Coupling two model engines together.

[Bentwings]

I was talking to a couple of my old racing friends and the twin engine dragsters came up. I then thought it would be a cool project for an enterprising model engine maker to add to the collection. Since that was during my growing and racing days and I knew many of the twin guys we often talked about them. There were a number of early favorite connections. The inclines were the most successful. The early coupling was with at least a four row chain and double row sprockets. Chain metallurgy has come a long way since then but that was the weak link in that system. One supplier of custom axels created the gear coupling which joined the front and rear of the crankshafts. The small block chev guys had crank problems with the front snout getting ripped off. The fix was to graft a big block snout on. It was a complex machining operation but the custom crankshaft suppliers simply built custom cranks with the big snout. Eventually the snouts became splined which solved the broken key ways of early designs. Today you could purchase a gear coupling but most would simply make it splined to start with. Certainly it would be a big but fun project. Building model v8 I would engines is not to be taken lightly but building them with the idea of coupling them from the start would get around the more complex issues. To make it even more interesting a Dyno could be built measuring torque which is easily converted into horse power. It doesn’t need to be confined to v8’s as about every type of engine has be tried as multiple. Briggs and Stratton are even done for cart racing. My interest is in radials but coupling them is not in the picture. Internally maybe but I haven’t explored that.

 

[Tim Wescott]

The thing that would resonate most with me (and I was never more than a reader of magazines) would be a pair of small-block-looking V-8's with a chain coupling. It should be easy enough to mod the front of the crankshaft of the rear engine, and to verify each engine individually. Then go to town.

 

[Tim Wescott]

For real complications, there were several aircraft engines, particularly toward the end of the piston-engine era, but even back in the 1930's (and maybe 20's?) that were essentially two stock engines coupled together one way or another. If you really had time on your hands you could build one of the 24-cylinder "H" engines.

 

[perko7]

The re-motored Silver City Comet railcars in Australia were fitted with 4 Detroit 6-110 diesels connected in pairs through a gearbox and torque converter to drive one of the bogies under the power car. One engine in each pair sat higher than the other to align with the gearbox input shafts. Not sure how it all worked but it was apparently quite reliable as their regular route was an 1800km round trip which they did three times a week.

 

[Bentwings]

The thing that would resonate most with me (and I was never more than a reader of magazines) would be a pair of small-block-looking V-8's with a chain coupling. It should be easy enough to mod the front of the crankshaft of the rear engine, and to verify each engine individually. Then go to town.

That was the early method. It didn’t take long before the chain strength became an issue. Then the 2 row appeared. About twice the strength but still an issue. Gear couplings had been around for some time so they were a natural. It took some good welding skills to add mountings or machining equipment to make them work. A large custom drive line shop cams up with the involuted feature coupling that allowed for the chassis flex that was popular then. These were bullet proof and are still used today in the top fuel dragster and funny cars as well as lower class cars. Since it’s possible to purchase splined shaft and sleeves I think I would use this. You could cut an involuted gear for a splined sleeve but it might wear strangely over time.gear couplings are incredibly strong and durable. I’ve used them in industrial applications with no issues. The nice thing with chains was the ability to phase the engines I think everyone that used these in race cars experimented with this. Often with closely guarded trick of the week setups. I’m sure there was some rattling around of the parts but with 16 pipes banging away you certainly could not hear it.LOL I had a complete motor and all the extra parts to convert our single engine car to a twin when the class was dropped. Most of us simply walked away from the spirt as a result. A lot of talent evaporated overnight. Watching two of these cars race was spectacular. The noise and motion was unreal. Fans loved them. Pits were James with people watching the crews scramble to change motors or install a new one. Some crews had special hoists on the trailers others just used raw muscle 6-8 guys lifting a 900 pound motor out with a couple wood boards was beyond belief. There was usually a cheer as one came out and the new one nested in.those were the days. I still think it would be fun to have two model engines running on a stand.

