Need help on a tough puzzle: tuning an old Le Roi V8

[Mimbrogno]

Greetings from the crew of the Arizona Railway Museum.

I came across this forum and thought you might be interested in taking a crack at a problem that's had us beat for months. Our small locomotive, a 1943 30 ton Plymouth, is powered by a 1943 Le Roi RX-1V 250hp V8 gasoline engine that has been poppen and backfiring. The engine has 6 3/4" cylinders, each with twin sparkplugs positioned to fire about 20 degrees apart (one's in the head, the other's in the block), and two seperate destributers firing the different banks of sparkplugs. The original two distributers were four position types with a second point added so it would work a V8 engine. These were replaced by two conventional Chevy 8 position single point distributers in an attenpt to resolve to backfiring. Other features of this engine are that it has only two valves per head, and the engine is made up of 4 individual engine blocks with 2 cylinders each, connected to a common baseplate that holds the crankshaft and camshaft. The exhaust manifold has a water jacket connected between the coolant outlet on the engine and the inlet on the radiator. There is no muffler.

You should also know a little of the engine's history; A few years ago when we were moving some cars around, one of the cylinders failed, resulting in a 2x3 inch hole in the cylinder wall of one of the engine blocks and a great deal of water being blown out of the smoke stack. We were able to repair the engine by using a sleeve and reinforcing the area over the hole by welding. A subsequent effect of the cylinder wall failure was that the head above it had also developed a water leak, and it took over a dozen repair attempts for finally fix it. The engine does not currently leak any water into the crankcase or any air chambers. Part of the repair required a new cylinder head gasket made of pure copper, where as the old gasket was laminated metal layers and was slightly thicker than the new gasket that is installed. I feel it might have altered the compression ratio slightly, but we feel that it is not severe enough to cause the backfiring.

These are the symptoms we are experiancing:
We have resolved the most severe backfiring by rewiring the ignition system and installing the new distributers, but it still pops quite a bit. It pops the worst when just starting up, and it takes a few minutes with the throttle raised before it dies down a little. The popping is also worse in damp weather when the air gets a little heavier. When we have the engine under load (especially a heavy one), the popping stops alltogether, but it will start again soon after the engine is relaxed.

If you are interested, a few vidoes of this engine in operation have been posted online , and you can clearly hear for yourself how the engine runs. The first is of the engine starting up. The other engine heard at the begining of the clip is our other locomotive with a 1950 Baldwin 600sc 1625hp inline 8 cylinder diesel.

http://www.arizonarails.com/images/museum_mtg_2005/MOV00617.MPG

This clip shows the Plymouth in motion. It is driven by a 4 speed mechanical gearbox. The big lever that the engineer steps on just before stopping is the clutch.

http://www.arizonarails.com/images/museum_mtg_2005/MOV00620.MPG

Please note that these vidoes were taken before the new distributers were installed, and it no longer makes the loudest BANGS you hear.

If anyone has any suggestions as to what we could do to fix this engine, or anything we should look into that we might have overlooked, please offer them! Any help that you could give is very greatfully appreciated!!

Matthew Imbrogno
Mechanical Vollenteer - Arizona Railway Museum.

 

[MikeHalloran]

Did the original distributors have any kind of spark advance mechanism?

I can't help thinking maybe the two plugs per cylinder were timed differently so that the trailing one would run all the time, and the leading one would be disabled until advance was necessary.

There should be some kind of map of the intended ignition timing in the engine's original shop manual ... if you can find one.



Mike Halloran
Pembroke Pines, FL, USA

 

[Fabrico]

That engine should have needs similar to any engine.

How did you adapt those new distributors? If you just plugged in every other plug wire, or something like that, you may be getting a scattered spark output. In addition to hooking up the outputs you need, you also need to kill or re-direct the unused ones. Otherwise they will still go somewhere inside the cap(s). You can either regrind/replace the points cam, or plug all the unused outputs into an external single spark plug. They could also be grounded but that can be hard on the ignition system.

Keep us posted, as a good friend of mine specializes in antique iron.

 

[franzh]

When researching large bore engines for propane, I found out that some of the flame fronts "die out" when moving across the piston top. Some engines I have seen in old firetrucks have as many as three plugs per cylinder. When using dual distributors or magnetos, old-school mechanics told me that you had to stagger the spark to keep the "fire going". Sort of like the Mazda did on the older RX rotaries.
There was a leading plug and a trailing plug. I suspect that is the case here too.

How'bout some photos?

Franz

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[Dieselpg]

I wasn't certain from the original post:
"twin sparkplugs positioned to fire about 20 degrees apart (one's in the head, the other's in the block)"
whether the 20 degrees was a physical measurement, or a timing seperation.
If the latter, if all block plugs were now fired by one distributor, and all head plugs fired by the other distributor, it should give a lot of flexibility about which plug in a cylinder fires first, and how much timing seperation there is before the second plug in that cylinder fires.

The danger, as I suspect many have found, is that 'too much' adjustability can lead to some right old c**k-ups.

