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View Full Version : Kawasaki FH721 FH680 23 25 HP Engine Blown With Pictures FYI


teckjohn
05-12-2012, 11:50 PM
here is a Kawasaki 23 HP engine off of a John Deere 757 737 The pics will show you what happens when the cooling fins on your head get clogged. This one got hot seized the valve to to the head, snatched the insert out of the head, the valve fell on top of the piston and seized the engine. The cylinder might hone out clean if that is only aluminum in the scaring of the cylinder. If not you can have it bored out for $80 bucks and put over sized pistons and rings in it. But the problem that caused it to happen in the first place was an oil leak. So you have to replace the bushing in the block and in the crank case cover along with both seals.. I can do this for you if you need me to.

teckjohn
05-13-2012, 09:46 AM
Here you can see where the oil leaked out of the front seal and also you can see the bushing in the block that has to be replaced. You can also see I honed the block and the marks did clear up. They felt rough at first, but turned out it was just aluminum from the piston and when i honed it, it came out. So next is to put both bushings in the block and seals then put 2 new pistons and rings in. Then I have a spare head to replace the bad one. Bead blast the heads and do a valve job on the heads. Put all new gaskets and seals in and rebuild the carb and she will be ready to fire up. I will keep you posted on the progress.

Walts John Deeres
09-08-2012, 08:42 PM
Teckjohn, I was searching on the internet and found your photos on here so I joined so I could view them. Im just finishing up a rebuild on an FH721. Bought my 757 used with bad 25 HP Kaw that was blown due to oil and grass clippings clogging the cooling system. I replaced every internal part with the exception of the crank and cam. Mine overheated and broke a rod but didn't harm anything else. I will finish it up tomorrow and hopefully get it running. My 757 only has 400 hours so I figured I would replace all the engine parts for longevity.My motor has an oil cooler behind the oil filter and would like to possibly add a real oil cooler to further aid in oil cooling. Do you know if this has ever been done and if so do you have any ideas on how to do it. I would also like to know if anyone is using snythetic oil and if so what weight. I have the old head from cylinder #1 that is like new but one of the valve guides moved about 1/8th inch towards the valve cover, I'm sure from overheating. I talked to several machine shops in the area and didn't feel comfortable with their opinions so I simply purchased a new head. I am willing to give this to someone as they might know a good fix for the guide. Any info would be helpful. Thanks,Walt

teckjohn
09-09-2012, 01:19 AM
I don't feel that there is a need to add anything other than what Kawasaki FH721D already have for cooling the oil. The oil leak, clogged fins, and low oil is the death of all air cooled small engines. DO NOT run synthetic in the engine for the first 10 hours. Use petroleum and then when you change your oil use synthetic then. Let it break in the new rings first. and use 15/40 20/50
you can send that head to me I can use it for parts. Or you can put it in an oven heat it to like 500 and then you can move that guide. but if you try any other way you will damage the head. http://zeroturnman.com/cart/ http://zeroturnman.com/ john@zeroturnman.com

BPS##
09-09-2012, 06:44 AM
John I have a 04 777 that I bought used at 636 hours for $3000.
On the JD show room floor they want $6000 for those units so I thought I got a deal until I got it home and discovered it was burning A LOT of oil.
Compression was 150 psi on both sides but judging by the spark plugs its burning the oil at about the same rate both sides. I discovered the breather tube had been off for some time. Who knows maybe from new.

Any way in about a month when my season ends my uncle is planning on taking it down and seeing whats wrong and hopefully it can be fixed without buying a new very expensive engine.

Any experience with this? and any ideas what he might find? or cost for repairs?


thanks

Patriot Services
09-09-2012, 08:26 AM
Do you Deere guys find this clogging problem often. I remember reading a few posts about coolers, rads and engines clogging frequently on them.
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BPS##
09-09-2012, 10:36 AM
Do you Deere guys find this clogging problem often. I remember reading a few posts about coolers, rads and engines clogging frequently on them.
Posted via Mobile Device





Yes on the 700 series air cooled models.

teckjohn
09-09-2012, 07:58 PM
Did you connect the hose and see if it was sucking oil from the crankcase and smoking? If so the vent breather needs to be replaced

BPS##
09-09-2012, 08:03 PM
Did you connect the hose and see if it was sucking oil from the crankcase and smoking? If so the vent breather needs to be replaced





Took it all apart and did that. The breather looks like its a reed valve set up. One for each cylinder. Reed valves not broken or sticky.

teckjohn
09-10-2012, 07:50 AM
Cracked cylinder sleeve? Hole in piston crack? Cracked head?