Ignition timing Yamaha two stroke

Now the painted engine is back in the frame I had to do some basic tuning before I could start the bike. First I had to charge the 6V battery. I used a power supply I bought for the DIY nickel plating jobs. The best voltage to charge a 6V battery is around 6.8V and the best current around 0.4A. If the battery is almost flat you'll see it draws a lower current, around 0.3A. After an hour or so it will go up to 0.4A.

Charging the 6V battery

Clutch, bleeding the oil pump and carbie adjustments are pretty straight forward but setting the ignition timing on a bike like this was new for me because it's based on the flywheel magneto principle. The Yamaha LS3 has a so called low tension magneto, because the ignition coil isn't inside the flywheel but right under the fuel tank.

With this 1 cylinder 2 stroke bike the ignition points are hidden behind the flywheel magneto and this flywheel has to stay on the bike if you want to set your ignition timing. This because the cam that opens and closes the points is part of the flywheel magneto.

Ignition points - flywheel magneto removed

If you have a set of brand new points it's, according to the manual, pretty simple; Just look for the max gap opening and make sure it's between 0.3 - 0.4 mm. That's it.

The points on this bike looked still pretty good so I decided to give them a second chance.
The manual says nothing about timing marks on the flywheel or other parts which I could use. Ah Well, maybe I'll find them while setting the ignition timing.

In order to set the ignition timing on two stroke bikes most manuals will give you a number BTDC (Before Top Dead Centre). For the Yamaha LS3 this is 1.8 mm BTDC. The spark plug has to fire at exactly that moment in order to give the best engine performance.

For this timing method you need a dial gauge which you can screw into the spark plug hole. You can buy them in a good bike shop but I already had made one myself from an old spark plug and some scrap metal which I used on the Yamaha RD125A

Dial gauge ignition timing tool

Dial gauge ignition timing tool two stroke Yamaha LS3

So the ignition points have to open at 1.8 mm BTDC. But how can you see when they open? First I tried it just by looking... not very accurate. You can also use a cigarette paper. Put it between the points and as soon as you can move it the points are starting to open.

Most old school bike shops use a buzzer to find the right spot. And in my pile of electronic waste I found an old  buzzer, the ones they use in cars to warn you when the lights are still on. Now you only need a 6V battery and some wire with crocodile clamps.

Connect the red wire to the pos (+) of the battery and the black to the black/black-white wire frome the iginition which goes to the ignition coil. Connect the Neg(-) of the battery to a ground/earth point on your bike. I used the chrome shift lever. Don't forget to turn the key of your bike. If it's switched off you won't hear any difference in tone while looking for the right spot.

Ignition timing tool two stroke engines - buzzer

Connecting the pos(+) wire to the black/blackwhite coil lead

Flywheel magneto ignition timing 2 stroke with a buzzer

Actually, before you connect the buzzer you have to look for the Top Dead Centre (TDC) of the piston with the dial gauge. From that point turn the flywheel clockwise till the piston has gone 3mm down, then turn it counter clockwise 1.2 mm, Now you're exactly 1.8 mm BTDC. The 3 mm turning clockwise is to rule out any play from the crankshaft.

So with the piston in this exact position the point have to open in order to generate a spark. Well  "exactly".. according to the manual it has to be between 2.0 mm and 1.3 mm BTDC.

Ignition - Timing specifications Yamaha LS3

As soon as you connect the buzzer it will start buzzing (of course.. it's a buzzer...) but the trick is to listen/look for a change in tone. At the moment the points open the tone of the buzzer will change. Probably not at the right spot, so you have to loosen the ignition mounting screw a bit and move the points a bit up or down till you find the right spot (between 2.0 and 1.3 mm BTDC)

Looking for the right ignition spot with a buzzer

I found the right spot but when I measured the max gap it was only between 0.25-0.30 mm. So I need a new set of points. The brown heel which makes contact with the flywheel cam was worn.