 

[Bentwings]

That was the early method. It didn’t take long before the chain strength became an issue. Then the 2 row appeared. About twice the strength but still an issue. Gear couplings had been around for some time so they were a natural. It took some good welding skills to add mountings or machining equipment to make them work. A large custom drive line shop cams up with the involuted feature coupling that allowed for the chassis flex that was popular then. These were bullet proof and are still used today in the top fuel dragster and funny cars as well as lower class cars. Since it’s possible to purchase splined shaft and sleeves I think I would use this. You could cut an involuted gear for a splined sleeve but it might wear strangely over time.gear couplings are incredibly strong and durable. I’ve used them in industrial applications with no issues. The nice thing with chains was the ability to phase the engines I think everyone that used these in race cars experimented with this. Often with closely guarded trick of the week setups. I’m sure there was some rattling around of the parts but with 16 pipes banging away you certainly could not hear it.LOL I had a complete motor and all the extra parts to convert our single engine car to a twin when the class was dropped. Most of us simply walked away from the spirt as a result. A lot of talent evaporated overnight. Watching two of these cars race was spectacular. The noise and motion was unreal. Fans loved them. Pits were James with people watching the crews scramble to change motors or install a new one. Some crews had special hoists on the trailers others just used raw muscle 6-8 guys lifting a 900 pound motor out with a couple wood boards was beyond belief. There was usually a cheer as one came out and the new one nested in.those were the days. I still think it would be fun to have two model engines running on a stand.

Sorry for the spelling errors this double vision thing is really frustrating.

 

[perko7]

A few of the tractor pull rigs use multiple motors, maybe they might have some ideas?

 

[Steamchick]

In the 1970s I saw a side car outfit with a "1000ccs Triumph engine" listed. The owner had a 500cc pre-unit twin installed conventionally, with an extension of the drive to couple (using an industrial flexible coupling) to a Reversed 500cc similar twin mounted on the frame extension that was a part of the racing sidecar frame. It went like stink! Didn't break, and lasted all season with only rebuilds as he would normally do with the over-tuned Triumphs.
K

 

[Peter Twissell]

I am part of a small group currently rebuilding a 1960s twin engine bike, which will be run in sprints and over the mile. The bike already holds a speed record.
The engines are 500cc pre unit Triumphs, coupled by gears.
There is much debate about how the engines should be timed to each other.

 

[Bentwings]

I am part of a small group currently rebuilding a 1960s twin engine bike, which will be run in sprints and over the mile. The bike already holds a speed record.
The engines are 500cc pre unit Triumphs, coupled by gears.
There is much debate about how the engines should be timed to each other.

there was a car called”freight train that used chain for a while until the gear coupler became popular. It was a good balance between power and weight. The big Chrysler twins were just to heavy. There was a maximum weight as well as weight per cu in displacement. Early cars had the traditional wire spoked wheels but most found these to not be adequate for the speeds the cars were reaching. The cast spoke magnesium wheels became the “hot tip” as they said.a pair of these originals are priceless today. There is a remake in aluminum for the nostalgia cars. They are not much heavier than the mag ones but safer. I don’t remember the weight per cu in number but the big Chryslers were very near max allowed at a stock stroke. The early Chrysler’s had to be about stock stroke to make it even though there were quality strokes available. There is a site called 2 to go that has almost every known twin listed. Many have been restored. NHRA only allows them to be started and run as noise makers. It’s called “cackle fest” even just running they are fun to watch. They run on gas only but still shake the ground.they all ran about 200 Mph and right around 7 seconds quarter mile.

 

[Bentwings]

Yeah there still is debate about phasing. It boils down to some vibration dynamics that cause excess bearing wear in the front or rear motor. Toda with aluminum blocks and heads and quality crankshafts it probably would be a moot point. They only had to run 7 seconds under full power total run time of only about 2 minutes. Mostly idling. Us guys with single engines had to run on the very edge all the time and just barely cold compete. Driver skill and luck . We often burned 2-4 pistons a run. at that time they were made of a weld able aluminum. I would machine the burned area out and weld them up. I had a nice lathe and ring grooving cutters. Even the pistons were about $150-200 each. So I would spend several nights a week repairing pistons then worked a 10 hour day. Youth is a big driver when you enjoy it. I played all sports to win. Sometimes even breaking parts of me In the process.

 

[Steamchick]

To simulate a v-configuration you can time them at 75 degrees apart, which should minimise vibration of rods whizzing fore and aft.
But the simple logic the smooth stresses downstream of the second engine (torque oscillation into the transmission) would be at 90 degrees apart. But not something I have any experience of, so your guess is as good as anything!
K

 

[Steamchick]

I never experienced drag racing. Seemed to me like the max power with shortest performance life. I.E. making grenades. Like rockets. 1 whoosh after ages of building. But I was taught engineering by ex-marine and aircraft machanics, where "failure to get home was not an option". So reliability was top-priority.
I would have thought there would be loads in text- books on balancing forces and torques from a couple of twins? Aka steam engine texts have lots on coupling and balance.
K

 

[Ken I]

