I am rebuilding the engine in my B7100. I know that the connecting rod is directional when installing but I do not see any markings on the new (or old) Kubota pistons. Attached is a picture of the bottom of the new piston which does have a number cast in one side and the opposite side is blank. Are they directional? Thank you in advance.
B7100 Piston Installation
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85Hokie
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Thanks, I did read that before I posted my question. I'm not sure what Mr. Wolfman is referring to as marks on the piston.
North Idaho Wolfman
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Stock, old pistons will have a name / numbers cast into the inside those numbers go towards the injection pump side, same as the rods.
Aftermarket pistons very typically will have a stamp on face of the piston, I've seen dimples, letters, arrows they will either go forward facing or injection pump facing.
It could even be on a skirt, but that's rare.
If the new piston is in first pic, this mark goes towards the injection pump.
North Idaho Wolfman, thanks for clarifying. The picture shows the mark on a new Kubota piston.
I hope someone can help!
I finally completed the engine work on my B7100. New Kubota pistons, head gasket w/o-ring, piston rings, rod bearings and a Kumar Bros. (KB) head. The original pistons and head were pitted but the bores and crank bearings measure well within specs. No taper or bulges in the bores and virtually no ridge at the top of the bores. I ball honed the cylinders and assembled the engine, everything torqued to specs.
Before attempting to start I did a compression test on all 3 cylinders with the following disappointing results:
Cyl #1: Before rebuild 240 psi. After rebuild 280 psi. 300 psi with a bit of oil.
Cyl #2: Before rebuild 200 psi. After rebuild 291 psi.
Cyl #3: Before rebuild 220 psi. After rebuild 265 psi.
I then did a leakdown test and all 3 cylinders show less than 10% leakage which I believe verifies the tightness of the engine. Those encouraging results led me down a rabbit hole. I can only think of two reasons for my low compression numbers:
1) KB head has more volume than original head which I foolishly scrapped so I can't measure the original volume.
2) The timing and/or valve lift duration is incorrect. I checked the cam lift and it is right on the money (.197) with the manual but the valve timing has me totally confused. I wanted to verify timing without removing the front gear cover so I installed a degree wheel on the crank and with a dial indicator I brought the #1 piston the TDC of the compression stroke. With TDC confirmed I have the following Intake and Exhaust readings:
Intake Opens at 12 deg BTDC, manual calls for 20 deg BTDC.
Intake Closes at 39 deg ABDC, manual calls for 45 deg ABDC.
Exhaust Opens at 37 deg BBDC, and manual calls for 50 deg BBDC
Exhaust Closes at 10 deg ATDC, and manual calls for 15 deg ATDC.
These reading make no sense to me. The Intake and Exhaust valves are opening late and they are closing early (if my logic is correct) but that can't be happening with an engine with a single cam.
My apology for the long post but I'm out of ideas. I'm thinking about just putting it back together and see if it will start. Thanks for any ideas.
Larry
I finally completed the engine work on my B7100. New Kubota pistons, head gasket w/o-ring, piston rings, rod bearings and a Kumar Bros. (KB) head. The original pistons and head were pitted but the bores and crank bearings measure well within specs. No taper or bulges in the bores and virtually no ridge at the top of the bores. I ball honed the cylinders and assembled the engine, everything torqued to specs.
Before attempting to start I did a compression test on all 3 cylinders with the following disappointing results:
Cyl #1: Before rebuild 240 psi. After rebuild 280 psi. 300 psi with a bit of oil.
Cyl #2: Before rebuild 200 psi. After rebuild 291 psi.
Cyl #3: Before rebuild 220 psi. After rebuild 265 psi.
I then did a leakdown test and all 3 cylinders show less than 10% leakage which I believe verifies the tightness of the engine. Those encouraging results led me down a rabbit hole. I can only think of two reasons for my low compression numbers:
1) KB head has more volume than original head which I foolishly scrapped so I can't measure the original volume.