Settled for 1.65 mm BTDC - Ignition timing Yamaha LS3

With those old 6V two strokes the points hardly wear (there's only about 3.5V between the points), but the points heel will after a while and this will make the max point gap smaller, thus resulting in less advance timing.
After working on the points I sanded them carefully with 180 grit sandpaper and cleaned them with some wax and grease remover.

Ow... I also found a factory mark on the flywheel which was exactly in line with a mark mounted on the stator plate (see pic below). This can't be a coincidence ;)

Flywheel magneto ignition timing Yamaha LS3 1972

After adjusting the points I started the engine for the first time after reassembly. A big moment :)

Running 2 stroke engine Yamaha LS3 

Replacing the crank shaft oil seals

When a two stroke engine hasn't been used for years you can be almost 100% sure the crankshaft oil seals are dried out and will start leaking when you gonna run the engine. If your bike has only minor air leaks and you don't red line your bike too often you can get away with it for a while and maybe don't even notice there's an air leak.

The seal on the flywheel side prevents air from getting into the combustion chamber. If the seal on this side goes bad, you’ll get air leaks. If it's a big leak, your idle will hang and/or the bike will rev erratic randomly. The bike will run lean, it's impossible to tune it and there's a real danger of melting a hole in your piston(s). When you remove the cover on this side and you see oil at the bottom, you can be sure it's leaking.
The seal on the clutch side prevents crankcase oil from getting into the combustion chamber. If the seal on this side is leaking the engine will suck oil into the combustion chamber. You get greasy spark plugs, high oil consumption, lots of smoke, etc...not good...

Leaking crankshaft oil seals two stroke engine

As the engine was already out of the frame I started taking off the engine covers. Using an impact screwdriver will make the job a bit easier. Don't forget the long screw-bolt on the right (clutch) side which is hidden underneath the smaller oil pump cover. You can leave the oil pump inside the cover, just disconnect the tubes to the cylinder and oil tank.

Don't forget this bolt above the oil pump spindle

Clutch cover inside with oil pump gear

After taking off the engine covers I had to remove the flywheel/magneto and the clutch assembly. In order to loosen the clutch- and primary gear nut you need a special tool, a clutch holder, but even then it can be really hard. However there's a nice little trick to loosen those nuts in a couple of seconds. Take an air impact wrench, hold the clutch assembly firmly with your other hand (wear a glove, just in case..) and it will be loose in a second.

Clutch boss and gear and primary gear crankshaft

Primary gear crankshaft Yamaha LS3

Same story on the other side with the nut that's holding the flywheel nut. But once the nut is off  you really need a special tool, a flywheel puller. Now install the flywheel puller in the thread and use the air impact wrench again.

Yamaha Flywheel puller and Flywheel Yamaha LS3

When the flywheel magneto is off the engine you can loosen the two screws that hold the timing plate with a impact screwdriver. This way there's less change you'll damage the two screws.

Impact screwdriver set

Using the impact screwdriver to loosen some screws

Finally I could reach and remove the old crankshaft oil seals. If you don't have a special seal remover tool you can also use a screw to remove the seals. The "problem" with the screw method can be that you scratch/damage the surrounding metal in which case you've created a permanent leak which can't be solved with a new oil seal. The oil seal on the flywheel side can out pretty easy without any collateral damage.

First oil seal out

However on the other side we have a different kind of oil seal; one with two lips. So it's a bit harder to put a screw in this seal. In my case it slipped a couple of times off of the seal and scratched the collar @#$^*!!
Luckily a new collar is only a couple of dollars so this issue was quickly resolved.

Old and new collar crankshaft clutch side

Underneath the collar is another oil seal which you have to replace, it's a simple tiny O-ring. With a wooden pick I could lift it and pull it off the crankshaft. The new O-ring was of course a bit thicker then the worn out old one so it was a bit harder to put the collar back onto the crankshaft. But with the help of the old collar it was easy as..

Removing the old crankshaft oil seal O-ring

Fitting the new collar over the new O-ring

Next time (on my Yamaha RD125A) I'm gonna use a special oil seal remover tool which I got in the mail today :)

Oil seal puller and installer set

When fitting the new oil seals you have to fill the lips with grease and  make sure they go in nice and even. I used a couple of pvc pipes to push 'm in. Make sure you're using a pipe with exactly the same outer diameter as the oil seal, otherwise you can easily damage the lips. Before I pushed them in I've put some oil on them to make things a bit easier.

