The Jumbo bites back….

Since I started riding a couple of years ago, I’ve had the odd bang and bruise but the latest injury didn’t actually occur at a trial, but in the shed…..

The SWM Jumbo build project was nearing completion and I’d the bike re-assembled with the right piston etc and was attempting to kick it over in the shed. The combination of lots of compression at the wrong time (still learning how to use the decompression lever at the right time) and a kickstart with some worn splines resulting in the Jumbo biting….

Jumbo leg

The Completed Bike

…well its just about complete and its “ready to trial”. Thought I’d add some pictures to show the finished article.

Been running the bike for a week and I’ve been able to get it road registered as well. The engine has been settling down and sounds a bit smoother. Also managed to put a stud into the striped thread for the exhaust manifold, so have got that tightened up.

SWM Jumbo 350TL

Did briefly consider taking the bike down to Robinson’s Quarry for the AL King trial series run by East South Wales Centre to give it its first trials outing, but had visitors etc, so it can wait a week or so [1]. Currently content to give it a run round the field and local roads (though do need to getting a number plate made up for it\). There is a bit of smoke, but all the gears are there and it pulls well. There also seems to be a slight ‘lurch’ with a noise when pulling away quickly under load and there is a noise from the rear wheel, but have a set of bearings to put in if needs be.

SWM Jumbo 350TL

When recovering the seat, noticed that the base was broken, so hence the swoop up on the front of the seat, something that could be a bit nasty.

I need to work on the specification sheets for the Jumbo and add in some of the facts and figures I’ve picked up during the project. The site / blog has been getting some visits and hopefully will be a useful resouce for people working on SWMs and other trials bikes.

SWM Jumbo 350TL

The Jumbo runs…

Starting at the end of August, its taken 4 months to get the Jumbo up and running. A spin round a rather wet and muddy garden and things sounded good.

After getting the new piston installed and the initial start up some further fettling was done prior to giving the bike a longer run:
– added the 50mm springs that were originally in the front forks; they aren’t stiff enough without them. The cap on the damaged fork doesn’t has much thread holding it in place so will need some further work, but being 35mm rather than 38mm forks means I can change them with the TL280 forks I already have.
– changed the rear shocks to a longer set (14″ instead on 13.4″), with a 50 rather than a 40lb spring rate. Need to look at getting the right shock set up now the bike is running.
– put in the lever adjuster for the clutch cable in place; the adjuster on the second cable seems to be threaded
– one of the threads for the exhaust manifold bolts is knackered, so will need some remedial engineering
– swapped the kickstart level over; the replacement I’d had from Martin Matthews seems to pretty badly worn, so have used the one from the recently acquired TL280.

Jumbo running...

After getting the bike running and the carb cleaned out the previous day, it was good that the bike fired up with the choke on the third kick. The engine seems to take a little while to warm up, but does sound ok and pull well after a couple of minutes.

The ignition timing is currently set to the middle of the adjustment, though I’ll look at advancing and retarding it later to see what will give the best trials performance.

Getting the bike on the road

Road registering the Jumbo. A How-to for all twinshock owners

I’d road registered a couple of bikes before (a Yamaha DT250 and a Honda TL125), so had an idea of what to do

What you need:
– Registration of vehicle form (V55/4) from the DVLA. Contact the DVLA help line and they can post you one. More information on the DVLA website .
– a dating letter (for the bike, not a lonely 40-something)
– an MOT
– insurance
– personal identification
– the first registration fee and the annual license fee.

Dating Letter
If you want an age-related plate, rather than a “Q” plate you will need a dating letter. This needs to come from a club, association or organisation that is recognised by the DVLA as able to provide an official dating letter.
There is a list of vehicle owner’s clubs on the DVLA site who can provide a letter authenticating the date of manufacture of the bike. I’ve used Roy Bacon a couple of times and he charges a £25 fee to provide the required letter. For the Jumbo, I provided him with some photos (including one of the VIN plate, which includes Anno Fab. 1983), a quote from Peter Knight / Rotax which showed the date the engine left Austria to go to the SWM factory in Milan and the engine and chassis numbers. Also worth including the engine capacity on the dating letter. As from the 1st January 2008, agencies that produce dating letters are required by the DVLA to have a photograph of the engine and frame numbers.

