My New Old Project

[Tom S.]

I posted this on the Ducati.ms board last week. Another fellow pointed me here, and I thought there might be some interest. I appreciate any input/tips/cautions that can be given. It's pretty much a straight copy from the other forum...

I have revived my long-stalled RT450 flat tracker project. It broke the connecting rod in the early 90s and has been shelved ever since.

Here's my '72 RT450. I'd wanted one since I saw the advertisement and road test in Cycle World in 1971. I bought this bike off a used car lot near my home in '84 for $450 when I was 27 years old. I used it as a trail bike, and even had a license plate on it for awhile. In '86 I modified it for flat track racing and have kept it in that trim ever since. The first pic is after a hard day of trail riding in about 1985. The second one is of me going over the jump at the TT track at Castle Rock, Washington, and then on the half mile track in Chehalis, Washington, in 1988 when the AMA held its dirt track amateur national championships in that state. In August '88, I crashed it hard at Castle Rock and was hospitalized for a month w/skull fractures and associated damage. The bike had a bent handlebar and broken clutch lever. The 4th pic is from the last time I rode it, at a short track practice day in Albany, Oregon, in the early 90s. Late that afternoon it broke the connecting rod. It's been in boxes ever since. I gathered the parts to fix it pretty quickly after it broke, then shelved the project until recently. Recently my buddy and I started to reassemble the engine. My buddy is a skilled mechanic and has built up numerous bevel twins and some singles. I had begun to fear that the parts might end up scattered, and it's too cool of a bike to let that happen. I do plan to race it again.







[IMG]http://steinthms.smugmug.com/photos/i-jfShKWs/0/M/i-jfShKWs-M.jpg[IMG]

[Tom S.]

It's getting a Carrillo con rod, and an Arias piston. The broken connecting rod tried to saw/punch through the cases and barrel. The case could be saved, but I had to get a different barrel. The piston hit both valves and bent them, so they were replaced w/stock items. Falicon built the crank up. Les Barker in Vancouver, Wash., built the head and barrel. Some material will be removed from the top of the piston before it goes back together.

[Tom S.]

To set the RT up for flat track, I used shorter fork legs of the same 35 mm dia from an '83 Honda CB650 that fit into the original Ducati clamps. I also replaced the bent fork tubes seen in the very first pic at the top of the tread w/stock items, but they've been off the bike for years.The hub and rotor are from a Suzuki GS1000, and squeezed by the Honda caliper. Buchanan's in Calif laced the 19" Sun rim. Tires are Carlisle. You cannot get those anymore. The master cylinder is from a Yamaha. I spent a lot of time at the motorcycle junk yard w/a micrometer searching for parts that would fit, and it all bolted right together w/no machining. It's kind of hard to use the rear brake when you've got a steel hotshoe on your left boot. My buddy devised a crossover that moved it to the other side, so the shifter and the brake are both on the right side. It works fine. Yet another friend built the exhaust pipe. I've been blessed w/great pals to help me w/this stuff. I've saved everything for it over the years, including the original parts, the diagram for the brake pedal conversion and other papers, and the Sept, '71 issue of Cycle World with the ad and road test that really lit my fire for this bike.

[Tom S.]

This might be ordinary stuff for some folks, but I don't build lots of motors, and this is the only one that's ever exploded on me. It made a lasting impression.

The rod that broke was not a Ducati part. The fellows who owned the local Ducati shop at the time, Eurosport, were, and still are good pals of mine. In 1987, I'd raced the bike for a year and we decided to look inside the stock motor for the first time since I'd owned it. There was some palpable play in the big end. The stock rod came out, and in went an inexpensive aftermarket item that the dealer had on the shelf. I don't recall the brand name, nor who assembled the crank. The handwritten invoice only says "Rod Kit, $65.00". I saved the box it came in, along with the old rod. When I find it I'll post a pic. Anyhow, it went back together with that rod and an '87mm Wiseco piston designed for a 900. That setup worked fine for a couple of years.

The rod broke at the end of a very long practice session on a hot summer day. I did a bunch of laps that day, way more than on a regular race day. Full throttle down the down the straight, just about to shut off for the turn and it goes "Bang". The sound was like like broken glass being shaken in a metal coffee can. The unrestrained piston hit the spark plug hard enough to push the electrode out the top. The piston rotated slightly in the bore and the valves hit the edges of the cutouts on the crown. The blunt end of the rod smacked the thrust side of the cylinder hard enough to shatter the liner and crack the barrel's mount flange. It also smashed into the case right at the oil passage between the two halves.