Installing a new crankshaft oil seal

With the new oil seals in place I had to put back the clutch assembly, primary gear and flywheel-magneto. This time no air wrench because those nuts need a specified torque: around 65 Nm for the primary gear and flywheel and around 55 Nm for the clutch assembly. But how do you stop those gears from turning. First I tried it with some rags between the primary gear and clutch gear, but the teeth were too sharp and the rags were simply eaten by the gears. Then I tried it with a 20 cent piece and it worked, however the coin is a bit damaged now ;)

Coin after use as "gear holder"

Oww...before I put the nuts back on used a bit of 243 Loctite threadlocker on the primary gear and flywheel nut.

Loctite 243 "Threadlocker"

Another thing I still needed was a clutch tool holder, but I couldn't find the right size on Internet so I made one myself. I used one of the metal clutch plates and attached a grinder spanner. It's a bit soft but it worked. Next time I will use 3-4 metal clutch plates together to make it a bit more solid.

Making a clutch holder tool

Home made Yamaha Clutch holder tool

Now I only have to buy me another clutch plate ;)

Rebuilding Yamaha Chassis

After reassembling the front fork I put all the wiring back in place. If you leave this till later is gonna be very fiddly. Before I took the wiring out I made lots of pics but even with those pics it was a bit of a puzzle to connect everything the right way. Actually I still don't know if it's all good; most of it can only be tested with the engine running.

Wiring diagram Yamaha 100 LS3 1972

Part number tag still on the original wiring harness 

Original Wiring head light Yamaha LS3

Next things were the handle bar, rear fender, tail light, indicators, rear wheel and freshly sprayed sprocket. The switch handle also needed some TLC and soldering. The original handle bar was stripped down, sanded and nickel plated and the aftermarket throttle handle was replaced with a NOS one including a new throttle cable and oil pump cable.

Taking the switch handle apart 

Rusty indicator switch

Indicator switch mechanism and horn button

Cleaning indicator switch mechanism

Rebuilding Yamaha LS3 handle bar

Tail light and rear fender Yamaha LS3

Painted original 36 rear sprocket Yamaha LS3 1972

Rear wheel Yamaha LS3

Rear mud guard Yamaha LS3 - Close up

Followed by rear shockers, front fender, front wheel and most cables. 

Night shift: mounting front fender

Left side front wheel Yamaha LS3

Right side front wheel Yamaha LS3

Rear wheel with brake rod and tension bar

Break switch rear

As with most older bikes not all parts are available anymore, so sometimes you have to be creative and make your own stuff. The old dampers for the right side cover mountings were almost perished and I couldn't find them so I made them from an old inner tube. In the middle of the tube is a weld which looks almost the same as the original part but above all it's functional.

Making cover dampers from an old inner tube 

Time to bring back the seventies! Mounting the side covers and a loose fit of the fuel tank, at this moment I'm starting to see why I'm putting all those hours in this once basket case, enough time has passed for the LS3 to be cool again :).

Oil tank with new oil level gauge

Fitting fuel tank

Right side fuel tank, cover and rear shocker

Right side fuel tank, cover and rear shocker

Luckily I took of the original sticker of the oil tank with a razor blade and kept it in a safe spot. Before putting on the clear coat I put it back on the oil tank with some transfer tape. In this pic you can also see the metallic silver shining trough the red dye/clear coats; That's what they call "candy".

Two stroke only !!

Chrome chain guard - Yamaha LS3

Exhaust

The buddy seat was almost ready. I only had to put on the original strap with the chrome button bolts. But because the new buddy seat had the bolts welded on I first had to carefully drill 'm out. The original bolts and chrome "buttons" were stripped of their old chrome, cleaned, sanded and nickel plated.

Welded bolts new buddy seat

Original bolt with pin in place

Yes, it's not in the middle, but that's how it should be