B7100 Head gasket

[botavt]

Rebuilt my b7100 with new con bearings, rings and valve reseating.
First start showed low compression and extending cranking to start. Oil burning until thoroughly warmed up. Gets better the more I break it in, But still needs a long crank. Runs good otherwise.

Today after 4 hours of total run time I discover that I failed to put the oring around the rear pin on the block and I have an oil leak out the gasket down the block. So, off with the head to replace.

Do I need a new head gasket or can I clean this one with brake cleaner and reuse? Also: there are 12 bolts and two studs. Where do the studs belong and why studs anyway? Thanks!

 

[eserv]

Rebuilt my b7100 with new con bearings, rings and valve reseating.
First start showed low compression and extending cranking to start. Oil burning until thoroughly warmed up. Gets better the more I break it in, But still needs a long crank. Runs good otherwise.

Today after 4 hours of total run time I discover that I failed to put the oring around the rear pin on the block and I have an oil leak out the gasket down the block. So, off with the head to replace.

Do I need a new head gasket or can I clean this one with brake cleaner and reuse? Also: there are 12 bolts and two studs. Where do the studs belong and why studs anyway? Thanks!

You would likely get away with it, but it is never considered good practise to reuse any gasket.

 

[rentthis]

I agree with eserv. Save yourself the potential grief.

 

[botavt]

Thanks! I will try to reuse knowing that I might have to replace. I would never try this on a diesel car, but the head is easy to get at here. Why are studs used in two places on this head?

 

[North Idaho Wolfman]

Ditto, the potential of it not resealing is way too high.

The reason for the studs is to make it easier to re align the head gasket and head.
No special location really, I like left side front and right side rear, newer motors just used all bolts.

 

[botavt]

Like the old guy said: If you aren***8217;t going to listen to me, why did you ask?

I removed the head and the head gasket did not seem to have sealed very well: I***8217;ll buy a new one! The torque for this head is so low (35 ft lbs). I don***8217;t see how it ever seals. My Mercedes wants at least 45 lbs and then 2 quarter turns after that, iirc.

 

[North Idaho Wolfman]

Like the old guy said: If you aren***8217;t going to listen to me, why did you ask?

I removed the head and the head gasket did not seem to have sealed very well: I***8217;ll buy a new one! The torque for this head is so low (35 ft lbs). I don***8217;t see how it ever seals. My Mercedes wants at least 45 lbs and then 2 quarter turns after that, iirc.

What do you mean, "head gasket did not seem to have sealed very well"
How are you gauging that?

 

[botavt]

Piston #3 had oily soot All around its metal ring. I***8217;ve already cleaned it up or I***8217;d post a photo. Oil reaches the head through a pin near #3. There is a crush washer affixed to the gasket that I think keeps the oil where it belongs, but I had a seep along the block on that side, which is why I pulled the head in the first place. It was an oily mess generally.

My torque wrench is the old style beam type and I wonder if it lied to me when I was torquing the first time.

 

[North Idaho Wolfman]

Piston #3 had oily soot All around its metal ring. I***8217;ve already cleaned it up or I***8217;d post a photo. Oil reaches the head through a pin near #3. There is a crush washer affixed to the gasket that I think keeps the oil where it belongs, but I had a seep along the block on that side, which is why I pulled the head in the first place. It was an oily mess generally.

My torque wrench is the old style beam type and I wonder if it lied to me when I was torquing the first time.

Or maybe when you didn't put the O-ring in oil was forced in between the gasket and the head?

Have you checked the block and more importantly the head for flatness?

 

[D2Cat]

I'd say, as North Idaho Wolfman suggested, be sure you have the O-ring installed. Some folks are not aware one is needed.

 

[botavt]

I'd say, as North Idaho Wolfman suggested, be sure you have the O-ring installed. Some folks are not aware one is needed.

In my defense the oring is shown on the crankcase fiche and not on the cylinder fiche, so I missed it there. The old head gasket is gone to the trash so I cant say if I just never saw it or it was missing... there was quite a sludge on that side of the block. Ive owned this tractor for ten years or more and never had the head off before this.

Wolf man: thanks for dragging me back into first steps. I checked the head for flatness and found it to be .001 or slightly more across 12”; spec is .002 in 4”.
So I’m pretty well within spec. I ordered a new head gasket and will install it on Wednesday. Did oil just migrate under the gasket and spoil everything or what?

 

[200mph]

What is the OP going to do to remedy the low compression?

I get the impression they feel the head was sealing combustion pressures and only taking apart due to the oil leak.

Since they claim to have "rebuilt" the engine block I wonder what type of cylinder preparation was done prior to the new rings and if the bore diameters/taper were checked.

 

[botavt]

The head was removed because one cylinder was starting later than the others. There was little oil consumption nor was the coolant compromised. I thought I might see a broken ring or a bad piston. Upon disassembly the pistons showed no sign of slap or excessive carbon buildup. The connecting rod bearings showed slight wear but no scratches. The valves however, were a carboned up mess. The liners showed a little cross hatching. I don***8217;t have a way to gauge roundness. Since nothing looked too bad and it ran pretty well before, I proceeded. I***8217;m not a professional mechanic but I have opened up Diesel engines before this. In my experience, a head gasket is a maintenance item, and this old girl has been used.

I changed the con rod bearings, installed new std rings, hand ground the valves through two different grade compounds, honed out the cylinders a very little bit, and put it back together with a new gasket kit. I did not open up the timing gear case or fiddle with the injector pump.