It was pretty easy to find another cylinder, and the cases were drilled at the broken point to accept a hollow dowel sealed w/o-rings that restored the oil passage.

The Wiseco piston wasn't available then, so I sourced an Arias from Syd's Cycles in Florida, along w/new valves. The Carrillo rod was provided by the local fellow who fixed the cases, rebuilt the head and fit the piston to the barrel. I dunno if it's for a 900, like the piston, or is specific to the 450. But he's a guy I trust when he says "do this." The new rod and the crank were sent to Falicon in Florida for the rebuild.

The valve springs were removed at that first rebuild in '87. The valves were lapped and carefully adjusted then, and the bike always started right up w/ease and ran strong. At least it did until the stator failed. I switched it to a total loss electrical system and things were back to normal.

Here's a pic of the broken spark plug I've saved for all these years.

[Tom S.]

The transmission has always seemed like a limiting factor on this bike. I'm sure this is familiar to many of you. Maybe because it has its origins in a motor of less than half the displacement, and the hardware wasn't upgraded at the same rate of development? The diameter of second gear is so small that the shift dogs have teeth cut into them and they break. The breakage reduces the contact area of the dog's face by half. I have three complete gear sets for it, and the second gear dogs are broken on every one. And two of those gearsets came from bikes that were never raced and have never been in my motor before. When I race at a really short track, like an indoor horse arena, the entire race is run in 2nd gear. You just start in second and leave it there. The final drive gearing is something like 12/50. On longer tracks I'll run taller final drive numbers, but still usually start the race in second gear.

The bike doesn't jump out of gear. But it does miss shifts very often, hitting false neutrals. Is there a connection to the broken dogs? I dunno. I'd like to hear from someone who's got some experience w/these.

I love those little indoor short tracks, BTW. It's like a boxing match w/6 guys going at it all together, but throwing elbows instead of fists.

[Eldert]

Hi Tom

have a look at the thread any restos going on this winter and look at page 3 .
there you can see what i did with to my RT gearbox ( amongst other things )

Eldert

BTW i reinforced the steering stops on my RT . i will take a picture and post later . of to work for now

[Tom S.]

Thanks for your input. A few questions:

and the new inputshaft witn new 2nd and 3rd gears . changed 2nd gear from Z =22 to Z =21
so we could put 3 dogs on a whole tooth

Very interesting. Are these parts available for purchase, or one-off?

...i made the rear swing arm 2 inches longer...

Modifying the swing arm is on my list, too. Right now I've got a 19" front wheel and an 18" rear. It really wants 19s on both ends. Modern dirt track tires are only sold in that size. When I built this bike in the 80s, you could still get 18" Carlisles. Problem is, the swingarm tapers towards the front, and is just a bit too narrow and the tire will rub. A 19 would fit if the axle is moved back about 2". Where did you lengthen yours? My plan so far has been to just weld longer plates to the tabs where the axle mounts now. Cutting and extending the tubes ahead of the shock mounts would be a pain, and would move the axle tabs further apart. I also believe the larger rear wheel and the lengthened swingarm will have positive effects on the handling.

Then there's the part where my rear hub is failing. Have you experienced this? It is cracking around the vanes where the cush drive engages, and the bearing hole on the drive side is very loose. I have some spare hubs, but none in really great shape. I am going to look into building a wheel around something more modern, but still with a drum brake. I don't think the cush drive is really needed for dirt riding. Best would be one that puts two bearings on the drive side, like every modern dirt bike has. A late 80's XR600 hub might work well, even though it doesn't have double bearings. It could easily be reversed from the stock position where the final drive is on he left side. A Barnes-type quick-change hub would also be nice, but then I'd have to mount a master cylinder and caliper and build a new pedal, and, well, that's just too much trouble. Any suggestions on improving the hub?

[Tom S.]

Found another old pic tonight while digging through a stack of papers. 1991, I think. Clark County fairgrounds, in Vancouver, Wash. I love racing in horse arenas.

[Tom S.]

The left case has been blasted w/walnut shells. Next comes the right half. Near the top of the image you can also see where the cases were damaged at the base of the cylinder by the flailing connecting rod. If there hadn't been a large bolt passing directly through that area, the rod prolly would have punched clear through the case. You can also see a prior repair of damage to the mount on the lower left corner from being dropped once. Several years ago I simply gave away two of these engines. If I'd only known then what a set of cases set will fetch on ebay these days...