HTH

 

[franzh]

I just listened to the mpg videos, that popping is a solid ignition misfire. Since it is not misfiring on every round, I tend to think it is not mechanical (ie: the coolant issue you describe). Crossfire is a distinct possibility (again, the wet weather will accentuate the problem.)

Can you disable one set of distributors on the fly and see if that has any effect on the running? A simple jumper wire should work.

We need to keep these relics alive, they are a direct link to our past, and future.

Franz

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[Mimbrogno]

Thank you all for your replies!! I'm sorry I hadn't gotten back sooner, but I have been unbelievably busy lately and I haven't had much spare time. I'll try to reply to all of the questions you asked me, but it may get a little messy so bear with me....

Let me clarify the configuration of the engine, specifically about the two sparkplugs:
Each cylinder has two sparkplugs, each on opposite sides of the cylinder. The spark plug on the outside of the engine is mounted in the engine block in the side of the cylinder wall itself. The other spark plug, on the inside of the "V", is mounted conventionally in the cylinder head. This means the plug in the cylinder head is about an inch higher than the plug in the block, and we estimate there is about 20 degrees of crankshaft rotation between where they are supposed to fire, as the sparkplug in the engine block is covered by the piston when the piston is TDC. We have surmised that with a piston diameter of 6 3/4", the second sparkplug in the block is necissary to ignite all of the fuel, as the flame front from just one sparkplug will not quite get across the cylinder before the exhaust stroke begins. So the some of fuel would still be unburned when it entered the exhaust manifold, where it finally is reached by the flame and ignites, making the little pop that's been bugging us.

The loud "shotgun" blasts (ironically the shape of this engines smoke stack is know as the "Shotgun Stack" style) on the other hand, were caused by one or two of the cylinder's not igniting at all, and the fuel vapor was released into the exhaust maifold where it built up until it reached the hot gases from the other cylinders and lit. We have been able to stop these loud blasts with the instalation of the new distributers. The old ones were so old that the insulation around two of the fixed points in one of the caps was burned completely away, so it could not trigger the spark plugs of one of the cylinders.

However, even though we have stopped these loud shotgun blasts, the performance of the engine did not improve. It still sounds exactly the same as it did, just without the deafening bangs. That backfiring occured entirely in the exhaust manifold, and it wouldn't have affected the pistons themselves one way or the other. If you ignore those loud bangs, you can hear the engine sputtering and coughing, which is the problem we are trying to solve right now.

Actually, we don't really care what it sounds like. I kinda even like the unusual rythem the engine has right now, just because it sounds interesting. And even if the only bad thing about backfiring was the noise, we could have simply put a muffler on it. Like I said, it's not the noise itself that's the problem, it's the cause of the noise that we are concerned about. The engine just does not run well. It doesn't have much power, certainitly not anything near the 250 it's supposed to have, and it stalls out chronically. This is a big problem for us because this engine is the primary means for moving our cars around, and the way it is right now we can't move the loads we need it to.

Then again, I just have to wonder if after we were able to make the engine run as good as new, it might put too much stress on the equally old and worn out transmission! I can imagine us taking it through its paces after we get everything running perfectly, only to blow a whole gear right off the transmission!! But I digress...

The two main questions I have are:
First, is there somethng we missed when we installed the new ignition system? If not, how do we get the timing right?

Second, is it possible (or even probable) that part of the problem lies in the exhaust or intake manifolds, or both?

To elaborate on the first question, when we set up the new system, we used two distributers originally made for a Chevy 357, and modified the end of the drive shaft to fit in the old mounting. I didn't do the work, and I don't know the specifics of the alteration, but I do know that each was set up to run one plug of every cylinder. The one on the left runs the inner plugs (all the plugs mounted in the cylinder heads), and the distributer on the right powers all the outer plugs. (all the plugs mounted in the engine block.) Electrically, it's like two seperate conventional V-8's.

The old (original) setup was strange. It had each distributer power both plugs of 4 cylinders, like two seperate I-4 engines. The distributers were very odd indeed. They were 8 position distributers, with two rotating points, and a pair of timing contacts on the bottom of the rotor. The two points were arranged almost 180 degrees opposite of each other on the same rotor, but not quite all the way. Lets say if one point is at 0*, the other would be at something like 170*. I think this was done to match up with the degree of seperation between the two sparkplugs in the cylinder. This way, when the top one (at 0*) fired, it took a few more degrees of rotation before the second point would connect, matching the position and timing of the piston at the second lower sparkplug. The timing contactor on the bottom of the rotor was attached to a cam that opened it on every other position, so the plugs wouldn't fire backwards half of the time.

It's all very complicated, I know!!

My second question is about the manifolds. I know that the backfiring we had before would have put excessive strain on the exhaust manifold, which happons to have a water jacket on it to pressumebly cool the exhaust. I was wondering if there was a crack in the manifold, would it effect the engine performance. We check the oilpan drain fro the presence of water before every startup, and there has not been any water present for a very long time, so I'm sure we don't have any water leaks in the engine or from the water jacket on the exhaust.

