Thorminator - stage 5

Stage 5 - Powerplant & Driveline

> Powerplant & Transmission

> The goods

Engine: 2 x OS FS 40S-CX (pullstart) engines

Flywheel: 2 x Kyosho 4-stroke (heavyweight) flywheels

Clutch: 2 x Kyosho Burns heavy duty clutch

Clutchbell / pinions: Kyosho threaded 2 speed bell w/pinions

Tranny: Ofna MP 2-speed tranny w/Hyper 7 2-speed steel gears

Mufflers: 2 x OS 91 Surpass Muffler

Exhaust pipes: 2 x OS Flex Pipe, long

> Engine & driveline configuration

I had already at an early stage determined the overall layout of the vehicle, and sorta knew what I wanted to mount and where. Front suspension & diff housing up front as on a buggy, engines mounted towards the rear of the chassis and a center tranny somewhere in between. This did however present some issues that needed resolving.

The center tranny would be located very close to the front diff, requiring a very short front driveshaft to hook these together. Furthermore I'd then have a very long run from the center tranny to the rear axle diff. And somewhere between all of this I'd need to mount some brakes.

In order to solve some of these issues I decided on a very short "coupling" between the center tranny and the front diff, then run a "standard" length driveshaft from the center tranny back towards the rear of the chassis. There I planned on installing another coupling from which I'd run another "stock" length driveshaft back to the rear axle diff.

Confused? yeah - so was I...

> Engine mount

I knew I wanted to run a pair of .40 4-stroke engines. Wanting to fit it all inside a Landmax body, and maintain a somewhat low center of gravity I found that a straight up & down install would not do. So I figured, well I got 2 engines - lets make it a VEE.

So after a massive amount of trial and error, I made me a 60 degree V-mount for the thumpers, which allowed for individual adjustement (gear mesh), and which would serve as a mount for the coupling of the 2 rear driveshafts (more on that in the "driveline" section).

The 2 engine mounts and the bottom mounting plate where made from 3mm 7075 T6, while the front & rear bulkheads where made from 10 mm "standard" aluminum. The front bulkhead was shaped to allow the rear driveshaft to pass thru, and the rear was bored to accept a bearing for the coupling of the 2 rear driveshafts. I then fitted the rear bulkhead with Hyper 7 brake parts, and made a "plunger" that I intended to use to activate the brakes.

Engine mount

Rear bulkhead showing coupling bearing & brake plunger

Coupling & brakes installed

Completed mount with engines installed

> Driveline

After eyeballing the exsisting parts, I decided to try and make a "direct connection" between the center tranny and the front differential. If I managed to do this, I'd be able to locate the engine mount as far up front as I needed it to be. In order to verify this, I made a coupling from a 12 mm thick steel bolt. It proved that the concept would work, unfortunatly I had problems making it run "true" due to my lack of a lathe. So I called upon the services of the excellent Mr Bill at RC Alloys. In no time flat he provided me with a custom coupling that connected the front diff input shaft with the center tranny. So I now had a contender for the title of "worlds shortest driveshaft"; a whopping 20 mm long front driveshaft!

The Mother of all drive shafts!

With a combination of a Kyosho input yoke, HoBao output yoke and a pair of bearings I made a coupling for the 2 shafts in the rear engine mount bulkhead. This let me run a pair of nice & beefy RC Alloys Mad Force driveshafts; one front tranny to rear "coupling", and one from the coupling all the way back to the rear axle diff.

Center driveline & brakes

W/engines installed

"And this driveline was brought to you by RC Alloys!"...

> Transmission & Gearing

Seeing that a 4-stroke revs approx 30% lower than a compatable 2-stroke, I wanted to ensure that all this torque was not wasted away. All along I'd been a tad concerned about undergearing this truck, considering my plan of using a "scale sized" set of wheels, and the gearing options available for the MP tranny. Even with the highest available gearing 52:48 / 16:12 I'd end up with a final ratio around 1:15.6 / 1:12.9.

Thank to some outstanding help from my very own gearing-guru (take a bow, Mr BOO) I found that through a combination of Kyoshos threaded clutchbell and pinions I could run a 26:22 pinion set. And with the 52:48 / 26:22 combo I now have a final ratio of 1:8.6 / 1:7.8. Much better!

Comparing old new new pinions

Engines w/ new gearing installed on chassis

> Exhaust system

With 2 engines comes twice the amount of pipes. Add that whole v-twin shape to the mix, and you end up with lots of twists and turns. With the 4-strokes I could have run with open headers or a pair of short pipes, but at the time I still intended to run the truck with the Landmax body. In order to route the exhaust to the outside of the lid, I'd have to somehow run the pipes out from the engines all the to the rear of the truck.

I was fortunate enough to get a great deal on a pair of OS 91 mufflers and a pair of long OS "flex pipes". These pipes would allow all those twists and turns that the exhaust have to make in order to go where I wanted it to go. I made a pair of mounts to the mufflers attached to the rear on each side of the tail section, and routed each flexi-pipe from the engine header to the muffler.

Flex-pipes mounted

Mufflers mounted

	Projects - Thorminator