Kawasaki FR730-ES09-R

Fat Toad

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KAW. FR730V exhaust valve guide in number 1 head moved up and out of position enough to keep the rocker from opening the valve and bending the p.rods.
Any ideas as to why this happened and advise on what to do about it .....time for new head , should I replace both etc.
 

bertsmobile1

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Over heating softens the alloy so the guide slips.
Now finding the reason for the overheating is another matter
 

cpurvis

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I used to think there was 'one' good mower engine brand to choose from.

Now I'm wondering if there are any.
 

bertsmobile1

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Firstly there is the problem of owners who never read the manual before they jump into a mower.
The most common "warranty" problem with new mowers is still people starting the engine up with no oil.
The most common problems I see in the shop are caused from low oil.

Next there is the assumption upon which the entire capitalist free enterprise system is based on .
The MARKET IS FULLY INFORMED & UNDERSTANDS THE INFORMATION PRESENTED TO THEM.
When it comes to making decisions the market is 99% ignorant and make their purchasing decisions based almost purely upon price.
Henry Ford proved this very well.
His famous model T was a trash pile that would only just barely hold together longer than warranty and if any part did it was downgraded till it didn't.
people who understood automobiles knew it was junk and expect Ford to go bust.
But the mechanically ignorant who did not have the capacity to properly evaluate the true value of the car bought them by the thousands then learned how to fix them then went out & bought a better car latter on.
The Ford family was elevated to one of the most wealthy in the world for near a century.
Henry Rolls make the highest quality car it was possible to build and warrantied them for the life of the original purchaser which passed down through generations of direct decendants.
This should have made him the wealthiest man on the planet, but he died a pauper and Rolls Royce motors had been bankrupt several times before he died and another 4 times since then.

Indian made excellent motorcycles that again would run forever while Harley made junk, but Indian went bust & Harley thrived and it was not till AMF took them over that they actually started making quality motorcycles that spent more time on the road than in the workshop.

Mowers are exactly the same to build a high quality durable engine will cost $ 3,000 + but Joe Average expects to get not only a good engine but the entire mower around it for under $ 2000.
Thus any one who makes a high quality vertical shaft engine will go bust and if you look at the engines that have gone bust ( ONAN is a great example ) or Honda , who refused to downgrade their engines that "the informed market" was willing to pay so they exited the vertical shaft market.
 

7394

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I hear ya guys. I let my Kawasaki warm up 3 -4 minutes or so, as per the OM I read. This gets the heads & guides to heat up. Which after expansion the guides in theory would be better held in place.
 

cpurvis

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I hear ya guys. I let my Kawasaki warm up 3 -4 minutes or so, as per the OM I read. This gets the heads & guides to heat up. Which after expansion the guides in theory would be better held in place.

I think it may be the opposite and that's what causes the guides to move.

The guide is steel and the head is aluminum. Aluminum has a higher coefficient of thermal expansion than steel. As the head warms up, the hole for the valve guide increases in diameter faster than the valve guide O.D. increases. The hotter the head gets, the looser the interference fit between the head and valve guide becomes.

Make sense?
 

bertsmobile1

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The guide is around 0.002" bigger diameter than the hole.
The difference between the expansion is in the order of 0.0001"

I have never seen a shifted guide without finding evidence of overheating all over the engine.
first reason is failures to remove the blower housing to remove debris & rats nests.
Next most common is allowing the engine to idle slowly for extended periods or running at less than full speed.
 

cpurvis

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How did you calculate the .0001" difference in expansion?
 

bertsmobile1

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It is actually less than 0.0001" which is why I said in the order of 0.0001"

Consider the hole as a cyllnder of AS 401 , a 4% Si 1% Cu gravity die casting alloy used for motorcycle heads and the chill cast iron valve guide also as a solid cylinder.
Cheat a little and call them both 0.5" diameter.
After that multiply out the linear co-efficient of thermal expansion for each one at 200 Deg C which is the maximum allowable temperature before you get in the thermal creep zone for the 401. Then subtract the alloy from the iron.
The actual calculation was done years ago when deciding if I could use the iron guides I had on hand in a 250cc BSA C15 or if I would have to turn up some bronze ones.
I use the same Neway valve cutters & pilots on the C 15 as I do for Briggs seats.

Then if you really want to get creative you can use the rates of thermal diffusion R values and you will find that iron ( or steel ) heats up a lot faster than the aluminium because the aluminium conducts the heat away at a faster rate than the iron guides

The interfearence fit of .002" comes out of an engine repair manual. the bikes are done 3-5 thou but they are not governed so get a lot hotter than a mower engine.
 

mhavanti

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As an engine machine shop owner of several decades, I would suffice a guess that the engine shroud was holding debris around the cooling fins of the head and thus overheating the entire combustion chamber as well as the head.

Once an "air cooled engine" or as I much prefer to call them: "Fuel Cooled Engine" has began to run overly high atmosphere the engine then will require more fuel in order to further cool the atmosphere. If additional fuel is not available, the atmosphere reaches critical mass and many things can and certainly will happen at some point. One such thing is galling the valve stem, reducing and clearance. The valve stem thence collects the valve guide and brings it on the upward or downward travel until something stops them both from moving such as breaking a rocker arm stopping any movement. Perhaps the push rods bend and the movement is much decreased until the push rod slides out of the rocker arm cup. Or the valve is so slow in movement due to the high temperatures the valve stays out the downward travel too long and thereby makes contact with the piston. Just a few of the scenarios you may experience with high temperatures due to lack of cooling either on the outer surfaces such as the cylinder cooling fins or the interior of the cylinder due to insufficient fuel.

Next thing to do is read the plugs. Are they reading the same on both sides, or, the one with the migrated valve guide, does it appear to have been extremely hot?

Boyeeeeeeeeee, we could go on for a while. I'll leave this to Bert to pick up as he will be a bit more technical than I when it comes to fuel cooled engines.

My shop's duty was always to do the autopsies on engines when dropped off for restoration.

Good luck and I don't feel your Kawasaki is the problem, it is something you'll find once all the evidence is in.

Max
 
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