Kohler Pro Command, 15hp - leaking head gasket?

Discussion in 'Mechanic and Repair' started by Roger, Nov 30, 2010.

  1. Roger

    Roger LawnSite Fanatic
    Messages: 5,940

    I have an Exmark Viking, 15 years old, with thousands of hours (maybe 6 or 7). The engine is a Kohler Pro Command, 15hp, recoil start, single cylinder. The machine was repowered with the same engine a few years ago. My expectation is the first engine had 2,500 to 3,000 hours, and this one has at least 3,000 hours. For many years, it was run very hard all season long.

    I expected this second engine to fail before this, but I think it now has a problem. It uses no oil, or perhaps just a little between changes (about 40 hours, new filter every 80, Shell Rotella 10W-30). But, I think the head gasket has just begun to leak.

    When cranking, I hear a leaking sound, a pffffft sound (sorry - the best I can do). Also, the engine starts much harder than a couple of weeks ago - then it was starting first pull, nearly every time. Now, it takes much choking, and many pulls. After a few pulls, with full choke, I see a bit of smoke come from under the front cowling, in the area where the exhaust pipe come, before running over to the pillow muffler.

    It still has power, but nothing I've done recently has required much power. I'm nearing the end, with final cuts, without much grass. All the heavy leaf mulching work is finished.

    Also, at WOT, it seems to be running at higher rpms that before. I'm throttling back a bit from full stop, thinking it might be over-reving.

    On engine shut-down, I also hear the leaking sound for the last few revolutions. These are pfffft sounds like on initial cranking on starting.

    I have never had a head gasket fail before. From my description, do you think this is my problem? If so, is a replacement a difficult thing to do? With a side-valve engine, taking off the head is a simple task. But, I'm unsure where the valve come through, how to deal with the OHV cover, and what is behind that cover. I have no service manual. Also, I don't have much in the way of diagnostic or test gear.

    As said before, my season is nearly finished. I still need it for a few mowings. So, I'm hoping it will continue to hang together for a short time longer.

    If a gasket replacement sounds reasonable, this is an off-season task. I know that I could repower with a new engine, but that seems a stretch for a machine this old. Otherwise, the mower remains in good condition. I know the hydro pumps are vulnerable to failure (I've replaced one of them a couple of years ago). But, I don't want to spend $750 on a new engine on this old piece of equipment.

    Any thoughts from the mechanics in the crowd? Some of you have been very helpful in times past, for which I appreciate. And, some of you have followed other repair efforts of mine, so know my capabilities -- this repair may be beyond my capabilities, or maybe not.


  2. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029


    From your description I'd bet the farm on a blown head gasket, They normally cut loose in the area you mentioned.

    You should be able to handle a gasket on this one without any problems.

    Hit this link and download a service manual and you can be on your way; http://www.kohlerengines.com/manuals/landing.htm

    If you have any issues, You know where the answer lays.....

    Good Luck
  3. Roger

    Roger LawnSite Fanatic
    Messages: 5,940

    Whew!!! You found my note.

    As usual, thanks for your help. I found the site, printed out the relevant pages of the service manual for disassembly and assembly. I also went to kohlerplus.com for parts lists. I think I found the head gasket I need, but am not sure yet of the cover gasket (if any). I need to download some viewer software to see the drawings. They are needed to be sure I have the right gasket(s).

    I will need to study the disassembly procedure to understand the valve connections, rods, rockers, etc. It all may become clear with the manual information and when things start coming off.

    I also printed out the spec sheets on torque specs, so I know what to do when tightening down the bolts. I do have access to a torque wrench.

    Thanks again. You have been so helpful. This is probably not a project to tackle for a few weeks, perhaps January. I hope I can get another five hours of use so that I get my season finished. This engine has been so solid for so long, it owes me nothing any longer. I should not be surprised at a problem the way it has been run, run, and run yet more.
  4. Roger

    Roger LawnSite Fanatic
    Messages: 5,940

    OK, I picked up a head gasket a while ago. We happened to have a nice, warm day at the end of December, so I pulled out the Exmark, intending to make the repair.

    Attached are a sequence of images I shot. First, the machine before I started work (up on some ramps so my back didn't cramp up), then taking off the cowling/starter, then the cover bolts. This exposed the valve rockers.

    I saw there were four bolts holding the rocker assembly in place. Two are inside the valve cover, the other two outside. I could see the push rods, the rockers, the valves, and the valve springs.