You will need to MOT the bike, usually for daylight use only. The detailed requirements are provided on the MOTUK web site. For me the key items to bear in mind are:
– finding an MOT tester (or testing station) that understands what testing a trials bike is about, ie testing for a daylight MOT
– if you don’t have working front and rear lights, you don’t need indicators, break lights or reflectors
– you do need an electric horn (not a bulb one) for a bike after 1.1.1973 and it has to be audible
– registration plate; the MOT tester’s manual talks about layout, but not size (?). For the first MOT before getting a registration, the MOT is done on the chassis/VIN number, not the registation.
– making sure the bike is put together correctly and bolts are tightened etc

I’ve used Ray Griffiths at Eric Rees Motorcycles in Hereford for my trials bikes and this is where the Jumbo was MOT’d. I took it on the van, but if you want to ride the bike to MOT testing station, you need to phone in advance and make an appointment (to cover yourself with the cops). The current bike MOT cost is £27.50, which is around half of the car cost (which is fair enough given it has half the number of wheels).

I’ve a road bike and a couple of trials bikes on my insurance policy with Carole Nash all part of the same policy, but the Jumbo presented a couple of challenges. Carole Nash’s classic policy only covers bikes up to 1982, and not the SWM, and my insurers (Admiral) required more information on the bike. I spoke to their Customer Services dept, because I had an existing policy, but getting a new quote might be a challenge.
Therefore, sent an email to CN, attached a couple of photo’s and a link to Martin’s web site SWM history page. About 30 minutes later, they confirmed they could insure the Jumbo also rating it the same as a Honda CR400 (?) and for £26.00 per annum fully comp.
The insure on the chassis number for 14 days only, so you need to have all the other documents in place and a trip to the DVLA office already planned.

Trip to the DVLA office
You will need to visit your local DVLA office
to submit the forms. I’ve used a couple of DVLA offices, Worcester and Cardiff and they don’t do things the same way.
At Worcester, they always have in the past always insisted on a vehicle inspection, despite having an MOT, and this can only be booked once you have submitted the application. Therefore you need to make two visits.
For the Jumbo, I went to the Cardiff DVLA office at Ty-Glas, taking the bike in the van. Submitted the form, with the supporting documentation and my personal ID (driving license) and that was it; they don’t require a vehicle inspection and the bike stayed in the van unlooked at. The Cardiff office was revamped in December and although parking is a bit of a problem, took 15 minutes to queue and complete the process.

The first registration fee is currently £38 and the license fee for a 150-400cc motorcycle is currently £31.00.

You now have a road-registered twinshock you can use for ‘proper trials’. The Jumbo is ready to go; it cost me £116.50 to get it on the road, not cheap, but does mean you can use it for Sammy Miller and ACU classic trials.

Alive Again !

Ok well lots to report since my last posting. The carb went back together nicely and I spent some time curing the distortion I mentioned from the overtightening of the mounting nuts. This basically consisted of a piece of 600 grade wet and dry on a flat surface upon which I gently sanded the carb mounting plate true again. I had to do the same to the carb to cylinder head mount as well which was displaying quite a pronounced warp.

Soaking the Carb
Finished carb

Following the carb re-build and re-attach to the cylinder head the tank was tackled. The tank is easily removed from the frame following removal of the seat. It slides back and away from the bike to reveal the bikes backbone that flares down towards the back wheel/swingarm mount. The latter part of the backbone is formed using a distinctive pressed steel construction. The newly liberated tank was cleaned carefully the mud was removed from the underside and the fuel tap was cleaned up.
Carb floats
Carb with gunk

A quick swill with fresh petrol and that was it at this stage. New fuel line was fitted and the tank offered back to the frame and plummed in. So now the little bike was ready for the first attempts at starting. I opened the fuel tap, put on the choke, and made sure there were no airlocks in the fuel system by backing off the float bowl screw until fuel seeped from it… ignition switch in the on position I gave the bike a hefty kick… there was a slight attempt to fire, another kick and a bit of throttle and away she went… a bit tentative at first I carefully listened for any tell tale rumblings, cam chain rattles or cam journal knocks… there was a slight miss fire and after setting the idle and pilot jet screws, conservatively to start with it appeared that the cam chain was a bit rattly.

