Low compression question.

[Corey13]

My friend has a 02 400ex with low compression that i have a chance to buy. He rebuilt the top end once because it needed to be done, then it had low compression after that. So he rebuilt it again and it still has low compression. He knows what he is doing also so i dont think he did it wrong. So my question is what can be causing it to have low compression?

[f150mann]

two rebuilds and lowcompression,he doesnt know what hes doing. maybe the cylinder is wore and needs a bore? so theres blowby with astock piston/ring on the wore cyl

[Corey13]

Im pretty sure it has a wiseco piston in it. I am going to go take a better look at it tonight. I am getting it for a pretty good deal but want to make sure i can fix the motor without sinking alot of money into it. Once i get it i was going to go through the motor and try to fix the problem, but i figured i'd post and see your guy's opinions on this.

[Corey13]

If the cylinder is wore, am i best off boring it to a 416 and getting a 416 kit or what?



Originally posted by f150mann
two rebuilds and lowcompression,he doesnt know what hes doing. maybe the cylinder is wore and needs a bore? so theres blowby with astock piston/ring on the wore cyl

[zrpilot]

Define low compression, because remember the stock cam has a de-compressor that lowers compression at cranking speeds.

[Corey13]

Once i go and take a look at it and find out more about it i will tell you exactly what i mean by "low compression". my buddy said after he rebuilt the top end it would run good for a while then it started to get low compression. I was also thinking about the de-compressor.