    When I saw this, I began to wonder what will happen when I remove the four bolts. I could envision the push rods falling out, the valve springs falling out, and any keepers associated with the valves. I could see that the rockers could be taken out first. But, I got cold feet to continue. If all these pieces suddenly fell out, could I get them correctly positioned upon reassembly? Getting the valve rocker assembly unit off, and getting the head gasket into position appears to be a minor issue. But, getting the pretensioned valves and push rods back, .... not so sure.

    Bottom line: I put the valve cover back on, put the exhaust back in place, and put the cowling/starter back. It started on first pull, so I am back at square one.

    The daylight was fast escaping, and I needed to get it wrapped up, and back into the garage. We have not had a work day since I did this excursion. Another day will come, so I want to be ready to retackle this problem.

    Now that I've seen what is inside, some questions:
    1. What about my concern that "it will all fall apart" when taking out the head bolts?
    2. Should the rockers be taken out first, loosening the forces on the push rods and valves? What are the risks associated with the valves, springs, and rods being loose? Do I risk not getting the rods properly positioned back on the cams, deep on the other end of the engine (looked at the parts diagram). BTW, the service manual does not show anything about taking off the rockers first, before taking out the head bolts.
    3. what should I be aware of on reassembly of the valves, push rods, etc.
    4. How to adjust the valves afterward? With a new head gasket, the tolerances between the cams and end of the push rods could be different, leaving the valves improperly adjusted. In the present state, finding TDC means the rod is just loose enough that it can be spun on its own axis. There is very little play. I see the adjusting screws, but do not want to tinker with them, unless I know exactly what I'm doing with regard to adjustments.

    Any help here? Or, am I into this too deeply, over my head? I can see that those who do this regularly should be able to make this gasket replacement in an hour or so.


    [Two pages of pics to follow]





  5. Roger

    Roger LawnSite Fanatic
    Messages: 5,940

  6. Roger

    Roger LawnSite Fanatic
    Messages: 5,940

    P.S. I realized I made a major mistake in not cleaning the engine up before starting. As soon as I had the covers back in place, and I fired it up, I used the pressure washer to get rid of the dirt. There is still some inside on some of the fins that I should have blown out with air when I had it open.
  7. ratfink

    ratfink LawnSite Member
    Messages: 77

    You shouldn't have that problem. The springs hold the valve shut, they aren't tensioned against the rods.

    You can take of out but unless you are going to you are planning on refacing your valves.

    You shouldn't need to remove the valves and the push rods should be pretty easy to maneuver to the right spot.
    Would need the spec number of the engine to tell you that. If it has hydrolic lifters though there isn't a need for adjustment.

    Few things. Kohler usually recommends you change the head bolts when you change the head gasket. If you do this or not is up to you but something to keep in mind.

    Make sure you have a torque wrench when tightening the bolts, proper torque is critical. Torque values should be in the repair manual.

    Follow proper tightening procedure by tightening bolts. Meaning you don't tighten bolts sequentially, rather you jump across what you tightening. Also dual stage tightening helps prevent the gasket deformation.
  8. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    ratfink is on the money.....

    But on this one;

    These valves are non-adjustable, Just hold the rocker arm square over the valve stem/spring and torque the hold-down screws to 100 in.lbs. as listed in the manual.....
  9. Roger

    Roger LawnSite Fanatic
    Messages: 5,940

    Thanks guys. This info is great, and I will proceed. I tend to always be on the non-risk side, ... wanted to be safe before proceeding. Now, I just need a reasonably warm day to get the machine outside again! Winter is terrible....
  10. Roger

    Roger LawnSite Fanatic
    Messages: 5,940

    OK, ... I finally had a day when I could work outside again. Yesterday was workable, but nothing between Dec 29, and yesterday. So, it was time to tackle the head gasket replacement task again. Comments made here, as well as PMs gave me more information, and the confidence, that I could do this task.

    Here are some pics of the project. I will let the pics speak for themselves. If somebody is really interested, PM and I will provide you with a link to an album of more pics, all of which have captions to describe what I was doing. The project took about 2:30. I've never done a project like this, so much of it was new.

    The outcome appears to be favorable. It started on second pull, runs well, the pffffft sounds of the leaking gasket are gone. You will see the gasket had channels where the air was leaking.

    If this is useful to somebody else considering such a project, then good. If not, then I'm not offended if you ignore.

    There are three sets of pics to follow.






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