Compression # on starting S&S 107?
- Thread starter EricH
- Start date
john sachs
Well-Known Member
What's the cranking compression with the releases disconnected? andddddd how are they checking the compression?
Throttle WIDE OPEN, :up: and crank until the gauge won't go any higher. :2thumbs:
John
Throttle WIDE OPEN, :up: and crank until the gauge won't go any higher. :2thumbs:
John
A difference of opinion about hot and cold compression readings; I want to know my cold compression reading. Why? Because, compression is all about initial start. Initial gas in the tank. Initial points open and close, or more or less, we have spark.
It says, the suggestion from s/s is like saying, warm up the bike so we know gas is in the system. Warm up the bike, so we know it has spark. Warm up bike... Hey, wait a minute!?! Bike does not start. I have my 3gaymigos, but someone says, my bike does not run, start my bike up, see if it has a tight valve. Now, what is the compression it holds it open in a warm condition?
You figure it needs to be torn down. Did you first set the valve lash before you tore it down, let alone make your initial C-check is the very first thing [Y0u set valve lash first].
Same says, cold crank my engine. If one day my bike does start, I need to do the very first thing about a no start condition, so that is out of the way, right? I have two to go. So, is it not smarter to check cold?
When a bike does not [initially] start, it usually has some low or no compression to begin with. When you set the valve lash, you do not warm up a bike, then check v-lash, right?
When you see a 10% difference between cylinders, it is tear down time.
When you have less than 100 psi, it usually won't start.
When you warm it up, it may start at 100 + psi, it may take more heat to get her going, i.e., cranking it over > a lot!
When you have over 175 psi cold, it is decent.
When you have over 200 psi cold, you are doing something right.
When you have 145 psi, it is about done or say, this is rebuild time, not at 100 psi...
... When you broke out in a sweat trying to start it.
It says, the suggestion from s/s is like saying, warm up the bike so we know gas is in the system. Warm up the bike, so we know it has spark. Warm up bike... Hey, wait a minute!?! Bike does not start. I have my 3gaymigos, but someone says, my bike does not run, start my bike up, see if it has a tight valve. Now, what is the compression it holds it open in a warm condition?
You figure it needs to be torn down. Did you first set the valve lash before you tore it down, let alone make your initial C-check is the very first thing [Y0u set valve lash first].
Same says, cold crank my engine. If one day my bike does start, I need to do the very first thing about a no start condition, so that is out of the way, right? I have two to go. So, is it not smarter to check cold?
When a bike does not [initially] start, it usually has some low or no compression to begin with. When you set the valve lash, you do not warm up a bike, then check v-lash, right?
When you see a 10% difference between cylinders, it is tear down time.
When you have less than 100 psi, it usually won't start.
When you warm it up, it may start at 100 + psi, it may take more heat to get her going, i.e., cranking it over > a lot!
When you have over 175 psi cold, it is decent.
When you have over 200 psi cold, you are doing something right.
When you have 145 psi, it is about done or say, this is rebuild time, not at 100 psi...
... When you broke out in a sweat trying to start it.
EricH
Member
So you are telling me if my bike is registering 130# while cranking the engine it most likely needs a rebuild? Where can I obtain this info for my service tech?
If so, this thing is hitting the classifieds! :angry:
Thors
Active Member
I wouldn't jump to any conclusions. Sven's answer may or may not be valid, but it doesn't address the question. Comp releases... John has the answer - test with them connected, then test without. If the readings are different they are working to some degree. It's quite possible 130# is good with the comp releases working...or they could be toast...or partially blocked with soot....
What led up to the starter and battery replacement?
What led up to the starter and battery replacement?
EricH
Member
For the past year, the bike would drag when pushing the starter button. Once the engine would turn over, it would start. However, the last time I shut the bike off and started it 30 seconds later. <Click> and all electronics went dead. It would reset after several hours and then do the same thing.
The place I took it had the battery and starter load tested. Both were shot. He replaced both (unaware of the names since I haven't picked it up yet) and says it starts right up now.
