Neils 1978 CB550 F2 Project - Newbie Let Loose

[Bryanj]

In the US that white plastic bit has 2 switches in it and turns the always on headlamp off before connecting the starter, this tends to make the white bit even more brittle till it crumbles to dust, somebody on us forum did 3d print some

[Oddjob]

Although you’d expect the internals to be the same, in many cases they aren’t. The starter button for instance can be either a one wire or two wire installation. The 550 uses the two wire version but many others used a one wire with the button earthing that wire and activating the starter motor. IIRC the early 500 used both versions depending on the market they were intended for.

I actually bought one of those non lighting switchgear. The wires aren’t long enough for the 550F, which have exceptionally long wires. I’m not sure if the internals are the same, never got round to checking tbh. I do have a spare 550f right hand switchgear but I’m loath to sell as it’s my just in case spare and is unique in its look.

[Neilw]

First Update

The bike is pretty clean, no major rust anywhere, but both the mudguards have pitting and some cracks, which have been masked with silver paint. I'll decide later what to do with them in the long term. I got a quote for fixing and rechroming them, but it seems steep at £480!

In any case, there are more important things to address.

My first assessment has revealed:

• RH Handle Bar switch broken - I did it trying to get it to work, but the bike wouldn't start on the button - so needs fixing/replacing.
• Most rubber parts on the bike are hard and perished, so all need replacing.
• Brake lights don't work, nor the horn, nor the lights on the clocks.
• The fuse box is damaged; will replace with a more modern unit from Hondaman.
• The saddle pan is rusted through in places and needs replacing - previous owner has bodged fibreglass to make it sturdy.
• Grab rail is missing
• The Fuel tank is completely clean inside, no rust and no liner material that I can see, so that's one less job to worry about!
• There is a small amount of paint damage on the side panels, and they lack decals, as does the tank.
• Some sketchy-looking wiring.
• THe Front brake binds a bit, back is ok, but both will need reconditioning.

Engine

The engine starts and produces white smoke. It wouldn't idle, but at least it started!

I've performed a compression test and the results aren't great.

No1 - 125 psi, then with a drop of oil in the clyinder  142.
No2 - 60 psi then 100 psi.
No3 - 66 psi then 140 psi.
No4 - 115 psi then 125 psi.


I assume i should just concentrate on checking the engine over now, before ordering more parts, so unless other's experience suggests otherwise i'll take the top end apart and have a look at the head, valves seats, pistons, bores and rings before deciding whether a rebuild of the top end will fix things or there is something more terminal. Unless of course i've missed a step!

Some general pics included.


I'll stop ordering other parts untill i know i have a decent engine,





[/list]RH Handle Bar switch broken - i did it, but bike wouldn't start on the button - so needs fixing/replacing.

[Bryanj]

Valves and seats first then pistons/bores

[Neilw]

Valves and seats first then pistons/bores

I take it that's the order I do them in? But do both while i have the top end apart?

[Bryanj]

Yes to both as when you remove the head it disturbs the base and if you dont replace gasket and O rings it may well leak later

[Neilw]

Valves and seats first then pistons/bores

Update 5th Feb 2026

I've stripped the top end down and it doesn't really look too bad. I'll post some pics later today.

I have a question about the Piston rings. I've managed to break the top one on 3 of the pistons while removing them from the bike. I always planned to replace the rings, but - how do i know what size are in there and what size to get? I have some feeler gauges, but I don't have a micrometre to measure the bore. Is there a straightfoward way to determine what you have and what to get?

[Bryanj]

Normaly it will have the size near the end of thecring, if nothing suspect standard.

In all honesty you should be able to measure sizewith a steel rule down to 1/4 of a mm which is the step sizes for rebore, or buy a pair of cheap vernier calipers of ebay.

You cant buy individual rings they come in sets for a piston

[Murf]

The switch has had 50 years of use and abuse ☹️ and although it is nice to repair things and keep them going I have replaced mine with after market ones from David silver.  It’s  not the cheapest option but will help give you the best chance of reliability.

I would also order a new fuse box while you are at it, the one you have has already had a bypass so is probably knackered, as they tend to be. 
Also give the harness a clean, pull the connectors apart to make sure they are clean, check and clean all the earth connections. Then sort of take it from there, checking, cleaning and redoing parts of the electrical system as needed. 

