B7100 start issues

[philm]

hi folks

started a rebuild on my old 92 B7100 back in summer.... which was an adventure. i was having issues with it not starting unless i gave i small shot of ether...yeah i know bad bad ...lol only had to first start of the day and then she would start right up every time. but first start of the day just a lot of smoke and no ignition.
long story short seem the compression was at the bottom of it even thought it only had about 400 hours on it. ( it was my dads i didn't use it much ) so tore it down sent it to the machine shop they did the head, new guilds, valves etc and said the cylinders were only out 1 thousands so we decided to just install new pistons, rings, hone it and install new bearings thru out as well.
sorry about the length of this post ...
anyway all done back togeather and same issue have not been able to get her to start .... just white smoke ... un burnt fuel i'm sure ... which is what started me on this rebuild journey in the begining

now i'm stumped...

any suggestions would be appreciated.

 

[Dave_eng]

Have you made certain the glow plugs are working?

They should be heating and heating up the glow indicator on the dash during preheat.

They should be powered/heating but bypassing the glow indicator in the key START position.

Each GP should measure around 1 ohm of resistance. Disconnect the wire to each GP and measure ohms between the terminal on the GP to the head.

A 12 volt test light is a cheap tool to verify power to the GP's during the two cycles mentioned.

Dave

 

[TheOldHokie]

hi folks

started a rebuild on my old 92 B7100 back in summer.... which was an adventure. i was having issues with it not starting unless i gave i small shot of ether...yeah i know bad bad ...lol only had to first start of the day and then she would start right up every time. but first start of the day just a lot of smoke and no ignition.
long story short seem the compression was at the bottom of it even thought it only had about 400 hours on it. ( it was my dads i didn't use it much ) so tore it down sent it to the machine shop they did the head, new guilds, valves etc and said the cylinders were only out 1 thousands so we decided to just install new pistons, rings, hone it and install new bearings thru out as well.
sorry about the length of this post ...
anyway all done back togeather and same issue have not been able to get her to start .... just white smoke ... un burnt fuel i'm sure ... which is what started me on this rebuild journey in the begining

now i'm stumped...

any suggestions would be appreciated.

You are using the decompression knob?

Dan

 

[philm]

You are using the decompression knob?

Dan

she doesn't have a decompression knob that i'm aware of ... never used it if it does.

 

[philm]

Have you made certain the glow plugs are working?

They should be heating and heating up the glow indicator on the dash during preheat.

They should be powered/heating but bypassing the glow indicator in the key START position.

Each GP should measure around 1 ohm of resistance. Disconnect the wire to each GP and measure ohms between the terminal on the GP to the head.

A 12 volt test light is a cheap tool to verify power to the GP's during the two cycles mentioned.

Dave

i replaced glow plugs i the process leading up to this rebuild ... but i cannot swear they are working .i'll try the test. is there a way to hot wire them ? just feed them 12 volts etc ?

.thanks dave

 

[TheOldHokie]

she doesn't have a decompression knob that i'm aware of ... never used it if it does.

According to the parts manual the B7100 is equipped with a decompression starting aide. These pictures are a B7200 but it appears to be identical to the B7100. To cold start the engine:

1. Preheat glow plugs
2. Pull decompression knob (left bottom pf dash) out and hold
3. Crank engine and as soon as engine spins up release decompression knob

You will be surprised how much faster the engine cranks and how much easier it starts using that procedure. If the cable/knob is missing just open the hood and operate the decompression lever (seconfd picture) on the back of the valve cover by hand while cranking the engine.

Dan

 

[philm]

interesting .... mine has niether ....

 

[ken erickson]

My late model B7100 does not have a decompression knob. I think the OP’s is a late model also from the year stated.

 

[Dave_eng]

i replaced glow plugs i the process leading up to this rebuild ... but i cannot swear they are working .i'll try the test. is there a way to hot wire them ? just feed them 12 volts etc ?

.thanks dave

Very bad idea to feed the GP's directly with 12 volts. You could end up with them breaking apart spreading hard ceramic pieces in the cylinder.

Re read my earlier description of when and how the GP's are powered.

The current flows through the GP indicator during preheat. This indicator is like a resistor in line with the GP's and it drops the GP voltage to around 10.5.

During the engine cranking or START on the key switch, the entire tractor voltage is lowered by the high current draw of the starter so again the GP's see around 10.5 volts.

Invest less than $20 in a 12 volt test light. It will help you easily see if and when the GP's are being powered.

