4.jpg for what happened in one trip. Once the valve doesn't close all the way or has a small bit taken out the flame cuts the valve quick. (When the valve burnt I had a vacuum gauge mounted and in one trip it went from normal to needle bouncing of the peg.)

The problem with the C60S with the radio body was that it had two throttle positions "on the floor" or "foot off the pedal". Because of the weight and non aerodynamic shape the engine basically spent its life at full power.

The fix for the Chev Stove Bolt 6s seems to be installing modern exhaust valves. Once that is done the valve wear seems to go away.

Lynn Eades · #4 30-03-10, 06:57

Its not the valves that wear. Its the heads. I had a customer with a Ford 351clevland, in a truck. it worked hard. (full throttle for long periods). With hydraulic lifters, it kept going until the valves had pounded their way, a full 1/4 of an inch, into the head. We imported some hard seats, and it was never again a problem

cletrac (RIP) · #5 30-03-10, 08:21

Valve wear with unleaded gas is more of a problem with high compression motors especially under hard use. The old low octane tractor gas that was around in the 60s didn't have much in the way of additives and still worked with low compression engines like the CMPs have. I've installed hardened seats in high performance 350 Chev engines to get around the problem but then had the seats come loose in the heads. It's sort of a no win situation. On the 350s I ended up going for heads with induction hardened seats and that worked.