He believes the compression releases are working but does not really have any technical info telling him what compression should be if they are. He merely stated that the compression is reading 130# while cranking. Does this mean they are working, or not. ???
The place I took it had the battery and starter load tested. Both were shot. He replaced both (unaware of the names since I haven't picked it up yet) and says it starts right up now.
He believes the compression releases are working but does not really have any technical info telling him what compression should be if they are. He merely stated that the compression is reading 130# while cranking. Does this mean they are working, or not. ???
Thors
Active Member
Personally, I would ask the mechanic to re-test with and without the comp. releases plugged in. If it's #180 with and #130 without, I'd guess they are working. If it's #130 both...not so good... Never worked on a chopper, but it seems the wires should be easy to find with all that clearance. My Pit is another story...
What you want to see is another angle of the cylinder's health. This is called a leak down test. It goes something like this:
1. I want air to push a gauge's needle to 100 on a scale. This represents something is open.
a. A bent valve or a tight valve, or a burnt valve, can move that scale to 100.
b. A leaking head gasket can move that scale to read a lower push of air at the gauge. It may be a pinhole leak. I may set the needle to 80, or a tiny leak. Not an open 100% leak, now call it.
c. A ring gap is you leak there and that is a loss of compression. This leak down is another angle as to view the health of these combined parts that all make up that one number, or the compression number.
2. Using the leak down tester has a whole different number percentage, and this is more we think of using the compression tester as a book's gauge. For example, book calls for a working range of 145 ~ 228 psi.
a. Notice how using a compression tester, 145 is the breakout number.
b. 145 is your 'serviceable limit' number. This says 144.9999999 psi is your breakout number.
c. I believe I have video of my compression numbers that read, in the 220 range. Therefore, I do not need a leak down tester. I am within book range. I have a high mileage bike with robust compression.
3. What I am suggesting to you is, buy the tool, buy the compressor. This tool setup is what you take to your classifies with. Before I come buying your bike, I don't need to know about your battery condition, fuel system. I more need to check a dead engine this way:
a. Find TDC (top dead center) on your potential buy. Stick it in top gear. Jam a long rod thru the wheel and sprocket. This jams the wheel from moving a valve from opening [in either direction].
b. Dial out the gauge to read 0%. This means the leak down is closed; no air is escaping. You set the connectors together, watch the needle's next move.
c. This is where an ideal number at a leak down is 1-2%. 1 is better, but still means, air loss at the ring gap. If we had the head off, filled the head with liquid, it should not leak. Therefore, the 1% drop is a perfect specimen.
d. If we saw 9% leak, this is tear down time. This is 100 psi time. This is watching the cylinders having a 10 to 15% pressure difference between cylinder psi's, using a compression test reading. It still means big bucks to return to 1% leak.
Again, if you do not have a spec book, cannot match breakout numbers in the shop man you will pay selling a high compression engine without reading a leak down first. Think you are upset now.
Quit guessing!
Harbor China Crap 38 bucks US.
Cylinder Leak-Down Tester
BadBrad
2005 Pitbull
Here's a post that Carlos sent me a while back that helped me. Should help you as well:
Got this from Biketalk.com
Your numbers look weak, hope this helps.
With a warm engine, turn off the fuel from the tank, make sure the choke is off and the transmission is in neutral. Remove both
spark plugs and insert the gauge adapter in one spark plug location. Now, holding the throttle wide open, turn on the starter motor
and read the pressure indicated on the gauge. Then repeat the procedure on the other cylinder. The figures on the next page give
some idea as to the significance of different pressure readings. Also some gauges have a rubber tip instead of a screw in adaptor.
Either way, reading the static pressure of your engine should be fairly easy. Generally, higher static pressures mean more
torque at lower RPM ranges but the trade off is that above a certain point (around185 PSI) the risk of detonation enters the picture. What happens at higher RPM is less predictable and can’t be easily determined from a static pressure reading. What is important is that the cam timing, duration and compression ratio all be properly matched so that each compliments the others.
