The 358 race bike project was started in August 2007, and fired up in May 2009. This was basically building a bike out of nothing. Not because I had “nothing” else to do, but because I needed a test mule for the Excelsior Board Tracker motor . . . where do you ride a bike that is exceedingly loud, has no brakes, clutch, or transmission? I don’t know either. Plus after checking with the local Vintage race rep, I was told my new racer would be eligible for the Formula 750 Vintage class because the 1000cc motor was pre-1967.
The fist job was to start gathering the vital parts. Here you can see Suzuki forks, Triumph transmission and hubs. Other parts would come from Excelsior, Aermacchi, Moto Guzzi, Honda, Kawasaki, Aprilia, Gas Gas and Jawa.
I decided to start work on the front end. I had some 7075 billet, so that was used. I knew the geometry and fork tube spacing I wanted, and I copied the triple clamp design from my Gas Gas trials bike. Here, the holes have been bored, and one clamp roughed out on the band saw.
Checking to see how it all fits together. Fork tubes are 43mm. I have made spacers to position the front hub.
I made up a fixture to bolt the triple clamps onto a plate, then handed them over to my friend Dan who works at a CNC shop. He milled the profiles and lightening pockets to the Autocad drawing I gave him. Thanks Dan! Also shown are the tapered roller headset bearings, and steerer tube complete with 6061 spacers and lock nuts.
The final steps are drilling and tapping the holes and threads for the 5mm allen screws, then slotting in the mill.
The powerplant will be the Excelsior OHC motor. I plan on using high compression pistons, larger carb, tuned exhaust and electronic ignition. All else is stock.
The frame geometry and design was drawn up on an old version of Autocad. Not sophisticated, but it did the job. The large diameter spine doubles as the oil tank. Transmission is pre-unit Triumph. Head angle is 24.5 degrees. The bottom part of the frame didn’t end up looking like this.
Here I’m trying to get a sense of what the final design might look like. Visualization is a very good tool. In the background you can see the 1894 Roper Steam Bike.
Front part of the frame. Material is 4130. You can see the heat stain from the Tig-welding. The oil filler cap is directly on top of the oil return line fitting.
The front part of the frame is held in a fixture on the milling machine table, and centred to the spindle with an indicator. Welding will always ovalize a tube, so boring afterwards is important for accuracy. Bearing press fit is .001″.
The lower end of the spine tube is clamped to a face plate on the mill table, to be machined for the sheet metal cap to close the oil tank.
Sheet metal cap is Tig-tacked in place before final welding.
Mockup of the swingarm. I cut up the heaviest Aermacchi swingarm made, machined it on the lathe, hammered it into oversize 4130 tubes, and Tig-welded it together. The white bristol board shows tire outline and position of the pivot tube.
This is the frame jig for the race frame. Everything is bolted together to avoid welding warpage.
The swingarm is finished and checked in the nearly completed frame.
One of the many stages of mockup. There is a lot of building and “un-building”. Rear shocks are Works Performance.
Figuring out the belt drive using the Jawa speedway clutch. 3/8″ plywood was an easy way to figure out the shape of the transmission plates.
Rear brake lever was Tig-welded together using the tapered and ovalized lower part of an Excelsior fork tube. Bronze bushing was machined for a slight press fit, then honed on a Sunnen “pin hole” grinder.
Rear brake lever is mocked up with the master cylinder from an Aprilia. You can see the bracing on the swingam, made from a curved tube and sheet steel.
It wasn’t easy to find this 40mm Spanish Amal. It’s the biggest one they made, and that was years ago. I had good luck using one on my Aermacchi road racer, so I thought I would try one on the Excelsior race motor.
I worked on the shape of the tank and seat using 1/8″ steel welding rods lightly tacked together. This basic outline was then filled in using 1/16″ aluminum welding rods and a hot glue gun.
I covered the welding rod framework with masking tape. The rest of the bike was draped in plastic to prevent fiberglass resin from sticking.
This is a couple of layers of fiberglass mat after application. Now I have a structure that has some rigidity as well as form.
