B7100 Piston Installation

[Schmotown]

Duck Wrangler, first I used a dial indicator at the center of the piston. I then used your "arbitrary" method to confirm TDC with a degree wheel Thats the way I always found TDC. Both methods provided the exact same results.

Wolfman, I did use .008 valve clearance. Just rechecked top of piston to bottom of head with solder.
Specs are .0237 to .0315. My readings 1) .037, 2) .038; 3) .038. I haven't found any data on volume for these heads. Don't know if milling approx. .008 would make any difference. I'm not an engine guy.

Thank you both for your advice. I'm gonna go look for a weedy area and roll this junker into them as a historical artifact!!

 

[Hugo Habicht]

Hi Larry,

I only read your first post in this thread, so I may have missed it, so please forgive me if I am repeating something you did already.

Did you grind in the valves with the new head?

Kind regards,

 

[Schmotown]

Hi Larry,

I only read your first post in this thread, so I may have missed it, so please forgive me if I am repeating something you did already.

Did you grind in the valves with the new head?

Kind regards,

Yes, I lapped the valves, Thanks for your input.

 

[North Idaho Wolfman]

Did you go to a dealer and get the head gasket, or was it online order?

 

[Schmotown]

Did you go to a dealer and get the head gasket, or was it online order?

I bought the gasket from Messick's. Best of my knowledge it is a genuine Kubota gasket. I've decided to go back to square one and review everything I've done to the engine. If I don't find anything I'll remove the front cover and confirm that the timing gears all line up. I'll keep you posted.

 

[North Idaho Wolfman]

Things that affect the volumetric numbers and compression numbers:

Doubling the injector compression gaskets (copper /clad sealing rings).
Wrong glow plugs:
Wrong valve fitment ( Did you buy the head complete or did you install your own old valves?)
Precambers left out.
Wrong or too think of head gasket
Installing metal head gasket shim when not needed.
Installing wrong pistons
Installing rings upside
Wrong head
Bent connecting rods

 

[Schmotown]

Things that affect the volumetric numbers and compression numbers:

Wolfman, my replies are in "red". Thanks for your thoughtful post.

Doubling the injector compression gaskets (copper /clad sealing rings).
There is one copper washer on each injector.
Wrong glow plugs:
Not sure but there are NGK Y103K glow plugs installed. I am having a bit of trouble cross referencing that number.
Wrong valve fitment ( Did you buy the head complete or did you install your own old valves?)
I bought the head complete from Kumar Bros (KB).
Precambers left out.
I don't think KB heads are made the same way as Kubota heads, I think their prechambers are cast into the heads and aren't removeable.
Wrong or too think of head gasket
I installed a Kubota head gasket. I have one that I originally used and when I pulled the head the 2nd time I kept that gasket. It measures .050 after being torqued. Manual specs .0413 to .0453.
Installing metal head gasket shim when not needed.
No shim installed.
Installing wrong pistons.
New Kubota pistons, rings, bearings. Verified part numbers.
Installing rings upside.
I'm 99% sure the rings are installed correctly.
Wrong head.
Not sure, that will take further research on my part. I foolishly sent my original head to the junk yard.
Bent connecting rods.
Not sure but the stick out above the block is per specs so I think they're okay.

I just redid my leak down test on all cylinders. 5% to 6% leakage range. If I have that tight of a rebuild on the engine then my low compression numbers must be due to a volumetric issue. But I have one consideration that may throw my logic off:

My leak down numbers were achieved with both valves closed and the piston on TDC of the compression stroke on a non-rotating engine. If the gear timing on the front of the engine is incorrect could that result in a low compression reading when cranking the engine? Could something mechanical be taking place that I'm not understanding?

Sorry for asking all the questions but I do appreciate everyone's experience.

 

[Schmotown]

Before I went any farther on my diagnosis of the low compression after a rebuild (265, 280, 295) I ran my B7100 for about 15 minutes pulling a lightweight driveway drag. It is so dry here that there wasn't really much of a load. The tractor was hard to start and blew a lot of gray smoke at startup. The smoke cleared up after about 20 seconds with just a little puff of black when I went to full throttle pulling my drag. It performed well and it seemed to have ample power.

