Geared Twins

[Jim Allen]

I have posted pictures of my geared twin setup. I will complete the pipe header information later with other subjects; molding carbon fiber cowls; inverted drum valve design; etc.

Jim Allen

 

[Norm Doerr]

I have posted pictures of my geared twin setup. I will complete the pipe header information later with other subjects; molding carbon fiber cowls; inverted drum valve design; etc.    
Jim Allen

112966[/snapback]

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Good Gosh!! Those sure bring back some memories. I have always loved the geared twins! Are they very noisey?

 

[Buckshot]

"Side view of geared twins. The engines fire alternately & with the gear wine they sound like a turbine. "

Jim,

1) Call me slow but, how do you control alternately fireing nitor motors??

2) VERY HOT work again!

-Buck-

 

[Ian Inverarity]

Jim,

That is very interesting! I, with a few others, had an idea a couple of years ago about building a geared 30cc two cylinder engine and had a long discussion on here a couple of years ago about it. I drew up some CAD layouts, and have posted a few pics in my gallery, so to see your engine is very interesting! B)

Thus I have a few questions:

Have you tried the engine in a boat? If so, how did it go and what props were used?

Did you make or buy the gears? Any details on them? (material, finish, heat treatment, pitch, face width) Are they lubricated in any way?

Do the two cylinders run in reverse with the output shaft running the conventional direction? Have you tried gearing up the output shaft to reduce torque effects on the boat?

I have heard that two cylinder 250cc Superkart engines fire both cylinders at the same time, have you tried that?

Good stuff!!

Ian.

 

[Mark]

Hey guys, would like to know how it runs in a boat.

I used to race superkarts (80cc) and a mate of mine had a 250cc twin cylinder and they fire 180 degrees apart to get revs, but I can tell you that when I raced sidecars one guy set up the 4 cylinders like a single. He said lots of torque but no revs but the standard 4 cylinder setup had tons more revs but a lot less torque. Horses for courses.

 

[Jim Allen]

I will answer all questions this weekend. Explanations to some questions asked are already with the posted pictures.

 

[EatMyShortsRacing]

I almost did this with a couple of old CMB 80 GP engines. The idea was to reverse the engines (ducted fan configuration) and use a slight overdrive. The output shaft was going to double back like the gear drive units for normal .21 engines so the engine rotation and shaft rotation would not require special props etc...

nice work!!!

 

[Jim Allen]

I almost did this with a couple of old CMB 80 GP engines.  The idea was to reverse the engines (ducted fan configuration) and use a slight overdrive.  The output shaft was going to double back like the gear drive units for normal .21 engines so the engine rotation and shaft rotation would not require special props etc...

nice work!!!

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Craig,

This was done on many of the older geared twins such as the Black Rushin (owner Ron Walker of Detroit). This boat also had a 1.1428 to 1 overdrive; 32 tooth gears on the motors & a 28 tooth gear on the output shaft. In my setup both motors rotate clockwise & the output shaft counter clockwise; therefore allowing left hand propellers to be used. Ron Brownshidle had a reverse type setup that was geared 3 to 2; 30 teeth on both motors & 20 teeth on the output for a overdrive of 1.5 to 1. John Bridge's, "The Lead Sled" also had over drive & a reversed gear setup.

Jim

 

[Mark]

Jim,

How did all those combinations work out for Ron Walker and Ron Brownshidle?

 

[Eric Perez]

I've seen some pictures of these geared .21 engine mounts over the last couple of years. Who makes them? How much do they cost? What hardware is used ? What is the gear shaft diameter for the smooth-bore flex-hex? Anyonne have some testimonials?

 

[Terry Keeley]

I've seen some pictures of these geared .21 engine mounts over the last couple of years. Who makes them? How much do they cost? What hardware is used ? What is the gear shaft diameter for the smooth-bore flex-hex? Anyonne have some testimonials?

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Na, it don't work worth a hill of beans, ain't worth the effort! h34r:

 

[Jim Allen]

I have posted pictures of my geared twin setup. I will complete the pipe header information later with other subjects; molding carbon fiber cowls; inverted drum valve design; etc.    
Jim Allen

112966[/snapback]

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Good Gosh!! Those sure bring back some memories. I have always loved the geared twins! Are they very noisey?

112980[/snapback]

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The noise level is 110 DB at 50 feet, & has a frequency of 64,000 rpm's because engines are alternately firing. My neighbors don't like me very much when I'm testing engines. Lots of noise & a tremendous amount of smoke! I do use proper ear protection.

Jim

 

[Tim_Duggan]

Jim,

Have you experienced any major failures with this set-up? I would imagine a HUGE hydraulic would occurr if the flame went out in one of the two cylinders at full throttle. Do you have some sort of "failsafe" arangement to prevent damage?

Also, Did you try staggering the pipe lengths to change the torque curves thoughout the rpm range or did they run at the same tuned length?

Tim.

 

[Jim Allen]

"Side view of geared twins. The engines fire alternately & with the gear wine they sound like a turbine. "
Jim,

1) Call me slow but, how do you control alternately fireing nitor motors??