One of the problems that plague V8's particularly is the problem of angular moment harmonics - ie the crank can ring like a bell angularly - hence the reason most V8's have substantial harmonic dampers on the V belt drive pulley (normally a heavy cast iron ring on a rubber annulus) - ignore it at your peril - particularly racing - if you hold an undamped motor at any of its harmonic points, it can rapidly do all sorts of damage - to gear and chain drives - up to snapping the crank. They make high performance dampers specifically for racing - that should tell you something - you would normally junk an apparently useless heavy piece of rotating hardware - I learned that one the hard way.
Even the early Morris Mini engines were plagued by timing chain slap that was caused by crank harmonics - you fitted a new chain and in no time it was slapping again. They uprated to a duplex chain which did nothing to solve the problem.
I can't begin to imagine the horrors of two inline 8's developing crank harmonics out of phase with each other.
My 2c worth - Regards - Ken

 

[Bentwings]

I never experienced drag racing. Seemed to me like the max power with shortest performance life. I.E. making grenades. Like rockets. 1 whoosh after ages of building. But I was taught engineering by ex-marine and aircraft machanics, where "failure to get home was not an option". So reliability was top-priority.
I would have thought there would be loads in text- books on balancing forces and torques from a couple of twins? Aka steam engine texts have lots on coupling and balance.
K

I’m sure there are loads of dynamics involved. I did some analysis in m my career but it didn’t involve engines.even modern v8 engines have issues. In the racing world the long distance racers I think just watched things and addressed them as they came along. In frag racing things happen very fast with little warning. But again, if there is a bear8ng failure for example the fix is usually alon* the lines of bigger is better. Oiling dynamics iare ptrtt6 well covered in physics so this is done “automatically” so to speak. Burning pistons was a fact of life. Cures were known but rules often didn’t allow the cures. You needed others means. Better fuel control and improved air flow were addressed and used. Today engine life in top fuel is under two minutes. Good times are under 4 seconds the balance is idling. I forget how many revolutions the motor makes on a run but it’s measured in the h7ndreds. The onboard computer data recording notes this. The crew chief can look that close and probably pin point the number of revolutions where a failure occurred. Fixes then can be adjusted. The actual race is very short. High speed video shows each cylinder firing . I find viewing the data much more interesting than the race. Some cars and trucks have data logging so you would be surprised at the number of hours running time and miles driven that are accumulated.

 

[Steamchick]

Ken I. Thanks for reminding me of crank torsional harmonics. Yes, you are correct! - Modern cars all have crank dampers - tuned to the particular crank engine size (dynamics) and the wrong crank pulley (for the poly-vee belts) can cause horrid failures. Thinking of it, I have heard of engines that are coupled and the couplings of the "designed" size failing at the first opportunity! - Due to torsional resonances being out-of-phase (or would it be in-phase but in opposition?).
Thanks,
K

 

[ddmckee54]

I think Chrysler wins the prize.

In WW2 they took five, count 'em FIVE, 6 cylinder gas engines and slapped then together into what they called the A57 Multibank engine that was used to power the Sherman M4A4 tank. A lot of Sherman's had Continental R975 radial engines in them and those engines were in short supply so Chrysler came up with a solution, however nutty it may seem now.

It must have had one helluva starter on it.

Don

 

[Peter Twissell]

We will be running multi channel data logging on the bike, including accelerometers on both engines at the main bearings on the drive sides. This should show up any harmonic vibration issues.
In drag racing, the power delivery is an important factor in managing the way the rear tyre slips and grips. Timing the engines for smooth power delivery is not necessarily ideal. The pulses of torque generated by single and twin cylinder engines cause the tyre to slip and grip in a manner similar to that achieved by ABS braking and can make tyre management a lot easier.

 

[Tim Wescott]

So, who's gonna make an A57?

 

[Steamchick]

No-one in their right mind - which means a lot of modellers will have a go , now...
But seriously. There were a lot of H24 engines - AKA Napier H24 for the Tornado in WW2... et al. H engine - Wikipedia

Lycoming : Lycoming XH-2470 - Wikipedia

But I have never seen a model of one of those, so maybe there is a point of complexity that modellers won't pass? After all, once there is a single bank of cylinders to prove the valve configuration etc, then the rest is just "mass production"? Fun for guys with CNC Machines, but days of boredom manually. And there are loads of jigs and fixtures needed to make all the parts the same. Most of us make one-offs - just because that's enough of a challenge in this lifetime.
But Tim, that should not stop you making an A57.... !
K