Still not happy with the smoking on startup I checked the injector timing and found it to be retarded. I removed one shim from the injector pump and the #1 piston is now lined up with the 1F mark. I also replaced the glow plugs because they took about 45 seconds to turn a dull red. The new plugs turn bright red in about 13 seconds. I hoped the timing change and glow plugs would help with the smoke at startup. It did start a little faster but still smoked a ton.

I then checked the valve timing, the compression and the exhaust runner temperatures. Timing did not change and was still at .007 and the compression went up in all cylinders to about 330 psi. Still not good but a little better. The exhaust runner temps were 145F on #1 and 195F on #2 and #3 and the radiator was 190F at the top and 135F at the bottom.

Because of the low temp on Cyl. #1 I suspected a fuel delivery issue (I have all new injectors from Oregon Fuel Injection) and did a "fountain" test and all 3 injectors. They all spurted the same amount (below). Then I swapped the #1 and #2 injectors and Cyl. #1 was still 145 F.

I would think a pump capable of injecting fuel at 2,000 psi would squirt a pulse of fuel higher than that but I don't know. I then installed a new fuel filter and the injection pump output was still the same.

Still thinking it may be a delivery issue I removed the outlet hose from the fuel pump and only a spurt of fuel came out with every rotation of the cam.

My questions:
1) Is 45F too big of a temperature difference between cylinders?
2) Should the injector pump output look like the output in the picture at WOT?
3) Does anyone know what the output of the fuel pump should be or if it puts out a pulse or stream at WOT.
4) Should I just keep running the tractor for an hour or so and see if the compression numbers go up?

I'm truly appreciate any input on my ramblings. Thanks, Larry.

 

[JohnDB]

Left field thought because I don't think that it has been covered here... the size (volume) of whatever you have between the cylinder head and your pressure gauge will affect the compression pressure registered. Simple maths. If you have an adapter or pipe that is larger or longer than whatever Kubota uses, measured compression pressure will be less than their figure.

 

[Schmotown]

Thanks for the reply. I've read that if there is a schrader valve at the glow plug adapter end of the compression hose then the volume of the hose does not become part of the equation.

There is a bit of discussion on the internet about hose volume during compression testing but here's my question if you can help me understand:

If a piston is capable of compressing air to 400 psi in a one cu. in of head space and the volume changes from one cu. inch to two cubic inches due to added hose length wouldn't I just cycle the engine for a few more revolutions and the added revs would pump the air back up to 400 psi? Please note that I am not arguing your point it's just that this is all new territory to me. Possible there is a limit to how long the engine is cranked? I don't know.... Thanks.

 

[Selkirk_D]

Before I went any farther on my diagnosis of the low compression after a rebuild (265, 280, 295) I ran my B7100 for about 15 minutes pulling a lightweight driveway drag. It is so dry here that there wasn't really much of a load. The tractor was hard to start and blew a lot of gray smoke at startup. The smoke cleared up after about 20 seconds with just a little puff of black when I went to full throttle pulling my drag. It performed well and it seemed to have ample power.

Still not happy with the smoking on startup I checked the injector timing and found it to be retarded. I removed one shim from the injector pump and the #1 piston is now lined up with the 1F mark. I also replaced the glow plugs because they took about 45 seconds to turn a dull red. The new plugs turn bright red in about 13 seconds. I hoped the timing change and glow plugs would help with the smoke at startup. It did start a little faster but still smoked a ton.

I then checked the valve timing, the compression and the exhaust runner temperatures. Timing did not change and was still at .007 and the compression went up in all cylinders to about 330 psi. Still not good but a little better. The exhaust runner temps were 145F on #1 and 195F on #2 and #3 and the radiator was 190F at the top and 135F at the bottom.

Because of the low temp on Cyl. #1 I suspected a fuel delivery issue (I have all new injectors from Oregon Fuel Injection) and did a "fountain" test and all 3 injectors. They all spurted the same amount (below). Then I swapped the #1 and #2 injectors and Cyl. #1 was still 145 F.
View attachment 159818

I would think a pump capable of injecting fuel at 2,000 psi would squirt a pulse of fuel higher than that but I don't know. I then installed a new fuel filter and the injection pump output was still the same.

Still thinking it may be a delivery issue I removed the outlet hose from the fuel pump and only a spurt of fuel came out with every rotation of the cam.

My questions:
1) Is 45F too big of a temperature difference between cylinders?
2) Should the injector pump output look like the output in the picture at WOT?
3) Does anyone know what the output of the fuel pump should be or if it puts out a pulse or stream at WOT.
4) Should I just keep running the tractor for an hour or so and see if the compression numbers go up?

