New 700cc Outfit

Fickle things, two strokes. When they are going well it’s only a gnats cock hair before catastrophe.
keep at it.
My condolences on the crank, I feel your pain.
Out on my Sunbeam last March, stopped dead, luckily just set off from a junction.
Only six miles from home, my friend towed me home with his 250 MZ.


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Brief Report on Boxing Day.

In qualifying the Team got a bit close to the curb on one corner and broke the end off the chamber at the weld. Luckily the stinger goes well into the rear diffuser and in combination with the springs could not come out. They also had problems with other bikes when trying to get a good lap but still managed to get 5th (3rd row).

The chamber was on the bottom pipe and that meant all the pipes had to come off to weld it. We opted to do a bodge job with rivets steel strips a hose clamp and lock wire.
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The team were confident and that 5th position although not ideal they could pass at least 2 bikes before the first corner and then work on the others. Feeling pretty good about things we started the bike, and I headed off to Robert Holden corner to watch the race and they headed off to the dummy grid.

The bike never made it, it made a death rattle on the way and died as soon as the clutch was pulled.

My mate pulled the motor today and No3’s piston skirt had collapsed which was a surprise as it only had 5 hours on it. It could be that it needs reboring, it looks ok it will be measured before pistons are ordered.

Oh well only 12 months before we can have another crack at winning this meeting.

My mate riding his F2 did little better with a thrown chain leading to a DNF, however he did finish 1 race and managed 3rd in the Suzuki Series which has Cemetery Circuit as the last meeting.

Photos of the carnage.
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I wonder if R5 pistons with a moderate cutaway in the rear skirt would be more robust. I guess at the expense of some power, all depending on how well the chambers aid the scavenging.
Oh yes reading back I can see the problem I put the photos of my mates F2 without any context sorry about that.
The Suzuki is an old Windle Chassis that found its way to NZ some time ago and was repowered with a 1000cc to race in F1.
When my mate bought the bike it was without a motor and in need of some love. He repowered it with a GSXR 600 Suzuki and tidied up the frame and fairings.
Time for a bit of an update.
I have been doing stuff but made an adjustment to my phone and could not send photos from it to my email. All fixed now but took a while to find out what I had done.

After the disaster of Boxing day the bike was repaired, new pistons and the pipe repaired turns out the wrong pistons were installed in the bike at its last motor strip, the pistons used were out of hours and you can see what happened.

Since the meeting at Pukekohe was the last classic meeting (the track is being closed) my mate thought he would run the bike without mufflers thinking that if they ban him so what.

Two surprises the bike was not that loud and had noticeably more horsepower. The lack of noise was not a huge surprise as the end of the stingers were placed inside the baffle cone for that very reason, but the extra power was. At present we are running without mufflers until told to do so.

We obviously got the muffler design wrong. The bike is running well and has been reliable. Some things we are looking at doing when the crank is rebuilt next is to make it a cross plane as loss of rear wheel traction is a problem when the bike comes on the pipe. Hopefully going away from the big bang motor will improve traction.

The crank is no problem but a new ignition will be required, I have been making a new rotor with two magnets and a backing plate to hold two pick up coils. They will feed into an Ignitech ignition so we will need to run a battery. The battery can also power the rain light and the gear position indicator which at the moment runs off a small 9V dry cell. The new ignition can still use the coils we have that are for CDI and can still be a wasted spark so we don’t need to mount new coils.

The rotor is keyed onto the tapered shaft, the 2 magnets 180 degrees apart are held in place by welding wire pins and the holes will be seal with epoxy, the 2 x 6mm holes are for mounting the rotor puller. The dot on the face is an error.
The pick ups are 90 degrees apart.

How the cross plane crank and ignition works.
Crank configuration:

Pistons 1 and 4 are 180 degrees offset, pistons 2 and 3 are 180 degrees off set.
Piston 1 is 0 degrees piston 2 is + 90 degrees piston 3 is +270 degrees piston 4 +180 degrees

For this explanation assume firing at TDC. This is a wasted spark ignition system.
Condition 1

Piston 1 is TDC , piston 2 is 90 degrees BBDC, piston 3 is 90 degrees BTDC, piston 4 is BDC.
Plugs 1 & 4 spark, cylinder 1 ignites, cylinder 4 has no compression and does not ignite.

Condition 2

Piston 1 is 90 degrees BBDC , piston 2 is BDC, piston 3 is TDC, piston 4 is 90 degrees BTDC
Plugs 2 & 3 spark, cylinder 3 ignites, cylinder 2 has no compression and does not ignite.

Condition 3

Piston 1 is BDC , piston 2 is 90 degrees BTDC, piston 3 is 90 degrees BBDC, piston 4 is TDC
Plugs 1 & 4 spark, cylinder 4 ignites, cylinder 1 has no compression and does not ignite.

Condition 4

Piston 1 is 90 degrees BTDC , piston 2 is TDC, piston 3 is BBDC, piston 4 is 90 degrees BBDC
Plugs 2 & 3 spark, cylinder 2 ignites, cylinder 3 has no compression and does not ignite.

