Hazard Marking, More About My Compressor, And CB250RS Cylinder And Seized Piston Removal

Happy New Year!

I took last week and yesterday off from posting due to Christmas and New Year, but I was able to get a few things done over the holiday period.

Firstly, I got sick of hitting my head on the shed doorway, so I decided it was time to remedy the situation.

First up, here’s the doorway in question from outside and inside the shed.

I measured the height from the highest part of the threshold and found it to be exactly 170 cm

As I’m 183 cm (about 6 foot) tall, this is low enough to be a real hazard for bumping my head on. Fortunately my local hardware store sells reflective hazard marking tape. Here’s the view of the same doorway from inside and outside the shed now.

Next up, while I was using the air compressor to inflate the tyre on one of my wheelbarrows so I could do some work in the garden I decided to use the compressed air gun to clean some cobwebs out of the compressor itself. The brown acrylic paint started coming off some parts of the motor (mostly the plastic ones) but I noticed something new on the electric motor – a brand name!

A quick Google search told me that CMG is an Australian company that still makes electric motors. I haven’t had any luck identifying the motor model yet though.

Finally, I decided I was sick of working on Scarlet’s carburetor, so I decided to move onto the seized engine.

The two remaining mounting bolts for the cylinder were easy to remove.

The cylinder itself came off very easily too.

Inspecting the barrel didn’t reveal much at first glance.

Looking at the piston told another story, however!

It turned out the piston was seized to the dowel mounting it to the conrod.

As it wasn’t moving back and forth freely, there was some severe scoring on the outer side of the piston, most likely caused when the motor was turned over after it had seized.

With the piston free, I was finally able to maneuver the cam chain out.

I had another look at the inside of the cylinder and sure enough there was some nasty scoring on the outer side too, while the rear was relatively unharmed.

I removed the piston rings as best I could and cleaned the piston a little to look at the damage again

After only getting one circlip out and finding the mounting dowel to be completely immobile, I decided to use a hacksaw to crack the top of the piston open. After that, I was able to wedge a screwdriver in and split the piston completely.

I noticed some numbering “471” and “1” on the side opposite the “HON” and “DA” – this might indicate the original size or part number.

The conrod and mounting dowel seem to have seized together too. If this motor is going to run again, it’ll need a re-bore, oversized piston and most likely a new conrod as well, as I was a little overzealous with the hacksaw and left a few lines in the top of the conrod!

That’s all for now, regularly scheduled updates will return next week. The next update will most likely be an update on how Sylvie has handled not being ridden for nearly a month. I’m expecting a flat battery at the very least!


Fixing The Chain Tool And The Seized Motor’s Cylinder Head Comes Off At Last!

A couple of weeks ago, I followed up the chain replacement with some maintenance on my chain tool.

The 520 pitch pin for the chain tool didn’t fare very well after riveting the new chain and burred over again, so I had left it in the vice ready to tidy up with my handheld rotary tool.

Returning to the chain breaker/riveting tool, a couple of days later, I found I was unable to remove the 520 pitch pin from the collar as it had burred over.

Some work with the rotary tool took care of that and I was able to remove the collar and retrieve the spring.

I put the 50 pitch pin and collar back in the chain tool kit and checked the smallest pin. It turned out to be just the right size for the cam chain pins on the seized CB250RS motor.

I assembled the pin with the spring and the matching collar.

I fitted the chain tool onto the cam chain and tightened it.

After a few minutes I was able to break the cam chain.

I packed away the chain tool in its box. I’ll need a new chain tool before attempting any further breaking or riveting of 520 pitch chains!

With the cam chain no longer in the way, I was finally able to remove the camshaft and cam gear.


Next I loosened the cylinder head mounting bolts.

Then I realsied I hadn’t removed the cam chain tensioner bolts, so the mounting bolts for it came off next. I still wasn’t able to remove the cam chain tensioner though, as the cam chain was still in the engine.

I removed the lower engine bracket next.


The cylinder head nuts were the last thing holing the cylinder head down.

Finally, the cylinder head was off!

The cam chain guide came out very easily, but I still wasn’t able to remove the cam chain tensioner.



While the cylinder head gasket was in reasonable shape, the valves looked like they could use a good clean!

I disassembled the cam shaft, then packed and labelled the small parts to make finding them easier when the time comes for reassembly.

While putting the motor back on the bench, I managed to knock over the pegboard and with it all the tools that were neatly hung up!

I spent a few minutes replacing the hooks and setting the tools up in a way that will work for me later.

Finally, I updated the lists for the seized engine and called it a day.

The next update will most likely be more disassembly of the spare engine, although I may find some time to work on Sylvie as well!

That’s all for now, the next update will most likely be more engine teardown, although I may fit some more work on Sylvie in at some stage…