XS 850 Re Model

[Signal]

I have struck a small obstacle in getting my frame painted as the guy I had lined up to paint it is away until late Jan so I am in the process of getting another painter.

Writing this later that scheme fell over as well so back to plan A with the frame paint.

I decided to get another set of con rod bearings and now have installed the crank and gearbox into the cases. I have assembled the head and checked the valve clearances and recorded the shim sizes.

I want to get the frame painted then install the cases in the frame and assemble the motor in situ.

The motor weighs a ton and doing it that way will make the job easier.

I did not like the finish on the top of the new pistons so I spent a bit of time polishing them and smoothing out any sharp edges that could be stress risers.


Also redrew my wiring diagram using Tiny Cad thanks for the tip Jim. I have been using Turbocad but the copy I have it is getting very buggy and I suspect that soon it will not work at all.

Thinking ahead I bought a throttle position sensor and have a plan to mount it on the Mikuni RS carbs. This is a test run for the GS1000 which will also get RS carbs.

If the ignition on the XS 850 dies it will get replaced with an Ignitech that has a TPS input, the GS ignition is slated for replacement with Ignitech after I stop it smoking.

The hard part of mounting the TPS was the driver mechanism after looking online at what others have done I decided a left hand carb mount would be the easiest.


The next challenge was to drill the throttle shaft, this should be no problem, remove the shaft and drill it in the lathe. However, these are new carbs and I could see that with my usual knack of wrecking stuff it was tempting fate.

I opted to drill in situ using a drill guide. I was able to do this but next time I will set the cabs up in the mill. The hole was then tapped to take a small stud to mount the TPS actuator /drive thingy.

Next was to make the mounting bracket and I got it good enough on the second attempt the TPS end up being under cut in a couple of places on the finished item which annoyed me but not enough to remake it (yet).


I turned some Delrin to make the adaptor that fits to the throttle shaft and turns the TPS. Then fitted it all up and made many small adjustments to make sure the throttle and TPS moved smoothly.


Finally some finishing to make the bracket look a bit nicer.


I have also decided to make some caps for the throttle shaft ends. Some banks of RS carbs have black caps on the shaft ends but this set didn’t come with any. The throttle shaft is not plated on the end and it time will rust.

The painter rang last night and the frame will be ready to collect Sunday. Hopefully things will go a bit faster now. Photos to come.

 

[Its been a long time]

The TPS is neat, it looks OEM fitment.

 

[Jim]

Thinking ahead I bought a throttle position sensor and have a plan to mount it on the Mikuni RS carbs. This is a test run for the GS1000 which will also get RS carbs.

If the ignition on the XS 850 dies it will get replaced with an Ignitech that has a TPS input, the GS ignition is slated for replacement with Ignitech after I stop it smoking.

Are Ignitech using TPS to adjust the advance, or some other wizardry?

 

[Signal]

Yes the TPS input feeds into the calculation to decide what the advance should be for any given RPM and throttle opening.
I dont really understand the process and i believe it requires a 3D ignition map.
The map is best set up on a dyno, the good news there is a tuner who is good at this in the country, the bad news is he is 4 hours away.
A bike with an ignitech will run very well without a TPS input but the TPS adds to the package.

 

[JAX71224]

consuming.

 

[Signal]

Picked up the frame this evening. Very pleased with the quality of the work.
The colour is Mitsubishi titanium Grey GU17. Will organise a helper to mount mount the engine bottom end.

 

[Signal]

I wrapped the frame in foam to protect the new paint. Then supporting the engine on its side with some help lowered the frame over the motor and installed the mounting bolts.


Job done no heavy lifting. After priming the oil pump it was fitted and then the sump.

Then onto filling the cases with all the other bits that make the motor run.

Everything was going swimmingly until it was time to fit the clutch. There was a lot more than the specified end float. Lots of checking and a look at the drawings on CSML website the problem was a missing washer on the gearbox shaft. It had been lost in a previous rebuild as it was not in the pull down photos.

Checking CSML the missing one had the same part number as the one fitted so I was able to make one on the lathe. After fitting the clutch end float is within spec.

The kick start mechanism is not being fitted along with associated gears leaves quite a bit of room. Clutch outrigger bearing not yet fitted.


Earlier I had to relocate the ignition advance drive pin 180 degrees offset due to the old one being a butchered mess. I thought it would be easy to relocate the timing marks on the auto advance mechanism, but it is going to be a bit more difficult. I have a plan and will post details if it works.

Further fun was discovered when cleaning the swingarm tapered bearings I discovered that some of the rollers were chipped and the cups were also worn.

I was told they were overtightened and looking at them you can see wear on the cone face. The manual has the torque figure in inch pounds and I suspect foot pounds were used as initially I misread it as ft/lbs.

I should have checked them before the swingarm was painted. Using a bit of thought I was able to get the cups out of the swing arm and install new bearings without damaging the paint.


The swing arm and final drive are now fitted just need to tighten the drive boss on the thiddle gearbox.
It took a while to figure out how to refit the swingarm and a couple of false starts. The manual is very vague in this area.

 

[Signal]

More slow progress,
After checking the ring gaps and fitting the pistons it was time to fit the barrell. The cylinders have been rebored and the lead in chamfer has been lost. I knew it was going to be a challenge to fit them but after only getting the No2 piston in after an hour I called a mate for help.
After another 30 mins struggle we chucked the sponge in.
We removed the barrell and I set it up in the mill to cut a lead in on the bottom of the cylinders.
In the picture you can see the last uncut liner.

Some may be horrified at the cutter I used but I have had good luck using wood router cutters on softer materials. It did chatter on the last cylinder but I took the last few passes turning the mill by hand and was able to get a good finish.


After doing this and another round of cleaning it was time to fit the barrels. This time I had help from the get go and we had them on in about 15min which is more how it should be.

I was massively over thinking the timing mark situation and one night in bed thinking about it realised that the position of the drive pin is irrelevant to the timing marks if the auto advance unit is installed in the original position..
I confirmed this with a degree wheel on the alternator (right side) of the crank and checked the timing marks. They were about 4 degrees off and this could even be how it left the factory, any how it was easy to loosen and reposition the datum pointer. I think I will recheck this when the head is finally torqued down.

The first picture is the degree wheel with the crank at TDC as indicated by the Auto advance marks, the second is the Auto advance unit with the crank at TDC as indicated by the degree wheel (which was correct).

I really dislike these spring weight fly out advances they belong on bloody Stephensons Rocket not a 1980's motorcycle for Pete's sake.
As an aside every time I look at a 1960's car technology I am reminded of the courage of the Apollo Astronauts.


The motor has been apart before and I dont know its history and considering the head has been dressed I thought the clearances needed to be checked.
I am not bothered about valve to valve as stock valves and cams are being used, even though I am using 2 inlet cams . Piston to valve and squish clearances need to be.

It has been fiddly but the inlet valve to piston has 1.3mm minimum clearance and the exhaust over 2mm minimum so they are ok.
However the squish is a concern and I will remeasure it tomorrow to confirm what needs to be done.
It would appear that the head re surfacing combined with the over bore has reduced the diameter of the squish area in the head leading to reduced clearance.
You can see in the photo the marker pen outline made using the new gasket as a stencil.
I think I can fix this pretty easily once I work out exactly how much I need to remove.



On a more positive note I fitted a part I made ages ago its a bit of a farkle really but the old breather was in a sad state.
The cap unscrews to allow the breather to be cleaned.

 

[Bjorn]

Good progress! Cool to read along