I'm truly appreciate any input on my ramblings. Thanks, Larry.

I recently had a smoking issue with my L2850 which ran great, just smoked. I checked compression and a couple cylinders were low. I tore it down and found a destroyed #1 rod bearing, but weirdly no knock. I pulled all the pistons, cleaned them, put in new rings and bearings, polished crank. No sign of bad head gasket, but I did find carbon deposits /pitting on exhaust valve seats. I touched up the exhaust seats with my seat grinder, replaced all the exhaust valves, and lapped in all the intake and exhaust valves. Checked guides and replaced all the valve guide seals too . Runs great now, compression was up like 65psi, but it still smokes a little on startup until she warms up. I also had injectors cleaned and tested.

 

[Schmotown]

Selkirk_D, thanks for the input. I have a new Kumar Bros. head complete with valves, springs, etc. and I lapped the valves when I received the head. New Kubota head gasket, pistons, rings, rod bearings, wrist pins. New injectors. Had the rods checked and they were not bent. Bores and rod journals were well within specs. I'm not sure of the age of this project tractor but it's turned into a "project" alright. Due to the tractor's age and zero emissions considerations when manufactured I expected a bit of smoke on startup and during hard acceleration. It's fine during hard acceleration with just a puff of smoke but the hard start and voluminous smoke is not acceptable. Good to hear that your tractor is running great.
Best regards, Larry.

 

[torch]

Thanks for the reply. I've read that if there is a schrader valve at the glow plug adapter end of the compression hose then the volume of the hose does not become part of the equation.

There are Schrader valves and then there are Schrader valves. Well, different valve cores anyway. Compression testers should be fitted with a special core having a low tension return spring such as Snap-On MT24DB1* or Milton 1251-2 . These are generally identifiable by having a white or clear sealing ring as opposed to the black or red sealing ring found on the common tire valve core. Tire valve cores are just too stiff and unresponsive, especially on small displacement cylinders.

I did my own (highly un-scientific or exhaustive) tests in the past. I found the Snap-on white cores exerted about 20 grams of pressure against a postal scale, an unidentified clear one about 5 grams and a sampling of tire valve cores were all around 250 grams each.

I don't know what make compression tester you have, but a lot of the generic or house-branded Chinese testers come with tire valve cores.

I have seen reports from some guys that they were able to successfully mod a tire valve core by cutting off a coil or two from the spring. Of course, this can only be done to cores that have a long exposed spring -- not really possible with a compact core that has an internal spring.

*That was the number when I last ordered some back in 2017. I just checked the Snap-on store and can't find them so they may be discontinued. Napa discontinued theirs. The Milton link is current and may be the only option now.

 

[JohnDB]

Thanks for the reply. I've read that if there is a schrader valve at the glow plug adapter end of the compression hose then the volume of the hose does not become part of the equation.

There is a bit of discussion on the internet about hose volume during compression testing but here's my question if you can help me understand:

If a piston is capable of compressing air to 400 psi in a one cu. in of head space and the volume changes from one cu. inch to two cubic inches due to added hose length wouldn't I just cycle the engine for a few more revolutions and the added revs would pump the air back up to 400 psi? Please note that I am not arguing your point it's just that this is all new territory to me. Possible there is a limit to how long the engine is cranked? I don't know.... Thanks.

Absolutely correct, I forgot to mention the valve! Where the valve is in the system is also important. Some adapters I've seen have more volume before that valve than the glow plug (or injector) that they replace, so that extra volume becomes part of the compression reduction equation. I'm not saying that its an issue in your case, I'm just trying to cover the possible scenarios and this one is a easy check/cheap fix. Also @torch s point about the type of valve is important. That aside, I think a rule of thumb is to allow up to 10 cycles to pump up the gauge, but the one I have does it in less, at correct cranking speed.

 

[torch]

I would think a pump capable of injecting fuel at 2,000 psi would squirt a pulse of fuel higher than that but I don't know. I then installed a new fuel filter and the injection pump output was still the same.

Still thinking it may be a delivery issue I removed the outlet hose from the fuel pump and only a spurt of fuel came out with every rotation of the cam.