ENGINE TUNING INFORMATION
STATIC COMPRESSION AND ENGINE TUNING
When installing cams with high lifts and long durations, a few general observations are worth keeping in mind. Remember that additional cam duration can produce more usable power but too much duration may actually hurt overall performance. The problem of poor engine response begins when too much duration results in lower cylinder compression pressure (at low RPM) which in turn can reduce low RPM torque and power. Too much duration in a camshaft is not necessarily a good thing.
Static Compression Pressure Ranges and Engine Performance:
Less than 115 psi: poor low speed response, hard starting. Pistons and cams well not matched or worn rings, valves.
125 to 145 psi: OK for stock or modified street motors. On the lower end of the best range for a stock motor.
145 to 165 psi: OK for modified street motors. Static pressures in this range will be best for stock street motors.
165 to 180 psi: Marginal for large displacement street motors, possible hard starting, detonation and overheating.
Over 180 psi: These are high performance numbers. Street motors over 185 PSI may need compression release.
The above numbers are not absolute but the point is that static compression is important. Proper matching of cams and compression ratio will allow engines to be modified for more performance and still run smoothly in street engines.
Carlos
__________________
When I first measured my compression, I did not follow the procedure listed above and got numbers close yours. I didn't remove both plugs and didn't apply throttle. After following this procedure, both my cylinders registered 185 psi. It was my first time to use a gauge to measure cylinder pressure, so live and learn. If your mechanic used the method above, both plugs out, engine warm, apply full throttle when motor is turning and you still got 130 psi, you probably have issues going on somewhere. Other than a .600 cam and RPGeez 2 into 1 exhaust, my dog is stock.
Got this from Biketalk.com
Your numbers look weak, hope this helps.
With a warm engine, turn off the fuel from the tank, make sure the choke is off and the transmission is in neutral. Remove both
spark plugs and insert the gauge adapter in one spark plug location. Now, holding the throttle wide open, turn on the starter motor
and read the pressure indicated on the gauge. Then repeat the procedure on the other cylinder. The figures on the next page give
some idea as to the significance of different pressure readings. Also some gauges have a rubber tip instead of a screw in adaptor.
Either way, reading the static pressure of your engine should be fairly easy. Generally, higher static pressures mean more
torque at lower RPM ranges but the trade off is that above a certain point (around185 PSI) the risk of detonation enters the picture. What happens at higher RPM is less predictable and can’t be easily determined from a static pressure reading. What is important is that the cam timing, duration and compression ratio all be properly matched so that each compliments the others.
ENGINE TUNING INFORMATION
STATIC COMPRESSION AND ENGINE TUNING
When installing cams with high lifts and long durations, a few general observations are worth keeping in mind. Remember that additional cam duration can produce more usable power but too much duration may actually hurt overall performance. The problem of poor engine response begins when too much duration results in lower cylinder compression pressure (at low RPM) which in turn can reduce low RPM torque and power. Too much duration in a camshaft is not necessarily a good thing.
Static Compression Pressure Ranges and Engine Performance:
Less than 115 psi: poor low speed response, hard starting. Pistons and cams well not matched or worn rings, valves.
125 to 145 psi: OK for stock or modified street motors. On the lower end of the best range for a stock motor.
145 to 165 psi: OK for modified street motors. Static pressures in this range will be best for stock street motors.
165 to 180 psi: Marginal for large displacement street motors, possible hard starting, detonation and overheating.
Over 180 psi: These are high performance numbers. Street motors over 185 PSI may need compression release.
The above numbers are not absolute but the point is that static compression is important. Proper matching of cams and compression ratio will allow engines to be modified for more performance and still run smoothly in street engines.
Carlos
__________________
When I first measured my compression, I did not follow the procedure listed above and got numbers close yours. I didn't remove both plugs and didn't apply throttle. After following this procedure, both my cylinders registered 185 psi. It was my first time to use a gauge to measure cylinder pressure, so live and learn. If your mechanic used the method above, both plugs out, engine warm, apply full throttle when motor is turning and you still got 130 psi, you probably have issues going on somewhere. Other than a .600 cam and RPGeez 2 into 1 exhaust, my dog is stock.
