Thread: Any Diesel or tractor mechs on here?

Yesterday on the way back from a job my tractor started to spew coolant from the reservoir and warming up, didn't overheat.
Topped it up to make it back home. Let it cool down then topped up coolant to proper level. Took belt off water pump and turned the engine on with reservoir cap off, few second later coolant was blowing out.
Am I right that it has a blown head gasket and combustion gas blows into cooling system?
There is no oil present in coolant , there were bubbles in tank first time I opened it.
No coolant in engine oil.

If it's a HG could I remove rockers without the need of re-setting timing? I think I can do a HG job (did a few on SJ413s) the only thing that worries me is the timing.
Water pump got replaced 15Hrs ago, cost me 2.5k so would be keen to fix myself. I would image this sort of work could go up to the 5-6K mark.
Engine is JD 4045TR

Any advice would be much appreciated.

Thanks
BF