My questions:
1) Is 45F too big of a temperature difference between cylinders?
2) Should the injector pump output look like the output in the picture at WOT?
3) Does anyone know what the output of the fuel pump should be or if it puts out a pulse or stream at WOT.
4) Should I just keep running the tractor for an hour or so and see if the compression numbers go up?

I'm truly appreciate any input on my ramblings. Thanks, Larry.

Don't mistake volume for pressure. Pressure only increases when volume is restricted and the discharge can be calculated by Q=K(P^-2), which can be rewritten as Pressure=(Volumetric Flow/K)^-2 (where K is a constant dependent upon fluid density, temperature, orifice area, etc. ).

In English, the pump is designed to deliver a small volume into a very small orifice. Removing the pipe to the injector can be thought of as a massive increase in orifice size and therefore a massive increase to K resulting in a massive decrease of P. The result, as you saw, is a small fountain rather than a massive spray.

And yes, the pump puts out pulses, which would likely look like a solid stream at WOT unless viewed with a high-speed camera.

As for the temperature difference, first of all how did you measure it? If you are using a non-contact "laser" thermometer be aware that they don't just view the spot, they average the temperature within an expanding cone. I assume you are counting #1 as being the front cylinder, closest to the radiator and fan? Any chance the cone is including space in front of the engine? The most accurate way to measure the EGT would be with a contact probe type instrument followed by a Thermal Imaging Camera showing spot temps.

Did you ever get your valve timing issue resolved? Reading back through this thread I saw you adjusted the fuel injection timing by changing shims, but that doesn't affect valve timing.

 

[torch]

That aside, I think a rule of thumb is to allow up to 10 cycles to pump up the gauge, but the one I have does it in less, at correct cranking speed.

FWIW: The B7100 WSM says crank it with the starter at 200 to 250rpm for 5 to 10 seconds. That's a range of 8 to 21 compression strokes, so your rule of thumb is a bit on the low end per Kubota but not a bad estimate.

 

[Schmotown]

Torch: " There are Schrader valves and then there are Schrader valves. Well, different valve cores anyway. Compression testers should be fitted with a special core having a low tension return spring such as Snap-On MT24DB1* or Milton 1251-2 ."
I ordered the Milton Schrader valves today and will give them a try. I swapped the gauge from the generic compression tester with a Marshall gauge so my readings should be pretty accurate.

Torch: "Don't mistake volume for pressure. Pressure only increases when volume is restricted and the discharge can be calculated by Q=K(P^-2), which can be rewritten as Pressure=(Volumetric Flow/K)^-2 (where K is a constant dependent upon fluid density, temperature, orifice area, etc. ).

In English, the pump is designed to deliver a small volume into a very small orifice. Removing the pipe to the injector can be thought of as a massive increase in orifice size and therefore a massive increase to K resulting in a massive decrease of P. The result, as you saw, is a small fountain rather than a massive spray.
I understand what you are saying. I thought I read in another OTT thread that the injection pump could pulse a stream 3" to 6" in height but maybe I misread that post. I was hoping that the small squirt that I got was indicative of a worn pump but I imagine the only way to tell is to have it shop tested.

Torch: " As for the temperature difference, first of all how did you measure it? If you are using a non-contact "laser" thermometer be aware that they don't just view the spot, they average the temperature within an expanding cone. "
I used a laser thermometer and a thermal imaging camera and my readings were pretty much the same with both devices.

Torch: "Did you ever get your valve timing issue resolved? Reading back through this thread I saw you adjusted the fuel injection timing by changing shims, but that doesn't affect valve timing.
Correct, my injection pump timing was off and I corrected it.

Originally I believed my valve and engine timing was correct based on the condition of the engine internals. Everything is in such good condition with virtually no signs of wear that I was "assuming" that the front cover has never been removed. And as I was unable to remove the splined adapter and the pulley on the end of the crankshaft I couldn't pull the front cover as suggested by NI Wolfman to verify gear timing.

Following is a copy and paste from my earlier post:

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 to 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. (Retarded?)
Intake Closes at 39 deg ABDC, manual calls for 45 deg ABDC. (Advanced?)
Exhaust Opens at 37 deg BBDC, and manual calls for 50 deg BBDC. (Retarded?)
Exhaust Closes at 10 deg ATDC, and manual calls for 15 deg ATDC. (Advanced?)

