Kubota HST7100 blowby in excess 600 hours

[Thomas Abel]

My 1991 Kubota Hst7100 has excessive blow by. The compression is low I think, because it is hard starting in cold weather. There is no exhaust smoke when it is warm. It runs well after starting. This is my first posting and I am new to this site. I have rebuilt a rabbit diesel and several large motorcycles and other autos, but not a tractor. The hours says 600 hours, but when I bought the tractor the fuse to the clock was open and the clock didn't work. It said 230 hours at that time. I have put on the rest. I would assume from the symptoms that the oil rings are okay, but the compression rings are weak or worn. I don't understand why this would be at 600 hours.

Thanks for any info on this. :anyone::anyone:

 

[Egon]

The Kubota B7100 I had was always hard to start when cold. Even in the summertime. When warm it started easily.

It always had what appeared to be blow by but the it never used any oil. 3000 hrs. on it when it was traded in.

Below -10C It usually had to be puged in to start.

Does your tractor start when warm?
On cold starts do you use the glow plugs ?
Does it use oil?

 

[Thomas Abel]

Without the antifreeze container under the crankcase vent tube it would drip into the garden and that wasn't good. I don't burn any oil out the exhaust. Yes, below 40 degrees F I use the glow plugs. I started it after 10 clicks of the clock and it was an instant start almost as fast am my TDI Jetta. No problem when warm. It didn't do this when I first bought it. I have hooked the glow plugs up to my 12 volt battery charger for 10 minutes or more to start it when it was cold. It might take 2 to 4 minutes of cranking to get it started. It's almost like the old gas engine starter on an old cat.

Thanks for the reply. Tom

 

[kevinj]

Without the antifreeze container under the crankcase vent tube it would drip into the garden and that wasn't good. I don't burn any oil out the exhaust. Yes, below 40 degrees F I use the glow plugs. I started it after 10 clicks of the clock and it was an instant start almost as fast am my TDI Jetta. No problem when warm. It didn't do this when I first bought it. I have hooked the glow plugs up to my 12 volt battery charger for 10 minutes or more to start it when it was cold. It might take 2 to 4 minutes of cranking to get it started. It's almost like the old gas engine starter on an old cat.

Thanks for the reply. Tom

Are you sure the glow plugs are working???? 1 minute was about what our old 7100 needed. Ours was about 3000 hours and still started good.

 

[EE_Bota]

I would do an actual compression check if possible.

Also, on an old turbocharged VW one time, it was hard starting, and I put a new battery in, and it would start just fine. The difference in cranking speed was barely noticeable, but the theory was that if the cranking speed is just a bit slow on a diesel, it allows just enough time for some of the heat of compression to be lost to the head and cylinder walls, causing it to be difficult to start, if it starts at all.

If the battery is top notch, I would check all connections.

Also, I would look about the head cover and see if there is any hoses, etc that are designed to reintroduce some of the blow by back into the clean air intake for burning. Not all tractors will have such a thing, but some do.

 

[KubotainNH]

My B6100 always needs some glow plugs for the first start even in warm weather. Runs like a top otherwise. The colder it is the longer I have to run the GP's. Below freezing is over a minute. Maybe you have a plug that is bad?

 

[Thomas Abel]

I think I will be good for the spring and summer, but I should get it fixed for the winter. I will check the voltage on the battery. The last time I checked it was over 13 volts. All the glow plugs are working. The battery only gives the glow plugs 10 volts. There is a resister inline to reduce the voltage. When I use the battery charger directly to the plugs I get more voltage and use them like a heater to heat the cylinder head as well. I will also remove and clean all the connections on the battery to be sure there is not a faulty connection. There is no crank case vent to the intake. The crank case vent is just vented to the atmosphere. I don't have a trailer strong enough to take the tractor to get a compression check. The dealer wouldn't loan me his compression tester. There may be a rental shop somewhere. I will check that out. My tester only goes up to 200lbs.

Thanks again guys. Tom