September 2000 Racing!
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    741 Racer or Hot Street Stroker
 By Craig Cate

Racing  was never part of the plan when Indian presented the US Army with the 741, a 30.50 cubic inch motorcycle, based on the Junior Scout but beefed up for severe duty. The legend on riding and instruction plate on the tank was "Maximum speed 60 mph". Although plenty of 741s exceeded 60 mph it would be another 40 years or so before the 741R became a reality.

It depends who you talk to but anywhere between 5000 and 18000 of the 741s came to New Zealand with the US Army Pacific deployment. After the war there were obviously a lot of them left and they got bought up by surplus companies. They were still available new until the early 70s and were used for cheap transport by many Kiwis, but it wasn't till the early eighties that Dave Blackwell, founder and life member of Indian Riders Organisation of New Zealand, IRONZ, built a race bike to compete in Classic Racing Register meetings. Graeme Care quickly followed and has taken the art of 741 tuning to extremes. More later.

Dave still has his bike and it will feature as part of this project along with the bikes of Indian Team New Zealand, (ITNZ), a group of racers who came together three years ago with the aim of racing at Bike Week in Daytona in 1999.

Now I am not the top Indian tuner in New Zealand, far from it (I will reveal my nomination for this in due course, I am probably not even the magicians apprentice) but I will chronicle the evolution of 741 racers in New Zealand and work through the build up of my new bike over the next few months. Much of the information here has been freely given by other racers. Some of it is my own ideas and only time will tell if I am right or wrong.

A lot of the work has already been done, so I will not have before and after pictures for this, but as much as I can, I will show the standard 741 part alongside the finished race part.

After the bike is going a racers diary will follow my antics on and off the track with the bike.

Modifying 741 parts is not heresy in my view as there seems to still be plenty of them available  around the world, certainly more NOS available in the US than I ever thought, granted the prices are rising so some parts would be best made from scratch for a racebike, I will take this into consideration as we progress. One more thing  comes to mind. The New Zealand Classic Racing Register is very strict with their rules, pre 40 and vintage classes cannot use post WWII  parts. Now this is a bit of a contentious issue here. As the Indians have got faster the pom bike racers have got more nervous, we have been banned from using aftermarket steering dampers, English brakes and a host of other go faster stuff which is legal under AHRMA rules. All this has done is make us more determined and more innovative. None of this will matter for US racers and those of you building hot street bikes. I will include these things as sidebars to the story. BMW K75 RS steering dampers fit right inside the steering head and cannot be seen, this will be legal because it is the silhouette of the bike that the purists complain about, or so they say.

Click on pictures for full size

The original 741 racer built by Dave Blackwell in the early eighties. Geronimo is still a competitive bike.

Tim Blackwell at speed on Geronimo, Dave was racing his Powerplus at this meeting.

Graeme Care's hot 741 racer, this one is a rocket, as several,
International Nortons and TT Triumphs have found out to their surprise. Steering damper has now been banned. Malcolm Brown's (Firedog to VI Listers) racer 741 in the background.

Team Indian lines up before the Pukekohe International Classic meeting in 1998. (Right to left) Paul Hanes' SS, Graeme Care's 741, Malcolm Brown's 741, and Geronimo  Dave Blackwell's original 741 racer. Way In the background is Dave's powerplus and Ken Campbell's eight valver.

Hot  Rod  45" 741

This month I will give a broad overview of making a 30.50 (500cc) into a 45 (750cc). This is the heart of the racer, no 741 could race successfully with the original capacity.

 The easiest way to make get the extra cubes is to gut the 741 cases and fit Sport Scout, bottom end, cylinders, heads and all. It all fits the 741 cases but as very few Sport Scouts came to New Zealand  the parts are hard to find. The next problem arises when you try to fit the engine back in the frame, the 741 front section does not have the clearance bend in the rear post for the cylinder head. In fact the 741 frame is totally different to the SS and 640 frames. More of that later.

Major components of the 741 race engine.
Special Pinion Shaft

The most common way to 45 is stroking with Harley WLA flywheels and rods. This involves making a special pinion (see picture) to fit the larger taper in the Harley  wheels .


Bore size is 70mm or about 2.75 inches. Obviously the 741 cylinders need boring, this is a simple machining exercise by your local automotive machine shop. More details on special race tricks later. Two and three quarter inches is close to the limit for a reliable 741 cylinder, after this they start to expand in strange places and do not always return to normal, in other words the piston and con-rod get a "viewing window", cutaway engines are neat for shows but are a pain for racing. The officials, for some reason, don't like oil on the track. I will leave ports and valves to another part of the story.

Original 741 pinion and new pinion to convert WLA flywheels to Indian cases. You can see the only difference is the bigger diameter at the flywheel, tapered end.

I have found a really nice slipper piston, the weight is about right  for easy balancing and has nice narrow compression rings for reduced friction, I do not however use the hi tech chrome faced rings that come with the pistons  for fear of damaging the already close to max bore. I buy a plain cast iron ring set with three piece oil rings, the good thing here is that they are made for a four cylinder car, so you get a spare set for emergencies at the track or the next freshen up. The piston top to wrist pin height is correct with the flat top piston at 29mm (a little over an inch). You can see the difference between standard 741 and stroker piston in picture. As you can see the skirt is shorter as well so there is no need for machine work here for case to deck clearance.