Bondo is used to smooth out the fiberglass shape. The bondo is green and the red dabs are putty to fill in the inevitable multitude of pin holes.
A mold was made from the “plug”, and these parts produced from that. There is quite a bit of work involved here.
This is the cardboard template for the “real” gas tank to go underneath the fiberglass shell. I only need enough gas for a 5 lap sprint race, and there will be room to mount other things under the shell.
This is the finished gas tank, constructed from .080″ 3003 aluminum, Tig-welded. The coil sits behind the tank. You can see the shape of the two header pipes. Calculated tuned length is 37″.
This is the start of the belly pan “plug”. I bent some 3003 aluminum, and now the end is being filled and shaped with bondo.
The belly pan will mount to this frame rail supported by a high strength s/s boating cable. I got the idea from a mountain bike in the 80’s that had a similar cable in place of the down tube.
This is the plug for the primary belt drive cover. Both pieces will be laid up with carbon fiber cloth.
Jumping ahead a bit here, these are the finished parts.
Using an electronic gram scale to help balance each flywheel. I use a long ground shaft resting on the wheel balancer, and a counterweight calculated to give a balance factor of 55%.
The flywheels are short stroke Sportster from Truett and Osborn. The (9) 1/2″ holes are drilled about .875″ deep.
The two halves of the crankcases; you can see the Carrillo rods.
JE piston with 12.5 to 1 compression ratio. Copper head gasket is used.
View of the intake port. Valve springs from RD; Aermacchi titanium caps from Germany.
No fancy tricks. Included valve angle is 52 degrees.
Programmable aftermarket Harley ignition. It works great and is reasonably priced. The red box on the right is a transponder to record laps and lap times at the track.
Trish checks out the ergonomics. The bike was fired up for the first time on a Thursday evening in May ’09. It sounded good, so we loaded it up in the van and headed for Seattle track the very next day with nervous anticipation. The bike never made it onto the track. Riding around the parking lot was difficult with so many false neutrals, and then the crankcase breather puked out a bunch of oil. We headed home. The engine was torn down for the first time, a crankcase baffle installed, complete with a frothing tower as part of the system . . .
The Triumph clutch actuating mechanism wasn’t a good match for the Jawa clutch, so I found it impossible to get a good adjustment with good cable feel. The solution seemed to be a hydraulic clutch. Here the Triumph tranny end cover gets modified in the mill. The machined piece on the left bottom will be welded on.
The cover has been welded and transitions smoothed out. The welding has caused the case to warp, and the red felt pen marks show where it needs to be straightened after heating with oxy-acetylene. The C-clamps will apply the pressure for it to bend controllably.
Hydraulic clutch cover is finished. Plus, it works very well with good feel at the lever.
May 2009 we had 358 on the Cypress dyno, Tuesday and Thursday evenings. I took a selection of main jets from 320 up to 390. It’s one of those dynos where it holds the engine under load at intervals up to redline, while the sensors record CO readings. 390 was WAY lean, so we went back Thursday armed with a selection of number drills, plus 450 and 500 main jets. The 500 was getting there, so I drilled it out to .081″, which is about a 550 main jet! The CO was now at 6, but the mid range was still too rich. The engine was run up to 5000 rpm quite a few times, and 6000 rpm a couple of times. Cylinder temperatures only reached 140 degrees F, while the rear tire got up to 167 degrees F on the 6000 rpm runs. Best rear wheel HP was 49 with 52 ft/lbs of torque.
We loaded the bike into the van and headed to the Seattle races. There was no time to get fatter needles to cure the mid-range richness. First practice showed the Triumph transmission still wasn’t great — too many false neutrals, especially down shifting into a corner. The richness wouldn’t allow the engine to pull cleanly; there just wasn’t any snap. The handling and brakes were very nice, however. On the second practice I was heading downhill into turn 3, got a neutral, got it back into second gear, and felt the engine slow, so I pulled in the clutch and called it a day.
