kubota engine rebuild

[Larry B]

 Over the last few months i have been gathering Kubota engine and generator bits and pieces to make one gen unit. GL7000 and a engine only from APU. had block bored for oversizes pistons ring bearings, etc. This is a two cylinder only . Wish I had room for a three. Parts for these are really expensive. A few more days and hopefully it will be running. Start up guidance is what I am looking for. Maybe other members have rebuilt one of these . I really do not want to messup now after all this work and money. The net down load gives good rebuild help but NO start up tips.
   How much will a head gasket crush?  The one in picture is0.050now. It will have a bearing on head to piston clearance. Book says 0.020clearance and piston is 0.023 above block at TDC. Is this consideres a normal amount of clearance or is this close?
   My thoughts are to back gov. off so it runs at about 800-1000 . and varry speed a little by hand every so often.  The Kubota book wants a new head gasket retorqued after 1/2 hr of run time. Do I do this hot or do I let engine cool down first?   
    What would be considered a safe amount of engine run time before I try the generator part and put a load on engine? This means bringing rpm up to about 3600 for generator to work proper.
     How important is engine exhaust backpressure?--muffler from GL70000 will not work in new application. Was just going to put hose on for now get noise and smell out side and deal with muffler issue later.
    What (in time) would be considered good breakin allowance?
    How long until I change oil on fresh engine?
    All start up pointers will be greatly appreciated. Both dos and don't. I will have water temperature and oil pressure sensors connected and IR gun. I think I wil leave engine shut down features diconnect for now. I just need to see this engine run for now and not be the third sc*** up Kubota to pass through shop doors.
    Thanks   Larry B

[wg4t50]

Larry B,
Sorry to hear about your 2 cylinder Kubota needing bored etc, am wondering how many thousand hours it has ?  What happened to it ?   KW rating, 7 kw, 58 Amp at 120 volts ?

I would run the half hour and re torque cold, double check valve lash,  also agree on run it a while at about 1500 rpm area keeping eye on both oil psi and water temp, then bring up to your 60 hertz for a few minutes, than start adding load .25, then .5, then .75 and let run for half hour at the 75% load, Then go with the 100%  load for a few minutes, just long enough to verify it can handle the load, (HP wise, oil psi & water temp), if all looks good & stable, reinstall it, close the door and enjoy.
Good luck
Dave M

[OneLapper]

Use break in engine oil and run it under load as soon as you verified it's got oil pressure and no leaks.  Re torquing the head is an absolute must.  The engine needs the load for the rings to seat correctly.  At the Deere dealership we ran fresh rebuilds on the dyno at 100% rated output for 8 or more hours, sometimes they needed even longer.  Break in oil was used for the first 50 hours at 50% load, then the recommended engine oil and 100% load there after.  Generators are a bit different, but stepping up the load over the first 60 minutes is not a bad idea.  It'll take a while to bleed the coolant system so keep an eye on that.

I'm about to fire up a fresh rebuild on my 8kw Westerbeke generator (as soon as the weather warms up a bit and it stops snowing).  I plan on letting it run for 50 hours straight to break it in.  Re-torquing the head and adjusting the valves is needed after the first couple of hours, after that it's full load while watching the oil pressure and temps.

[TomC]

Too bad there wasn't room for at least a 3 cylinder. The two cylinder is literally a 4 cylinder with 2 cylinders cut off. Hence, it runs rough. This is why low RPM won't be a good choice. I'd run at least 1800 if not more like 2500rpm. I had a truck driver friend with the Powertech 8kw 3 cylinder Kubota that when he sold his truck, had over 23,000hrs on the engine without overhaul. These engines are very long lasting. Run them up in the rpm so it gets warm and not build up carbon. Good Luck, TomC

[luvrbus]

It depend on the grade of Kubota engine how long one lasts they are not all equal

[bevans6]

I normally count on .003" to .005" of crush on the non-crush portion of the gasket - the black part of your gasket.  You should have enough piston to head clearance, depending on where you measured your .050".  But different gaskets crush different amounts, I would either do a test (and waste a gasket), measure the old one, or get the crush spec from the manufacturer, which you can do with high buck racing gaskets.

