Kubota F2503

[libertairegv]

Hi all,

I have a question regarding a Kubota F2503 knocking noise on the 5th cylinder.
The engine is on a boat but there is no such forum on Kubota for boat!

The engine is 6000 hours. I had a small knocking noise since nearly +/- 1000 hours but it was very small so I didn't do anything as it's a noisy tractor engine, and in fact I don't hear anything outside of the engine compartment. The engine runs fine, doesn't burn oil, has good power, doesn't smoke.

After the winter I found the noise a bit louder and I tried to precisely identify the origin and it's the 5th cylinder only (no more noise when I loosen the injector nut of this cylinder). I' ve checked the valve clearance as I do every 2 years and it's OK for the 5 cylinder.

I asked a a friend of mine who is a mechanical engineer on tugs to listen to the noise. He checked the valve rockers and pushers, everythings fine, no play. No air coming from the oil filling hole at high RPM so valves are airtight. Lots of oil on the pushers & rockers so good lubrification. We don't hear the noise specifically from the oil filler hole. He thinks it's a weird noise but apart from that anything looks fine. He says it may be the valves closure noise if there seat is full of carbide. He tell me what he would do next is asking Kubota's specialist if there is any specific problem regarding this engine as he is more used to big caterpillar, and there is nothing more on his inspection that worries him.

So that's why I am writing here, do someone has the knowledge of any specific valve problem/noise on this kind of engine?

Thanks for your unvaluable help!

Damien

 

[North Idaho Wolfman]

If your getting the noise to stop when you loosen the injector line, then I would lean to a wrist pin issue, or possibly an injector issue.
Move the injector and see if noise follows the injector or not.
Then if it doesn't move pull all of the injectors and rock the engine back and forth listening for a tick.

 

[libertairegv]

Thanks for your reply.
I first thought it was a fuel knock so I already put a brand new fuel injector on the 5th cylinder and the noise still there.
The noise appears quiet low-pitched and doesn’t sound like a metal to metal sound.
Another clue, when I tried to adjust valve clearance on the 5th cylinder once I had the noise disappear for a few minutes and then slowly it reappears.
I’ll try again today readjusting the valve.
If I don’t manage to get the noise going I’ll do what you tell me to rotate the engine without injectors to see if there is a tick that can be a sign of wrist pin issue if I understand well. Will it work the same if I remove the glow plugs ? (Indirect injection engine)
Thanks again for your help and have a nice day.

 

[Russell King]

What type of injector did you install? Was is OEM or something else from reputable source or something from the internet?

I think you should move the injectors from 5 to 1 and see what happens with the noise. You might want to replace the crush washers under the injectors to make sure they are sealed properly.

 

[libertairegv]

What type of injector did you install? Was is OEM or something else from reputable source or something from the internet?

I think you should move the injectors from 5 to 1 and see what happens with the noise. You might want to replace the crush washers under the injectors to make sure they are sealed properly.

I install a brand new OEM injector and I also changed the heat seal and the ring injector gasket…
I can still try another cylinder but I am pretty sure fuel injection is fine. I don’t think my inline injection pump can suffer a one line break down. And the engine doesn’t smoke at all without or with load.

 

[Russell King]

Well that makes it less likely for it to be an injector problem.

You may want to check with this company if you are looking for injection pump replacement or repair

Home

Oregon Fuel Injection specializes in the repair of diesel fuel injection systems, replacement diesel parts, performance parts, drive-in service, repairs and diagnostics.

oregonfuelinjection.com

 

[GeoHorn]

(deleted previous comment… due to my confusion as to cylinder numbering system.)

I was previously under the belief that No 5 cyl was the one closest to the radiator. However, the WSM states that cyls are numbered starting at the “gear case” ….(which led me to think of the transmission/clutch area)…

However, the WSM later comments (in the section addressing disassembly) referencing a “gear case” at the front of the engine. This would seem to indicate Cyl No 5 at the rear. (which would place No 5 farthest from the oil pump….although theoretically they all receive the same pressure and the oil press sending unit is at the rear of this engine next to the starter.)

The cut-away depiction of this engine also shows both cyls 5 and 4 to be at TDC and cyls 2 and 3 at BDC …simultaneously….which doesn’t seem likely. I’ve not been able to find the crankshaft throw-degrees info.

