Anything else to do when changing a head gasket?

Lobanz · Jul 16, 2014

[I'm definitely not an experienced mechanic, but I have changed a head gasket before, but that was a LONG time ago. Remind me of any gatchas?]

My Kubota G5200 HST (3 cyl diesel mower) is overheating. Seems like a common problem. Only seems to overheats under load.

Anyway, I DID see air bubbles in my radiator. AND it uses water (but haven't noticed any in the oil). AND I can see some faint smoke coming out of the radiator when still cool (just after starting it up). So I am about to change the head gasket.

Wondering what else to do while I'm in there doing the head gasket. Already thinking about the following:

Fan Belt
Radiator Hoses
Exhaust and intake gaskets and bolts
Valve adjustment
Head resurfaced
Coolant system flush and, obviously, new coolant.
[Already had radiator boiled out not long ago]
Any sensors that should be replaced?
Anything to check on water pump?
Can you reuse the head bolts? (Service Manual (pg 1-53) doesn't mention replacing them, so I assume reuse is OK.)

Any other ideas?

I have noticed that the coolant drain cock on the block is rusted shut. Wondering if the cooling passage is also clogged. Don't know how to check.

Does your G5200 have a radiator fan shroud? Mine doesn't, but the Kubota Parts Site shows one (search G5200, click open, go to Cooling System / Radiator and it's part 110, #15852-72330). They are about $55. Wonder if it would fit mine and if it would help.

Also, does yours have an coolant overflow bottle? Mine doesn't, but it has a tube coming out of the neck of the radiator. So I just wedged a aluminum can in the frame and stuck the tube in the can. Don't know if it helps.

rswyan · Jul 16, 2014

Not familiar with that engine, but I'd make sure that it isn't an "interference" engine before you have anyone start shaving anything off the head ...

(I'd also have it checked for warpage)

Zebrafive · Jul 17, 2014

Look for evidence the head gasket failed after apart. If you can not determine the head gasket failed, have the head checked for cracks.

IH3444 · Jul 17, 2014

After head removal, and top of block cleaning it is advisable to check the top of block with a ground stock bar and a feeler gauge to ensure the top block deck is not warped. The manual should spec out the tolerance, but within 0.002" is good to go. Do the same to the mating surface of the cylinder head. It's much easier of course to have the head surface milled to spec, usually 0.005" will do. Also head gaskets for diesel engines may come in different thicknesses. You measure the piston at TDC, top dead center, take into account if any resurfacing of cylinder head was done, or top block deck resurfaced. Then calculate total difference. A chart usually tells you which head gasket to use. I'd bet all you need to do is check surfaces, then install new Kubota head gasket.

Lobanz · Jul 17, 2014

So, if I use a straight edge (like an aluminum square or something, or I have a level with a machined edge), and it looks pretty good in all directions (less than 0.005"), then do I really NEED to get it resurfaced?

Also, do I really NEED to take off the intake and exhaust manifolds? Would rather not deal with breaking rusted bolts if I don't have to.

If resurfacing is called for, will the machine shop require that the manifolds be off? How bout the valves and such?

Good stuff. Thanks!

rsallen · Jul 17, 2014

You are not going to have a handy tool laying just laying about that has those kinds of tolerances. A straight edge is precisely ground to specs for measurement....not a general purpose level or aluminum T-square or any wood working tools for that matter.
Checking the block is not a bad thing to do and necessary if theres a sleeve height needed for gasket sealing (ie. wet sleeves).
No you don't have to take off the manifolds IF you can check the head yourself. Otherwise the machine shop will, and charge you for it. Valves? Shrug, are you sure everything is okay there? Nows the time on find out not a hundred hours down the road. So yes, check those seats, guides and put in new stem seals.

brain55 · Jul 17, 2014

I have never seen a Kubota block warp (doesn't mean they can't). I've always used a straight edge and a .002" feeler gauge to check. I would check the head for cracks. The most common place these heads crack is in between the exhaust valve seat and the pre-combustion chamber on #2 cylinder (typically visible to the naked eye). If the head is not cracked you should have it resurfaced, usually it doesn't take much. If it does require removal of a lot of metal Kubota makes an .008" head gasket shim to correct the valve to piston clearance.

Brian

rsallen · Jul 17, 2014

Just a smatter for my own info brain, do those cracks run into the water jacket or is an easy repair to keep the seat from coming loose?

brain55 · Jul 17, 2014

rsallen said:
Just a smatter for my own info brain, do those cracks run into the water jacket or is an easy repair to keep the seat from coming loose?