A word about the rings: I put one in each cylinder and checked end gap. In spec. I installed the compression rings 90d from the wrist pins one on each side. I took a guess on the oil ring and put it 45d off the wrist pin. Maybe this was wrong.

From the first, it ran on with the starter and lots of black smoke, but was hard to keep running until warm. Four hours in, it started to be more willing to start, but still was not as good as before I started. I regapped the valves to .010 thinking they might be a little tight at .007. After a thorough warm up of 10 minutes or so, it burned pretty clean. Then I noticed the seep on the side of my newly cleaned block, which led me here. I might not have done anything if not for the seeping gasket, which seems to be a missing oring that my manual did not show.

So yes, I throw the word ***8220;rebuilt***8221; around a bit. But its a 35yr old 16hp motorized wheelbarrow, so I***8217;d say it lucky to get this much attention! But I am fond of it as it has a big heart for a machine designed to run in rice paddies.... oh so slowly.

 

[200mph]

Thanks for the clarification of the work performed previously.

Can you quantify the compression results and specification for this motor?

Bolt torque: I believe I read that you used a beam style torque wrench. I’d recommend either renting or purchasing a different style as they tend to be more accurate. Might also want to make certain you working in the upper 50% of wrench range. Clamp load is highly dependent on bolt friction, so make certain threads and under side of bolt head and mating surfaces are clean and smooth. Also follow recommendations if any lube is required and what type.

Ideally bolt stretch is measured as this is the best way to achieve clamp load but not always possible. When using torque as a surrogate for bolt stretch it is highly dependent on friction to achieve proper and uniform clamp load across the head.

Good luck and keep us posted on how the repair goes.

 

[botavt]

Currently the head is off but I will check compression if needed later.

Re head bolts. My experience is with MBZ w201s.. I followed my procedure here, which is to chase the bolt holes with a tap, fill the holes with wd40, and then vacuum out the holes. I put oil on the head bolts. Kubota does not give bolt stretch values, so I felt safe in reusing the bolts, which are not cheap. I had one broken head bolt (!) so I bought a new replacement. The old ones have washers, but the new one had a flanged head, so I did not use a washer on it. That made the installed length equal to the others. The spec is for 30-35 ft lbs. This seems very low to me, as the MB head is 45lb and then two cranks of 90d, but I used my beam wrench and went to 35. I will check my wrench against my neighbors expensive one to see if that***8217;s my problem, which I hope it is.

 

[North Idaho Wolfman]

You've mentioned low compression, did you ever test it and get numbers or just assume that is the issue?

Long crank times and hard starts can be caused by several things.

1: Low compression, could be caused by, bad piston sealing (rings, oversized liners, too large of ring gaps and such), bad head gasket seal, bad valves, leaking injectors, or leaking glow plugs.

2: Bad fuel quality, delivery, or management, cause by bad / worn injectors, bad / contaminated fuel, worn fuel injection pump.

3: Worn out / bad glow plugs or wiring, even the glow plug indicator can go bad and cause issues, you need to test the entire system and components, the glow plugs get power from the ignition switch in glow, through the indicator then onto to glow plugs, and from the ignition switch in crank directly to the glow plugs.

4: Bad / worn out starter, battery, or wiring, have the battery load tested, if it sounds like it might be cranking slow have the starter tested too.

The number one things I find on these style engines is bad Injectors, bad glow plugs, and low compression from wear.

 

[botavt]

Thanks wolf man:
Glow plugs were bench tested>. Aluminum wires between plugs were filed clean. Voltage at glow plug was 8.7volts, in spec.
Starter spins well. Tractor smokes black when first cranking.
Fuel was the same as prior to tear down but is summer blend. Added a quart of kerosene.
Injectors were replaced with new about a year ago as the first step in troubleshooting.
Tomorrow I***8217;m going to check my torque wrench against a spring scale.

Stay tuned.

 

[200mph]

I don't know where I got it, but I happen to have a B7100 WSM and it does state the upper torque range to be 35 FT-LB for the head bolts using oil. (See attachment)

Even checked the NM to FT-LB conversion to make certain they were correct.



DISCLAIMER: I don't know if this WSM has been revised or not, so please verify before relying on this info.

 

[North Idaho Wolfman]

Thanks wolf man:
Glow plugs were bench tested>. Aluminum wires between plugs were filed clean. Voltage at glow plug was 8.7volts, in spec.
Starter spins well. Tractor smokes black when first cranking.
Fuel was the same as prior to tear down but is summer blend. Added a quart of kerosene.
Injectors were replaced with new about a year ago as the first step in troubleshooting.
Tomorrow I***8217;m going to check my torque wrench against a spring scale.

Stay tuned.

Where were the injectors from, as there are a ton of bad one's out there.
More bad than good I've found.

One quick and dirty test is too hook up a injector remotely off the injection pump and tests it that way.
If either it drips or doesn't put out a very clean and defined mist pattern then it's bad.
Also when it was giving you issues did you try swapping the injectors from a known good running cylinder to the one giving you issues?

Some, like very little, black smoke on startup is normal but too much and you more than likely have a bad injector /s, or low compression.

 

[botavt]

The simplest answer is usually the right answer, and that***8217;s just that the compression is too low at startup. I***8217;m going on the assumption that I didn***8217;t tighten up the head enough.

It runs very nicely after about ten minutes, and burns cleanly, so I***8217;m encouraged that this is something simple. Head torque is my vote. Ill know more on Thursday.