[AT] Kubota M5700 noise

Wed Apr 8 07:11:30 PDT 2020

By reducing compression, would ignition take place at the proper time?
Would combustion be complete, or would there be leftover fuel that could
change things on next compression stroke, and maybe pre ignite causing the
knock?

Dave

On Wed, Apr 8, 2020, 5:18 AM Stephen Offiler <soffiler at gmail.com> wrote:

> 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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