Dave

 

[TheOldHokie]

My late model B7100 does not have a decompression knob. I think the OP’s is a late model also from the year stated.

I stand corrected. I intentionally looked up the parts list for the "old type" never thinking they would delete it and then add it back on the B7200.

Dan

 

[philm]

I stand corrected. I intentionally looked up the parts list for the "old type" never thinking they would delete it and then add it back on the B7200.

Dan

well seems the glow plugs are bad ...
they are all homing out at about 4 ohms
it was a new set installed 4 months before the rebuild ..may have never been right lol
i ordered a set of NGK's for it .....this time i'll check the ohm's before installing them
the power to them cycles on at the correct times switch wise so i'll let you know what happens !!!


as always i appreciate all the assistance !!!

 

[North Idaho Wolfman]

well seems the glow plugs are bad ...
they are all homing out at about 4 ohms
it was a new set installed 4 months before the rebuild ..may have never been right lol
i ordered a set of NGK's for it .....this time i'll check the ohm's before installing them
the power to them cycles on at the correct times switch wise so i'll let you know what happens !!!


as always i appreciate all the assistance !!!

Did anyone work on it before you rebuilt it?
Sounds like the injection pump timing could be off.
Read the manual on how to check the injection pump spill timing.
Do a compression test, just because you rebuilt it doesn't mean it's right.
4 Ohm's on those glow plugs would still work, so I don't think that's your issue.
Did you bleed all the air out of injection pump Lines and injectors.
Did you have the injectors POP tested as bad injectors will give you the same issue as having the injection timing off.

 

[philm]

Did anyone work on it before you rebuilt it?
Sounds like the injection pump timing could be off.
Read the manual on how to check the injection pump spill timing.
Do a compression test, just because you rebuilt it doesn't mean it's right.
4 Ohm's on those glow plugs would still work, so I don't think that's your issue.
Did you bleed all the air out of injection pump Lines and injectors.
Did you have the injectors POP tested as bad injectors will give you the same issue as having the injection timing off.

''ok ... no one has worked on it but me ...
i did read about injection pump timing and have considered it.. but doing one thing ata a time
i'll look into spill timing if i can get info on it
i did bleed it completely
i did not have the injectors tested


the machine shop said it was only 1000th over stock so didn't bore and sleeve it.
it's the same machine shop the local kubota dealers use.
so i think they should know what's going on ...i hope
i have not done a post compression test no

 

[North Idaho Wolfman]

If no one else has worked on it, and all the shims that originally were under the injection pump are still there, do a compression test , and have the injectors tested.

 

[philm]

If no one else has worked on it, and all the shims that originally were under the injection pump are still there, do a compression test , and have the injectors tested.

there were no shims under the injection pump ...is that odd? i read somewhere in the manual to keep track of them but found none.

 

[North Idaho Wolfman]

there were no shims under the injection pump ...is that odd? i read somewhere in the manual to keep track of them but found none.

Yea that sounds wrong!
I've never worked on a Kubota engine without shims under the pump, usual count is 3.

 

[philm]

anyway ..

I bled out all the air in the fuel system and installed the new glow plugs ...which ohmed exactly 1 ohm and she did start after a lot of smoke and spinning ...it was very noisy a lot of knock like to much advance in a gas engine (detonation) once it was up to speed sounded normal ...a little smoke probably from the new rings not being seated.
but still hard to start ...a lot of white smoke and trying to start hut takes a long time. eventually it starts and runs ok and idles fine etc.
I have noted that if i preheat for 10 to 15 seconds prior to engaging the starter she starts right up like before.... never had to do that before so i think something is still out of skew..


any ideas ? or is this just due to not being broken in ?


thanks in advance as always you guys are a wealth of knowledge and help !!!!

 

[philm]

Yea that sounds wrong!
I've never worked on a Kubota engine without shims under the pump, usual count is 3.

how would one know how many are required ?

 

[North Idaho Wolfman]

how would one know how many are required ?

You would need to do a spill test per the WSM, that will tell you how thick and how many shims are need.

I would pull the pump and double check for shims, they are very thin with no gasket or sealer and they do get stuck to the pump.

 

[philm]

You would need to do a spill test per the WSM, that will tell you how thick and how many shims are need.

I would pull the pump and double check for shims, they are very thin with no gasket or sealer and they do get stuck to the pump.

Ican do that but i checked when i tore it down and looked further after the fact... wher can i find info on this spill test ? or is that a dealer thing ?

thanks again for the info