Dont give me one but two Mac's side by side

[david martin]

I would be hard pressed to explain it in scientific terms but I have run two engines in series the front engine has a centrifugal clutch its chain connects to a direct drive sprocket on the pto of the rear engine then outboard of that sprocket another centrifugal clutch has a chain that is connected to the axle sprocket
and it behaves in the manner that I explained in my earlyer post
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McBob's setup is the same minus the chain connecting the two engines
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the best way I can explain it is to say that the clutch allows slippage between the two engines and the firing pulses wont let the clutch fully enguage until they find their (happy spot) where they work together with the least differential resistance and this just happens to be when they are in sync.
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I can understand being puzzled by this sometimes things just work out
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I really dont have anything else I can add to this other than to say put it together and give it a try if it dosent auto sync. then I will be even more confused by this mystery
(time will tell)
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I think it is interesting the way you connected the pto side of one engine to the flywheel of another using a clutch I have 3 small engines that I would like to couple as close together as possible (so many projects so little time & money)

[Al Klusman Jr-Torque]

Steve,
If the 2 Macs are clutched they will start out random fireing, but they will "seek" and not "Lockup" until they are 180 degrees apart.
I well know due to years of running duel Macs on a Margay duel engine gearbox. In fact as they seek they will pulse closer and closer to 180 degrees and you can hear and count the difference between them. Strange but true.
Best Reguards, and GO FAST!!,
TORQUE

[Ronald Cubel]

Same here with Dual Briggs. Ran years ago and thought it was cool the way they found each other going down the straightaway. Ron

[steveohara]

OK Guys, tell me how you know they were in "sync"? Were you using a scope of some kind to record the crank position of one motor when the other fired? I've raced many twin engine karts over the years with Macs, Yamahas, TKMs etc in sprint, enduro and dirt track racing applications using engine clutches and axle clutches... yet I have never seen any evidence that the two motors will magically synchronize at some particular speed. Without a doubt, there are times when they may sound at though they are firing together..... and there are times when they sound like they are phased perfectly at 180 out.... then again there are times when I could only hear one motor... this happened mostly with Macs

I suspect you are all saying that they "sound" like they are in sync but I doubt they are actually timed perfectly to each other unless they are mechanically connected that way when they are sitting still with no clutch involved. Here is an interesting analogy.... in road racing we used to have some real close racing before all the bodywork came along and we would run side by side down some pretty long straights and there were times when it would sound like the kart right next to me was in perfect sync and the motors would set up a very cool resonance.... kind of like some of those old Emerson, Lake & Palmer tunes from the old days where they would make the sound move back and forth between the stereo channels. The interesting thing is this.... I have ridden many two cylinder two stroke motorcycles that were obviously in "sync" yet they never sounded like that so I suspect it has more to do with sound waves than crank position.
I guess ole Bob will have to hook up some crank position sensors on his new beast and take some readings to see what happens
Regards,
Steve O'Hara

[Ronald Cubel]

Real easy to know if they fire at same time. I just grabbed both spark plugs and they shocked me at the same time.

Ron

[david martin]

logic and reason has convinced me that the engines auto sync. but I also completely understand that this condition is less than perfect and everchanging based on variable rpm and clutch slipage
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I just find it really interesting that on this kind of setup the engines will seek balance with each other.
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can we discuss what type of setup will or wont auto sync?

[mcbob]

Well fellas looks as if i have opened another can of them good ole worms, i enjoy reading what each of you have to say thats how some fellas learn i suppose.

I hope in the next few months to get this beast set up but i have to find and obtain another 101 to match the one i already have so i end up with a pair.

I look forward to seeing if i can get those kissing cousins to run as a team if not it will still look kinda pretty sitting in my shed ...................

Mc Bob.

[Rob Voska]

Don't remember the magazing but there was an article on linking 820's togehter. I think Shoemaker Motorsports wrote it way back when.......

[Darvin Jahnke]

It is interesting to hear Steve say that at times you only hear one engine on a dual installation. I've had this happen running dual Mcs. It sounds like you lost one engine but no loss of power,then it comes back. I thought it was just my old race tortured ears playing tricks on me.

[steveohara]

Darvin,

In all honesty I was poking fun at the propensity for Macs to self destruct. But, your experience is not all that uncommon either as there are times when you can have one motor with the mixture way too rich and it will never clean out because it never finds enough load. You'll see that happen some times if you have one running up on the kart stand and you try to rev the motor and it just won't clean out but if you apply the brakes and make it pull hard it will eventually clean out and run.
I've thought about this subject quite a bit and my intuition tells me that a pair of motors coupled the way Bob has his would ( if they were to index at all once the clutch engaged) tend to move toward both firing at the same time rather than 180 degrees apart. When you consider that the crank in a single cylinder motor does not turn the same speed throughout each revolution, speeding up in the power stroke and slowing down as it completes the rest of the cycle, it is possible the clutch on the motor connecting them together could slip a fraction on each power stroke as that motors crank speeds up while the driven motor is slowing. Once it indexed around to the point where both were firing together the two cranks would both be trying the speed up and slow down together. That being said... the loads the two motors are seeing are not the same since only one crank is driving the load (chain, belt gera etc.) while the other crank is driving the other motor. I will be interested in hearing how it runs and especially interested to find out if Ron's method of checking the spark timing is effective
Regards,
Steve O'Hara