twin engine??

alright, so my had had this crazy idea... i have a 11hp and a 12hp briggs flat head, and there another craftsman right down the street from me the same model and everything with a 12hp flatty, so he told me i should try to buy that mower, take the 12hp outta it, stuff it in my other craftsman with the 12hp build a crazy carb linkage and ungovern them then put a stop on the throttle cable to limit it to a certain rpm, he says to face them opposite of eachother back to back, use a single pulley on the front engine and a double pulley on the rear and run 24hp of flat head. does this sound feasible? would there be and downsides to this? other than fuel consumption and double maintenance?

well, mostly my idea, he just came up with solutions to my problems, i would also have to flip a carb to face the same direction as the front one.

i'll draw a diagram and post it here in a few minutes

sure as hell is interesting. i think it could work.. i would put electric clutches on them though, that way if one goes down or you dont need both, you can isolate one

yah that's also what i was kinda thinking, i just saw some pulling tractors with like 4 v8's so i started getting idea's haha

i would need to add a barbed fitting to each each intake so i can balance the carbs, pretty simple so far. i hope i will have to compression check them also

It's certainly not the BEST way to get a 24hp oppy twin, but it is feasible. Adjusting the throttle on two ungoverned engines to try to get them to max out at the same RPM (independantly) under load is an absolute impossibility. Throttle position does not 100% decide max loaded RPM.

That said, the engines will be mechanically coupled via a belt, therefore no matter what the throttle settings, they will always turn the same RPM.

Here's why trying to set a throttle opening won't work:

1) Load. The very same reason the governor does what it does, and why. No load will allow the engine to easily spin up to your desired RPM with say, half throttle. Now, apply a moderate load to that engine. It will now require more charge (air and fuel) to meet that same RPM. Maybe 3/4 throttle. Now- apply a heavy load- top gear trying to go up a hill. That may require WOT, as the engine is very hungry.

2) Variables between the engines. One will have better compression. One will have more friction. One might just have an exhaust valve that's not quite sealing properly. There's always differences. So the amount of throttle required to bring one engine up to say 4000RPM under heavy load, will probably not be the exact amount for the other.

The upshot? Tie the engines together with a common throttle control. Once the cables are in place, apply throttle and adjust until BOTH throttle plates begin to open at the exact same time. Now, ensure that they both hit WOT at the exact same time. That's really the best you can do.

Using the governors may cause difficulty. As the load comes off one engine, the governor will back off the throttle and the second engine will se an increased load an open the throttle a bit. This may be slight, this may be a clash of the titans. Better IMO to run ungoverned.

it's not only power i'm going for, but something someone hasn't done, before or when you go to show it off, it just gives it a wow factor!

Oh- no argument there! As a proof-of-concept or conversation starter, it's a winner. Let's be aware that go karts have long used twin engines when a larger single would be simpler!

Personally, I'd like to see it done. Go for it!

Note: suspected issue:

If the engines are mechanically locked together, starting may be a problem. One starter probably won't have the juice to crank both engines fast enough. Both starters running in tandem might work but if one engine doesn't start right away, it might drag the other one down. Perhaps having one engine on an electric clutch is a do-able idea- it would allow you to start them up independantly and couple them when they reach operating temp.

i guess someone beat me too it! lol but i want it to be a race mower with the two engines! make it unique haha

and using the electric clutch is a good idea! i have one on hand too!

I think there's a mower on YouTube named cub ca-debt, not shire if that the name but there's a cub with 5 or so sngines.

i was thinking of a setup somewhat like this


i would try to tuck the other engine under the dash and maybe even into the tunnel

i think that could work...

that moment when it takes you half and hour to edit and post a picture cause it was like 9500x18900 pixels

For the most part, that looks pretty good! You're sure going to be pushing things to the limit with a 7" drive pulley and a 3" driven pulley into the tranny, though! I sure hope you're building the rest of the machine with that kind of speed in mind. Death sucks, be safe!

are you going to put clutches on each engine?

yeah, i was kinda thinking about trying to squeeze them into my next race mower, still not sure yet...

only a electric clutch on the front engine, and either a double pulley or maybe 2 separate pulleys on the back one

I know I was watching a show with a double engine car and the builder was explaining how he did it and how he had to get them to perfectly sync. Im not aure if there would be a difference seeing as how it is belt drive so it will allow slip but my concern would be wheter or not they would truly run in sync to run correctly. If one engine bogs down, what would happen to the other engine?

Doug Fackler wrote:

I know I was watching a show with a double engine car and the builder was explaining how he did it and how he had to get them to perfectly sync. Im not aure if there would be a difference seeing as how it is belt drive so it will allow slip but my concern would be wheter or not they would truly run in sync to run correctly. If one engine bogs down, what would happen to the other engine?

Counting cars, with the blue model t bucket, twin blown engine'd?

Well- if one engine bogs, it will increase the load on the other. Why is why I'm not so sure that you'd want the governors in there. Might get weird. WITHOUT the governors, it'd just bog a bit.

With the ratios you got there, you will be hitting 50+ I did 45, with 6.5 to 2.5. Not safely ether lol

i had a 7 and a 3 on my last race mower, had way to big of a belt and had tons on slip but reached about 35 with the 18" tires, i was considering 16" for the racer, not sure yet

if it slips, get a tighter tensioner, or maybe a ribbed belt. might help it grab more

Sounds like it should work its gonna be awesome

ive seen someone mate the 2 engine's blocks to make an oppy.. i'll find the vid when i get home. basically the same concept but different

redlinemotorsportts wrote:

Doug Fackler wrote:

I know I was watching a show with a double engine car and the builder was explaining how he did it and how he had to get them to perfectly sync. Im not aure if there would be a difference seeing as how it is belt drive so it will allow slip but my concern would be wheter or not they would truly run in sync to run correctly. If one engine bogs down, what would happen to the other engine?

Counting cars, with the blue model t bucket, twin blown engine'd?

Might have been.

if you put an electric clutch on the front one and the double pulley on the rear you can start one at a time and then engage the electric clutch to connect both engines. removing all doubt of hard starting. plus that also eliminates any issue of running only one engine to just mope around when you dont need to be guzzling the gas