New Sidecar Motor


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New Zealand
Building Sidecar Motor

I started collecting parts for this motor a while ago and then got side tracked building the two-stroke outfit.

This is not intended to be a how to build a motor it is more of a show and tell what I have done to build a race motor for a sidecar. Most of what is shown is not necessary on solos and certainly a waste of effort on a road bike. Having said that you can take a motor straight out of a bike and throw it in a sidecar and have great fun, its just as you start to go faster and tune your motor more problems start to arise. I have also included some stuff about fuel pumps and batteries.

This did not start as a complete motor it is made up from parts boxes, all the parts were cleaned before assembly. I have a bead blaster and homemade vapour blaster still the cleaning and looking for missing parts took a lot of time. I have also zinc plated most of the XS special hardware that was looking a bit tatty.
Parts Sources:

Apart from the normal XS parts used other specialist parts were sourced from the following:
Smed Speed UK
880 Pistons, copper base and head gaskets and a used Euro 533 crank. Howard kindly disassembled the crank to save shipping weight. The busines has changes hands and Howard is no longer at Smed speed but they are well worth a look if you want performance parts.

Westwood Liners.
Westwood manufacture the liners to Howard’s specification. Howard generously arranged for me to purchase the liners direct from Westwood. Talk to Smed speed about liners.

Heiden Tuning
533 Con Rod kits, big bore cylinders without sleeves. 8 plate clutch kit, clutch hub spring kit.

650 Central
Lillie Replica head

Sources of information
Smed speed
XS 650 Club of Australia Racer Stuff/Club Racer.htm these pages from Jim and Hotdog

To give you background on to what is needed to be done read through the how to on Smed Speeds website.
As a refresher have a look at Jim’s excellent top end rebuild how to in the tech section.
The gearbox mods are also detailed on Smed speeds web site.
Lot of good info from Hotdog on his thread about making go fast parts.

Putting it all together
Cleaning the cases, remove the starter post. Blast media can get in a manufacturing pocket behind the post and is a pain to clean it out. To remove the starter post prop the case on its side with the post facing down in a barbeque or oven. Heat the case and eventually the case will expand enough, and the post will fall out.

Installing the post again is the reverse you heat the case and cool the post. Make a simple guide to ensure the retaining screw hole is aligned.

The studs were pulled using two nuts tightened against each other and a lot of heat (MAP gas) on the cases around the stud bosses. Measure and record the heights and locations of all studs before you start.
All the threads were filled with old bolts and the cases were vapour blasted. Glass beads will lock a thread better and faster than any Loctite product.

Strengthen cases
The cases had external and internal strengthening welded in place.
The area under the upper rear mount had a plate welded to it to make to a diaphragm. Significant internal cross braces were welded in place and the lower rear mount was strengthened by an external plate bent round the existing mount. These are where cracks happened in the past.
Case Welding 1.jpgCase Welding.jpg

After this the cases were then taken to a specialist machine shop to be shot peened and have the throats bored to take the 880 liners from memory 91mm.
The con rods and clutch basket were also shot peened to increase strength.

On return the cases were scrubbed in hot soapy water. Then an oil dead spot in the lower case was filled with epoxy putty. If the case cracks in this area it is impossible to weld so the epoxy may help keep the case oil tight.
Case Packing.jpg

The front oil gallery plug was removed, and all the oil ways were cleaned. It was a shock what came out of the front oil passage. After drying (there is a ferrous tube in the case) the gallery was replunged.

The cases were Scrubbed again and the starter post reinstalled.
I dont know the size limit per post so will stop here and start another.


  • Case Packing.jpg
    Case Packing.jpg
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The crank was rephased, rebuilt with new bearings, 533 rods and welded. The crank pins have oil ways in them unlike the 447 rods that I have seen. Incidentally this was the hardest crank to true I have ever encountered I got fed up and it ended up under the bench for a while. This crank was being particularly stubborn eventually I asked my mate to sort it which he did but even he had some trouble.
crank pin.jpg
The transmission was rebuilt as normal with new bearings. The gear box had the XS750 gear upgrades added and the dogs on 1st gear were back cut.

On rough tracks sometimes an XS sidecars gear selector shift claw bounces out of the shift star, and you are stuck in gear. If you are unlucky the shift claw hits the back of the clutch basket and snaps.
To prevent this, we modify the mechanism and relace the star with a couple of circular guides, so the shift claw runs in a slot. The end of the claw is also rounded and shortened slightly.
The arm of the shift shaft in strengthened and lastly a heavier tension spring is fitted to the claw.
shafts 1.jpgshift shaft.jpgShift star 1.jpgarm.jpg

These mods have cured the stuck in gear phenomenon for us.

