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Compression

A

A2WheelCpl

Tuned and Synch'ed
Joined
Oct 29, 2008
Messages
30
I was wondering, when doing a compression test on a SP1000/CX 100 motor what sorta numbers should they be? I know they should be only about 10% differance between the two, but I can't find what they should be. Thanks, Biff
 
That's with a wide open throttle with both plugs out crank equal amount of time for both sides. My 83 SP has 170 lbs on both sides, 90,000 + miles heads have never been off, hell the valve cover gaskets are original.
 
100 in the right and 85 in the left.............. now is wasn't warm and I don't know if I did it right, I think I kept the other plug in and I know I didn't open up the throttle. I'll wait until the weather breaks a bit and warm it up and try it over again. The bike only has 14, 000 miles on it. and it surley doesn't look like 100 and 14,000 miles. We'll see
 
Without the throttle pinned open the number means little. Taking the other plug out is not as critical in my opinion but still a good idea.
 
If your numbers stay too low after the warmed up and full throttle compression test, do a leak down test, any car shop should have the tool and it takes only minutes. You just need to know how to set your crank in TDC with both valves closed.The leak down % will tell you something about how severe the problem is. Listen for air coming out of your exhaust, carburetors or crank case(just remove the dipstick) while doing the test and investigate: no valve clearance, worn valves or carbon build up from loose valve guides, or worn/stuck piston rings. Kinda nice to know what's up before you're advised to just redo your heads and buy new cylinder$$$$$.
If there is a lot of carbon try 'engine tuner' before deciding the big overhaul; spray in the intake while running the engine, then let it sit for as long as the instructions allow and fire it up again. Once the smoke clears from the neighbourhood, you might have an ok running engine again if the engine was reasonably sound to start with.
We sometimes work wonders with this stuff after for example an engine has run too cold due to a stuck open thermostat; engine tuner clears all the oily crap right out, cleans the valves and seats and actually does un-stick piston rings, so it's worth a $7.50 try.
Cheers, JR
 
thanks for the imput, I will try it when I get back from daytona (weather should be much better then)............. I can't believe the motor is that bad at only 14 thousand miles. Hopefully it might make it better, tnanks again
 
Compression test is utterly meaningless without throttles wide open. Pull both plugs, ground them out on engine block and then crank over. Use WOT. Check cold, then check hot. This will give you some idea of engine condition.
 
Feeling my through this stuff, I would have never believed open throttle would make that much differance. Cold/closed throttle, it was like 100 right and 85 left, but after you guys told me to check it open. Today I got 150 in both with it cold........ well, now I'm starting to at least get in a better mood ! (LOL) .......... thanks again, I'll keep ya posted when we come back from Daytona and I start to play with it again. ................ gee maybe if I take it to Daytona, someone will want to swap a Jackal for it?
 
A2WheelCpl wrote:
Feeling my through this stuff, I would have never believed open throttle would make that much differance. Cold/closed throttle, it was like 100 right and 85 left, but after you guys told me to check it open. Today I got 150 in both with it cold........ well, now I'm starting to at least get in a better mood ! (LOL) .......... thanks again, I'll keep ya posted when we come back from Daytona and I start to play with it again. ................ gee maybe if I take it to Daytona, someone will want to swap a Jackal for it?
Click to expand...

Are you going to the track on the 2nd and the Guzzi dinner ?
 
Yes we are. I don't think I've missed but one Monday night Pizza night in 10 years maybe more? (LOL) We'll be on new style Triumphs, mine's a Bonnie, my wife's a Thruxton. Sure wish they'd bring back the Wil Stoner swap meet and Concours at the track on monday's, it really was something I looked forward to.
 
I will be on a RED (faster) Norge licence plate "I HONK" or a V7 Classic Licence plate "V7C-1" haven't made up my mind yet and weather will play apart in the decision. Look me up and introduce yourself.

Dan
 
A2WheelCpl wrote:
Feeling my through this stuff, I would have never believed open throttle would make that much differance.
Click to expand...

Think about it for a moment. If the throttle is closed both the carb slides will be blocking the carb venturis with only the tiniest gap underneath through which air can pass. Even at cranking speed there isn't much time for air to pass under the slide when the inlet valve is open and the piston is decending on the induction stroke. There is no such thing as 'Suck'. The air is being pushed into the low pressure area created by the decending piston by atmospheric pressure outside the carburetor which is a measly 14 PSI.

A simple comparison.

Hold your nose and inhale deeply with your mouth wide open. Easy innit, your lungs fill instantly near enough. Now purse your lips and pretend you're kissing a particularly unpleasant and incontinent old relative and try inhaling again. A lot more difficult and takes a lot longer to get yer lungs full doesn't it?

That's why you take the carbs off or hold the throttle fully open. An engine is simply a self propelling air pump. The aim is to introduce the correct amount of air and fuel into the cylinder through the inlet valve to produce the required amount of work. At idle all the engine has to do is produce enough power to keep the crank and valvetrain working. When it is propelling the vehice the pumps volumetric efficiency must be increased, this is done by introducing more air/fuel mixture by 'Unblocking' the venturi.

Remamber nothing is 'Made' in the engine. Exactly the same number of molecules come out of the exhaust pipe as go in through the carburetor, (Bar a few billion that blow past the rings and leak past the valves etc.) It's just that they go in calm and come out excited. When the fuel burns it creates heat which causes the gas in the combustion chamber to expand. Since the only bit tht can move is the piston it pushes the piston down the bore. As the piston decends the volume in the cylinder increases so the temperature drops and the force acting on the piston diminishes. If everything is designed right by the point that the exhaust valve starts to open what little unused energy that isn't heat can be utilised to cause the gas to exit out of the exhaust port. If the exhaust is tuned properly a combination of the sonic waves in the pipe and the mass of the exiting gas keeping it moving will, at the engines ideal RPM, create a low pressure area in the cylinder just as the inlet valve opens again. This greater than atmospheric pressure discrepancy helps ensure the expulsion of the spent charge and encourages the ingress of the new, fresh charge, and so it goes........

Pete
 
Anyone who has met me will attest that I don't have a big head. And ugly one maybe, but not big.

Yes, I know and understand this stuff and I don't suffer gladly being told I'm wrong by retards. I am MORE than willing to be told I'm wrong by clever people because I then learn stuff.

I'm a good teacher. If I have one skill it is being able to make the comparatively complex understandable. The reason for this is that I had good teachers.

I'm always happy to share what I know and if I'm wrong I will always happily admit it. I have no axe to grind and have enough confidence to not feel that I either have to bluster to cover my ignorance or claim any knowledge greater than I posess.

I am also well into my fifties and happy with my life on the whole. I don't need to bullshit because, being comfortably off, I have nothing to *Gain* by doing so. My skills are what they are. The way I present myself is as I am. If people find me caustic and offensive on occasion I apologise but suggest, with my hand on my heart, that if you find me offensive you should Harden The Fuck Up.

I'm really quite nice in person, even with the body hair and the smells.

Pete
 
draidt wrote:
Chuck in Indiana wrote:
Pete, you have a gift..:laugh:
Click to expand...

Jeez Chuck he's got a big enough head already !!!!!!!:cheer:
Click to expand...

:laugh:
IMG_7872.jpg
 
pete roper wrote:
Anyone who has met me will attest that I don't have a big head. And ugly one maybe, but not big.
Click to expand...

Quite so, quite so... in fact, it's so small one might liken it to a pin! :laugh:














Sorry, Pete: I couldn't resist. Too tempting a straight line to pass up! ;)
 
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