Is my old 1968 240 good with todays fuels or should I add a lead substitue once in a while like I do for my old 52 tractor to keep the valves seating properly?

 

Lead lubricates the valve guides so it is probly a good idea to run a lead substitute in any engine built before the mid 70s unless the heads have been reworked and newer valve guides installed

Some marine and industrial engines needed lead substitute until the late 80s

 

I drove a '69 302 over 90,000 miles on todays fuels with no problems at at all. It would have kept running just fine except I decided to give it a make-over. If you don't drive it too hard, it shouldn't be a problem IMHO.

 

Thanks I apprecoiate the feedback.

 

I don't think tetraethyl lead is needed in older vehicles. Lead free gasoline has been around since the 50's. It's an anti-knock compound added to gasoline and doesn't have lubricating properties.

 

Mercury Marine reccomended using leaded fuel up untill around 1979 or 1980. Im not an OMC specialist, but on MerCruiser products from around '66 to 79-80 there is always a bright red sticker on the valve cover, and on the boat by the filler depending on the boat manufacturer that states "USE LEADED AUTOMOTIVE FUEL ONLY MIN 89 OCTANE." Since a marine engine runs at higher RPMS for long periods of time, like while your cruising at fast speeds, I would DEFINATELY use a lead additive. Makes the motor happy, and i'll last a little longer!

 

Marine engines had heavy duty upgrades like medium-duty truck engines, due to the hard work that was expected of them. These are not passenger car engines internally. Hardened valve seats and positive valve rotators are probably part of the package. I would not worry too much. "Marine white" gasoline was not acceptable due the low octane, leading to detonation, not the lead content.

Jim

 

Well, I am working on a 1968 marine Chr. V-8 318 and it broke a valve stem and punched a hole right through the piston. Hard to tell exactly what caused it, but, I have already recommended the guy use a lead additive or something so the engine on the other side does not go the same way.

It came in dead, stalled out. Funny thing is I had it running well, but, could not set the carb. (vac. gauge bounced all over) that someone else installed to "fix" the rough running. So, I did a compression test, all the cyl. were 140-150 psi ... until I got to #6 = 0.

OMC went bankrupt around 2000, so no new parts and to remove the transmission from the motor in an OMC can be a real pain. A lot cheaper and easier to use the additive then replace the motor.

 

A broken valve stem has nothing to do with lack of lead. If anything, lead deposits have been known to cause valves to stick open, potentially leading to damage. My 1966 Dodge truck engine had solid lifters. Is it possible that the marine engine that broke a valve has solid lifters and never had a valve adjustment?

Jim

 

No, hydraulic lifters.

 

OMC was scattered to the winds and parts are avail today (I just ordered a fuel punmp for my 97 'volvo' that has an 'omc' stickered chevy bolted to it.

more of the problem is the age of the motor. the big heavy I6 has not drank water in a long time.

whereas marine engines get heavier and simpler parts (like shim head gaskets instead of composite) the heads/block etc are off the shelf. If the 68 240 did not have hardened seats in a car/truck, it wont in a boat. Since the engine will always operate in an overfueled condition, tulip-ing the valves or valve recession are gonna be a problem. shy of re-machining new seats into the head, a TEL additive is called for.