Topic: Compression Testing Questions

[campbmic]

I have a 19750 CB 550 which is running very poorly. I'm planning on doing a compression test and I have some questions;

1) To get the best reading should I test with my exhaust and carbs off?
2) Should I use the electric start or kick start?
3) I haven't bought a compression tester yet where can I get one locally (wal-mart, Autozone, etc?)
4) What specific size do I need for my bike?
5) What is the brand new, great condition, right off the assembly line psi?

Any other tip, tricks, tutorials, or thoughts on the matter are greatly appreciated!

[TwoTired]

I have a 19750 CB 550 which is running very poorly. I'm planning on doing a compression test and I have some questions;

1) To get the best reading should I test with my exhaust and carbs off?

Right idea, but not necessary.  Just make sure slides are open and the choke plates are open during the test, so it can gulp the most air.

2) Should I use the electric start or kick start?

Either, if you have a very strong battery.  Otherwise kick it until you get the max reading.

3) I haven't bought a compression tester yet where can I get one locally (wal-mart, Autozone, etc?)

I don't know your area.  

4) What specific size do I need for my bike?

Ideally, you want one that adds low volume for the small cylinder engine you are testing.  See link posted below.

5) What is the brand new, great condition, right off the assembly line psi?

That would be an engine with the rings and cylinder wall not broken in and not generating peak pressure.
However, the Honda shop manual does list the expected compression of an engine in good working order  (Pg 18).
If you use the exact same low volume device Honda service techs used to get a measurement, about 170 psi.  

Any other tip, tricks, tutorials, or thoughts on the matter are greatly appreciated![/quote]
You might want to check out the FAQs on this site.
http://forums.sohc4.net/index.php?topic=369.msg476032#msg476032

[campbmic]

Thanks TT

Well I did the compression tests with the exhaust on and carbs off. I used the kick start instead of the electric start and got readings in the 40s-60s area.

I rode the bike very roughly for about 6 miles or so, is this possible to do with compression this bad or did I mess up my testing?

If the compression is this bad what is the next thing to do? How can I figure out where the leaks are coming from?

I live in Dallas and I plan on rebuilding the bike to attempt a 15,000 mile trip this summer so any advice would be nice to have my end goal in mind.

[City Boy]

Hi.I think you need to check your testing procedure.I don't think the engine will start at less than 90p.s.i. or so.As stated earlier make sure carb is wide open if still installed and use the lectric starter if possible to get a faster pressure rise and minimize faulty pressure  reading if using gauge  lacking a manual pressure release valve.Good luck and Rock On

[City Boy]

I just reread your last post.Apologies for mentioning carbs.

[TwoTired]

Jeez, those are low numbers. 
What does your test apparatus look like? Can you post a pic?

If you are kicking it, take all the spark plugs out and then kick it for the highest readings.  You need to kick for several cycles and use the highest reading the gauge will store.  Most important is that all cylinders be within 10% of each other.

I wouldn't expect the engine to run with 40 psi. (unless your test connection is very high volume.)

If you repeat the pressure test with 4 or 5 drops of oil in each cylinder (to temporarily seal the piston rings), does the pressure improve markedly?