The clutch push rod seal is replaced with a machined carrier when the cases are open that takes an over-the-counter seal that is pushed in place and with a small dab of Yamabond stays there. The seal can be replaced now without splitting the cases.
Looking at the photo I didn't do a good job of cleaning off the excess Yamabond.
Sump plugs are modified take bolts that are lighter and have smaller heads. The bolt is drilled, and a small magnet is set into the end.20220901_174549.jpg
The clutch basket was not too badly rilled, so it was smoothed as evenly as possible. The cush springs were replaced. An 8-plate clutch is fitted and a new old stock pressure plate with heavier springs and the upgrade type of thrust washer. The basket was shot blasted to strengthen it as we have had one break a tooth off during a race.
Shot blasting Aluminium gives a speckled/ pitted surface.

The kick starter mechanism is removed the motor will be roller or electric start. The kick start shaft hole is plugged.
The stock oil pump is perfectly adequate for a high power XS (as proved by top level flat track racers) the robustness of the roller bearing crank is also a big help no doubt.
The case half of the pump was scored by debris, to improve pump performance I smoothed these out with valve grinding paste and a round of mild steel. This was time consuming but rewarding. I also resurfaced the housing and set the clearance as per XS John's suggestion.
Top End

The head dowls were relocated on the block as per Smed Speed’s instructions and the stud holes filled as well.
I had the bare big bore cylinder block bored to take the Westwood liners and the liners bored and honed to take the pistons by a specialist machine shop. My skills are not up to doing this job and the machine shop did an excellent job.

Getting the barrels ready I wiped the bores with clean engine oil and a white cloth, you keep wiping and changing the cloth until the cloth goes in and comes out the same colour. Then they got a hot soapy bath and some more clean oil.

This motor is to run methanol, so I assembled the top end with the supplied gaskets and measured the combustion chamber with a burette and glycol. Then calculated the compression ratio. My calcs came very close to the as advertised CR but running methanol higher compression can be used. I was able to source some 22 Thou copper sheet, and this will give close to 11:1 and still have enough squish. You can go considerably higher on meth but 11:1 is easy to get and still have good squish clearance.

The motor will run a Lillie replica head that has bigger valves. I assembled the head with checking springs and a cardboard 22 thou head gasket. Using plasticine, I rechecked the squish. All ok.
Note the relocated dowels.
Then with the head removed and the cam in situ the valve-to-valve clearance was checked, all ok.
I noticed earlier when flow testing the head the number 1 spark plug had a thread insert fitted that allowed the spark plug to sit lower in the chamber and the bigger inlet valve would strike it. I have made a brass spacer washer and engraved the word WASHER above the plug hole.

The head was refitted and then the cam dialled in (3 degrees retarded Megacycle 250-30) using an adjustable cam sprocket. The valves were hitting the piston, so I needed to recut the pockets.
After recutting the pockets and checking with plasticine the clearance was above the minimum. This doesn’t sound much of a job, but I had to devise and make a fitting to hold the pistons first. As my vise was not big enough to hold them. Unfortunately, some compression was lost but the pockets had to be enlarged.
piston pocket.jpg
Dialing in the facet.
Some of the rocker arms needed refacing and to hard chromed again. They all have been modified to take elephant foot adjusters (Porsche). A start decompressor off an early XS is being used. The lift mechanism has been modified to limit lift to less than 1mm to absolutely prevent the valve hitting the piston.

Seals are not fitted to the exhaust guides and the spring steel baffle in the breather vent is left out of the head.

An older two tube breather vent case is used minus the baffles and the twin tube outlet removed.
A single large diameter hose is run into a catch bottle.

It is intended to start the bike rollers and use the electric start as an emergency, start line stalls, spin out sort of thing.

Kibblewhite valve springs were installed in the head I spent a lot of time checking clearances and installed heights.

Actually I spent an inordinate amount of time checking and re checking all clearances and cam timing. I am slower than a skilled mechanic but I can see where the money goes paying someone to build a race motor.

After assembling the top end, the cam lobe centre timing was rechecked, and the sprocket screws were Loctite (red) and lock wired.

Oops getting a bit out of sequence , the cam chain tensioner needs to be modified to clear the liners.
As a precaution the front cam chain guide mounting threads are drilled square and Heli coiled before install. I have seen these break on race outfits.

Cam chain guide.jpg

I made some fancy cam end caps to add a bit of bling. They are copies of Heiden tuning’s design.
Off to bed will finish this soon.
I am most curious about your crankcase vent setup. Wouldn't a Reed valve breather be beneficial? Especially with 880 cc instead of 653.
JJames, here are some links to threads on this site with photos of
XS sidecars.