2) VERY HOT work again!

-Buck-

112984[/snapback]

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I'm not sure I understand this question; but, geared alternate firing twins are similiar to a twin cylinder motor with one crankshaft. In this unit there are two crankshafts & two cylinders that are geared together. Piston & liner combinations are tested on the test stand to get two cylinders (motors) that are the same.

Jim

 

[Jim Allen]

Jim,
How did all those combinations work out for Ron Walker and Ron Brownshidle?

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All properly built geared twins run or ran very strong. Quality hardware for these boats; gears, universals, engine mounts, etc. cannot be purchased in any store. If you don't have access to a machine shop & the knowledge to make quality hardware these boats can be a nightmare. Jim Whitlatch, John bridge, Earl Mundt & others had boats that were very successful.

 

[Jim Allen]

Jim,
That is very interesting! I, with a few others, had an idea a couple of years ago about building a geared 30cc two cylinder engine and had a long discussion on here a couple of years ago about it. I drew up some CAD layouts, and have posted a few pics in my gallery, so to see your engine is very interesting!  B)

Thus I have a few questions:

Have you tried the engine in a boat? If so, how did it go and what props were used?

Did you make or buy the gears? Any details on them? (material, finish, heat treatment, pitch, face width) Are they lubricated in any way?

Do the two cylinders run in reverse with the output shaft running the conventional direction? Have you tried gearing up the output shaft to reduce torque effects on the boat?

I have heard that two cylinder 250cc Superkart engines fire both cylinders at the same time, have you tried that?

Good stuff!! 

Ian.

113002[/snapback]

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The geared twin unit runs fine in my Eagle SG Twin. The hull center section was made a little wider by Andy Brown to accept the special mount. The biggest prop I had to use was a full diameter 2170 with 5.625 leading edge pitch & 8.375 cup (.250 width for the cup on the entire trailing edge). This is not enough diameter or pitch for this setup!

I machined the gear blanks & the split tapered sleeves in the same setup to ensure concentricity. North Shore Gear & tool Corp. cut 9, P2 gears (.0005 on the total composite & .0003 tooth to tooth). Pre-heat treated (Rc-38) un-leaded 4340 steel was top hobbed for the final gear profile. The gear face is .500 wide; 20 pitch; 20 deg pressure angle; 30 teeth; 1.5 pitch dia. They are not lubricated & run dry without wear indefinitely. I have been told that John Bridge & Ron Walker never used their back up set. In some geared twin boats I was told that soft gears were case hardened after cutting; don't know if this works.

I run both engines in reverse by making my own induction valves. I did not choose to gear up the output shaft because of the high reliable rpm's of my engines. Andy's twin has an adjustable widened stance to help with torque problems.

Jim

 

[Jim Allen]

Jim,Have you experienced any major failures with this set-up? I would imagine a HUGE hydraulic would occurr if the flame went out in one of the two cylinders at full throttle. Do you have some sort of "failsafe" arangement to prevent damage?

Also, Did you try staggering the pipe lengths to change the torque curves thoughout the rpm range or did they run at the same tuned length?

Tim.

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Tim,

I have had no mechanical failures with my setup during testing & runing. Both engines have both plugs lit continuously. I think my high performance rod will survive in a possible flame out situation. This was a problem with boats with aluminum rods; if one engine failed it usually took out the other one!

Both machined pipes are exactly the same tunned length; diameter; volume; etc.; as well as the maxium HP each engine produces. These are set up on the dyno before mounting in the geared setup. I use a special designed needle valve (not a tapered needle); & no seperate fuel mixture controls as used on some other boats. Design of this needle valve will be shown latter. It eliminates the problem when needles are leaned & then go rich only to go overlean suddenly.

Jim

 

[Tim_Duggan]

The biggest prop I had to use was a full diameter 2170 with 5.625 leading edge pitch & 8.375 cup (.250 width for the cup on the entire trailing edge). This is not enough diameter or pitch for this setup!

I did not choose to gear up the output shaft because of the high reliable rpm's of my engines. Andy's twin has an adjustable widened stance to help with torque problems.    

Jim

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Jim,

With the huge amount of torque you have on tap, and the problems associated with props that are too big for a boat hull's size, I would have thought over-driving the prop shaft would be a valid proposition. By your own admission - the monster prop you have used is too small in terms of pitch and diameter to load it. Gear multiplication = a mechanical torque reduction at faster prop rpm. High reliable engine rpm is great, but I can't see how this would be compromised with an over-drive. Unless of course the propellor or drive shaft is unstable or too inefficient at higher than 32,000rpm (nice problem to have B) )

I'd imagine that propellor at 30,000+ rpm would be capable of some seriously fast top end speed provided it didn't slip too badly - any recorded speeds?

Thanks again for sharing this stuff with us! It is appreciated!

Tim.

 

[shoboat]

Jim,

You may want to try the 2175 propeller on that Monster,it will be enough

propeller.

Good Luck Testing,

Mark Sholund

 

[Big Red Machine]

Where are the photos?