Can lead substitute help lubricate bearings?

[bysior]

I would like to improve lubrication of the big end conrod bearings in my two stroke engine and want to run by you the thought I have. Is there any chance that the lead substitute may help lubricate these bearings? I am not thinking of “octane booster” type of substitute but the one which is supposed to “lubricate” valves. I understand that it creates some sort of coating on the valves which separates them from the seats and prevents micro-welding in high temperature. This layer contains sodium oxides which apparently do the job quite well .
Is there a possibility that the same process could work in needle bearings and reduce friction in them?

 

[Kestas]

Most conn rod bearings already have free lead in the matrix to accomplish (or prevent) exactly what you suggest. There's no way you can get that much lead in solution to accomplish the same thing.

As for needle bearings, many lubricants are formulated with EP additives and ZDDP to prevent microwelding during momentary contact conditions. Also keep in mind these lubricants were developed before the push to eliminate lead from our products. I don't think the addition of free lead would help any further.

 

[Steve S]

I am almost positive the lead subsitutes form an ash type layer that does the cushion or lube process.

 

[Boomer]

Tetraethyl lead forms lead oxide (white pigment used in old lead paints) upon combustion. This is what "cushioned" or "lubricated" the valves and prevented microwelding between the valve face and valve seat. However, you had to get rid of this as well or it would have clogged up the engine eventually. So dibromoethane was added to gas. This reacted at high temps with lead oxide to form lead bromide, a gaseous material that went out the tailpipe. However, when it encountered moisture (outside air, cold muffler, etc) it reformed lead oxides and / or plumbous acids and hydrobromic acid. This is why mufflers rotted out so quickly in the "olden days"(which I remember all too well. Tetraethyl lead also had a great effect on raising the octane value of gasoline and was used more and more as engine compression started to go up in the late forties through the sixties.

 

[boraticus]

Being an avid two stroke enthusiast, I have to question why one would consider a lead additive? Proper fuel to oil ratio has provided more than sufficient lubrication for bottom end bearing in two cycle engines for generations.

I've got a vintage Yamaha RD350 and an RD400. Both modified to make considerably more power than stock and each electronically set to cut engine rpms at 10000. The RD350 can run up to a maximum of 11300 with stock bearings but it's not advisable to run it at that speed due to main bearing failure, not con rod needle bearing failure. Racers using RD350 engines use TZ racing main bearings to allow for extended periods of very high rpms.

What type of engine and at what speeds are you running them at to cause you to feel the need for enhanced lubrication for the needle bearings?

 

[spasm3]

Valve seats are harder now and unless its vintage, lead substitute is unneeded .

 

[bysior]

Thank you all for your responses.
I need to add that lead substitutes contain no lead whatsoever. The one I know is based on sodium and creates sodium oxide which is supposed to do the same job the lead oxide used to do.

Originally Posted By: boraticus
Being an avid two stroke enthusiast, I have to question why one would consider a lead additive? Proper fuel to oil ratio has provided more than sufficient lubrication for bottom end bearing in two cycle engines for generations.

What type of engine and at what speeds are you running them at to cause you to feel the need for enhanced lubrication for the needle bearings?


You are probably right saying that proper oil/fuel ratio should suffice but I managed to seize my big end bearings twice recently and I still can not figure out why. I believe everything was the way it should have been and that is why I started looking for some additional protection.
My engine is 3 cyl. 850 ccm car engine very similar to the DKW engine from 50's. It runs on 30:1 premix. Big end bearings are double row 5 mm dia. rollers in cast aluminum cage. As you see it is not a modern needle roller bearing with a steel cage. Your Yamahas with oil injection are light years ahead of my engine. I run it at 3500-4000 rpm. and its max. is 4500 rpm.

One more thing about modern conrod needle bearings KZK type. Many manufacturers offer them with silver or copper plated cages for additional protection in case of insufficient lubrication. Some offer fosfated cages for improved oil retention. The very fact that they do that confirms that lubrication in that area may be far from what is needed. These bearings constantly accelerate and decelerate even if engine is running at steady speed.

That is more or less why I started thinking of improving lubrication using lead substitute. If it worked it would be quite cheap and easy way.

 

[boraticus]

Is there any possibility that excessive moisture is getting into your crank case creating steam that may be washing the oil off of your bearings? It's not an impossibility.



You mention silver plated cages, that's what the TZ bearings have.

 

[Cujet]

Even with "modern" 2 strokes, leaded fuel extends bearing life. While it's not clear to the average Joe, those of us who switched from leaded race gas to unleaded paid the price in shorter life.

The easy solution is to use Avgas. 100LL aviation gas. It's not an ideal fuel for very high revving 2 strokes as most racers notice soft throttle response. Maybe even some power loss. It is quite good in lower RPM 2 strokes, such as the mighty CR500. However, it will result in longer con rod bearing life regardless of displacement when compared to unleaded.

I was using a 50% Avgas mix in my Husqvarna 360cc 2 stroke. Any more and the engine felt soft. Straight unleaded resulted in con rod life of 16 hours, vs about 50 hours with 100% Avgas use. I really cannot say about the 50-50 mix, other than to say that the bike is still running.

I'm still using Avgas in my Echo from time to time. I notice that it's unusually sensitive to oil type. It certainly runs better with Castrol TT-S/Avgas than it does with Echo oil/Avgas.

 

[boraticus]

bysior:

Is that engine liquid cooled? If it is, is it a pressurized system and do you ever have to top off the coolant?

Coolant can play serious havoc on engine internals if it finds it's way in.

 

[bysior]

boraticus - yes, it is water cooled. I do have to top off but the problem is that the water pump is leaking a bit and I never know if water gets to the engine as well.
Do you know any other method veryfying if this is happening? I have heard that liquid droplets condensate an the spark plug after engine cools down. But I have not seen any condensation in my engine.

 

[boraticus]

You could try to pressurize your coolant system to find external coolant leaks. Before doing so, all existing known leaks should be repaired.

I've taken an old radiator cap removed the pressure release stuff, put a backing piece on the underside and JB welded a schraeder valve with locking nut to it. Then I could apply compressed air to the engine to look for external leaks. If there were no obvious leaks on the outside and the coolant level dropped, that will be a clear indicator that there must be an internal leak.

I was at my camp once and was watching my neighbour trying to pull his kids around on a knee board behind a small boat with an older 20 h.p. outboard motor. I noticed he was having trouble starting the engine and once running, had very little power. I went over to take a look at his motor. It appeared to me that it was running on one cylinder only. Just by feeling the engine head, I could tell that the top cylinder was much cooler than the bottom. I pulled the spark plug from the top cylinder and fired up the motor. I was amazed how much water was being pumped out the spark plug hole. I pulled the engine head off and found that the head gasket was missing a piece nearly 1/2 an inch long right near a water gallery from the block to the engine head.