[Larry B]

Thanks for alll the replies. I can see from them that i would not have been running engine at a high enough rpm or adding load soon enough. I bought unit not running, it had 2700 hours on it, and after taking it apart I suspect the piston was hit the head. The piston was destroyed and so was cylinder wall. Reason for buying APU unit - to get a usable block..The piston has a letter 3 stamped in top. If I look at old head on the side that still had a good piston this letter 3 is faintly visible in the discolored dark part of head.
    You may think I lost it after telling this. The cardboard box that the new piston-ring- wrist pin and pin bushing came in measures .020 thick. The same as my minimum thickness. I cut two piston size circles from cardboard, set on top of piston and bolted head on with old head gasket and torqued up. When front piston passed through TDC felt nothing. With rear piston at TDC a slight clunk was heard and resistance was felt. If you look at the pictures of the cardboard circles, the piston shape and letter 3 is noticible on both- but felt nothing on front piston.   
    Brian I measured at metal part.  If I do same thing tomorrow with new head gasket and new cardboard rings would this be a satisfactory test for min clearance (.020") and find out gasket crush. Will measure black part before gasket install. Believing this engine went into self destruct from piston to head contact first time would like to avoid same thing this time. The second picture is old head gasket, metal 2 black layers with silver in middle
 
      Thanks  Larry B

[Larry B]

cardboard picture missed-- try again

[bevans6]

Just get you some old fashioned plasticine, put it on top of the pistons and turn it over once.  the plasticine will squish out to the thickness of your gap.  Measure the thickness of the old head gasket - if they are the same brand, that should tell you what the crushed height is. 

Brian

[OneLapper]

Were you able to get the rear cylinder past TDC?  If the rear cylinder hits the head, you should check the connecting rod for stretch and also check the crank shaft to make sure it's true.

Measure the piston to make certain it's identical to the front piston.

Next test would be to swap the conrod with the front cylinder and determine if it still hits the head.  If the rear still hits with the front's piston and conrod, the issue is with the crank.  If the rear piston and conrod hits in the front cylinder, then the issue is is that assembly.

Make sure conrod bearing shells are the correct thickness.

Keep us posted

[bevans6]

Also check your methodology for measuring the height of the piston and make sure you do both.  They can be tricky buggers, they rock all over the place if the rings aren't on or if the piston to bore clearance is loose.  I use a depth mic along the axis of the piston pin, even then it can take a few tries to get accurate to .001".

Brian

[luvrbus]

I would check the deck height on that engine at both pistons   

[Oonrahnjay]

I would check the deck height on that engine at both pistons   

   That's what I was thinking, too.  If someone skimmed the headgasket surface on the cylinder (to maybe get rid of earlier damage from a blown head gasket) or put in an incorrect gasket where the cylinder meets the block, that will drop the head down closer to the piston.  (I'm not familiar with these engines, but this is what I would have looked at with a similar problem with a motorcycle engine.)  Measure everywhere, including length from piston top at Bottom Dead Center to headgasket surface on both pistons.  If something measures up wrong, that will show you where to look next. 

    That being said, my WAIG is bent/stretched conrod or bent crank, probably.  But check and measure everywhere.

(BTW, Brian mentions "plasticine" in his post -- in the US, we'd call that "modeling clay"; it works very well for this purpose.)

[bevans6]

Is plasticine not a thing in the US?  Who knew?  The other old trick is to use a piece of lead fishing weight, like a little BB, but plasticine/modeling clay also lets you measure the exhaust piston to valve clearance, which makes sure the cam timing is set right.  If the cam chain is off a tooth you can get the piston hitting the exhaust valve about 10 degrees BTDC on the exhaust stroke.  Boy, it's a long time since I built an engine from scratch and had to measure all this stuff.  2008, the last formula ford engine I built.

Brian

[luvrbus]

It's called Plastigauge here it's been around since the 60's times have changed the first time I bought the Plastigauge it was 10 cents the last was 6 bucks a stick