compression check question!!!!

[chadsheffield]

1997 speedster.
Just got my cylinders done and new pistons and rings and put it all back together with new gaskets. compression read a little under 120 on both but i havent put the exhuast system on yet or manifold. is that the reason why its not around 150? i thought it wouldnt matter but hopefully wrong. if that isnt the case please help before i finish putting it together if i shouldnt have too.

 

[CaptSteve]

On a car that uses intake and exhaust valves with seats, your right it doesn't matter. However, these engines use reed valves and rave valves, so I think you really need to have the whole engine pretty much together to get an accurate reading.

Having said that, I would have expected the numbers to be higher, but I have never checked with the engine apart.

 

[Phildoo]

If it's all new the rings haven't seated yet. Like a car.
I would imagine.

 

[LouDoo]

It's also going to take some time for the rings to wear into the cylinders (probably about 10 hours), also you are testing without or with very little lubrication.

Lou

 

[chadsheffield]

ya my rings probably just havent seated now that i think about it since i havent even let it start yet. Thanks guys i appreciate the help

 

[Dr Honda]

On a new rebuild... you should still have more pressure than that. (no, having the exhaust off won't make a difference)

1) did you check the ring end gap?
2) did you check the squash gap?
3) are you sure you gauge is good?

The rings shouldn't be dry at this point, since you should ave lubed the parts as you assembled the engine.