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Discussion Starter · #1 · (Edited by Moderator)
Was out riding this past weekend when my '13 Backcountry 800 which had a CV tech short block installed about 14 months ago, lost power instantaneously and threw a knock code. I've been down this road before so I pulled the spark plug to find it bent out of shape severely.

800 Etec Broken Rave 8.jpg

We towed it home and when I compression tested it, the PTO side only had 100PSI.

800 Etec Broken Rave 7.jpg

I didn't know what the cause was yet so I did a leak-down test and it held for 30 minutes. I then found the broken rave valve as I tore the engine down, and a slightly melted piston. The head has no marks in it fortunately and it appears that the chunk of metal had been shot out of my exhaust before any more damage was done, as I cant find any fragments in the pipe or engine.

800 Etec Broken Rave 5.jpg

800 Etec Broken Rave 4.jpg

My question is, what would cause this? Is it possible the exhaust valve came into contact with the piston rings? What can be done to reassure I don't have this happen again? The valves were cleaned and had them synced by dealer when the shortblock was installed 1300 miles back.
 

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Discussion Starter · #2 ·
Also, going forward will I be safe to check the motor over and just replace the piston and rave valve if that's all that was damaged? I don't see any metal fragments in the exhaust, reeds or bottom end. I'd hate to replace the crank again as it's so new.
 

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Discussion Starter · #3 ·
So after further investigation, I can find obvious signs of the rave contacting the piston

146616043_1824313971060115_8193717253393495591_n.jpg

(as seen on side of piston and wear marks on rave).

145908790_3704244399695344_3230863882920507538_n_LI.jpg

I'm leaning towards wear on the upper exhaust valve where it bottoms out on the cylinder ports, allowing it to stick further in/separate from the other valve and rub the piston. When I stick a ring back in the cylinder with the rave installed I can't possibly make it contact, if anything there is .015 clearance there.
 

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0.015 is good. Spark plug suggests it is running exceptionally lean. Could the valve have broken from excess heat over time?
 

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I've seen that wear on my Rav valves too. Got 18,000 mi on them now. New short block at 13,000. Really hope that wear didn't cause it to make contact cuz if it did I'm doomed.
 
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