Blown Head Gasket

[RobJ]

if you don't have the head milled and the block decked, I like to take a file and/or a random orbitor sander and clean up the surfaces. You don't have to hit it much. it may expose good news or bad news.

Rob

 

[greg_g]

The first head gasket probably went because the 50 hour head bolt retorquing never happened. But that horse is already out of the barn. When you install a subsequent head gasket, the 50 hour clock starts again.

The second one could have gone for any number of reasons. Just out of curiosity, did you succumb to the popular misconception about oiling the head bolt threads? what tightening pattern did you follow? and how much torque did you apply?

//greg//

 

[RobJ]

The first head gasket probably went because the 50 hour head bolt retorquing never happened. But that horse is already out of the barn. When you install a subsequent head gasket, the 50 hour clock starts again.

//greg//

Greg,

Where are you getting this 50 hour number? My service manual says 30 minutes. No where in the shop manual or owners manual does it say 50 hours. Kubota doesn't even recommend adjusting the valves until 600 hours, then every 850 after that.

I've never gone back and tighten the head bolts on anything. Even my L when I changed out the head gasket. If it's overheating in less than a minute...I think something is wrong in that head.

Rob

 

[greg_g]

Greg, Where are you getting this 50 hour number?

Not from your Kubota manual, that's for sure. Odd are extremely high that the OP's Jinma has the YangDong Y385 engine. I took the 50 hour head bolt retorquing requirement straight out of the YangDong Y85 Operations & Maintenance manual.

The Y85 family of engines will overheat after a head gasket change IF you don't make provisions to bleed the air while refilling the cooling system. The easiest way to bleed is to loosen the temperature sending unit while pouring in the anti-freeze and water. Which reminds me, this is a wet sleeved engine. SCA (anti-cavitation) coolant should be used to reduce water pump wear and prevent premature performation of the cylinder liners. Not that I am endorsing any particular brand, but Final Charge 50/50 is available in most WalMart auto departments at ~$10/gal.

//greg//

 

[RobJ]

Interesting, as a former mechanic I had a tough time digesting the 30 minute rule on my L. Does Kubota really assemble an engine, run it for 30 minutes, then take it apart to tighten the head bolts? And I guess this is while warm??? My manual isn't specific on that that issue. Just says run for 30 minutes then re torque. MY assumptionis while hot.

I also learned about bleeding the coolant on my kids 3.8l mustangs because the engine parts are higher than the radaitor.

Rob

 

[Jinma284]

Rob, the machine shop in our town said he could not mill the head because of the stainless steel inserts. His machine would not cut them. We will follow your advise before installing.
Greg, we did not oil the bolts before tighting. We had a tighting pattern given to us by a dealor and used the proper tool to tighten. I do not remember the pattern off the top of my head. We will redo the tighten deal after 50 hours. I only had about 20 hours this time.

 

[greg_g]

MY assumptionis while hot.

Thanks for mentioning that, I forgot to specify in my earlier post. The Y85 manual says to do headbolts and valve lash on a cold engine

//greg//

 

[greg_g]

We had a tighting pattern given to us by a dealor and used the proper tool to tighten. I do not remember the pattern off the top of my head. We will redo the tighten deal after 50 hours. I only had about 20 hours this time.

I just hope "the proper tool" was a torque wrench. If you want the headbolt tightening sequence, torque spec, and valve lash specs, let me know.

Oh, and I mentioned valve lash because - every time you remove the valve train - you should at least verify the gaps haven't changed. That includes the decompression screws.

//greg//

 

[Dave_Lilly]

You have a problem of coolant leaking into one or more cylinders. Coolant leaking into one or more cylinders will blow a head gasket because water is not compressible and has nowhere to go except out through the head gasket.
Did you notice white smoke coming out of the exhaust pipe?
Both the engine block and the cylinder head should be checked for warpage before replacing the head gasket, along with checking the cylinder sleeves, head and block, etc using magnaflux.
Extreme overheating can warp both the cylinder head and the engine block.

 

[greg_g]

Coolant leaking into one or more cylinders will blow a head gasket because water is not compressible and has nowhere to go except out through the head gasket.

Not entirely true. Yes, water is essentially not compressible. But but opened valves permit water to be pushed out.

Did you notice white smoke coming out of the exhaust pipe?

If white smoke comes out of a cold muffler for more than a few seconds, that pretty much confirms that some form of water is coming out the exhaust valves. This can also be accompanied by thin (watery) grey oil. It can run down the side of the block, leak out of the exhaust manifold, or - under advanced throttle - spray out of the muffler.

That said, I agree that it's extremely important to clean the milled edges completely, followed by a very thorough visual inspection for damage. A trued metal straight-edge should be used to check both head and block faces for warpage. A crack doesn't always look like a crack. Any suspected areas or unexplained blemishes are candidates for MagnaFluxing.

But I'm not yet convinced that this is a head/block issue. Being a wet-sleeved engine, a hole in a cylinder lining would almost certainly permit coolant into the oil pan. So far, the OP says that's not happening. For now, I'm still thinking the issue is procedural.[/quote]

//greg//