[AT] Kubota M5700 noise

Spencer Yost spencer at rdfarms.com
Wed Apr 8 11:25:35 PDT 2020 

I have been able to read part/casting numbers on rods with my inspection scope.  If the oil drain bolt hole is close enough to #5 you might get the access  you need for looking around with a scope.   it can be tedious but usually can be done.  But if you’re luck is like mine that oil drain bolt will be on the wrong side of the engine :-).  Push comes to shove you can pull the pan for inspection.   

Long story but I actually had to do this once to see which one of three available rods I needed to buy to replace the one that was broken. One of the three was only available in overseas markets and took 2-3 months to get so wanted to start the ordering process if needed before I started the tear down.

Spencer

Sent from my iPhone

> On Apr 8, 2020, at 1:28 PM, Jim Becker <mr.jebecker at gmail.com> wrote:
> 
> 
> Compression ratio is of the swept volume plus combustion chamber volume divided by the chamber volume.  It looks like you used swept volume divided by chamber volume.
>  
> If I ignore the bore, which is just a multiplier on top of everything:
>  
> If stroke is S, C is the average height of the combustion chamber, and R is the compression ratio:
> R = (S + C)/C
> R = S/C + 1
> R – 1 = S/C
> (R – 1) * C = S
> C = S/(R – 1)
>  
> C = 92/(23 – 1) = 92/22 = 4.18
>  
> A shorter rod increases C by the same amount to the new value C1.  Thus the new compression ratio R1 is:
> R1 = S/C1 + 1
> R1 = 92/(4.18 + 1) + 1 = 92/5.18 + 1 = 17.75 + 1 = 18.75 call it 18.8
>  
> Back to the original problem, it isn’t clear to me that it matters whether the ratio is 18.4 or 18.8.  It seems that is low enough to cause a misfire.  If there isn’t enough compression to get ignition, it seem unlikely the left over fuel from a misfire would cause preignition on the next cycle.  But who knows what all the behavior might be.
>  
> I can’t come up with any way to identify a mismatched connecting rod without disassembly.  Once the head is off, it should be easy to find by bringing each piston up to TDC and measuring the height relative to the deck of the block.
>  
> Jim Becker
>  
> From: Stephen Offiler
> Sent: Wednesday, April 08, 2020 4:18 AM
> To: Antique Tractor Email Discussion Group
> Subject: Re: [AT] Kubota M5700 noise
>  
> I just worked out some math.  That engine is 87mm bore x 92mm stroke.  23:1 compression.  Swept volume is .547 liter, giving combustion chamber volume of .0238 liter.  Now, what-if the con rod was 1mm too short?  That adds .0059 liter to the combustion chamber, now .0297 liter, which drops compression down to 18.4:1
>  
> SO
>  
>  
> On Tue, Apr 7, 2020 at 7:02 PM Doug Tallman <dtallman at accnorwalk.com> wrote:
>> The rod being too short can't change injector timing or cause pre-ignition. It would just mean less compression because the piston wouldn't come up as far.  Doug T
>> 
>> On 4/6/2020 6:24 PM, Dave Maynard wrote:
>>> I know the piston is correct as we replaced it. But James makes a good point to ponder, if the rod is too short, it may change injector timing.
>>>  
>>> Dave
>>>  
>>> On Mon, Apr 6, 2020, 6:03 PM Bo Hinch <bohinch at gmail.com> wrote:
>>>> Or the wrong Piston ( too short or tall ) .
>>>>  
>>>> On Mon, Apr 6, 2020 at 12:40 PM Dave Maynard <dave at themaplehillfarm.com> wrote:
>>>>> Actually, did not check length of connecting rod and its clearance from head at TDC. But it's not traveling to close to the head as there would be damage showing. Just have this new concern about the wrong rod being put in by mistake, but that would have been short, not long.
>>>>>  
>>>>> Dave
>>>>>  
>>>>> On Mon, Apr 6, 2020, 1:01 PM Mike M <meulenms at gmx.com> wrote:
>>>>>> When you had it apart, did you check all the piston,ring and bearing clearances?
>>>>>> 
>>>>>> Mike M
>>>>>> 
>>>>>> 
>>>>>> On 4/6/2020 11:35 AM, Dave Maynard wrote:
>>>>>>> No sleeves in this engine. Someone had this engine apart before and #5 had a new piston and rod and bearings. The seller said it was his father's tractor since new and never been apart....he lied! There was more RTV on oil pan than you could imagine and obviously that piston and rod and bearings had been replaced and I thought they had been chasing the noise. Unless there was some other reason, but dont know. 
>>>>>>>      My friend and mechanic help has a Jacobson mower he's is rebuilding that has a 4 cylinder version of this motor that appears identical except the number of cyl's. He found the rod to be the same except it a tweak shorter by an almost immeasurable amount, maybe .005 or .010. Part number is almost the same except last digit and now I'm wondering if that could be someone's mistake. Would shorter rod cause preignition? By the way, there is no part number on the rods so they would have to be accurately measured.
>>>>>>>      It's going to be a bit before I can get this back apart again, but hoping to have this fixed in time to plow.
>>>>>>>  
>>>>>>> Dave
>>>>>>>  
>>>>>>> On Mon, Apr 6, 2020, 9:08 AM Cecil Bearden <crbearden at copper.net> wrote:
>>>>>>>> That was one of my thoughts, but my experience has been that the liner movement was a double "thud" once on down stroke and once on upstroke.  
>>>>>>>> Cecil
>>>>>>>> 
>>>>>>>> On 4/6/2020 1:12 AM, k7jdj at aol.com wrote:
>>>>>>>>> Cylinder liner loose.  Don't know if this engine even has cylinder liners if it does and that liner is moving you would get click. Did you look carefully at the head when you had it off and look for any sign of head distress?
>>>>>>>>> I would do a compression check as well.
>>>>>>>>> 
>>>>>>>>> Gary
>>>>>>>>> 
>>>>>>>>> Renton, WA.
>>>>>>>>>  
>>>>>>>>>  
>>>>>>>>> -----Original Message-----
>>>>>>>>> From: Roger Moffat mailto:rogerkiwi at gmail.com
>>>>>>>>> To: Antique Tractor Email Discussion Group mailto:at at lists.antique-tractor.com
>>>>>>>>> Sent: Sun, Apr 5, 2020 7:43 pm
>>>>>>>>> Subject: Re: [AT] Kubota M5700 noise
>>>>>>>>> 
>>>>>>>>>  
>>>>>>>>> 
>>>>>>>>>> On Apr 5, 2020, at 9:59 PM, Dave Maynard <dave at themaplehillfarm.com> wrote:
>>>>>>>>>>  
>>>>>>>>>> Have cracked injector lines one at a time, and it gets quieter on #5
>>>>>>>>> 
>>>>>>>>>  
>>>>>>>>> But only on #5?
>>>>>>>>>  
>>>>>>>>> When you crack the others the engine misses, but the noise remains?
>>>>>>>>>  
>>>>>>>>> I wonder if something about cylinder 5 is somehow different so that the compression is higher, and so it’s igniting (pre-igniting) too much before top dead centre in just that cylinder?
>>>>>>>>>  
>>>>>>>>> Eg #5 piston slightly higher than the other 4?
>>>>>>>>>  
>>>>>>>>> Roger
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