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