[AT] Kubota M5700 noise

Wed Apr 8 02:18:24 PDT 2020

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 <rogerkiwi at gmail.com> <rogerkiwi at gmail.com>
>>>>> To: Antique Tractor Email Discussion Group
>>>>> <at at lists.antique-tractor.com> <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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