So it runs and not at all badly by all accounts. This alleviated a few of my fears as to the history of the bike and the extent of the restoration work ahead. As I was playing in the garden with the carb settings my neighbour leaned over the garden fence to find out what the noise was all about. I told him of my attempts at ressurecting the TL todate and that I was not sure it would start to which he replied:

“What do you mean you didnt think it would run… its a Honda!”

Tank Side

So now the engine is running with no smoke or strange noises its a tune up and check through… The points cover was removed (something I had not done to date as I had initially observed that there was a good spark from the ignition) I was greeted by a clean and tidy set of points but all of the surrounding screws including the nut that secures the mechanical advance weights to the cam were chewed up beyond all recognition! I had to use some very specific screw driver bits and a bit of force to remove them and even had to resort to an impact wrench to drift the cam nut out. (These were all replaced with equivalent allen head bolts on re-assembly except for the points gap adjusting screws.) After removing the timing plate and points the mechanical ignition advance unit was clearly visible. Essentially working on the same principles as a traction engine regulator unit and relying on centrifugal force generated by the cam spinning as the engine runs to advance the ignition timing the weights are retained by a pair of light springs and two magnets. There appeared to be a few mm’s of play in the wieghts so the springs were carefully nipped up and the play was removed completely. Removal of the cam nut using the impact wrench meant that I could take the newly reconditioned advance unit off the cam, remove the ignition houseing and reveal the cam sprocket behind.

The heads of these early tl machines were a single casting with no cam bearings as such, they just run in the head, which means that there was no option when they become worn other than to replace the head or insert some sort of bearing or bush using a local machine shop. the cam seemed solid and as the initial engine run had shown it seemed that there were no real signs of serious wear other than a rather tired looking cam sprocket that had obviously suffered from a loose cam chain thrashing around for quite some time… so I will put the cam sprocket on the xmas list and after spending an hour soaking the cam chain adjuster and lock nut in penetrating oil adjusted the cam chain to a more acceptable tension. Once all was done and put back together it was just a matter of adjusting the dynamic timing using a strobe light to align the F mark on the flyweel with the middle of the observation window in the caseing…… more to follow, it will soon be time for engine to come out and focus to switch to the frame and suspension components.

SWM TL350 Jumbo: Replacing the Piston

After getting the right piston, a simple (sort of) job of installing the new piston and getting the bike running

After identifying that the barrel was worn and that piston I had was too small (see article), I bit the bullet and ordered a new 84.25mm 2nd overbore piston from Peter Knight. It took a couple of weeks to come over from Austria and when it arrived, it turned out to be the same size, 84.17mm, as the piston that was already in the bike. The sizing must therefore be for the barrel, rather than for the piston, so sent it back and promptly got the 3rd overbore, 84.50mm piston back.

However, by then it was Christmas Eve, so no real opportunity to get the barrel bored out to the New Year. After a quick chat to a couple of people at the Herefordshire Classic trial on News Year Eve, took the piston and barrel to Hereford Rebore

Quick service, got the bored barrel back the following day. The barrel hadn’t work evenly, so there was an area low down on the barrel that didn’t get machined. Re-assembly took a couple of hours, mainly due to time taken to get the new gudgeon pin and circlips in the piston. The Rotax pistons have an arrow marked “Aus” (which I assumed was something like Ausgang or exit, ie the exhaust port), so after some deliberation decided that the this pointed to the front of the bike. When I stripped the engine, the piston had the arrow pointing to the rear, inlet port.

Jumbo in the workshop

Initially the bike didn’t want to fire up and the kickstart lever kept running off the shaft after a few kicks. You can’t overtighten the shaft as this then pinches in the internal gear change shaft, so as a shortcut, while I look at the lever later, took the kickstart off of the SWM TL280 I’d just acquired.

