Repairing a Kubota D600 engine with a cracked head
Posted July 27, 2020 - 06:07 AM
- KennyP, Cvans, chieffan and 2 others have said thanks
Posted July 27, 2020 - 06:51 AM
- chieffan said thank you
Posted July 27, 2020 - 11:38 AM
Several years ago I bought a Kubota with the d600 engine with a cracked ?? Was getting water in the oil. Put in 1/2 bottle of K-Seal and run it for a couple hours, drainer the oil and water out, refilled and put the rest of the K-Seal in with antifreeze. It had a 6' deck so put about 10-12 hours on it mowing. No issues. It went down the road and a year later it was still running OK. Buyer was mowing cemeteries with it. Some times you win, some times you don't.
Posted July 31, 2020 - 09:10 PM
After repairing the crack in the head, the engine ran a lot better and was able to handle mowing. However the coolant started finding its way into the sump again, and the engine was overheating after a while. Pulled the head again, and sure enough, it had cracked through the braze repair. So I notched the crack out deeper and repaired it. By dumb luck (I discovered this when notching it out) the crack had only gone as far as the valve seat and had penetrated only about 4mm (just over 5/32") into the casting.
I came to the conclusion that the new crack was caused by the deck surface not being flat enough, having been the result of bending forces being applied when I torqued up the head bolts.
So I set the head up in my old metal shaper to deck it. I found a bit of a dip in it (about 0.1-0.15mm from memory) when I was using a dial indicator to check that I had it square to the machine. I suspect it had warped when it was overheating. I used the shaper because I haven't trammed my mill properly yet.
Here's what it looked like after decking.
When I stuck the head back on and started filling the radiator, the coolant got into the sump and sent grey stuff pouring out from around the pushrods! Pulled the head and tried adding water and the same thing happened. This leak was not in the head, but somewhere in the block. Which meant that this engine had to come out and be stripped down to find the problem.
Rigging in place.
Engine removed successfully
On the bench ready for the teardown.
Ah ha! Failed welch plugs. The previous owner said he'd replaced them, but he'd only replaced the ones on the sides of the block! This is why you need to be a bit suspicious when a private seller claims that a vehicle or machine has been worked on. For some reason Kubota was (are they still?) using steel welch plugs rather than brass ones. I have no idea why they did that; cost cutting perhaps?
This was an easy fix, I just knocked the old ones out and stuck in some brass ones, which won't rust out and should hopefully last the life of the engine. I've since replaced all the remaining steel welch plugs with brass after having another one let go in the cylinder head.
That's all for now. I actually did this work a couple of weeks ago but was preoccupied with actually getting my hands dirty; not to mention having no internet for a week a while back while we were being upgraded to a faster connection.
- olcowhand, Cvans and sharkman have said thanks
Posted July 31, 2020 - 10:46 PM
Thanks for the follow up.
Posted August 01, 2020 - 08:32 AM
good work thanks for the post update