Leaded Fuels

[whaler23]

My 71Chrysler engine manual says leaded fuel only. What type of additives are best to use for occasional use of this engine.

[captddis]

Not sure what engine[s] you want to run it in, but I would not worry about a additive for reasonable and intermittant use.
When the lead was removed, I started using Relead in my old Chris Craft as well as reccomending my customers use the additive.
The additive crudded up the plugs something awful and left this brown film in the carbs and bottom of the filters.
I installed a couple Ampco oilers that I ran mystery oil in. I could never get them regulated properly and gave up on them.
I gave up on the additives in the early 90s and have never had any problems. I have a 1968 Chris I play with that has the origanol 327s with non hardened seats. No problems and no more gunk on the plugs.
My brother has a 1951 pontiac with a straight 8, he does use the Ampco oiler but no additive. 70,000 mi since we rebuilt it and no problems.
As long as you don't run at high speeds for extended periods, you should be fine. Dave

[ohiohatteras]

I've been adding CD2 Lead to my ole 1976 454's for the last 12 years! Figured it can only help! You can buy it at Walmart for about 6 bucks and it treats 320 gallons....It's in the automotive section.

[Boatsb]

Lead was to cushion the valves as they closed on the valve seats mostly. Anh heads that have been rebuilt since the late 70's do not need the lead in that capacity. Many engines do not need it but were marked for leaded fuel anyway. If the heads have been rebuilt it should be OK. If not add a simple lead replacement but use it sparingly as it has some other problems if used too much.

[yachtsmanbill]

My Merc 454s have induction hardened seats... not enough meat to install inserts. When I rebuilt them 500 hours ago I had the shop install stainless valves and so far so good. Used the viton seals and they smoked, so we changed out the seals with the old umbrella seals IN PLACE and no more haze. ws

[Maynard Rupp]

Here is the difference. When we had lead, they used valve guide seals to keep the overhead oil out of the intake and exhaust ports. The lead lubricated the valve stems quite well. It also cushioned the valves on their seats which often were just gropund into the cast iron of the heads. The newer engines have bronse valve guides, no valve seals, and hardened valve seat inserts. Some older engine's heads can be modified, others can't. They need lots of meat around the valve seats, and preferably, pressed in valve guides. Most older engines had valve guides that were machined right into the iron. Some can be machined to accept bronse guides, but you are talking lots of boat bucks. If I had older, leaded fuel engines, I would try to retrofit newer heads or change the engines.

[spartonboat1]

Lead was to cushion the valves as they closed on the valve seats mostly. Anh heads that have been rebuilt since the late 70's do not need the lead in that capacity. Many engines do not need it but were marked for leaded fuel anyway. If the heads have been rebuilt it should be OK. If not add a simple lead replacement but use it sparingly as it has some other problems if used too much.

Lead was never intended as a valve coating, although the effects of lead was to coat the valves and valve seats. However, that was strictly a by-product of the engineering purpose of lead, which was to raise the octane rating of gasoline by reducing the combustion flame burn rate. This was probably first seen around WWII in fighter aircraft that ran "high-test" (high octane) grade gasoline with "tetra-ethyl lead" in their fuels. Hence the old term for filling up with high octane (today, premium), which was fill it up with "ethyl".

The lead was found to be actually damaging to valves and valves seats, resulting in "burned" valves, because of un-uniform lead accumulation on valves. Therefore, where leaded fuel was commonly used, valve "rotators" were installed, e.g. by Mercedes-Benz in the 60's and 70's and by Oldsmobile in the early 70's, in order to cause uniform accumulation of the lead coating. A big deal then, but later commonplace.

Nowadays, if the valve rotators are in place, should they run without the coating effect of the lead, i.e. running unleaded fuel, this will cause pre-mature "recession" of valves into the seats, i.e. the seats wear prematurely. So an engine designed for lead, should probably run some type of lead replacement to keep the valves coated.

However, if there is a desire to run unleaded gasoline, then hardened valve seats and valves, but without valve rotators, is would be the preferred configuration and indicated.

P.s., strictly an aside, but in the late 60 and 70's Benz's ran a hard nylon type of valve stem seal, that would wear out. At about 90k miles, they would start leaking, and would always smoke at startup from oil that leaked into the combustion chamber. When and if the seals were replaced, MB supplied a nice soft material replacement seal, that was much less prone to wear and would stop the smoking. However, the valve guides would also wear, resulting in valve that would still seat, but no perfectly. M-B expected a certain amount of oil to be allowed past the seals to lube the valve stems, since they ran at 6,500rpm all day in Germany. End of speech...

my old-timer 2cw...

[Norm Mayer]

If the engine was run with leaded gas in the past, there is already a coating on the valves and seats. Running unleaded will be no problem, just make sure you are using the recommended octane for the engine, as typically, unleaded fuels had lower octane. If a valve or seat needs to be replaced, however, it needs to be of the hardened variety. It is common practice when rebuilding heads these days. If valves and seats are ground, it looses the built-up lead barrier and needs to be replaced.