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Compression

  • Thread starter Thread starter srg
  • Start date Start date
S

srg

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I was just wondering what you guys think about these compression numbers on my bike. I know the theory, but not the practice. I know what a compression test tests, but not what numbers are good or bad.

..............#1.....#2.....#3......#4
Test 1.....117....107....100.....112
Test 2.....116....109.....94......99

And that's when the battery died. This is with *no pipes* on it, no carbs on it, and a dying battery (not sure if that affects it all). All in psi.

Thanks!
 
Last edited:
For a cold engine and a dead battery, those numbers are good. The important thing is that they are fairly even, no dead or really low cylinder. I'd adjust the valve clearances, run it a thousand miles or so and check it again with a hot engine.
 
you need to test when warm and with throttle wide open but the numbers are all close to each other so looking good
 
Hard to warm up the engine and hold the throttle wide open when the carburetors are removed.
 
Sounds good, that's what I wanted to hear!

Unfortunately the bike is in too many pieces to test warm. The carbs aren't even on it yet. But it sounds like good news so far.

Once I get it all assembled, I'll start it up and take it to a shop to adjust the valves and sync the carbs.

Thanks!
 
srg said:
Once I get it all assembled, I'll start it up and take it to a shop to adjust the valves and sync the carbs.
Click to expand...

No no no no no ! If you can remove and replace carbs you can adjust the valves and synch the carbs.
Shops make theor money selling new bikes, not prolonging the usefullness of old ones.
Do it yourself. It's easy.
 
Why not save some $$$$ and do it yourself? It is not that big a deal plus you will need to know this later anyway.

Go to Basscliff's site to learn how it's done.
 
We all need to be able to wrench on these relics if we are going to have 'em:)

Besides, that's where the pleasure of owning something classic comes from.
Enjoy......

Larry
 
Yeah yeah, I suppose I should. I'm just excited to start riding it, so I guess I was taking the fast/lazy way out :-P

I also don't have any tools to do any of this. I imagine I need a set of gauges to sync the carbs and some sort of shim tool for the valves?

I'll read up on it and come back here if I have any questions.
 
Simple metric ratchet set, couple screw drivers, shim tool, sync tool, feeler gauge, can of cab dip, carb spray, and a fresh valve cover gasket is about all you need. The sync tool is kinda pricey, but you'll probably spend less money buying that stuff and there is something deeply satisfying about doing it your self.
 
Actually a 10mm wrench and a 19mm, phillip's head screwdriver and a feeler guage are all you need to check the valves. If they need an adjustment add a big zip tie.
 
If you have questions along the way, everyone here is willing to help. Also, if you need some hands on help or guidance, there are members here from Philly. Usually folks are happy to help out. Ray
 
tkent02 said:
Actually a 10mm wrench and a 19mm, phillip's head screwdriver and a feeler guage are all you need to check the valves. If they need an adjustment add a big zip tie.
Click to expand...

Ditto on that zip tie - but throw in a pair of pliers for a tight seam!

I put off checking my valves for way too long on my 850. It's considered critical maintenance, and it's deceptively easy. I was always intimidated by my manual and the fear that I'd screw something up. Takes just a little bit of time to check each valve - plus, neglect this and you eventually face burned up valves... I nearly had to learn that the hard way.

Zip tie method here: http://members.dslextreme.com/users/bikecliff/images/valve_tool_zip_tie.pdf

Pretty thorough description of what you'll be doing here:
http://members.dslextreme.com/users/bikecliff/images/gs850valve_adjust.pdf
 
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