There is one other possibility with the intake. It doesn't have one anymore.....well not the one it was intended to anyway. The rubber hose that connected the air filter with the carborator has ruptured, clearly blown out by backfiring (the real kind). We have not found a replacement yet, so it essentially does not have an air filter. I was wondering if the engine needs the slight resistance that an airfilter creates to run smoothly, and if not having one might be a small part of out problem.

Well, thank you again for all of your input! Sorry to make such a lengthy post, but I wanted to be thorough.

Matthew Imbrogno
Mechanical Vollenteer - Arizona Railway Museum.

PS: If any of you are particularly interested in this little old locomotive, I could tell you alot more about it than I have room for hear. It really is an odd little critter, and it is one of only a handfull that still have their original Le Roi engine intact. Not to mention the fact that the transmission (also by Le Roi) is a mechanical 4 speed unit that is twice as big and heavy as the whole gasoline engine! It is driven by a pair of massive bicycle chains connected to each axle. Sometimes I think they took the most unusual technology they could use and put it all on one locomotive!

 

[patprimmer]

Removal of the air cleaner will not have any impact on how the engine runs, but will have an effect on wear.

A small leak in the exhaust will cause a misfire and might not show up as water in the oil.

Regards

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[Mimbrogno]

Thanks for the response!

I didn't think that the air filter would have much effect on the backfiring.

I'm curious about how a crack in the exhaust manifold will cause misfiring. I've heard that it will, but I have no idea why it would. I also would like to know how it might not show up in the oil.

Thanks again!

Matthew Imbrogno
Mechanical Vollenteer - Arizona Railway Museum.

 

[patprimmer]

I have boats with water cooled exhausts, and the first sign of a corroded through exhaust manifold is a misfire.

I have always presumed reversion in the exhaust system drew to much liquid water into a cylinder and shorted out the plug.

Water is a major product of combustion of petrol and air. a little more will not show up in the oil, as it is evaporated out of the oil at normal operating temperatures.



Regards

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[JoeDiesel]

You may try this site. They have a Le Roi that was overhauled in 2000.

http://www.minermfgco.com/minerville/Rolling Stock.htm

 

[CCycle]

It was quite common with big cylinder, low compression engines to use vibrator coils that provide a continuos arc at the plug through the time the fuel is burning. The Model T Ford was this way and this technique is still used on some turbocharged aircraft engines to get them started. Because of the turbo charging, these engines are very low compression and also large bore. Unless the "shower spark", as it is called in aviation terminology, is working you usually cannot get the engine started. Once the engine starts and the turbo ramps effective compression up, the system reverts to conventional single spark.

You mentioned that the breaker points of the original distributor opened once every two positions of the HV output rotor. The first position is probably the upper plug and the second the lower plug of the same cylinder. The vibrator coil provided a continual shower of sparks through the dwell of the breaker points. The reason they used two distributors was that the dwell was too long to do it on all eight cylinders with one distributor.

You may not be able to get this old monster working properly without shower spark. Hope you did not throw out the old coils and distributors. I know a machinist that does an excellent job repairing old distributors but understand he is in the hospital now.

Another option would be to turbocharge the thing. Then you could do a four wheel burn out. That ought to be a real crowd pleaser. I wouldn't want to be standing too close.

 

[kenre]

To add to CCycle, if you have junked the original stuff and do need the shower sparks, maybe a MSD type ignition system could help.

Ken

 

[swall]

Just out of curiosity, what grade of gasoline does this beast use?

 

[CCycle]

Good point Ken. I looked at the MSD site and see just about everything has changed since I was using them. So I called their tech line. He said they make a continuos firing unit they call 5800 Continuous Fire Ignitor. It is not on their web page. I don't know what it is. It may be the unit they use on top fuel engines that burn the electrodes off the plugs in 4 sec. Does anyone know about this?

Swall: The only fuel they had when this engine was made was what we now call white gas. It was distillate which included everything up to about C7. It had negative octane. Back then refineries were simple All they had was a toping still. This engine probably has around 4.5:1 mechanical compression ratio. It will run on todays gas but may have trouble fouling plugs.

 

[MWPC]

You mentioned that you changed to GM distributors. Is it a 90 degree V? Ken

 

[EHudson]

On a related idea, how did you determine the firing order?
Could this engine have a flat (all journals in one plane) crank? That would have been the easiest shape to forge in 1943 (and still is today) as opposed to the cruciform crank cast for most automotive V8s.

 

[patprimmer]

I would just turn the engine through 720 deg and note the sequence at which each cylinder goes through valve overlap. That will be the firing order.

Regards

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[unclesyd]

Just like the one we had in our yard the late fifties.

The fuel maybe an issue as the sound brings back memories of shrimp boat engines (4 Cylinder) that were originally built to run on "casing head gasoline" having to run on higher octane fuels especially after WWII with the new gasoline.

During the war they would blend Sloss Benzol (Benzine) with just about any gasoline they could get to get a usable mix.