ArticXS , on the long rod 750 engine we had a condensation tank from the top breather that drained into a fitting put into the top of the clutch cover, the condensate tank was vented via a crankvent breather. It worked quite well but what we found that by using 2 Litres of oil (like the flat track racers of old) the motor did not spray any out.
I intend to try the single large breather and 2 litres of oil and see how it goes.

Will post further on the 880 but have hit a small holdup with a cracked clutch hub.
ArticXS , on the long rod 750 engine we had a condensation tank from the top breather that drained into a fitting put into the top of the clutch cover, the condensate tank was vented via a crankvent breather. It worked quite well but what we found that by using 2 Litres of oil (like the flat track racers of old) the motor did not spray any out.
I intend to try the single large breather and 2 litres of oil and see how it goes.
Now, I am definitely not an experienced XS engine builder, nor a race engine tuner. But as far as I understand, lowering the crankcase pressure as much as practicable, is generally a good thing. Following that line of thought, a reed valve or other suitable check valve, connected directly to crankcase/ cylinder head, with minimum added volume on the crankcase side, would be most efficient. By adding volume, like a catch tank, without a check valve or at least a restriction, wouldn't that just lead to air and oil mist just rushing back and forth between crankcase and the catch tank?
Obviously, a rephased engine is better than a 360 degree twin when it comes to crankcase pressure fluctuations, but added displacement would add to these pressure fluctuations.
I am still just curious about what works or not in real life, so bear with me :)
Artic, I can follow your thinking and you may well be right.
We are all learning and I am certainly no expert tuner or engine builder. My main concern is preventing the engine from spraying oil out but I have noticed that well vented crankcases do feature on race motors.

The system we used on the long rod motor was taken from Craig Weekes performance guide. Crankvent is a brand of check valve marketed for Harley Davidsons.
A lot of people think negative pressure is good, I personally think you would have a suction as the pistons go up, I have mine on the oil fill, cross drilled so oil doesn't spray out with a large hose on the top
Wow! What an incredible amount of work, I’ve heard of a lot of the types of things you are doing, but never actually seen it done. I’m super impressed. I hope you will post a video of it running?
Another small update.
While fitting the clutch I found one of the spring mounts in the hub was cracked. I had a spare, but it was a newer hub with the spring wire holding the first steel plate on.

After a cleaning the hub I turned the steps off the hub beneath the steel plate so that an 8-plate set can be used.

I also took the time to file the sharp edges off the friction plates and the steels left by the manufacturing process. The idea is to help smooth operation of the clutch by reducing friction of the steels on the hub and the frictions on the basket.

The steel plates are new and have a checker pattern stamped into them I think the idea is to improve bite. I did not bead blast the steel plates, but this can be done to improve grip.

The alto friction plates supplied in the 8 plate kit also fit Suzuki GS1000 motors (9 plates not sure of year). I suspect There may be carbon fibre plates available that are made for GS1000, I will research this if we have problems.

The Heiden heavy duty clutch springs have been up to the job on the 750 LR motor but if we get clutch slip, we can put in heavier springs still. It could end up a combination heaver and lighter springs.

I made a jig a long time ago to hold the alternator cover on the mill. I use it to bore the cover for a clutch slave cylinder.

It has a centre point concentric to the clutch actuator, centre the hole then screw the cover down and its good to bore. This is the 5th XS engine to have this mod done with this jig. I also spot face the cover so the slave cylinder sits mostly flat and has a small spacer under the upper fixing.
On the underside to add strength to the case I usually get some ally plate welded in but as an experiment have used an epoxy his time.

Honda VFR/VTR slave cylinders work well and with a 14mm master cylinder have a nice feel.

In the past we have had problems when changing the gearing on a sidecar . With the alternator cover removed and set aside the spring in the hydraulic clutch pushes the piston out. Not what you want when in a hurry.To stop this I drilled the slave cylinder to take a couple of stainless wire pins. The 700’s clutch slave has an circlip which is neater.
I need to fit the cover and adjust the length of the push rod. The only hold up is I need to take the engine out of the stand to do so.

I also made a couple of oil Filter adaptors, internally they are the same as Mikes offering but are different cosmetically. One for my tracker and one for this motor.

Heat is not expected to be a problem since the motor will be on methanol and no provision for an oil cooler has been made. Where possible I like to avoid oil coolers as it is another cause of problems, simple is best.
I also prefer pulse fuel pumps over electric for the same reason.
That's all for now will post a picture of it completed but the carb and exhaust spigots will be a while coming.