Unleaded v. Leaded

[bulldozerman]

I was just thinking about it the other day, were the 420c engines built to run on leaded or unleaded gas? And if it was, how much damage would using unleaded gas cause.
Thanks,
Branden

[Stan Disbrow]

Hi,

Well, it was leaded in the day for most bands. Amoco was always unleaded, but can't think of another brand that was in 1956.

When leaded was being phased out, all our older stuff was weaned off of lead by mixing leaded and unleaded with progressively less leaded tankful by tankful. This was to prevent the lead coatings on the valves and seats from forming cracks that would lead to burning as hot gases slipped past thru the cracks.

The scheme worked well. Nothing (tractors, trucks, cars, motorcycles, etc) at the time suffered from burned valves. Some with higher compression engines suffered from detonation, but that does not apply to the low compression tractor engines. I don't know how you'd pull this stunt off today, though. I think you just have to run unleaded and hope it doesn't have an issue. That's if the thing runs OK. If you're in there fixing things up, just clean up the valves and seats and it'll be fine.

There is another problem, though. These days, there are issues to be had with pump gas as the various gov't agencies constantly mess with the additives used on a seasonal basis. I have run into formuations that don't burn well at all in the old engines. This is a different issue from leaded vs. unleaded, though. The worst damage I've seen from this is a tendency to not want to start and sometimes shorter life to the sparkplugs. The not starting issue can be frustrating as all get-out, though!

I fixed this particular issue by switching to a 50/50 mix of regular pump gas and 100 octane unleaded racing gas. 100 UL aviation gas would work just as well. The 100 octane stuff is far more volatile than the pump gas, and so there's never any starting trouble or loss of power with whatever blend of pump gas is currently being served up at the local station.

Originally, I was using 100% 100 octane - hell, I don't run this stuff enough for the extra cost of the fuel to matter I just want it to work when I need it - but then discovered that updraft carbs don't like it in the summer as the volatility causes the carb to ice up like a snowball. Oops. This is not a bad thing, though, as race gas is at least 2x the price of pump gas and so mixing it makes the end result a little cheaper.

The only problem you might have is where to get the race gas. I have a station a few miles away that caters to a local race track, and so get it there......

Later!

Stan

[jdemaris]

I was just thinking about it the other day, were the 420c engines built to run on leaded or unleaded gas? And if it was, how much damage would using unleaded gas cause.
Thanks,
Branden

There was a lot of controlled testing done on that subject. The only issue as it pertains to a 420 is the valve-seats. If they are still original and cast-in-head, they will not last as long as they would of with leaded gasoline. That has been proven. If it's had a recent valve job and got hardened seats installed, then there's no problem at all.

The reality is - if this machine is not being used heavy all the time, you'll never know the difference regardless. And - if at some point it needs a valve-job? It's pretty easy to do and not worth worrying about.

What occurs overtime from using unleaded gas is valve -seat recession. This happens anyway with any fuel with soft cast-in seats - but happens at a faster rate with unleaded.

We used to put lead addtives in the fuel when leaded gas first became unavailable. Then, after the test results came back - many users chose to not worry about it - and - when the time came for a valve job- added hardened seats.

I'd be more worried about the ZDDP anti-wear additives being removed from the newest blends of motor-oils.