October 2000 Racing!
Home / Features / NZ 741 Racers
   741 Racer or Hot Street Stroker
 By Craig Cate Part Two
(Part One here)
Well, the promised cylinders, valves and  porting story has not come to fruition this month, my machinist had a hiccup with the rebore, in fact he destroyed my carefully ported, polished, rear cylinder. Instead, I will give you my slant on the frame, and a few other ways to horsepower. Once again these ideas come mostly from my interrogation of Indian Team New Zealand riders.

Jim Wall mentioned  the 741 front frame section in his first Sport Scout Racers column. While I agree that the head stock angle on a 741b is steeper than a Sport Scout,  there plenty of fast 741 racers in New Zealand using the stock front frame and fork.

Jim Wall's Sport Scout. Click pic for first part of Jim's series of columns.
The fork should be carefully checked for alignment and all axles and bushings  brought up to specs. Jim Wall's racer story has details of straightening and narrowing the fork and frame sections. Jim also goes into the mods for the rear section, but for the street and roadracing do not cut off the crossover tube unless you intend to use a cable for the rear brake. The 741 frame is already made from Chromemoly tubing, it is strong and light and I don't think struts are needed for road or roadracing.

The only common modification that the New Zealand racers use is to move the front axle up the fork to the hole which was originally for the guard stays. This involves simply drilling the hole and moving the axle. Most of TINZ bikes have the excess material below the new axle location removed .

 We all used to have a hydraulic steering damper replacing the stock friction damper, but the classic race organisation in New Zealand has banned them on pre war bikes.

For those of you building street bikes, I would recommend using a hydraulic damper. The normal aftermarket adjustable ones are reasonably priced and sometimes available  from bike wreckers. As I mentioned in the first story I will be experimenting with the BMW K75s damper, which like the Indian damper is a rotary one, it is however, hidden within the steering head.

NZ racers move the front wheel axle.

Hydraulic steering dampers, here on Graeme Care's 741, are banned in NZ racing but a god idea for fast street 741s.

The next frame change is to make up some extra braces for the top of the motor. From the steering head to a from cylinder head stud and from the rear of the front frame near the top of the seat post to a rear cylinder head stud. Bolt these at both ends there is no need to weld to the frame. The idea here is to triangulate the top of the frame and reduce twisting. It is important to check the fit of the top frame connection. The bolts should be new high tensile and should fit  without any discernible movement. If the frame is worn here drill carefully and ream to fit the next diameter bolt. The engine and gearbox plates should also be a sliding fit. For race bikes all the unused castings can be removed. These include the front seat mount, generator mount and ammeter/ignition switch castings. The 741 frame is made from chrome moly tubing so there is no point in stripping and retubing unless there is some damage.
Extra braces between frame and heads.
Now although Jim has no brakes on his flat track bikes for road and road racing bikes there is no point in going faster if you cannot stop. 741 brakes barely  do justice to stopping the bike at 50 mph so the brakes need some help.

The first thing is to make sure the brake cams are not worn badly. Next take the lobes and carefully grind the lobes down about 1/8 " at the narrowest point, this reduces the base circle of the lobes and  effectively gives more lift. You will need to blend the  ground part in with a oilstone. Stock 741 brake shoes can be  fitted  with your choice of  aftermarket linings. Soft linings stop best but wear out fast. Fine for racing where they can be replaced between meetings, but for the street a compromise between wear and  high friction is called for. I am sure the brake shop in your area will be able to advise and help here. The other option is to can the heavy steel Indian items and go with GS 400 Suzuki shoes and linings, they fit with minimal changes, are made of alloy and have bonded shoes, I don't think they make race items for the GS but once again your brake man should be able to fit  your choice of linings. They are slightly wider too so you will get a small increase in  brake surface area.

The brake drums will expand at the outer (open) side with heavy use. The problem with this, apart from the brakes losing  efficiency is that the outer spokes  become loose, you can imagine the consequences for a race bike. After tightening the spokes a few times the drum is no longer square and cylindrical. The TINZ racers have one again found the answer. A ring of 1/8" sheetmetal is machined to fit around the outside of the drum at the inside and outside edges and one for the center of the rim. They are welded or brazed to the drum before the wheel is laced, (preferably with alloy rims), and then the drum is machined true inside. Once the wheel is relaced and trued you have a nice strong brake drum with fins for extra cooling.

741 rear frame can be braced like Sport Scouts.

741 frame alignment dimensions.

640 Frame alignment dimensions.

Use the longest brake arms on both front and rear and an aftermarket front brake lever with better leverage. Keep the stock lever for restorations, they are heavy, hard to find and don't work as well as proper race items. A heavier front cable is better too, it will reduce stretch and maintain feel throughout the race, this will probably mean new custom made clevis and linkage parts or small modifications to the stops. The backing plates can be cut down for better cooling and weight reduction and cooling scoops fitted to get more of that cool air in, the drums can have some holes in the back to let  the old hot air out again, but be careful not to weaken the drum, and therefore negate all your good work so far. While I am talking about controls, we use conventional right hand twist grip and left hand gear lever for racing, a spring return is required by the rules, I don't think left hand throttle would please the powers that be. Indian bars and controls are hard enough to find without using them for racing.

Most of us use wider and higher, rather than narrow clip-on type bars even for road racing, Graeme Care (bike 180) tried narrow bars when he first raced but after  the Indian shook its head and spat him off he revised the configuration. Most of the mods I have mentioned here came from his development work after that incident about fifteen years ago. Graeme is continually developing his bike, always thinking ahead with innovative ways to keep up with the competition.

741 brakes can be improved... Picture shows new repro hub and drum from Juergen Mattern in Germany.

Wide handlebars (here on Brent's 741). A good idea...

Another area where changes are needed is gearing, for racing 16-20 tooth  gearbox sprockets are needed and 34, 36, 38 and 40 tooth wheel sprockets, these will give you a range for most tracks. For the street a 16 tooth gearbox sprocket is probably about right for a 37" motor, and 17 or 18 for the 45". If you are going to try out the 57" motor for a real harley eating torque monster a 21 tooth gearbox sprocket  will give you about 85 mph at a lazy 3000 rpm.

I was going to make a bore and stroke chart but Guy already made one, its in the archives for April issue. The only thing I need to mention here is a couple of other options for more cubes. You can build a 45 with the same bore and stroke as the WLA wheels and 70 mm bore using a set of wheels and rods from a later model K series Harley parts or iron Sporster, Malcolm Brown's racer, #269 (or not to 69) has 883 sporty wheels with fixed shafts, it takes some machining but is very stable, the final choice is the 57" motor made with 70 mm bore and Chief flywheels. Dave Blackwell has just finished one for his street bike, he is still running it in but as I said 3000rpm at 85mph, I can't wait for a ride. I will report back.

Next month I hope to have the cylinders story done and a report from the first race meeting of the NZCMRR season. Also a story about Ken Campbell's 1912 eight valve replica which he built from scratch. Here is a teaser picture.

More NZ Indian Racing at Indian Downunder (which may soon go offline for a major facelift?)

Click for Stroker Data
Stroker data, there's also a chart of shaft dimensions for Indians and HDs + chain dimensions on this page.

Ken Campbell's 1912 replica, more to follow...

Home  -  Features  - Archives  -  Back Issues  -  VI Network  -  VI Mailing List  -  Contact VI