Yes, they go into the water jacket and are not repairable. There are companies that say they can repair them, but I've never seen one do it successfully. If the head cracks the best thing to do is replace it.

Brian

rsallen · Jul 17, 2014

Thanks brain.

RSA

Lobanz · Jul 17, 2014

Yes. Valve seals. Excellent.

brain55 · Jul 17, 2014

Lobanz said:
Yes. Valve seals. Excellent.

Valve seals will come with the upper gasket kit. They won't fix worn valve guides though.

Brian

Baby Grand · Jul 17, 2014

Lobanz said:
[I'm definitely not an experienced mechanic, but I have changed a head gasket before, but that was a LONG time ago. Remind me of any gatchas?]

Does your G5200 have a radiator fan shroud? Mine doesn't, but the Kubota Parts Site shows one (search G5200, click open, go to Cooling System / Radiator and it's part 110, #15852-72330). They are about $55. Wonder if it would fit mine and if it would help.

Also, does yours have an coolant overflow bottle? Mine doesn't, but it has a tube coming out of the neck of the radiator. So I just wedged a aluminum can in the frame and stuck the tube in the can. Don't know if it helps.

Yes, our G5200 has a radiator fan shroud (it was missing when I got the tractor). It collects a lot of mowing debris that would otherwise plug up the radiator.

No, ours does not have a coolant bottle, but it has an overflow tube with a whistle attached to the end. But I don't see any reason that a collection bottle couldn't be installed between the radiator & the whistle ...

buickanddeere · Jul 17, 2014

Don't grind the seats and valves without correcting for sinking the valves . Otherwise compression will be lost.
Odd how nobody mentioned chasing the block threads with a bottoming tap. Champhering the top thread out of the block to ensure their isn't a raised thread holding the head up. No mention of checking across the flat of the head over the thread bosses looking for raised metal around threaded holes. And no mention of using new fasteners. Why trust old stretched head bolts , in particar when there may have been a head gasket leak.

brain55 · Jul 17, 2014

buickanddeere said:
Don't grind the seats and valves without correcting for sinking the valves . Otherwise compression will be lost.
Odd how nobody mentioned chasing the block threads with a bottoming tap. Champhering the top thread out of the block to ensure their isn't a raised thread holding the head up. No mention of checking across the flat of the head over the thread bosses looking for raised metal around threaded holes. And no mention of using new fasteners. Why trust old stretched head bolts , in particar when there may have been a head gasket leak.

You're right. I was answering specific to that engine without adding general knowledge in. I do that stuff as second nature, not because it's a Kubota.

Brian

rsallen · Jul 17, 2014

Sinking of the valves!??? WTF is that? This isn't overhead cam engine, and even if it were all the machine shop does is grind off the end of the valve stem to make up the difference for clearance.. Sinking of the valves....never heard of such a thing.
Cleaning the threads on both the bolts and the block are standard operating procedure along with the top of mating surfaces of block and head. Spelled out and written in every instruction I've ever read. No mystery.

Block threads don't deform at the torques heads are typically wound down to without cracking the block. If you want to check the old fashion alloy bolts against each other to check if one or more have started necking out that's fair enough, and if you have the designed stretch head bolts then renew all of them. Otherwise buck, stick with what you know and don't confuse the op.

buickanddeere · Jul 17, 2014

If you are not familiar with lost compression caused by sinking the valves by grinding the valves and seats. You can not claim to be an expert.
So there is something wrong with mentioning the thread chasing and chamfering the top thread? Or just jealous because you never thought of it? Using new fasteners is a given as previously used bolts can not be 100% trusted without using non destructive testing. Which is beyond the abilities of the Kubota owner.

brain55 · Jul 17, 2014

Any competent machine is going to address valve and seat height.

Brian

Coyote machine · Jul 18, 2014

Head bolts, new, and torque spec, dry, or lightly oiled?

rswyan · Jul 18, 2014

rsallen said:
Sinking of the valves!??? WTF is that? This isn't overhead cam engine, and even if it were all the machine shop does is grind off the end of the valve stem to make up the difference for clearance.. Sinking of the valves....never heard of such a thing.

Yup ... that's exactly what R & R Engine and Machine did when I had them do the cylinder head off my OM647 engine ... and it is overhead cam (dual) ...

BTW ... I reused the head bolts ... they were all well within spec (within the tolerance range for stretching) ... that was about 60K miles ago (at least 1000 hours ago, roughly) ... no problems yet