More Kohler Lessons

WV Sawmiller · August 26, 2021, 02:52:02 PM

As mentioned in other threads my LT35HG25 died unexpectedly after about 10 minutes of sawing Tuesday. I have a little over 930 hours on the mill/engine. We decided it was electrical in nature but could not determine the cause or a fix at the site. I took it to my mechanic and he decided it was the RH coil so I ordered and picked up a replacement yesterday. (The coils are interchangeable and when I say LH or RH it is just as we happen to have them installed on my mill.) We put it on but then we had problems with the LH coil which I had replaced 11 months ago. We tried different troubleshooting and discovered with the new coil on when we connected the wire with the kill switch between the 2 coils the LH coil did not run. With the kill switch removed it runs fine on both cylinders. We replaced the LH coil with the removed/old RH coil and it would not run. With the original LH coil in back place and the kill switch wire removed the mill runs on both cylinders. I could get by with this situation in a jam but went ahead and ordered a replacement LH coil. What we determined/think is when the RH coil failed it damaged the diode in the LH coil. I called and ordered a new LH coil. The new coil should be here tomorrow and replace it Saturday morning. The local dealer confirmed there is a diode in the coil and it failing is consistent with what we are experiencing.

Evidently when you turn the switch off the kill switch wire between the coils instantly shuts off the engine. With the diode not working when you shut off the switch the engine runs a few more seconds until the engine dies of fuel starvation. Again, I could saw with it like this in a pinch but I figured we'd fix it right especially since threatening weather is not going to allow me to go saw for a few days anyway.

BTW - I don't know what the normal life expectancy of a coil is supposed to be or what caused this one to fail Tuesday. I had no indication and it had sawed good for 6.4 engine hours the day before.

I don't know if others have experienced similar issues with Kohler engines but if you get similar problems it is something to consider. If you have a better understanding and explanation, please add them here in hopes it will help others in the future.

Magicman · August 26, 2021, 03:02:26 PM

Just for reference, what is the model# on your engine. The G25 in your sawmill's description indicates that it is 25hp.

Southside · August 26, 2021, 03:35:11 PM

Was the replacement coil OEM or knockoff?

barbender · August 26, 2021, 03:47:35 PM

Good to know. My Kohler on my firewood processor is still short of 150 hours. It has ran very well once I figured out a few bugs caused by someone messing with stuff they had no business touching. I bought it sight unseen through an online auction with only 35 hours. I got it home, it's a 2014 model so obviously it had been sitting with only 35 hours on it. Fired it up and it ran really weird. Actually it ran fine but when you opened the throttle it would go about 1000 rpms over governed speed, and hunt and circle badly. I cleaned the carb- it was spotless. I tried adjusting the carb. No good. As it turns out, someone had replaced the factory governor springs, why I have no idea. That was fun to troubleshoot😬 Next problem, it would cut great and then suddenly the feed would just stop in the middle of the cut. I tried everything I could think of, finally got some new chains. When I pulled the one on it off, I realized it was an .063 Chainsaw .404 chain, instead of an .80 harvester chain. The wrong guage chain was allowing the chain to walk to one side, and then the bar would catch. That's quite a bit of stuff to screw up in 35 hours, just think what they would have done to the poor machine if they would've made it to 100?🤦🏻‍♂️These are probably the same people that go on Facebook and trash manufacturers, "My Dyna processor won't even cut through a log!" or, "that Kohler never ran right!". No, you should never be allowed to touch a machine!

WV Sawmiller · August 26, 2021, 05:20:21 PM

It seems like it will turn out to be a relatively easy repair and it has been an eye opener for my mechanic who is pretty danged good and seems to love a challenging repair. I just wanted to post as a heads up if you find some odd performance issues that are similar in nature.

Lynn,

Yes, it is a 25 hp Kohler, model CH 740 IIRC. You are correct in the WM nomenclature of the mill indicating it is hydraulic, gas powered and 25 hp.

SS,

Both coils I bought from the authorized local Kohler dealer and I am sure they were OEM. He is one of the most responsive vendors I deal with and normally if he does not have it in stock he has it the next day and sometimes even the same day, depending on what time of day you call him.

Magicman · August 26, 2021, 05:27:41 PM

I will be interested to hear the outcome.

WV Sawmiller · August 26, 2021, 05:34:55 PM

Thanks. I will keep everyone posted.

Dewey · August 27, 2021, 09:23:46 AM

Over the years I've gone through 4 Kohlers I think I have only replaced 1-2 coils.
The part that I have replaced on every one ,is the Fuel Pump/Valve cover on the oil dipstick side.
The most hours I have got was 6800 hours on one .The others have been 3500-4500 hrs.
The thing that I have done that helps the most is running synthetic oil and change oil and filter between 85-100 hrs.

sawguy21 · August 27, 2021, 01:42:29 PM

Absolutely amazing what can be accomplished with regular maintenance. ;D

WV Sawmiller · August 27, 2021, 11:00:48 PM

I religiously follow the WM maintenance schedule on my mill and I think the engine manual listed oil changes every 100 hours or so which I have done. I have not tried the synthetic oil.

I picked up my new coil this afternoon and talked with the rep there about what could cause a coil to fail prematurely and he indicated moisture could be a contributing factor. I told him I keep the mill stored outside but always with the WM vinyl cover over it when not in use. He made a valid observation that while the cover keeps the rain out it does allow/contribute to condensation. I had not thought about that but it make sense. I may have to seriously consider a sawing shed or at least one to cover the head unit when it is here at home.

I'll take the coil to my mechanic in the morning and with any luck the mill will be coming home with me. I'll keep the old coil as a back up and mark the box as "Bad diode" and if I have to use it I'll be sure to keep the kill switch wire disconnected.

WV Sawmiller · August 28, 2021, 11:29:02 AM

Well, as far as I can see the mill is fixed again. I took the new coil over this morning and my mechanic put it right on, everything seems to be working fine, so he buttoned it all up and I brought it home. Now I just need to find a 3 day window of predicted good weather when my customer is available and go finish my job 50 miles away.