2) The timing and/or valve lift duration is incorrect. I checked the cam lift and it is right on the money (.197) with the manual but the valve timing has me totally confused. I wanted to verify timing without removing the front gear cover so I installed a degree wheel on the crank and with a dial indicator I brought the #1 piston the TDC of the compression stroke. With TDC confirmed I have the following Intake and Exhaust readings:
Intake Opens at 12 deg BTDC, manual calls for 20 deg BTDC.
Intake Closes at 39 deg ABDC, manual calls for 45 deg ABDC.
Exhaust Opens at 37 deg BBDC, and manual calls for 50 deg BBDC
Exhaust Closes at 10 deg ATDC, and manual calls for 15 deg ATDC.
These reading make no sense to me. The Intake and Exhaust valves are opening late and they are closing early (if my logic is correct) but that can't be happening with an engine with a single cam.
My apology for the long post but I'm out of ideas. I'm thinking about just putting it back together and see if it will start. Thanks for any ideas.
Larry
North Idaho Wolfman
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Did you line up all the marks on the all the gears when you assembled it?
(Note: If you open it up and look at the marks they very likely will not be lined up (They only align every 248 revolutions or there about) you will need to remove the center gear and align them all up at the same time to make sure they are set up right).
Did you use an OEM head gasket?
(Note: If you open it up and look at the marks they very likely will not be lined up (They only align every 248 revolutions or there about) you will need to remove the center gear and align them all up at the same time to make sure they are set up right).
Did you use an OEM head gasket?
I did use an OEM gasket but I used a degree wheel to verify valve timing instead of removing the gear case cover. I was hoping the degree wheel would verify that the timing was correct and I wouldn't have to remove that cover. The tractor ran when I purchased it last fall and I was thinking the only work would be freshening-up the top end.
Do you think I should abandon the degree wheel method and pull the cover and visually verify the timing?
Thanks for your input.
Do you think I should abandon the degree wheel method and pull the cover and visually verify the timing?
Thanks for your input.
North Idaho Wolfman
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Did you pull the gears off during your work?
If you did and didn't realign them then there is your issue.
If you didn't pull any of the gears then they can't be wrong.
Check valve lash to make sure they are not too tight.
Check that the glow plugs are sealing check that the Injectors are sealing.
If all of that is correct, fire it up and run it for a bit to seat the rings.
Then check the compression after that.
DO NOT USE ANY starting aid!
If you did and didn't realign them then there is your issue.
If you didn't pull any of the gears then they can't be wrong.
Check valve lash to make sure they are not too tight.
Check that the glow plugs are sealing check that the Injectors are sealing.
If all of that is correct, fire it up and run it for a bit to seat the rings.
Then check the compression after that.
DO NOT USE ANY starting aid!
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North Idaho Wolfman
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As long as you installed the pistons and rings properly then, bleed the fuel system to the injectors
Then fire it up and run it for a bit to seat the rings.
It's going to start a little hard the first go around, then should get much better fairly quickly.
Then fire it up and run it for a bit to seat the rings.
It's going to start a little hard the first go around, then should get much better fairly quickly.
Like the wolfman said as long as you installed the pistons and rings correctly you should be OK. What grit ball hone did you use and what angle crosshatch di you achieve? If too coarse a grit it could cause lower compression until the rings seat in but that could extend the seating time and shorten ring life as well.
240 grit is not a bad choice. The only I may have done differently is hone with a 220-260 grit straight hone and touch up a with a 320 grit ball hone to create a plateau finish.
As long as the rings are installed correctly I would run it and see what becomes of her.
As long as the rings are installed correctly I would run it and see what becomes of her.
With a rebuild you don't want it idling or running at very high RPM during initial operation. Best break-in to get the rings to set in is to operate at mid RPM range and fairly heavy load varying the RPM some during break-in but avoiding both idle speed and RPM near governed speed. And definitely don't lug the engine with heavy load at too low RPM.
I am not at all surprised that compression readings were less than you expected before this initial break-in time takes place.
Rodger
I am not at all surprised that compression readings were less than you expected before this initial break-in time takes place.
Rodger