These readings make no sense to me. The Intake and Exhaust valves are for the #1 cylinder are opening late and they are closing early (if my logic is correct) but that can't be happening on an engine with a single cam to my thinking but again I may totally wrong.

After writing this reply and with time to think about what has been suggested it seems to me that I should start all over. I should disassemble the tractor again, get the splined shaft and pulley off of the crank, remove the cover and verify that the engine is in time. I think this will remove any questions regarding timing and poor compression readings and then explore any other issues that may occur after reassembly.

Does this sound like a reasonable approach? Any tips on removing the splined shaft and pulley other than penetrating fluid and heat and an appropriately sized puller? Does anyone have any thoughts about my cam timing? I should probably disregard them until I verify timing marks behind the front cover...

Thanks to all for their time and effort in reading and replying to my posts. You gents have tons of experience and I am grateful to you for sharing your knowledge.

Best Regards, Larry.

 

[torch]

I checked the cam lift and it is right on the money (.197) with the manual

That argues the camshaft is not worn.

Intake Opens at 12 deg BTDC, manual calls for 20 deg BTDC. (Retarded?)
Intake Closes at 39 deg ABDC, manual calls for 45 deg ABDC. (Advanced?)
Exhaust Opens at 37 deg BBDC, and manual calls for 50 deg BBDC. (Retarded?)
Exhaust Closes at 10 deg ATDC, and manual calls for 15 deg ATDC. (Advanced?)

Intake opens 8° after spec.
Intake closes 6° before spec.
Exhaust opens 13° after spec.
Exhaust closes 5° before spec.

That argues the camshaft is worn. Or the spec is wrong. Or there was an error in measurement. But the numbers you list match the numbers in both my B7100HST WSM and a generic Kubota 70mm stroke engine manual.

What year is your tractor? Maybe the spec changed over the years.

These readings make no sense to me. The Intake and Exhaust valves are for the #1 cylinder are opening late and they are closing early (if my logic is correct) but that can't be happening on an engine with a single cam to my thinking but again I may totally wrong.

You are correct in saying the relationship between intake and exhaust opening and closing are fixed. If the camshaft was simply out of time, all values should be off by the same amount in the same direction. Do all cylinders exhibit the same magnitude and variances?

After writing this reply and with time to think about what has been suggested it seems to me that I should start all over. I should disassemble the tractor again, get the splined shaft and pulley off of the crank, remove the cover and verify that the engine is in time. I think this will remove any questions regarding timing and poor compression readings and then explore any other issues that may occur after reassembly.

I think that might be premature at this stage. The EGT difference seems odd, but otherwise your results seem pretty decent:

I ran my B7100 for about 15 minutes pulling a lightweight driveway drag.
...
just a little puff of black when I went to full throttle pulling my drag. It performed well and it seemed to have ample power.
...
the compression went up in all cylinders to about 330 psi. Still not good but a little better. The exhaust runner temps were 145F on #1 and 195F on #2 and #3 and the radiator was 190F at the top and 135F at the bottom.

...
Then I swapped the #1 and #2 injectors and Cyl. #1 was still 145 F.

I think I'd be inclined to wait, see what the compression is with the proper Schrader valve core (I'm assuming your compression tester had a black or red seat?) and if things improve with continued break-in. Ultimately, the proof of the pudding is in the eating and if the tractor is running well with good power that's really the important part, right?

Any tips on removing the splined shaft and pulley other than penetrating fluid and heat and an appropriately sized puller?

Heat and shock are your friends. I have had success with similarly stubborn flywheels and pulleys by installing an applying force with the puller while heating around the perimeter of the shaft to expand things and applying an air chisel with a blunt bit to the top of the puller bolt and/or around the perimeter. Some just whack it with a BFG, but I think the air chisel is better controlled and higher frequency.

 

[Schmotown]

Torch, I didn't check the variance on the other (2) cylinders but due to the condition of the engine I can't imagine the other four lobes are worn to such an extent. I don't know the year but it is an "old" type. I imagine the goofy valve degree readings are simply an error on my part so I'll ignore those readings for now.

You've convinced me to just use it as long as is runs normally after startup. The oil pressure is 45 psi so it's good there. I checked the Schrader valve seal and it's black so I'll see if there is a different compression reading when I receive my replacement valves. After a few hours of driveway maintenance I'll recheck the cylinder compression and exhaust runner temps and report my findings. Just have to wait for rain to soften things up!

Thanks, Larry.