sleddineinar
VIP Member
I've heard there is a correct method to testing the compression on a sled. What is that? Also on a Redhead 700 with reed spacers and head gaskets thinned to 1 layer, what should the proper compression be? I thought I would like to test mine just to have a benchmark...
the correct way is to
you should do this to a warm engine(more accruate)
take measurements cold and hot if you can for your notes
remove all plugs and pull the sled over a few times,
hold the throttle open, pull it over at least 3 times.
what ever number you pull it over, use the same number for the others.
the compresion number is going to vary from guage to guage depending on the lenght of hose to the guage and the size of the hose. this area will now be added to the combustion chamber size and give a lower compression than a guage with shorter hose.
so, dont go by what some guy got for compression accross the country on his sled with his guage. use your guage on your sled and if you want to compare use your guage on a few other sleds of the same model then you will have a real comparison. keep track of what your sled has and then later you will know what is high, low etc.
mostly you are looking to see if you have any large variation between cylinders.
on that sled, Dont use regular and make any 2-3mile wide open runs.
you should do this to a warm engine(more accruate)
take measurements cold and hot if you can for your notes
remove all plugs and pull the sled over a few times,
hold the throttle open, pull it over at least 3 times.
what ever number you pull it over, use the same number for the others.
the compresion number is going to vary from guage to guage depending on the lenght of hose to the guage and the size of the hose. this area will now be added to the combustion chamber size and give a lower compression than a guage with shorter hose.
so, dont go by what some guy got for compression accross the country on his sled with his guage. use your guage on your sled and if you want to compare use your guage on a few other sleds of the same model then you will have a real comparison. keep track of what your sled has and then later you will know what is high, low etc.
mostly you are looking to see if you have any large variation between cylinders.
on that sled, Dont use regular and make any 2-3mile wide open runs.
Last edited:
sleddineinar
VIP Member
I forgot that I posted this thread. It just thought about it today, couldn't even remember my question until I found it. Thanks. Do you know what a ballpark figure should be for the compression?
SNOWRULES
New member
on my 2000 sxr with one layer of head gasket i used to get 140-150psi cold depending on the tester i used. that was with 10 000 km on the motor
FuzzButt
New member
I get just about 120 on my 600 twin with one layer gasket and about 2000 miles on the rings.
Compression is a subjective thing that is really just a variable. You can really only compare apples to apples. Same gauge, same conditions, same testing style.
Also the readings the gauge gives us are only at very slow engine speeds. Since we don't usually run out sleds at 40 RPM the reading you get is a real limited sample.
Basically all the readings are really good for is to compare cylinders with each other to determine the condition of the motor at that time.
For instance the last compression test I ran was back in August on my Johnson V4 outboard. On the right pair I got the same reading of 145 PSI. The left pair I got 135 PSI. The right side was repaired at some point before I purchased the motor and these results show that. So now I have a baseline and if the readings drop I will know where to look.
Compression is a subjective thing that is really just a variable. You can really only compare apples to apples. Same gauge, same conditions, same testing style.
Also the readings the gauge gives us are only at very slow engine speeds. Since we don't usually run out sleds at 40 RPM the reading you get is a real limited sample.
Basically all the readings are really good for is to compare cylinders with each other to determine the condition of the motor at that time.
For instance the last compression test I ran was back in August on my Johnson V4 outboard. On the right pair I got the same reading of 145 PSI. The left pair I got 135 PSI. The right side was repaired at some point before I purchased the motor and these results show that. So now I have a baseline and if the readings drop I will know where to look.