Topic: Dead Project

[Bodain]

8 weeks ago I purchase a beater, rusted bucket of bolts. 1975 CB 550.  Just wanted something to tinker with. When I purchased it. The engine would turn over, but not run.. I got it and brought it home. Where to begin!

1. Stop or eliminate all rust or new rusting and general clean up.... Done!

2. Will the engine run!  No! Nothing in the carbs will move. Gunked up!   Clean and rebuild... Done!

3. Internal gas tank full of rust!   Done! Fixed.

4. Buy battery and try to fire it up... Turns over fine, but no attempt to start. Many days of fiddling and it's running.
Poorly, but it is running!

5. Time to check the compression..  80 PSI per cylinder    OUCH!  Apply small amount of oil to cylinders  175 PSI...

Rings are toast!

Now I start investigating options.....        This part doesn't look good... Right now I'm dead in my tracks....

Honda can order standard new rings..   Hone and new rings?  A cheap and not very good way out. Only as last resort!

What do you think? I've not actually pulled the upper end yet to look at cylinders and pistons.

Been looking for overbore pistons and rings options. Wiesco doesn't seem to offer it. They appear to be almost non-existant for a 1975 CB 550.

I've read the messages where people have used the overbore kits for the CB 500 in a 550.
Does anyone have any info on possibilities here?

Everything else on this bike can be fixed/replaced.. This is the one area that is shutting me down.

[TwoTired]

5. Time to check the compression..  80 PSI per cylinder    OUCH!  Apply small amount of oil to cylinders  175 PSI...

Rings are toast!

The compression test is indeed not good.  However, you should find out if the rings are just stuck in the piston grooves, whereby new standard rings on existing pistons and slight cylinder hone will fix you up. 

Also, did you do the test with the engine cold?  The comp might be better when warm.

There is also the possibility that some engine run time might free up the rings to get them to press onto the cylinder walls and seal again.  If the engine has been sitting a long while the rings glue themselves onto the piston ring lands. On car engines, some Marvel mystery oil was used to good effect for a cure.  But, I don't know what this oil would do to a wet cltuch.  Maybe nothing, adverse.

If you are certain the rings and cylinder walls are worn out, there is little choice but bore, new pistons and rings.
Cheers,

[Lumbee]

...I would just got with a top end rebuild and forgo the honing/boring, assuming the cylinders look OK.  New rings and gaskets puts you at a couple hundred bucks...

[kghost]

hell, just fill the cylinders with marvel mystry oil and let it sit a couple days.

Then turn it over with the spark plugs out (to clear the oil).

fire it up and run it around. check the compression again hot in a couple of days....

Rings might loosen up, the cylinders could be a tad rusty.

Won't cost ya nothin and the compression may come up.

Give it a try before ya tear it all appart.

[bryanj]

If you must have pistons and rings get one of the 550 kits for a 500 as it is exactly the same as a 2nd oversize (0.5mm) rebore kit for a 550. Also cylinders and pistons do turn up on ebay fairly regularly. If you strip this engine you MUST use a new top gasket set with all the "O" rings in it

[Bodain]

Today things are looking up. Today I pulled it all apart. I really didn't find any frozen rings like I expected. All rings were free. It was clear the head gasket had what I thought was a minor leak. I don,t think it so minor now. The entire head gaset area was saturated with oil. I don't really have the proper measuring tools to measure piston and cylinder wear, so I was gonna take the head and pistons to be checked.

This afternoon I hit EBay hard.. Searching for that CB 500 overboar kit. Found one and bought it for $120.00 also lucked into complete engine gasket kit for $26.00. Normally they are listed" Buy it Now" for $85.00

If things go well I should be putting it back together next weekend.

I've been putting so much time in the Honda the 01 Kawasaki ZRX 1200R is  feeling neglected...

[bryanj]

Secret of getting these oil tight is SUPER clean gasket surfaces and VERY careful fittment of the "O" rings

[SteveD CB500F]

Have you checked the valve clearances?  This may be the cause of your poor running and low compression.

Once you get this running sweetly, you can forget the ZRX 

[Bodain]

Yes I checked valve clearances. That was the single thing I had to do before the compression test. I didn't want to be fooled by a tight valve hanging open.

Forget the ZRX... Bite you tounge! <GRIN> I want to hit curves at speed and not worry about speed wobbles. In 1975 the Japanese still didn't have a clue how to make a motorcycle handle in anything other than a straight line. When I removed the swingarm to clean it up.
I was amazed. The only thing holding the rear wheel and swing arm on is a 3/8 in. rod. I never had a reason to remove the swingarm back in
the 70's.

I'm kinda looking forward to riding this thing and feeling the sheer terror of a speed wobble again.