Thread: Valve Clearances
04-20-2009, 08:02 PM #1
Does anyone know how valve clearance affects the 250X? Is it better to be on the low side or high side?
I have major GIO in my 2007 (prevented from getting back in oil by catch can block-off) and I'm trying to determine why I have it but another 2007 in the area doesn't.
I checked my valve clearances and found the intake to be 0.006 to 0.007 which is within spec. but the exhaust clearances were all either 0.011 or 0.012. The spec for the exhaust valves are 0.0126 to 0.0161 so I'm below the spec (tight side). Could this have anything to do with a lower top end and possibly more GIO? The machine has 50 hours so maybe there is some exhaust valve or seat damage from being on the tight side??
I did notice when doing a leakdown test that 2 cylinders had major leakage. Determined to be from the exhaust valves that I "cured" by tapping on the top of the valves and re-doing the test.
04-20-2009, 08:28 PM #2
Some will say that a Tighter clearances will get more lift from the cam
But this will cause the valve to run hotter , because the heat transfere time on the seat has been reduced,
others say loose is safer,
I have always just set inlet on the tighter side of the specs!
exhaust on the middle to loose side , as exhaust valves are normally the ones to recess first.
if you exhaust is way out of spec ( meaninf tight , because they have stretched) and the seat condition is ok, You would want to replace them.
But yours dont fall into that catagory of Bad from those spec's you gave.
04-21-2009, 09:53 AM #3
So do you think it's worth the effort of taking it apart and getting them shimmed based on the clearances I gave for the exhaust valves? The clearances should get larger over time, right?
04-21-2009, 02:38 PM #4snapper455Guest
there is no mystery here. setting the valves loose = more pwr. we set the EX valves on our stock and race boats at 17 thousands. the IN valves at 8 thousands
04-21-2009, 03:38 PM #5
04-21-2009, 07:02 PM #6
Could get tighter as valve wears into the seat.
04-21-2009, 07:59 PM #7
04-21-2009, 08:08 PM #8
As a matter of fact we used to set them loose to rev better and tight if you wanted low end power. No huge difference but noticeable on the old honda accord fuel injected motors.
04-21-2009, 08:19 PM #9
Tighter will change cam lift , thus altering engine ouput
for the 8 years I work on a production car series over here,
we used to run the std cam clearances down to 3 tho, ( on that engine dyno showed best results)
but every engine is different as we know
04-21-2009, 09:18 PM #10
Ok started reading through the service manual to see what's involved in changing the valve shims. The manual says that the cylinder head and camshafts have to be removed and to do this the engine has to come out. Has anyone done this with the engine in. Is it possible? If I have to take the engine out I'm thinking I might put in the 08 pistons and rings.
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