Seeking a bit of advice with a valve train problem

Isj0321 · Two Stroke Sniffer Joined: 04 Apr 2017 Karma :

Bike was running rough, hard to start, spluttering and cutting out. Ive stripped it down and found an oil leak, oil dripping through a leak sprung in a spark plug tunnel. Fixed that suspecting a gasket seal failure, nothing more, but still running like crap afterwards.
Decided to check the clearances suspecting the worst and found a tight gap
.63-.76 where it should be 1.5-2 in that same cylinder as the leak, my thinking is i've likely a bent valve and the head needs stripping. Do i strip the head or just reshim it and hope for the best?
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Hahadumball · World Chat Champion Joined: 07 Oct 2015 Karma :

try prying the head apart with 2 screwdrivers
and then push the valve up using a screwdriver through the gap
and then push it back down and repeat this a few times.
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Fin: no matter how much I look at It I can't understand what was going through my head, all I remember is going about 80 and redlining it to stop it seizing.
360 Deg... Five 1/4 turns. :- Teflon-Mike 18 Jan 2015

mentalboy · World Chat Champion Joined: 05 May 2012 Karma :

FFS, I got my mac and notebook out but, other than some vague reference to a tunnel, nobody is talking about trains.
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Snod Blatter · Crazy Courier Joined: 21 Nov 2014 Karma :

It will surely take more than the gap being a bit tight to get the valve to touch the piston, I doubt that is your problem. My personal guess would be the oil on the plug allowing the spark to crawl down the outside, giving you a weak spark in the combustion chamber. A new plug is usually required, just cleaning them never seems to work.

Of course putting the clearance back into spec is also a very good idea!
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Baggyman · Crazy Courier Joined: 20 Feb 2017 Karma :

mentalboy · World Chat Champion Joined: 05 May 2012 Karma :

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

A bent valve would give you a larger valve clearance, not a smaller one. The valve doesn't sit square in its seat but protrudes into the combustion chamber, meaning the valve sits lower and there is more space between valve and follower.

I'm also a bit confused by what you say the measurements should be. .63-.76 mm sounds like a rather large gap, 1.5-2 mm sounds enormous. Are you using imperial measurements with the decimal point in a funny place?

What bike is it?