Ec300 top end rebuild observations

[Eric K]

The last time I previously had the top end apart on my ’06 EC300 was to tune the squish band. The engine at that time had 41 hours on it since new. The top ring end gap measured 0.017”. Compression measured 190 psi after tuning the squish band. That was the original piston and rings, which I left in.

Now the engine has 90 hours since new – an additional 49 hours since I last had it apart. It still had the original piston and rings. The top end ring gap measured 0.018”. Compression measured 188 psi.

Overall, very little wear.

As a precaution, I replaced the piston, rings, wrist pin and bearing. I measured the squish band with the new piston. I found the top of the new Vertex piston was 0.2 mm higher than the original piston. I compensated by increasing the thickness of the base gaskets.

[oldgoat]

Thanks Eric, Nice to know we can go a long time between top end rebuilds.
I have an 2003 with about 20 hours on it, (I know, have to ride more)So i should be good till 2012 ,Ha ha

[GMP]

I have 49 hrs on my 250. Top end looks like new. I always do a top end off season in the dead of winter, but I got the bike a bit late last year. Our first race is in the sand (usually wet) and cold. This year I'll run the original top end through the first rides and races and replace after that.