compression testing question

[dedede]

Building 78 cafe style bike now working on frame,suspension, brakes,ect. Engine is on stand no carbs and no exhaust. Decided I would check compression I put a little oil in each cylinder and cranked by hand. Then used jump pack on starter and came up with 250 on one side 175 on the other I have done nothing to the motor yet 22000mi started it when purchased and run it for a minute. Is this normal for a bike that sat with no adjustments. Any helpful comments welcome.

 

[gggGary]

Define "a little oil"? 250/175 are not normal (believable?) XS650 numbers, take the plugs out, crank it for a while to blow out excess oil then test compression again. If the starter is spinning it good about 150 155 is a healthy engine. anything over 100 is acceptable for one that hasn't run for quite a while. I kinda doubt you could kick over an engine with 250 of compression. The highest I have seen out of an XS650 is 170, rumour was it had a 750 kit but no way to know for sure now.

 

[dedede]

Thanks gary for your reply I was hoping to here from you or one of the other gurus. I have been snooping here for sometime during this little build and have a lot of respect for your knowledge. An ounce or so of oil in each cylinder cranked by hand and then with jump pack I an now engine expert but have been tinkering since the early 70s it seemed real high to me after reading many posts here.

 

[dedede]

Also it is a new tester just received it today.

 

[speez]

you should do a blow-by test, i think its more acurate but let the gures answer that

 

[dedede]

I'll try it again tomorrow gettin late. thanks

 

[gggGary]

The old saw on compression testing, is the cylinders should be close to each other and that, that matters more than the number.
PS I am no guru, just an old fart.
Leak down is more useful but a real (NOT harbor fright) gauge is serious money.
More better answers should be coming along.
Yeah we want to hear the results of a retest.

 

[speez]

i made mine it very easy to make,20 bucks heres basic setup...

http://en.wikipedia.org/wiki/Leak-down_tester.

 

[dedede]

OK rechecked today 175 and 173 wish I had a picture of the 250 thanks for the posts. WhenI get time I'll post pics of the build.

 

[gggGary]

That sounds good, a first sign of a healthy engine....