blew my 400 eng, advice needed

I flipped my 99 Yz400f on top of myself after a stupid mistake at Glamis. To make a long story short, it broke my rip and dislocated my shoulder, after going over the bars. I thought I was only laying there only a minute or so, and belive my bike was only on its side running for a few seconds. When my buddies lifted the bike up the eng. was seized. We also noticed that the thottle was sticky from sand. Anyhow, now I'm wondering if maybe I was uncouncious for a while and the bike seized from lack of oil, and high rpms. I originally thought it just died from lack of fuel, but now maybe it was a lubrication problem. My question for you guys is, has anyone seized their bike like this and what was the damage? Would I be better off buying a used eng off ebay or parting the bike? If only the cylinder and piston are damaged, is it possible to fit a 426 jug on it. I thought I read somewhere one here that there was a way to do a 426 conversion for more bottom end power. I'm hoping for a little insight before I tear into the bike, thanks

I managed to lose my drain plug and drain all the oil from my old 426 while riding. I replaced the cylinder & piston and rode it for 2 or 3 seasons after that, no problems.

I don't think a 426 cylinder is a direct swap on the 400. However, I'm sure that others on TT probably have more background on the subject...

- Nick

Thanks teamtoxic, so I take it you didn't see any cam wear? I'm hoping I only trashed my cyl. and piston, but I figure if the heads gone the bike may be junked. Anyone else done this, I can't be the only one to have dumped it and let it run.

I had an experience similar to teamtoxic. It badly scored the piston and also damaged the cylinder. No wear on the cams or much of anything else. A 420 kit later and it has been running great ever since. If you want to do a 426 conversion it will require splitting the case because the 426 uses a different diameter con rod than the 400 so you would have to put a 426 crank in. Although if siezing it scored the con rod bad enough then the 426 conversion would be the way to go.

I am thinking about parting out my 02 426 Supermoto. Make me a respectable offer.

nimiz, thanks for that link thats what I was looking for but could'nt remember where I saw it. Lumpy I'll send you a pm, but I probably need a week or so to pull mine apart to see if its rebuildable.

IM returned.

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