DKW Hercules by admin SUZUKIRE5

[wayne]

I was looking on youtube and found this movie of the Hercules W2000 like Frank T has.

[rotoryguy]

A bunch of guys standing around a running engine - Completely NORMAL!!!

I really like this design.  A Sachs engine I think.  No radiator and no fancy-schmancy systems.

Very COOL

[wiznorton]

I have three of these now. Very under-rated little bike in my opinion. Yes, it's a Fichtel & Sachs engine (originally fitted in a snowmobile) mated to a KTM 6 speed gearbox via a bevel shaft to move the plane of rotation by 90 degrees. The Norton engine was based on this design, in fact the rotors are interchangeable between the two bikes. Norton bought all the tooling when Hercules ceased production. Very simple design, but the cooling and lubrication to the back eccentric shaft bearing is a little dubious for prolonged high speed use. Not a motorway bike! I'm still struggling to work out why Suzuki saw fit to put such a complicated carb on the RE5. The Hercules has a very basic Bing CV carb (like the units fitted to airhead BMWs) and it is perfectly tractable and drives without any flat spots or hiccups. If you like your RE5, I'm sure you'd love a Hercules!!!!

[Jess]

Quote: I'm still struggling to work out why Suzuki saw fit to put such a complicated carb on the RE5.

Because the Re5 is a peripheral port design.

Simple.

Best

[wiznorton]

Hi Jess, the Nortons are peripheral, I've run them with CV, Flatslide FCR, and SU carbs without any problems at all. The factory racers used Amal round slide carbs, but they were prone to slides sticking due to the high inlet vacuum and needed very heavy springs to counteract that. Hislops' TT winner was on CV carbs, and a good friend has ridden that and it pulled very well throughout the rpm range. Big advantage of the CV of course is that the throttle is linked to a butterfly, (not a slide) so you get positive closing.

I have also converted a Hercules to peripheral port too, and it runs great on a CV carb, actually more tractable than I've ever managed to get a Norton.

I am of course learning about the Suzuki and always listen to marque specialists like yourself who have much more experience than I have, but I do know for sure that other designs of peripheral port engines can run very well with relatively simple carbs.

[Jess]

My understanding after all these years has been that due to the PP design of inlet over exhaust, there is so little timing that there is bleed between intake and exhaust.

My experiance is that PP engines run really good at idle, and flat out, but not much in between. As Suzuki wanted max power for displacement, this is why they chose to build it this way.

The port valve was a complication to get it to run in the middle.

All of the above is my opinion. I have no reference with the Norton design other than it was based upon the DKW. I had no idea they were PP.

What I can say with authority is, a properly tuned stock Re5 has no flat spot hesitation, spitting and is a beautiful thing to ride.

Best,

[wayne]

Wiznorton I'm wondering if there's an even simple explanation for the RE5 carb. I'm sure someone somewhere found diagrams or pictures of this carb in use on another vehicle. Was it the RO80 car? It gave the impression that rather than designing a new carb from scratch, Suzuki had pinched the design and adapted it for their single rotor. I could be completely wrong but this rings a bell.

[wiznorton]

Here's a couple of images of ports being done on a Norton race chamber, and a 'stage 1' Hercules chamber with very modest port timing.  I have run much larger ports, and bleed between exhaust and inlet has never raised its' head as an issue.

Jess, do you have figures for the Suzuki port timing please.

I have quite a lot of Norton factory data, and they found that on the models fitted with SU carbs, placing the butterfly as close as possible to the rotor housing worked best for overall street performance.

The Hercules with the ports shown fuels perfectly throughout the rev range running a downdraught CV carb.   You can tune for mid range by altering the overall inlet tract length.  Brian Crighton currently runs variable length.

I'm tempted to believe Waynes' explanation, that they adapted a known unit (because it was already available) I just feel due to the size and complexity of that unit, it was never primarily intended to go on a motorcycle!

[wiznorton]

Hercules chamber  (sorry, couldn't attach to first post!) 

[rotoryguy]

Guys, I am not engineer but I'd like to understand a bit of the discussion more.

First: Port Timing: is this the ratio or relationship of the intake v the exhaust?  In other words, we know the rotor has 3 sides and each side has Intake, compression, Bang, and exhaust.  Just to be clear is this the amount of time between those cycles, or is it more focused on 2: the Bang and Exhaust?

Wiz, in your photo the blue clearly is showing the right port enlarged.  Which port is this?

Thanks!!

[wiznorton]

Hi there, port timing is measured as shaft rotation in degrees from (what would be on a piston engine) top dead centre, i.e. maximum compression.

The inlet port is the larger one. ( Enlargement is limited on the Hercules by the presence of a through stud, but I'm working on a solution for that!)

[rotoryguy]

Ah!  I think I've got it.

With the intake port enlarged on the rotory, the engine can take in more fuel-air for a longer period of time in the cycles.

I guess the goal being similar to ram air, turbocharging and so on.

I suppose there's a fine line as to how much can be ingested at a time, compressed and when and how long each portion of the cycles take.

I know with VVT on a piston engine, the goal is to accomplish the cycles with continuous variations based upon rpm, load, and other factors.

[goandy]

The biggest factor is overlap. You want to minimise the overlap between the exhaust port and inlet port- just like having a large overlap cam in a piston motor. Becomes all lumpy and uses more fuel. Like the bridgeport Mazda rotaries. Great higher up in the rev range but crappy down low.

The larger the ports are on the rotary like ours (with more exhaust duration and earlier opening of intake), the more chance of overlap- where both ports are open or exposed by a pair of apex seals as the rotor rotates past them.