Last edited:
BadBrad; Got this from Biketalk.com:
There are only a few degrees before you start tagging valve to piston. It says, within those few degree changes, you do not have 14.7 enter is what abstract is saying.:roll:
If less air when in, how did the piston draw, grow short? Did they change the piston bore? No. Did they swap rod lengths? No. So, will the same amount be drawn in? Yes. Will the valves leaving their seats too late or too early effect the torque? Yes.
Once again, the basics score one more time, you read some whack on line. Now, dispute it. Get carlos in here 
And after that, it goes downhill. To me, carlos has no clue with every step in his abstract.
Now, do you see anywhere in that rip of instructions is there mention of grounding plugs? Not only that, have you ever seen a whoosh of raw gas shoot out of the open cylinder with plug removed? MMI (missed most instructions) graduates over there?
See how the 'more air' kind of guy thinks? If he knew duration, it says, I blow off on the power stroke too early, or I am burning ignition too late. The same amount of air went in. The same compression is going to show. The same 14.7 (pressure) entered and closed on the stroke.
There are only a few degrees before you start tagging valve to piston. It says, within those few degree changes, you do not have 14.7 enter is what abstract is saying.:roll:
If less air when in, how did the piston draw, grow short? Did they change the piston bore? No. Did they swap rod lengths? No. So, will the same amount be drawn in? Yes. Will the valves leaving their seats too late or too early effect the torque? Yes.
Once again, the basics score one more time, you read some whack on line. Now, dispute it. Get carlos in here
Bhawkins854
Member
Sounds simple but did you feel the comp. Release to see if its picking up? When you hit the start button you should be able to feel them snap in and then out when you come off the start button.
BadBrad
2005 Pitbull
Sven may have a point, but I don't know what the hell it is! He's either way over my head or he's on dope or dog food. There's a right way and obviously an incorrect way to read compression. In Sven's own words, I was a "squid" when I first attempted to read the compression on my cylinders. With Carlos' instructions, I graduated to an........octopussy? Either way, I did learn the correct method to read compression on the cylinders and my readings changed dramatically using the correct method. All I'm saying is that if you don't use the common/correct method to read compression, then your results are not going to give the information that might lead you to the root cause. The method Carlos gave me resulted in readings that showed me that my compression was good and the root cause of your problem may be something that's not related to compression. Get a correct reading using the correct method for compression readings and let's go from there.BadBrad; Got this from Biketalk.com:
And after that, it goes downhill. To me, carlos has no clue with every step in his abstract.
Now, do you see anywhere in that rip of instructions is there mention of grounding plugs? Not only that, have you ever seen a whoosh of raw gas shoot out of the open cylinder with plug removed? MMI (missed most instructions) graduates over there?
See how the 'more air' kind of guy thinks? If he knew duration, it says, I blow off on the power stroke too early, or I am burning ignition too late. The same amount of air went in. The same compression is going to show. The same 14.7 (pressure) entered and closed on the stroke.
There are only a few degrees before you start tagging valve to piston. It says, within those few degree changes, you do not have 14.7 enter is what abstract is saying.:roll:
If less air when in, how did the piston draw, grow short? Did they change the piston bore? No. Did they swap rod lengths? No. So, will the same amount be drawn in? Yes. Will the valves leaving their seats too late or too early effect the torque? Yes.
Once again, the basics score one more time, you read some whack on line. Now, dispute it. Get carlos in here
john sachs
Well-Known Member
If you do it my way, which is the CORRECT way, :argue: you can't go wrong. :2thumbs: You WILL get an accurate reading with the compression releases disconnected. Cold cranking is the favorite method hands down....
John
John
TapioK
Well-Known Member
Mechanic I’m not, but just remembered reading about this: Dan's Motorcycle Compression Testing
and Testing BMW motorcycle compression
Tapio
and Testing BMW motorcycle compression
Tapio