How much pitting on head is ok?

[nadrojcote]

Just picked up an ol 2003 570f mountain cat that popped. Looks like the cylinders were tapping the spark plugs, even though they're the correct plugs. I'm guessing needle bearings are shot.

Anyways, the head is pitted pretty bad. Is this still useable for a beater for the kids to putt around on? I ordered a new top end kit, but not sure if I should dish out to get a replacement head.

 

[kiliki]

Bet you have lost the lower rod bearing and will need a full rebuild or used motor.

 

[Old & slow]

I would clean the head up with sand paper/emery cloth and run it. I have ran them that bad before with a lot more power. Good luck!

 

[PSI 800]

like kiliki said. could run the head but there are more issues that need to be fixed first

 

[MrIQR]

What’s that sound? I don’t know! Keep going!

Impressive.

I’d buy another motor rather then spending time and money doing a full rebuild on that one. I wouldn’t run it without rebuilding the crank, don’t ask why.

 

[nadrojcote]

I've pulled it apart. Bottom end is fine, can't find anything wrong with it. All bearings are tight. Pretty sure I found the issue. The old owner told me he was at 7800 rpm when it blew. From what I can find you want to target 7100-7300 with this engine. So Clutching is probably not setup right. If it's set for high elevation like they came stock (I'm in the prairies) then I can also assume it has the wrong jets in it. Causing it to run lean (spark plugs confirm this). Lastly I found a cracked impulse line to the fuel pump, which would also cause a lean condition. So it was over revving while running lean. Going to rebuild the top end so my kids can ride it around the field in the back. I'm not concerned if it blows. I got it so cheap I can still part it out for well over what I paid for it. After rebuilding top end with new crank seals too I'm into if for less than $600 Canadian.

 

[Old & slow]

One thing I would suggest is to check the squish after reassembly.

 

[kiliki]

I've pulled it apart. Bottom end is fine, can't find anything wrong with it. All bearings are tight. Pretty sure I found the issue. The old owner told me he was at 7800 rpm when it blew. From what I can find you want to target 7100-7300 with this engine. So Clutching is probably not setup right. If it's set for high elevation like they came stock (I'm in the prairies) then I can also assume it has the wrong jets in it. Causing it to run lean (spark plugs confirm this). Lastly I found a cracked impulse line to the fuel pump, which would also cause a lean condition. So it was over revving while running lean. Going to rebuild the top end so my kids can ride it around the field in the back. I'm not concerned if it blows. I got it so cheap I can still part it out for well over what I paid for it. After rebuilding top end with new crank seals too I'm into if for less than $600 Canadian.

Also I would drain the fuel if you don't know how old it is and start fresh. As for the head just clean it up and run it. On a motor with that much debris you did the right thing by pulling it down. That's how you found the bad pulse line too.

 

[thakgya44]

That pitting looks a bit like damage from certain kinds of detonation. Did it break a piston, or rings?

You can probably clean up that head and run it. I would surface it, if possible. You need to address the cause of the pitting and

 

[mtncat1]

I've pulled it apart. Bottom end is fine, can't find anything wrong with it. All bearings are tight. Pretty sure I found the issue. The old owner told me he was at 7800 rpm when it blew. From what I can find you want to target 7100-7300 with this engine. So Clutching is probably not setup right. If it's set for high elevation like they came stock (I'm in the prairies) then I can also assume it has the wrong jets in it. Causing it to run lean (spark plugs confirm this). Lastly I found a cracked impulse line to the fuel pump, which would also cause a lean condition. So it was over revving while running lean. Going to rebuild the top end so my kids can ride it around the field in the back. I'm not concerned if it blows. I got it so cheap I can still part it out for well over what I paid for it. After rebuilding top end with new crank seals too I'm into if for less than $600 Canadian.

it's lean rejet and clean the carbs you should be fine

 

[thakgya44]

You can probably clean up that head and run it. I would surface it, if possible. You need to address the cause of the pitting and
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