Teardown #002 showed the big end of the rods lacking oil, and the clearance a little lacking also. The sprocket bearings needed more oil too. So, the oil squirters got a third hole to aim at the crankpin assembly, and an oil gallery was drilled to lubricate the sprocket shaft bearings. Five different Mukini needles were ordered from Sudco to cure the mid-range richness.
A couple of different generations of exhaust guide oilers. This is what Porsche has on some of its’ models. A small hole feeds oil into the middle of the exhaust guide, providing lubrication.
Exhaust guide oilers installed . . . I had problems making them sturdy enough. The engine would vibrate enough to loosen threads. Also, the rear cylinder always used more oil, so it might get a metering valve one day.
The oil reservoirs are master cylinders from a Gas Gas trials bike.
Third time on the track, this time using 5000 rpm as the redline. It’s going OK, but the motor just isn’t pulling. It feels like a dog. On the second last lap, there’s a lot more noise coming from the motor, but it’s hard to tell where from. In the pits, I take apart the clutch, and spin the basket. The bearing is shot! At least, that’s what I think.
The autopsy showed it was much more serious. The transmission had been running dry, and there was some damage. I have an old Triumph tranny and the overflow tube was poorly designed, and consequently changed in later models. As you pour in the oil, it can fool you into thinking there was enough, and there was not.
Nikola to the rescue here, thank you very much! I gave the motor teardown #003, and discovered that all the places that were needing oil were getting it.. Good news! Put it all back together again. Meantime, I re-did the exhausts 3″ shorter, and reset the ignition with a timing light, and the motor was starting to come alive.
Fourth time at Seattle. First race. 5500 redline. Beat Duncan up to turn 2. Stayed with the leaders for a lap. Second lap I did a 1:56 before I felt my left foot slide on the brake pedal . . . I looked down and saw oil and pulled off. Apparently, my bike had smoked a LOT for a lap and I wasn’t black flagged. I felt bad, but it was done. We slunk home. Motor subjected to teardown #004.
Obviously it was time to figure out the oiling issues. At first I thought the scavenge pump had stopped working, and that’s why the cases had filled up and puked out. I mounted the cases in the mill and ran the lubrication system. You can see the pressure gauge and a squirter working below. I discovered several things. Some sections of the oil lines were too small, the pressure was much too high and scavenging stopped above 5000 rpm. Taking the engine above this limit caused the problem. All scavenge lines were opened up, and the (3) squirters were drilled out to .035″.
To solve the pressure problem, a modified relief valve from a 675 Triumph was used. I could now run it continuously at 5-6000 rpm with no cavitation for 15 minutes at a time. The pressure would average 40-45 lbs, and scavenging was very good. The cases never filled up.
The bevel case is getting filled up. On the left is the end of the pressure relief valve (with the circlip), and outside on the right is the fitting for the oil pressure gauge. At the very bottom are the (2) oil pumps, CNC machined from bronze.
After getting a handle on the lubrication system, it was time to go back to the dyno at Cypress. The changes to the ignition timing, exhaust length and jetting were starting to have an effect. We did several runs and got 64 ft/lbs of torque with 61 HP @ 5000 rpm before the cylinder cracked. Redline is 6000 rpm. Dave was impressed! I just had more work to do.
I took this photo a few years ago at a drag event. Here, the flange stayed intact but the studs were pulled right out of the cases. On engines that don’t have through studs (going all the way from the cases to the top of the head), the bottom of the cylinder is always the weakest point.
I switched foundries for the barrels and the heads to get better quality. Kevin Holland modified the barrel patterns to give a heavier wall thickness and much larger radiuses that could be machined for greater strength. I bought a 3/8″ circular insert and made a tool-holder for it.
I found out about a “back spot facing” tool, and ordered one after doing a little Google. You can see the job it does below.. It was the rear cylinder that broke, and the cam support on that cylinder was rubber mounted to the frame. That will be changed to a more rigid system soon.
Shot next to an underpass in rural Langley. The cable is still in place supporting the motor, but that will change soon . . .
358 Vintage Road Racer (BikeExif.com)