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Piston compression psi help

You know the answer; posted on HDForums and Bubbie has confirmed. Just remember that the numbers are calculated and while they should match up to those produced by a compression test, they may vary a bit based on altitude, actual deck height and chamber volume. Stock TC heads should run between 85-86cc but I have seen them measure near 90cc.
 
As for altitude I'm at sea level. (The ocean is right across the street).
Looked at Big Boyz calculator and it seemed to require more info than I have access to for a PSI number.
 
Hey I need some help finding the correct PSI reading when doing a compression test on a 2012 wide glide with a stock unmodified 103 engine. Anybody know what it is? All the searching I've done here and other places has only given me PSI readings on modified engines. Not a stock 103.

Thanks in advance for any help

What numbers are you getting so far with your compression test. That might be a better way to represent question, for the difference in numbers can have multiple reasons. And how are you performing compression test and have you compared dry and wet compression test and what are those numbers. Is there a problem with the performance of bike?
 
As for altitude I'm at sea level. (The ocean is right across the street). Looked at Big Boyz calculator and it seemed to require more info than I have access to for a PSI number.

You have the numbers. Displacement is 103"; 3.875 x 4.375; OEM head gasket at .045", chamber volume at 85cc (the default value); piston dome volume of -1.5cc (the default value); ignore deck height for your purposes. The piece missing from the BigBoyz calculator is the cam selection/intake valve close which is 30* and you don't have to adjust for sea level.:p

I am interested in answers to dbmg's questions as well. I have pulled compression tests on several 103" motor, stock and with the race kit installed and have never seen one under 190psi; have seen them as high as 210 with the race kit.
 
I have compression release valves on the 103 engine correct? Do they need to be disabled by a fuse pull?
Before I go any further with testing the compression let me ask if I'm missing a step. So far I have first heated the engine to operating temps. Then screwed in the compression test hose. Held the throttle wide open and turn the engine over until the needle stopped moving. 6 or 7 cranks. Both cylinders were about 5 to 6 psi apart. One a little over 120 psi the other under 120.
Side note, the spark plugs were "ALL" black with soot. Not wet or shiny black but flat black. Is that a symptom of blow-by?
And thanks for the calculator # I'll try them next.
 
I have compression release valves on the 103 engine correct? Do they need to be disabled by a fuse pull?
Before I go any further with testing the compression let me ask if I'm missing a step. So far I have first heated the engine to operating temps. Then screwed in the compression test hose. Held the throttle wide open and turn the engine over until the needle stopped moving. 6 or 7 cranks. Both cylinders were about 5 to 6 psi apart. One a little over 120 psi the other under 120.
Side note, the spark plugs were "ALL" black with soot. Not wet or shiny black but flat black. Is that a symptom of blow-by?
And thanks for the calculator # I'll try them next.

If you had compression releases you would have them mounted near where the spark plugs are and are mechanical. If bike is running fine install a new set of O.E. plugs and go for a ride. Do you start and stop your bike frequently with out running bike till complete warmed up. You may have no problem at all especially if both plugs are identical.
I would not do a compression test on a hot engine for may run the risk of stripping out the aluminum threads for the spark plugs. How are you disabling the spark and fuel while performing compression test???
 
Ok thanks. I was confused by the pull a fuse suggestion I received. I thought the valves were mechanical. Still do they need to be disabled somehow to correctly preform this test?
As for the spark disabling ,All I did was remove them. The fuel was not disabled. No on/off valve on the tank because its fuel injected. But if you think that not turning it off has affected the test let me know. Then pulling a fuse is an option to shut off the fuel. If you have the fuse number just let me know. Or I'm sure its listed on the bike.
 
Ok thanks. I was confused by the pull a fuse suggestion I received. I thought the valves were mechanical. Still do they need to be disabled somehow to correctly preform this test?
As for the spark disabling ,All I did was remove them. The fuel was not disabled. No on/off valve on the tank because its fuel injected. But if you think that not turning it off has affected the test let me know. Then pulling a fuse is an option to shut off the fuel. If you have the fuse number just let me know. Or I'm sure its listed on the bike.

Remove the system relay from fuse block to disable ACR. IIRC, system relay is #11 in fuse block location; the procedure is in the service manual. If you plan on working on your bike; get one. Don't worry about getting the motor to operating temp; CCP = "cold" cranking compression. If CCP is low on "cold" motor, then you run the test on a "hot" motor to see if there is a significant difference. If the top end is in good condition, you won't see much difference.:s If there is a significant increase in CCP, rings are not sealing. If there is a significant drop in CCP, time for a leak down test.

As for your plugs, unless you do a "plug cut" it's hard to judge. Once you do the compression test, ride the bike, let the motor see some high rpms. When you roll back into the garage, clutch, engine off and pull the plugs. True plug cuts are done with new plugs and the motor is shut off in the condition one wishes to read the plugs, usually WOT. Install fresh plugs, get the motor up to operating temp and run her up to near the rev limiter, say in 4th gear. Clutch, kill the motor, pull to the shoulder and pull the plugs. If one wants to check AFR at cruise, same procedure. New plugs, operating temp, cruise for a bit in top gear, light load/throttle, clutch, kill motor, pull to the shoulder, pull plugs.:s
 
All this info I am asking for is to help me check on the condition of a used bike I'm looking into buying. I want to move up from a Sportster to something bigger that will carry two. Checking the compression is a way for me to get an idea if the bike has any hidden issues. So no I don't have a manual yet. "If" I get one of the bikes I considering then I will buy one for that particular model. Not all the bikes I'm checking out have the same engine.
Anyways Thank you to all who gave me helpful advice
 
The manual I have says motor hot, remove air filter, Full throttle (kills fuel injectors), 6-7 revolutions, 125 psi minimum with less than 10% difference from front to rear.
 
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