B7100 D750 won't rev up

Fiftybucks · May 23, 2019

Hi all, I have a B7100 with a D750 A few weeks ago i noticed a head bolt had actually broken the head off of the bolt. I bled the injector lines and some of the diesel pooled around the base of the injectors, and while it was there and the engine running, there were bubbles around each injector (one quite badly), and actually one of the glow plugs. I replaced the bolt with a new one and checked the others. I figure the the head gasket for sure. I removed the injectors, and replaced the copper crush washers.. upon getting it started (hard to start), the engine no longer wants to rev up above medium range, runs rough. I double checked the injectors, and they have a spray pattern.. not great, but OK...

Now is hard to start, probably compression, and won't rev up like just a few weeks ago. No water in the oil or oil in the coolant. Is it time to give up, and get a new tractor?

North Idaho Wolfman · May 23, 2019

Fiftybucks said:
Hi all, I have a B7100 with a D750 A few weeks ago i noticed a head bolt had actually broken the head off of the bolt. I bled the injector lines and some of the diesel pooled around the base of the injectors, and while it was there and the engine running, there were bubbles around each injector (one quite badly), and actually one of the glow plugs. I replaced the bolt with a new one and checked the others. I figure the the head gasket for sure. I removed the injectors, and replaced the copper crush washers.. upon getting it started (hard to start), the engine no longer wants to rev up above medium range, runs rough. I double checked the injectors, and they have a spray pattern.. not great, but OK...

Now is hard to start, probably compression, and won't rev up like just a few weeks ago. No water in the oil or oil in the coolant. Is it time to give up, and get a new tractor?

You need to do a compression test on it before I can tell you which way to go.

Low compression - Rebuild / Replace
High compression - Way more options.

flashover1969 · May 23, 2019

What's the condition of your fuel filter?

motorhead · May 23, 2019

When you changed the broken head bolt, did you re-torque the rest of the head bolts? If so, did you check your valve clearances after? Might have some tight valves.

Fiftybucks · May 24, 2019

Fuel filter seems OK... but I will double check...
I really only tried to re-torque the new head bolt, and one of the neighboring bolts. What would cause the head to break off a head bolt?
I did not check valve clearance.. I'll look today.. something may be causing compression loss... hopefully not a hole in a piston. Are all those bubbles normal around the injectors and head...

How bad a job to remove head...?

85Hokie · May 24, 2019

What would cause the head to break off a head bolt?

the previous owner had to try to remove it and it broke....

Are all those bubbles normal around the injectors and head...

the bubbles are AIR in the lines.....not good at all and can be part of your problem....when the injector "fires" there should be no bubbles at all rather a stream of fuel with no bubbles. YOU still have air in the line...and it still could be coming via your fuel filter.

How bad a job to remove head...?

Removing the head is the easy part.........placing it back with correct gasket and torque specs will be a more difficult part

thepumpguysc · May 25, 2019

85, I think u misread the parts about the air?? or I did.??
IF its bubbling around the base of the injector while its still in the head, its not air in the lines, its a bad seal between the injector & head & the bubbles are compression leaking up past the injector..
If it was air in the lines, why was the glow plug bubbling.?? Lol.

That is an odd problem tho.. after tightening everything up its hard to start..
The valve clearance it a good tip.. along w/ torqueing ALL the head bolts..
1 more thing>> the spray pattern is VERY important for a good starting engine..
OK, 2 more things.. u said theres no water in the oil.. how about water in the fuel.?? & that's the reason it wont rev up..
U could pull the line before the filter & drain it in a 5 gal buck to check the flow & use a glass to catch some fuel & let it sit for 24/48hrs to see if it separates.?? {water will be on the bottom}
Good luck.

Fiftybucks · May 25, 2019

good suggestion on the water in the fuel.
also the bubble are around the base of the injector not in the fuel line

spray pattern is poor on 1 injector...
i will re-torque all head bolts as i will have to have the valve cover off to check valves... oh no... valve cover gasket is going to be leaky..

what are the head bolt torques... and i know about tightening center toward outside in 2 or 3 sequences..

North Idaho Wolfman · May 25, 2019

Fiftybucks said:
good suggestion on the water in the fuel.
also the bubble are around the base of the injector not in the fuel line

spray pattern is poor on 1 injector...
i will re-torque all head bolts as i will have to have the valve cover off to check valves... oh no... valve cover gasket is going to be leaky..

what are the head bolt torques... and i know about tightening center toward outside in 2 or 3 sequences..

Go to Kubotabooks.com and download the WSM (aka Service manual) it will have a lot of information that you need.

Did you put a new head gasket in it?
If not, You need to do that, you can not get an old head gasket to seal.

If it's leaking air around the injector at the head, then you have either not torqued the injectors down properly, have bad sealing washers under the injector, have dirty surfaces on the head sealing surface or the injector or washer, or Very Very Very less like have a cracked head.
If it's also leaking out where the glow plug goes, you either have a taper seal damaged glow plug or you have not torqued them down properly.

It will not start and run properly with those leaks as it can not get to the 325+ PSI in order to fire, so fix those issues first.

Fiftybucks · May 26, 2019

thx wolfman

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