The electrical system is the part of the bike that has the greatest ability to leave you sat at the side of the road waiting for the AA.  it’s worth spending some time and money on if you are going to use the bike.
Good luck with the project, they are nice bikes to work on.

[Neilw]

The switch has had 50 years of use and abuse ☹️ and although it is nice to repair things and keep them going I have replaced mine with after market ones from David silver.  It’s  not the cheapest option but will help give you the best chance of reliability.

I would also order a new fuse box while you are at it, the one you have has already had a bypass so is probably knackered, as they tend to be. 
Also give the harness a clean, pull the connectors apart to make sure they are clean, check and clean all the earth connections. Then sort of take it from there, checking, cleaning and redoing parts of the electrical system as needed. 

The electrical system is the part of the bike that has the greatest ability to leave you sat at the side of the road waiting for the AA.  it’s worth spending some time and money on if you are going to use the bike.
Good luck with the project, they are nice bikes to work on.

I've ordered a replacement switch unit, figured it would be the cheaper option, and if I can repair the original when I'm finished, I'll do that and sell it on (I love the patenia on it!).

Regarding the electrics - I plan to upgrade the fuse box and maybe at the end put electronic ignition in, but that's a long way off.

The wiring and connectors, especially under the left cover, are dusty with 50 years of accumulated grime. How do i go about cleaning the mess. Do i spray it with something?

[Bryanj]

If you are ordering Hondamans fusebox consider his electronic ignition box, it keeps the points but reduces the current flow so points dont wear out.
No matter what some members say the 500/550 has only just enough generator power, especially with the later halogen headlight and needs to be turning at quite high revs to charge, most electronic ignitions use more power than points as they leave the coil "turned on" for longer and if you fit 3 ohm coils its even worse.

Setting points and timing can take a bit of time but once do is usually ok for at least 3,000 miles so how much riding are you going to do in a year?

If you insist i still have a couple of dyna knock offs i imported last year for a reasonable price, me i am sticking to points

[Oddjob]

I second those comments. Plus, as the harness ages the connectors start to deteriorate and more and more resistance builds up lowering the charging even further. Heavy traffic and constant use of brake lights and indicators can drain the battery to the extent that the engine stops.

Using the Hondaman fuse box also stops the theft problem the old fuse box had which meant you could get the bike started using no tools at all.

[Neilw]

I second those comments. Plus, as the harness ages the connectors start to deteriorate and more and more resistance builds up lowering the charging even further. Heavy traffic and constant use of brake lights and indicators can drain the battery to the extent that the engine stops.

Using the Hondaman fuse box also stops the theft problem the old fuse box had which meant you could get the bike started using no tools at all.

Do you think its worth just replacing the harness for one from David Silvers to head off any potential problems, alongside the new upgraded fusebox?

Also, I've just got to the cleaning stage, engine, carbs and purchased the Berryman® Chem-Dip® - Carburettor & Parts Cleaner, as I saw a demo on YouTube. But the instructions that came with it have scared the life out of me, and I don't think I could use the product safely. What do others use to clean the grease, carbon desposts and the carbs?

[Oddjob]

Lots of negative reports on the DS harnesses, wrong colours used and no literature to tell you what they are meant to be.

My harness I removed from my 500 is actually from a 550F2 I bought as a write off back in the late 70s. I liked the fact it had multiple fuses instead of the single one on the 500 so I ended up with a lot of 550 parts on my 500, something I’m quite happy with. A few years ago I bought a NOS F2 harness still sealed in its bag. My existing harness is in really good condition with just one splice where I installed a dual ignition lock. Easy to revert back to standard. Not sure yet what harness I’ll use when I rebuild the bike later this year. I also have a brand new aftermarket harness made by one of our members on here called Big Al. It’s very good. That’s for sale if you’re interested.

[Neilw]

Small Update

I've been working on taking the head apart, with a view to relapping the valves and also painting. I've decided to get the top-end soda blasted, as it's taking me ages to get them clean and the paint removed.

I had a go at cleaning the tops of the pistons; they all have a coating of carbon, which I've mostly removed.

However, at the edge of one of the pistons are two small chips, almost opposite each other, and I wonder if the piston is still okay to use? There is no damage in the cylinder, it was from. See pics.

One of the pistons has some light pitting, which I can't really feel with my finger and may polish out. Is this something to worry about?