WR400 Compression issues
Posted November 18, 2013 - 02:54 PM
I have asked similar questions before, but am now trying to get the bike running again.
I've got a 2000MY WR400. Over time it got harder to start, particularly when hot. So, I checked and adjusted the valve clearances. It had been put away after washing and lacked compression, so at the advice of people on here, I put a little oil down the bore, and it started straight up. Since then it's refused to start, and I think it's a low compression issue.
I don't have access to a leak down tester, but have compression tested it, and get around 70psi. With a little oil down the bore, I get around 90psi.
Can someone tell me what values I should be expecting, as I can't find anything in the manual?
I'm thinking maybe it's time for a piston, as some on here have already suggested. What are people's thoughts? I'd like to be sure it's that before tearing it apart.
Posted November 20, 2013 - 08:43 PM
I would think anything under 150 psi would require rings / rebuild. Normal range is 170 - 240 (I think...)
Only thing running on 70-90 psi is a lawn mower!
Posted November 20, 2013 - 09:23 PM
You have no auto decompression system, so you are absolutely low on compression, BUT, YOU ARE TESTING A COLD MOTOR which means just about nothing
A 14 year old motor; if you have not rebuilt it, if you have no proof that the prior owner has rebuilt it, it's time to rebuild it. The top end anyway...