Changed the plugs a couple of times, though they were “wet” and had a good spark, but then the bike fired up. No rattle or slap from the barrel, but the bike would only run with the choke on and only then for a couple of minutes.

Seemed like possible fuel starvation, so took the carb back off the bike. It took a couple of go’s but where I’d changed the float needle before (see), the housing had become clogged with the stale petrol being washed through, so petrol was only seeping through into the bowl.


Changed the fuel pipe from the tank to the carb, as it had split and put the carb and tank back on the bike. Again a few kicks required and she fired up, again no rattle. Time for test spin round the garden, though by now it was 20h00, very dark and raining. Managed to negiotiate my way up a pitch black and very muddy lawn to ride round in lights on the drive, all sounded good. Had to adjust the clutch in further and also moved the bars further forwarded, as well as apply some cable ties to the main cables so that the routing under the tank was ok.

Well, its a running bike, with a few small items to finish off, this includes:
– the seat needs recovering
– front brake mounting bolt sheared and was fixed with araldite; a more permanent solution is needed
– cleaning the plastics, mainly the tank and side panels
– replace some of the old original cables and put the adjusters into the cable system

Hopefully can get an MOT done fairly soon, work commitments allowing.

Herefordshire Classic Trials Club: Trial 31 Dec 2006

It had rained for 4 days before the trial, but the woods at Clyro were ok for the trial. Conditions were nothing if not challenging.

With the modified TL rear suspension ready for a test and the SWM prep’d for Lee to ride, I signed on both of us for the Alternative Route and we made our way down to Section 8, at the bottom of the big gully. The rain had moved things around quite a bit and the waterfall/step at the top of the section seemed larger than normal. No surprise then that I couldn’t get the TL over it on the first attempt, a five. Section 9 had the awkward corner and step, but got round for a one. Section 10 was the normal climb out to the right, which was a lot more greasy than normal, so after watching the two riders in front both fail on the climb, I took the safer option and got out easily after a solid couple of dabs.

However, halfway up the climb the SWM decided to expire on Lee and after getting 3 other guys to help us pull it out a quick exploration showed that there was no spark. Change of plug and still no spark, and the lead to the ignition coil was loose, so possibly the condenser had blown [1]. That was the end of the trial for Lee after only 3 sections.

Moved on down to Section 1, again one that had been used before, but the alternative route didn’t drop all the way into the first part of the streamway. However, took a five here also trying to get up a routed step. Then noticed that the fuel pipe had a nick in it and was leaking. Section 2 was up through a tight gully with an awkward exit, and the best I managed on this on four laps was a 3. Section 3 was a hillclimb, which was also a little muddy, but the Honda on full-bore made it fairly easily. I then changed the fuel pipe over with the petrol tank breather and then dropped a couple of dabs through the tight and twisty section 4. Section 5 and 6 were again up through another gully and then 7 a slippery hill climb.

The TL decided to pack up prior to Section 7 on the first lap, refusing to run without the choke. A not-so-quick run back up to the car park to get the tools and then changed the plug and re-cut the fuel line. A couple of kicks and the mighty roar returned and despite getting off the right line in S7 managed to clean it.

With the all delays, a brisk pace and agressive action was required. Hauling the mighty beast up through Section 8, the best of the day, got a 3,0,2 for the other three laps. Only one more 5, on Section 1 when the front wheel slipped out on a log in a mudhole, but also managed to clean this on lap 3.

Comin into Section 5 on the last lap and the chain decided to come off the rear sprocket and thus the bike did try to eject me over the front handlebars. Put the bike in neutral and put the chain back on, but it looked like the side-stand was interferring with the chain. This will need modification. Also, the mounting for the fuel tank must have got bent at somepoint and one had dropped out during the trial.

All in all, didn’t ride that well, but its enjoyable when you can get the TL through some tricky sections. Finished all 4 laps, at the back of the field. Waiting for the results, but an excellent trial and a really good venue.