737 Kawa680 valve guide and pushrods.

[coachlarry]

Has anyone successfully modified this engine to have better cooling at the cylinder by the muffler? We live in a warm climate and this head has been fixed a couple times. I bought a salvaged head and replaced it but am looking at the configuration for some mods hat might be interesting. I have a Small mill and lathe at home. The three things that might be changed are the cooling under the shrouds, the location of the muffler, and the valve guides in the head. I was thinking about trying to relocate the muffler
Away from the head or insulate somehow. My other thought is to modify the head. Has anyone used a better valve guide arrangement? Perhaps a different material or threaded guide? Or possibly pin the guide in laterally? Anyway, I am able to do some small machining work so if anyone has a good idea to bullet proof this mower issue please feel free to chime in.

Thanks

 

[Kyle_in_Tex]

I saw 3 of these on auction. I did not no there are inherent problems. My LT180 has a v twin Kawi that is stated to have 17 hp. Maybe try synthetic oil? I know it takes more heat.
Also guessing that you have made sure there are no wasp nests or mud dauber nest in the air way paths.

This isn't the liquid cooled Kawi is it?

Can you wrap the muffler with heat wrap tape? What actually goes wrong with the head? Does the valve guide get worn out? Maybe try a Ti6Al4V grade guide?

 

[Richard001]

Larry,

A few suggestions.
Could be several things causing the problem.

a. Is the engine running lean? Check your spark plugs for correct fuel mixture.
A lean running engine will ruin valves and could cause head warping.

b. As someone else suggested, make sure that there are no obstructions for air flow over the head. Is the problem always the same head?

c. Is the baffle in place that is shown in the top left of this photo?



d. Are you getting proper oil lubrication in the heads?

e. If all else fails, you may want to add the oil cooler that is use on the 721 engine.
See photo.



Here is a link to the engine shop manual:
https://www.google.com/url?sa=t&rct...02.pdf&usg=AFQjCNGzzGkuf6_H4H8Odhc9ZEwS3WdVDQ

Richard

 

[coachlarry]

I saw 3 of these on auction. I did not no there are inherent problems. My LT180 has a v twin Kawi that is stated to have 17 hp. Maybe try synthetic oil? I know it takes more heat.
Also guessing that you have made sure there are no wasp nests or mud dauber nest in the air way paths.

This isn't the liquid cooled Kawi is it?

Can you wrap the muffler with heat wrap tape? What actually goes wrong with the head? Does the valve guide get worn out? Maybe try a Ti6Al4V grade guide?

Kyle - This an air cooled engine with a known issue (primarily) in this cylinder located near the muffler. The muffler in the Deere configuration is vertical and on the #1 cylinder as shown below. The valve guides are steel, and the heads aluminum.
The guides are well known to slip causing further damage to pushrods.

 

[coachlarry]

Larry,

A few suggestions.
Could be several things causing the problem.

a. Is the engine running lean? Check your spark plugs for correct fuel mixture.
A lean running engine will ruin valves and could cause head warping.

There is no lean condition, the engine runs fine, but does run hot.

b. As someone else suggested, make sure that there are no obstructions for air flow over the head. Is the problem always the same head?

c. Is the baffle in place that is shown in the top left of this photo?

View attachment 502801

The problem on this model is usually on the same head, but both heads can be affected. In our case, it is on the same head. The baffle is in place, and has been known to trap debris. It would be nice to have good flow over fins without this debris trap.

d. Are you getting proper oil lubrication in the heads?

It appears that there is sufficient lubrication when I inspect under head cover.

e. If all else fails, you may want to add the oil cooler that is use on the 721 engine.

See photo.
View attachment 502802

This is intriguing! Do you think this would keep the temperatures in that head more constant? cooler?

Here is a link to the engine shop manual:
https://www.google.com/url?sa=t&rct...02.pdf&usg=AFQjCNGzzGkuf6_H4H8Odhc9ZEwS3WdVDQ

Richard

Very Helpful!!

 

[Richard001]

Well yes, the oil cooler will help if sufficient amount of oil is getting to the top of the head.

A engine will run fine when lean. Just because it runs OK, doesn't mean that it is not lean.

Try this, run the engine at 3/4 rpm for about a minute, then, while still holding the throttle in the same position, shut the engine off. Pull the plugs and look closely at the tip, should be light to dark brown. Take some photos of them and post them here.

Richard

 

[coachlarry]

ok, will do on the plug check; thanks. Just saw youtube of oil cooler install from tallfarmnboy. pretty straightforward. Any other cooling mods that improve air flow? Also, any oil recommendations? I think we have 10-30 Mobil 1 as I see container in shed. Should we be running HDEO in this machine?

 

[coachlarry]

Here is the plug from the 737 #1 cylinder. I did a compression test and came up at 75 PSI after replacing head with a salvaged piece, with #2 at 90 PSI. 57 is minimum in service manual. Also, I attached a picture of a proposed hack, whereby I would drill into head and valve guide (behind first fin), and press a pin into hole to prevent slipping. Optionally, I could tap it and use a set screw. Anyone have a thought as to what material to use for pin and interference that would prevent slippage?

 

[coachlarry]

Related to this thread is a picture of why these engines are known to have problems. This is the other cylinder side, but raises another question. I recently replaced the crank seal on the PTO side and it solved a major oil leak problem. Now, after seeing this, I am wondering if oil from the PTO side could blow into these fins, or if I might have a front seal leaking. We are not using much oil, and I don't see much towards the front, but this is troublesome. I got the oil cooler for 13 bucks from Jack's and will install and clean this area up to see if I can identify a leak.

 

[Kyle_in_Tex]

On most engines, you want your compression readings within 10% of each other.

I would think the valve guide is too hard to tap. A standard pin should be press fit into place. If not press fit, it could back out and cause trouble.

The last pic would explain a lot about overheating to me.

Clean everything and hope the cooler helps.