I hope you find this of interest.

In addition to this I would like to fit larger reed blocks (I have them on the shelf) and bore the carbs they are rather asthmatic (28mm) before buying larger ones.

Of interest to other RD 350 owners is that US spec ported new cylinders are being made by China now. I have read they have also fixed the casting so that the liners do not slip out of the castings as well. There are old and new cylinders on the market at the moment, you can tell them apart apparently but I am awaiting photos. This is good news because fixing the Indian spec cylinders is a ton of work.

In other news
There are changes coming to the modern sidecar class as well the type of motors allowed is changing and they are proposing allowing two strokes up to 500cc. I went to see my mate a few weeks ago and he had these 250's on his bench….
Not to say I told ya so... But I suggested a cross plane back when you were building it. So yeah.... guess I an saying told ya so... :lmao:

On the other hand, it weren't me good enough to build a 4 cyl engine from a pair of twins in the first place. :bow:
Signal, your comment about reproduction cylinders makes me wonder. OEM Yamaha cylinders did have cast in liners that could not be pressed out, even if using heat. So if the liners would slip, then the design was altered by whoever made the repops. What the aftermarket SHOULD DO, both for RDs and the XS 650, is make Nikasil cylinders.
More on the ignition, after talking to the local Ignitech agent I had to make some changes to my trigger. A magnet is not suitable to trigger with inductive pickups.

Ignitech ignitions fire of the trailing edge of the trigger at low RPM and off the leading edge at high RPMs. So I had to remake the trigger like a bow tie.


I then fitted a speed controller to my router table and made a rough test rig. I had an initial problem with the supplied software but a 5 min phone call to the supplier and it was all fixed. I was able to use the timing light to watch the ignition advance then retard as the revs went up. The display on the laptop has a rev counter so you can set the revs and then check. You can even offset the pickups in the software if your pickup placement is not perfect.
The computer connects to the ignition via serial to USB cable.
Test rig.jpg

I am impressed with the ignition it has many features that we will never use but it is easy to program and modify the advance curves. Some features are launch control, rev limiter both hard and soft, switching advance curves on the go or at set RPM the list goes on and on. I will be using one on the XS 880 and will start on the trigger for an XS soon.

With the ignition sorted (final advance curve will be done on a dyno) it can go into the cupboard and brought out when needed.

Making the trigger and pickup mounts has taken quiet a bit of time, the next one will be easier I hope.
Today we fired up the bike with the new cross plan crank.

The bike has basically been rewired with the kill and tether switches controlling a main relay that isolates the ignition, gear indicator and rain light.

The battery and ignition are in a small box that sits on the platform below the kneeler trough. The CDI coils are reused and in the same location as before.

We spent a great deal of time checking that the base advance was correct. This is important to be accurate as all the advance and retard points are worked from there so if it’s a few degrees out all the points that are programmed in will also be out.

As a start for the advance curve, we copied as best we could the curve from the Electrex world CDI ignition as published by manufacturer as it has been working well.

The bike fired up quickly with the ignition advancing then retarding as it should, it also idled nicely when cold. That is something the CDI ignition and big bang set up never did. Quite pleased with how it turned out however the downside is that the Scitsu tacho now reads twice as high as it should, this is because the coils are now firing twice every revolution. Didn’t think about that during the planning. We also could not detect a change in the sound of the motor when we were standing beside it. It may sound different on the track though.

Our plans to take the bike to the Ignitech specialist with a dyno for final tuning have been dashed as the outfit won’t fit on his dyno. We will just have to use a local dyno. The bike has an outing at Taupo next weekend at a track day and the classic season kicks off again soon in early September.
Another update, the cross plane crank is a failure we have has 2 broken cranks in short order so we have gone back to to big bang 1&3, then 2 &4.
The only change required to the ignition was repositioning the second crank pickup 180 degrees from the first.
The bike then went down south to the Southern Classic a 3 day meeting and in the last race of day 2 seized number 1 cylinder.
Fortunately I had other stuff to do and did not go down south although there are people at the meeting I wanted to talk to.

The upshot was my friend and co conspirator had miscalculated how much fuel to take and ran out of the AV gas we normally run and used 100 octane pump gas. We later found out pump 100 octane burns faster than AV gas so you can see what happened.

Why did it burn only #1?
#2 and 3 heads were machined to have lower compression than cylinders 1 and 4.
#4 on the tear down had a blown O ring that we use for head gaskets so this probably saved it.
Another possibility was an air leak the crank seal failing or a blocked main jet. The seal looks good but will be replaced and the carb is clean.

Some pictures of the motor as it has been many times this year and the offending piston. The cylinder is ok the piston residue came off with oven cleaner and some careful scrubbing. We have a spare piston on the shelf.

Next big race Boxing Day our home track but there will be some tough competition there this year. Next year will see the appearance of another fast BMW (they are becoming the go to now) and a water bus that is being built locally for a local team. It will be good to have another 2 stroke on the track.