Here is the new piston and an original 741 piston, the difference in pin height and skirt clearance is easily seen here.
If you bore a 741 to 2.75" and don't stroke it, you get a 37 cu inch, 600cc motor, but the piston pin height is wrong in the stroker pistons .

These pistons are made to metric sizes and Indians are imperial so from here on I will only give approximate imperial sizes. Everything needs to be measured and machined individually for each engine anyway. I will make a specification sheet/ parts list  to go with the project, and as this is an interactive magazine I expect readers to report any mistakes (and there will be some), additions and alternatives, to me for inclusion in future issues.

Crank and Rods

The rest of the setup is common American V twin, male and female rods, Harley roller bearing big end and crankpin with your favourite oiling mods and the 741 Indian driveshaft fits the Harley flywheels. Main bearings are stock Indian. Spacing and shimming I will leave up to you and your machinist or engine builder. Now the Harley rods need rebushing to fit the  wrist pins, this is easy because the pins are smaller than stock Harley, I used a piece of phosphor bronze which was in the off cuts bin.

Valves, Ports, Carb and Inlet Manifold

When it comes to valves and ports  you have a real balancing act with 741 motors, valve size and lift is restricted by proximity to the bore, and the size of the combustion chamber/valve relief, port size likewise to some extent but more to the wall thickness and  flow available after the valves. Here is where  we have to really balance our thinking. Compression is restricted by the fact that the combustion chamber is formed in part by the valve pocket.  A supercharger is the real answer here but not allowed under the racing rules for which I am building my bike.

Harley WLA flywheels, rods, already re bushed for the new pistons, old little end bushes in foreground, special pinion center right.

WLA conrods with the new bushings in the small end, the old WLA bushings are shown for comparison.

I have considered various valve combinations and have decided to run with 44mm inlets and standard size 741 exhausts, three angle seats and the best porting job I can do at home for now. I will relieve the cylinder deck area between the valves and the  side of the bore but not excessively. Later on I will build another set of cylinders when I have time and money for some flow bench time.

The inlet ports and manifold is the next point of restriction, and is easily solved. The inlet port nipples are removed and replaced with tubing tig welded or brazed in. (Before you bore the cylinders if you are brazing) if you have already done this job you should carefully preheat the cylinders before hand so as to avoid distortion in the bore from localised heat. The inlet manifold is either a fabricated one or a modified on from a bigger V Twin,  i.e. Chief or Harley. A larger carb like an M88 Linkert is desirable and the corresponding manifold is a good starting point. I an going to try the Wal Phillips Fuel Injector shown in some of the pictures, this is the only type of fuel injection allowed in Classic Racing here in NZ, I am going to try it because it is there, I will probably revert to an M88 or similar if the Wal Phillips gives me any trouble.

Wal Phillips Fuel Injector. Not actually a 'real' FI, this device has no needles or jets. The throttle disc shaft is linked to a barrel valve, which line up more or less with a hole in the roof of the main bore for fuel metering. The only thing restricting air flow at full bore is the throttle disc/shaft. The Wal Phillips was popular for racing (and 'cafe racers') in the '60s.
Valve train

As far as I know the valve train , cams  followers and  pushrods are the same in a 741 as a Sport Scout so and of the known combinations will work.. I have a choice from a set of  Shunks,  Bonnevilles,  Sport Scouts, stock 741, and some specials. I also have various sets of followers. The only rule here is to use new rollers in your followers and make sure the cams are not damaged. New cam bushings are recommended.

Assembly and Buttoning Up

That is all there is to the 741 45 inch conversion using the WLA bits, the rest of the motor is just careful assembly and whatever special tricks you know. (If you have something to add to this build up let me know I will present all options as the series progresses. I recommend extra care in balancing but after consulting all of the experts I am still to decide on the balance factor for my motor.

Here are the 741 cases inside. They differ slightly from SS cases but most of the parts interchange. Note the cam shaft bushings, the guy I bought this bike from told me that it ran for 20 minutes on a new engine and then stopped, sounding expensive. These bushings and a broken cam follower were the only problem.

This one is simple, I will be using a magneto from a KR Harley, with a modified cam as speced by Joe Hunts an Sacramento. It is a standard Fairbanks Morse unit which is the same as Joe Hunts, Morris, ARD and a host of others use. Other options include the Edison RM and modern electronics.

Cylinder heads

If you use flat top pistons there is not much to do to the heads unless you think you need more compression yet, it will be increased by the 50% engine capacity and is probably best left in the meantime, careful blending around the edges to avoid any hot spots and surface finished in your favourite manner is the order of the day. Everyone has their own ideas.

Next Month: Detail work on the cylinders, including valves, ports and rebore.

Wal Phillips fuel injector and converted KR Harley mag.

More NZ Racing Indians on Craig's "Indian Downunder" site!

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