engine noise

[G1of5]

bought the bike, new; off of the floor; 2 years ago.

[5th_bike]

Originally Posted by raul10141964

sound like sowing machine is normal

More like a lawn mower I think

[RuffRoad]

I just bought a 2007 GZ250 a few days ago. The top end noise was unbelieveably loud, however, I thought "It's just badly adjusted valve tappets". I measured the existing clearances and found: 0.005" intake, and 0.008" exhaust. So, I adjusted them (when cold) to : 0.002" intake, and 0.003" exhaust. Thought to myself, "This is really gonna solve the noise problem". Went for a gentle test drive, not exceeding 40 mph. The noise was still just as bad - even after the engine was brought up to full operating temperature.
Next day, I decided to pull the gas tank and get a closer look at the valve cover assembly. All the bolts were there, so I gently, gently, tightened them, just "a tad". Lo and behold, I discovered that one of the bolts refused to tighten - it just spun around uselessly. Obviously someone had sheared the bolt, and left the hex head and shank in place, making it appear as though nothing was amiss.
So, sigh, pull the valve cover assembly. Sure enough, the broken bolt was one of the bolts holding down the camshaft journal bearing. Only ONE bolt, on one side of the camshaft journal bearing was actually keeping the camshaft bolted in place.
MORAL OF THE STORY: If you are having intractable top end noise, and valve adjustment has no beneficial effect, trying gently cinching up the camshaft bearing bolts - you may find that one has been broken in half by an overzealous, wrench-bearing, ham-fisted amateur.

[RuffRoad]

Here is a tip that may help during valve adjustment: Most of us do not have a feeler gage 0.001" thick (minimum clearance specified on the intake valves). Here is a way to approximate that small of a clearance measurement.

The valve adjuster screw on the GZ250 (at least on my 2007 model) has the following thread measurements:
Major diameter of valve adjuster screw = 4.81 to 4.83 mm (as measured by digital calipers).
Thread pitch of valve adjuster screw = 0.50 mm (as measured by standard thread pitch gage).

Doing the conversion math: 0.50 mm = 0.019685 inches. So, every full revolution of the valve adjuster screw will advance the screw 0.019 ". It follows that:

TURNS OF MOVEMENT
ADJUSTER OF SCREW (inches)
SCREW
1 0.019 68
1/2 0.009 84
1/4 0.004 92
1/8 0.002 46
1/16 0.001 23

Therefore, adjusting the intake valve to very light contact, followed by backing off the screw 1/16 of a turn will approximate a 0.001" clearance.

[raul10141964]

do not trust MRGZ250 he is spanning all the treads

[isaac]

I had "noise" in my top end and discovered a valve seat was so loose it could be taken out by hand. It likely had been dancing around in there every time the valve opened. That's a matter of miles before the seat cocks sideways, snaps a valve head and causes total engine failure. I caught it just in time.

And in case perusing these forums hasn't been example enough, these engines have a proclivity toward snapping valves in half and replacement heads are ludicrously expensive and very hard to find used. You'll be doing yourself a favor if you bite the bullet and spend the $30 worth of gaskets to open it up.

[Water Warrior 2]

Originally Posted by isaac

I had "noise" in my top end and discovered a valve seat was so loose it could be taken out by hand. It likely had been dancing around in there every time the valve opened. That's a matter of miles before the seat cocks sideways, snaps a valve head and causes total engine failure. I caught it just in time.

And in case perusing these forums hasn't been example enough, these engines have a proclivity toward snapping valves in half and replacement heads are ludicrously expensive and very hard to find used. You'll be doing yourself a favor if you bite the bullet and spend the $30 worth of gaskets to open it up.

BRR! That made my blood run cold just trying to visualize that scenario. Over the years I have noticed the bikes that have valve failures are the bikes that spend their time at higher revs and speeds. Might be the 1st owner doing this and the next owner buys a potential problem that will eventually bite him/her.
All in all you made a good call and saved yourself a lot of grief.

[OldNTired]

Originally Posted by Water Warrior

BRR! That made my blood run cold just trying to visualize that scenario. Over the years I have noticed the bikes that have valve failures are the bikes that spend their time at higher revs and speeds. Might be the 1st owner doing this and the next owner buys a potential problem that will eventually bite him/her.
All in all you made a good call and saved yourself a lot of grief.

High revs, higher speed (you forgot high temps) - is someone playing my theme song?
Luckily, mine is still running fine!