B7100: Newbie Replace Head Gasket?

klipto · Jul 26, 2014

Hello OTT,

I recently acquired a well used B7100 (~1650 hours) with FEL for a reasonable price. I promptly replaced all fluids and filters and used the tractor for a week or so before I realized the clutch was going. I split the tractor and replaced the clutch / throwout bearing, etc. Felt pretty good about myself once I got the tractor back together, it turned over, and the clutch engaged on a small incline (something it did not do before)! The drivetrain works great now.

However, I am getting a lot of white steam at idle and even more at higher rpm. I just checked and there are bubbles in the radiator: pretty sure it is a blown head gasket (hope not a cracked head). Further I am pretty sure I bought it with this issue---like the title says, I am a newbie. I am chalking this one up to a learning experience...

How long should I budget to (i) remove the head, (ii) replace the gasket, and (iii) reassemble and adjust the valves? (Anything else I am missing?)

I have never done this type of work before---replacing the clutch took me about 3 weeks off and on (work and family keep me from spending more than a few hours at a time on the tractor). A good portion of that time was spent reading these forums.

Thanks for your help.

D2Cat · Jul 26, 2014

"How long should I budget to (i) remove the head, (ii) replace the gasket, and (iii) reassemble and adjust the valves? (Anything else I am missing?)"

Based on your last paragraph budget 3 weeks. Family won't be upset, you won't be stressed to work on it and if you get done sooner---that's a bonus!

It's all based on time available to you and your experience. Some would have it off and at the machine shop in 3 hours. However, they have done it before, have all the correct tools, even some air wrenches, and know the procedure.

klipto · Jul 26, 2014

Thanks for the quick response!

Follow up question: should I be using the tractor in its current state? Put another way, can I wait till the fall?

To be clear, the radiator bubbles are weak (once per minute) and the white smoke / steam is not as bad as other tractors I have seen with a blown head gasket.

North Idaho Wolfman · Jul 26, 2014

The longer you wait the more damage can be done, all it takes is one time of it getting a little too hot to crack the head or block then you're in for major repair.
Changing the head gasket on a B7100 takes me about 30 min to an hour to complete, I can split a tractor and replace the entire motor and parts in about 6hours, but the wife said I did it with zero distractions, no food, no caffeine, no breaks, standing on my head in my underwear, in sub zero weather, yep she's the smart ass.

For most it should take an easy day to do the head gasket.

meanjean · Jul 27, 2014

If you've got all tools on hand it's safe to say 3-5 hours.
That's without rushing.
Certainly helps to have a helper on hand.

klipto · Jul 27, 2014

I started taking the head apart this morning --- I'll post back if I have any troubles. I think it looks like a pretty easy job. Plus it is an excuse to get a few more tools. Adjusting the valves looked a bit intimidating but after a few youtube videos I think I can handle it.

As soon as I started to ask whether I could wait till fall, I knew the answer

Wish I had it down to a 3 hour job like you pros, though!

meanjean · Jul 27, 2014

Search for the post: L175 valve adjustment. Everything you need for
adjusting the valves. Trail dust made it very clear.

INTAKE VALVE --- CLOSING ----- ADJUST EXHAUST VALVE
EXHAUT VALVE ---OPENING ----- ADJUST INTAKE VALVE

I turned the engine over with a wrench on the alternator nut. Some guys are happy to adjust multiple cylinders at one time but not me. I work my way one at a time.

The valve furthest from you when seated is the intake valve, then exhaust valve and that's the first cylinder. Work your way back from cylinder 1 to 3 and take your time with it. (2 cylinders or 3 in that sweet ride?)

Proper gap is .006 to .008 thousandths.

Make sure to verify torque specs for the head bolts and also find the proper torque pattern.

Keep everything hospital clean and do NOT use a sealant on the head gasket.

Also

Make sure you replace any o-rings for oil galleries. I missed this step 3 times. That's part of the reason I've done the bloody job 5 times now.

Tooljunkie · Jul 27, 2014

You will have to set your valves again after head is re-torqued. Use a good quality torque wrench.

Take your time, ask at the dealer if they can print off that part of the workshop manual. Some might help. Some dont. Even if its for just the torque pattern ( critical) and specs.

Dont forget oil change and fresh coolant.

85Hokie · Jul 27, 2014

North Idaho Wolfman said:
The longer you wait the more damage can be done, all it takes is one time of it getting a little too hot to crack the head or block then you're in for major repair.
Changing the head gasket on a B7100 takes me about 30 min to an hour to complete, I can split a tractor and replace the entire motor and parts in about 6hours, but the wife said I did it with zero distractions, no food, no caffeine, no breaks, standing on my head in my underwear, in sub zero weather, yep she's the smart ass.

