Please help - been through 2 new jugs now.

[Iliketogofast]

Here goes - I blew my quad up a long, long time ago riding across a field. While I was getting pulled home I noticed coolant was leaking from in between the head and the jug, so I figured it was because of the head gasket.

About 6 months after that I finally got it fixed, put it all together and it was hard to start (it was very hard to kick, like there was resistance). Like a dumbass, I finally got it started and it ran okay, but not great. So I turned it off and took it apart, and there was scoring all over the new piston and freshly bored walls. That evening I got a call from the guy who bored it telling me the piston was a size too small. Wtf.

So he takes it and bores it again and gets me another piston free, but while I wait I ordered an ESR 310 kit, installed it and it was hard to get started (there was no resistance, it just didn't want to start - I credit it to weak spark). I pull started it and it ran INCREDIBLE. It didn't have any problems starting after that, except for the fact that after about 20 minutes of running time it blew, and there was scoring in the same area.

Any idea what the problem could be?

[250Renvy]

Hard to say. Maybe your crank is out of spec and needed replacing as well.

[Iliketogofast]

It has a little side to side movement and very, very minimal up/down, if that helps any.

I'm afraid to tear the bottom end down. :( I've never done it before.

Someone told me it could be the CDI, but I don't see how that has anything to do with it.

[fireburns99]

Originally posted by Iliketogofast
It has a little side to side movement and very, very minimal up/down, if that helps any.

I'm afraid to tear the bottom end down. :( I've never done it before.

Someone told me it could be the CDI, but I don't see how that has anything to do with it.
Its definitely something mechanical, so it can't be the CDI.
It definitely sounds like you have a bad rod bearing, or crank needs to be rebuilt etc.

If i were you i wouldn't be too worried about tearing into bottom end. I would be more afraid of blowing another top-end. Thats like $250 a shot, and i know that 310 was substantially more.

[jon370r]

One possibility would be since you haven't had the bottom end apart there could be debris down there from when you blew the 1st top end. Every time you start a new top end it stirs the crap up top to drag between the new piston and cylinder walls.

[honda300EXtreme]

Originally posted by jon370r
One possibility would be since you haven't had the bottom end apart there could be debris down there from when you blew the 1st top end. Every time you start a new top end it stirs the crap up top to drag between the new piston and cylinder walls.

yea thats a good posibility, i would definatly tear into the bottom end,, theres either metal in the engine orr your crank i out of spec.

[criminalpoet]

If there is any up and down play what so ever in your rod then your bottom end is definitely due for a rebuild. A little bit of side to side movement is normal, but up and down play indicates that your rod bearings are worn/wearing out.
Also, when you pulled the top end after it blowing, was there still two cir-clips holding your piston on/in place? If not then they were installed wrong. When you install the cir-clips the openings should be facing either up or down. If they are installed so that the openings face to the side, they will sometimes pop out and destroy your fresh bore and piston.
Also make sure to do a compression check always, and when your doing so, pay close attention for any noise that would indicate piston slap. If that piston is hitting your squish on the head thats bad too.