Ok, it's a long winded story so stick with me. My 2006 Honda VTR1000F's motor is currently getting most of it's bottom end rebuilt along with replacing both cam chain tensioners, a cam chain and 2 bent exhaust valves thanks to the bike running on 1ltr of oil instead of it's required 4. It was taken in for a major service roughly 4,000k's ago. Since then the bike has sounded fine and been riding fine until one day developing a serious knocking noise in the motor and losing alot of power. Since the service it has not blown any smoke or leaked any oil and the mechanic that is rebuilding it has assured me there is no way it could have lost 3 ltr's of oil in those 4,000k's. I have not changed the oil myself in that time either. Now I'm up for a repair bill of approx $4500 and as logic dictates to me that the previous service is the source of the problem I'd like some advice on whether I can chase up the original mechanic for costs of the repair, and if so, how to go about it. It has also been pointed out to me by the current mechanic that the valve covers looked as if they hadn't even been taken off, which I understand is a necessity for checking valve clearances in a major service. I have since looked back over the invoice and they haven't listed valve checking at all. Thanks in advance for any replies. And please no 'you should've checked your oil' replies, I'm already feeling flipping stupid about it.