For most it should take an easy day to do the head gasket.

wolf, how the hell you do that WITHOUT any caffeine ??? the rest I get !

North Idaho Wolfman · Jul 27, 2014

85Hokie said:
wolf, how the hell you do that WITHOUT any caffeine ??? the rest I get !

Shear determination!

klipto,
If you don't have all the manuals yet, go to Kubota.com and download all the manuals, there is great information in all of them.

klipto · Aug 30, 2014

Thanks for the advice so far, everyone. I do have all the manuals I need and parts descriptions from Kubota. I went on vacation so my progress was stalled...

I removed the head (easy) and the gasket looks fine. Given this, I was a bit stumped as to why I was seeing white smoke in exhaust, bubbles in the radiator, and a preponderance of overheating. Then I looked at the block and saw this!

This is the middle piston and clearly is chipped. Somehow this debris has traveled to the first piston too (note the last piston looks great):

Does anyone know how this can happen? Ether? The prior owner said he never used it (and I never have either as the machine starts right up and I know it is bad for these engines).

So, can people advise me on how to proceed? As it stands, I am currently removing the oil pan to see if I can pop out this piston from below while the block is still in the machine. I would like to prioritize solutions which keep the block in the machine (if possible) and costs/time to a minimum. Plus, I am doing this all myself and as the title suggests, everything is new to me here.

The tractor has 1700 hours or so and the cylinders still have some cross-hatching. Should I hone the walls or can I get away with just popping in a new piston?

Should I worry about replacing/honing all pistons or just the middle one?

Thanks for your advice.

North Idaho Wolfman · Aug 30, 2014

First before you go any farther pull the head gasket off the block and take another set of pictures of around the middle piston and a set of the head too.

The debris is pieces of piston and carbon that have steam fired off the center piston.

When it goes to redoing it, just buy a rebuild kit and do all three pistons and bearings, other wise you'll be kicking yourself later.

klipto · Aug 30, 2014

Ok: if i am going to do one, I'll do em all! Those kits seem reasonable too, give the cost of just one piston/rings.

Here is a pic of the gasket:

And here is a picture of the head:

The head has carbon on it which brushes off easily. Using a straight edge and my feeler gauge, it looks like it is within tolerances (done after cleaning head in this pic).

North Idaho Wolfman · Aug 30, 2014

Just by the pic's what I'm seeing is just plain old head gasket seal failure.
Get a long file and surface the head and block and look very, very, closely for any signs of a crack.

klipto · Aug 30, 2014

Thanks for your quick response. Just to clarify, are you saying I don't have to worry about the chip in the middle piston?

North Idaho Wolfman · Aug 30, 2014

No I would still pull the pistons, hone the cylinders, the water/steam damage is pretty great on that piston and you wouldn't want it doing a total failure while running.

Apogee · Aug 31, 2014

Klipto,

You might as well do it right.

Since you're in it this far and with the number of hours it has on it, I would take the head to a machine shop have it pressure checked, magnafluxed, surfaced and a valve job done. Then you'll know for sure the head is perfect.

I agree with replacing all the pistons, rings, hone, and possibly bearings. I would do this not only because of the failure, but also because of the number of hours on the engine. Once you're done, you'll know what you've got and you won't have any further problems.

For the record, the B7100's will overhead if the radiator fins get plugged from weeds and dust because most iterations didn't come with a water pump. That might have been what happened in this case.

Hang in there. You will love this thing once it's fixed.

Steve

Tooljunkie · Aug 31, 2014

Its a coin toss,pulling pistons will tell you how much further you need to go.
If a set of cookies (snowmobile jargon for guys that like to tune and kaboom)is an acceptable price on your part then go for it. My tractor is in decent shape, i would do it if i was in your situation. Happy wrenching.

klipto · Aug 31, 2014

Steve, Wolfman, Tooljunkie,

Thanks for the advice. At this point, I am going to dive in and replace anything that looks warn. I am going to try to pull the pistons tomorrow. The head looks great after I cleaned it so at least I have that going for me.

I'll let you all know how it turns out or if I run into any troubles!

Todd.

P.S. Does anyone know a good shop in the greater Redmond, WA area which can resurface a head?

klipto · Sep 9, 2014

Hi Folks,

Getting around to ordering parts: Kubota wants ~280 bucks for a piston/ring kit while Kumar bros has the same parts for ~90 bucks.

Has anyone used a Kumar bro's piston / ring set? I know OEM parts are expensive but if people have had good luck with aftermarket, I'll go that route.

B7100: Newbie Replace Head Gasket?

New member

Well-known member

New member

Moderator

Member

New member

Member

Well-known member

Moderator

Moderator

New member

Attachments

Moderator

New member

Attachments

Moderator

New member

Moderator

Member

Well-known member

New member

New member