Topic: CB550 Compression Test

[Fraserimoore]

Morning Guys,

I'm sure this may have been asked before but I cant find the info anywhere...

I will be carrying out a compression test shortly on my 550 K1 and would like to know if there is a "normal/standard range" (psi) I should be expecting or aiming for?

Thanks in advance!

Fraser

[brewsky]

170 psi is shown in the book, but what you get  depends  on several factors, including the gage used.

The important thing is your values across the cylinders are close to the same reading...say within 10-15%.

Make sure the valves are adjusted and choke and throttle are both completely open before starting the test.

[Fraserimoore]

Thank for the reply, ill post my findings once I've carried it out...taking on board what you've said 

[Fraserimoore]

So... I carried out the compression test.

From cold with throttle wide open and using kick only:

C1- 144
C2- 105
C3- 147
C4- 141

So there seems to be an issue with C2.

What steps should I be taking now and what are your opinions?

Thanks again!
Fraser

[WaxhawFive]

I guess you could do a leak-down test and listen for the leakage out of the exhaust or the intake for a valve leak, or the breather cover vent if it's rings.  You can rent a leak-down tester for free from some parts stores.

[Fraserimoore]

Cheers Guys,

I'm going to put a drop of oil into the plug hole on #2 and see if it increases at all. If not, I will double check the valve adjustments and continue the investigation!

Will post my findings as I carry out the tests.

Cheers, fraser

[brewsky]

Is this a running bike?
Motor been apart?
Been sitting a while?

[Fraserimoore]

Just carried out another compression test #2 adding a couple of drops of oil down the plug hole.

Original (dry) reading - 105 psi
New (wet) reading - 200 psi !

I also carried out the oil method on one if the better cylinders (#1), this only increased by 20 psi.

...which I believe is pointing me to poor rings on #2

Brewsky - The bike was imported from the US to the UK in April, I've been carrying out bits and bobs on the bike when my 9 month old daughter lets me!

Im not sure what its situation back in the US was, but it only has 8000 on the clock...the rest is a mystery.

Time to strip if down I guess...Why do you guys think based on my findings?

Thanks Again!

Whilst its been in my hands, its never ran, but it turns over fine and I've rebuilt the carbs.

Thanks Guys

[Fraserimoore]

Thanks calj737!

Ill take that on board, I might take the head off just to give it a bit of a clean because it looks pretty horrid from what I can see down the plug holes.

Once I've cleared away the grime I'll get the valve adjustments spot on and attempt to get it running and then do some more compression tests.

...lets be honest, buying a bike thats 40+ yrs old with no history was never going to be easy!

[brewsky]

Before you go tearing into it, I'd get it running. Its very common for a motor thats sat for a length of time to register low readings, even individual cylinders. Numerous heat cycles may free up stuck rings and see a return of the compression equally among all four bores.

And of course, check the valve clearances!

+1
Get it running and ride it before you tear it down. You probably will find out you don't need to.

[b52bombardier1]

You might find that running modern fuel with good detergents and cleansers in it will take care of your carbon problem chemically rather you doing it mechanically.

I wouldn't touch it until you have ridden it a while. If it ain’t broke, don't fix it.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[rtbmrgl]

Compression the same hot, all 120psi.

[Fraserimoore]

Just to keep you all updated...

I decided to strip the engine down, any boy I'm glad I did!

When I took the head off I found 4 nicely formed sand/grit mounds on each of the pistons.

So now the plan is to strip the barrels and renew the pistons and rings (1 of the pistons was slightly pitted)

Once I've done all this lovely work (replacing gaskets of course) I will hopefully get her running with nice uniformed compression.

Fingers crossed she will be built back up by next weekend!

Will keep you all posted...and I'll upload the pics of the pistons for a bit of a laugh!

[bochnak]

This video will help you out: