Compression test ST1100

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Oslo, Norway
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ST1100AX
Experience with "Compression test" on ST1100, what values do you get in "psi" on a warm vs cold engine?

Thinking of the procedure, top-charged battery, warm engine, full throttle, all spark plugs out, turn engine with starter on each cylinder until the pressure gauge reaches the top.

For those who have also tested on a cold engine, what difference?
 
Question: Would you ground the spark plug leads to the frame or to some wire that leads to the frame --to give that high voltage electricity a place to go if it can't go through the spark plug?
 
gunsmoker said:
Question: Would you ground the spark plug leads to the frame or to some wire that leads to the frame --to give that high voltage electricity a place to go if it can't go through the spark plug?
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Never on car or motorcycle, disassembling ignition cables and letting them hang freely during a compression test.
 
gunsmoker said:
Question: Would you ground the spark plug leads to the frame or to some wire that leads to the frame --to give that high voltage electricity a place to go if it can't go through the spark plug?
Click to expand...
Don't understand the purpose of the action in your question...
 
On some electronic ignition systems not allowing the high voltage generated by the ignition system to discharge somewhere can cause damage to one of the electrical components. Grounding the spark plug wires allows this electrical energy to safely dissipate to ground. I doubt that this is the case with the ST1300 as it is old technology. Doing so also prevents accidentally shocking one's self if you get to close to one of the high tension wires. Unexpected flash explosions can be created if the high tension wire is left close enough to a ground source near a spark plug hole when the engine is being cranked. The un-burned air/fuel being expelled can be unexpectedly ignited in your face if you are in the wrong place. This is more of a concern with carbureted engines as fuel is drawn in whenever the engine is cranked over. With fuel injected engines there should not be any fuel being injected if, using the ST1300 as an example, the instructions state to unplug the fuel pump which prevents any fuel from being injected. Grounding the high tension wires prevents the possibility of any of these things from happening. It is often easier to simply disable the ignition system completely rather than trying to ground all of the spark plug wires.
 
I have no experience with the aforementioned problem, it's just making the most of a situation. We're talking about a 1999 ST1100 where this is not a problem.

My question was what PSI readings you've gotten from a compression test, cold or hot engine?
 
Have you tried turning the spunkonator down to level four, and then ramping up the gauge on your farkle convertor?

Just a suggestion seeing as how helpful the other comments here have been.
 
When I tested my st1100 all 4 holes where between 140 and 145 PSI. It seemed like a low number yet they were all within a few psi of each other and the bike ran great. I think I'd look more for close numbers between the cylinders than a high psi.
 
CV carbs make it difficult to get an accurate compression measurement. Opening the throttle (butterfly) will not cause the slide to fully open. The video above shows readings obtained with the carbs removed. I can't spin wrenches fast enough to warm the engine up, remove the carb assembly, and take 4 readings. But that's just me.
 
static said:
CV carbs make it difficult to get an accurate compression measurement. Opening the throttle (butterfly) will not cause the slide to fully open. The video above shows readings obtained with the carbs removed. I can't spin wrenches fast enough to warm the engine up, remove the carb assembly, and take 4 readings. But that's just me.
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The above is the most correct. The CV slides are closed, impede airflow, leading to low numbers. AND the above junk yard engine on video is no way at operating temp...
I have done a compression test on 3 separate ST1100's while stone cold and carbs installed ( funny I've never done one at temp). All of them were between 170-180 PSI.
 
AI overview:
A compression test on a Honda ST1100 requires the engine to be warm, with all spark plugs removed and the throttle held wide open. You should see readings in a healthy range, such as 120-150 psi, but the exact spec should be checked in a service manual. It is crucial for the two cylinders to have consistent readings, within about 10% of each other, for the engine to be in good health.
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Will come back with measurement results on both cold and hot engine as soon as I have done the test. Have run a pressure test and no leaks on valves. Pasting results from search on AI search shows 120 - 150 PSI, I note @John OoSTerhuis numbers from the workshop manual on the new engine. This is an engine that has driven 105,000 kilometers so expectations for results from the workshop manual are not there, but expect equal compression on all four as there are no leaks on the valves and the engine runs smoothly and nicely.
 
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