 

[North Idaho Wolfman]

Thanks for your reply.
I first thought it was a fuel knock so I already put a brand new fuel injector on the 5th cylinder and the noise still there.
The noise appears quiet low-pitched and doesn’t sound like a metal to metal sound.
Another clue, when I tried to adjust valve clearance on the 5th cylinder once I had the noise disappear for a few minutes and then slowly it reappears.
I’ll try again today readjusting the valve.
If I don’t manage to get the noise going I’ll do what you tell me to rotate the engine without injectors to see if there is a tick that can be a sign of wrist pin issue if I understand well. Will it work the same if I remove the glow plugs ? (Indirect injection engine)
Thanks again for your help and have a nice day.

Yes you can remove the glow plugs and get the same result (no compression).
A wrist pin loose will sound more tick / dull than a main or rod bearing issue.
And they will run for years and years with a loose wrist pin

 

[libertairegv]

Yes

(deleted previous comment… due to my confusion as to cylinder numbering system.)

I was previously under the belief that No 5 cyl was the one closest to the radiator. However, the WSM states that cyls are numbered starting at the “gear case” ….(which led me to think of the transmission/clutch area)…

However, the WSM later comments (in the section addressing disassembly) referencing a “gear case” at the front of the engine. This would seem to indicate Cyl No 5 at the rear. (which would place No 5 farthest from the oil pump….although theoretically they all receive the same pressure and the oil press sending unit is at the rear of this engine next to the starter.)

The cut-away depiction of this engine also shows both cyls 5 and 4 to be at TDC and cyls 2 and 3 at BDC …simultaneously….which doesn’t seem likely. I’ve not been able to find the crankshaft throw-degrees info.

yes cylinder n5 is the one near the gearbox / turbocharger, at least on my workshop manual!

 

[GeoHorn]

Yes

yes cylinder n5 is the one near the gearbox / turbocharger, at least on my workshop manual!

The confusion may continue since Your Installation is in a boat/ship/tug ….not a tractor, etc. The “gear box” referred-to is the cam/timing gear-case…. also near the water pump…. what is referred to in a tractor as being the front of the engine. So the cyl numbering is front to rear 1 to 5.

 

[libertairegv]

The confusion may continue since Your Installation is in a boat/ship/tug ….not a tractor, etc. The “gear box” referred-to is the cam/timing gear-case…. also near the water pump…. what is referred to in a tractor as being the front of the engine. So the cyl numbering is front to rear 1 to 5.

Lol, it would have been easier if I had trouble with cylinder n3, we wouldn’t care of which gearbox we are talking…
Anyway thanks for the precision!

 

[rbargeron]

I'll add a couple points - the two diagrams above don't really show how Kubota 5-cylinder engines are built. The drawing below is from my L5450 WSM which has the F2803 version of the 5-cylinder layout.

Notice that at the back cylinder (No 5) the crank has thrust bearings on each side of the connecting rod. The purpose of thrust bearings on cranks is to counteract end thrust in applications where there's some axial force - like from a clutch release mechanism. I wonder if the marine clutch/gearbox in this case exerts some thrust on the flywheel ?

Thrust bearings on cranks are polished rings, bronze or stainless steel. They are like the journal shells, in two halves, maybe bolted together around crank. Since they are well oiled, running in an oily environment, they almost never act up. But in 6000 hours a lot can happen - like low oil, contaminants, etc. Once they start deteriorating, the journal bearings may get worn from debris in the oil. That might lead to the crank knocking at that end when the cylinder fires. Disconnecting the fuel to that cylinder might reduce crank deflection and reduce the knock.

This is rank speculation, not experience - but it is a plausible line-up with the symptoms.

Replacing crank bearings is a big job - engine taken out, disassembled, crank goes out the back end of the block. The bearings themselves are not likely to "jam" or wedge, causing the engine to stop - but anything coming apart in the bottom end is never beneficial.

Hope more grey beards chime in on this one. Best luck - Dick B.

 

[libertairegv]

Hi all,
Small update on the work.
I removed the glow plugs and turns the engine by hand. I got only some squeezing noise coming from every cylinder from time to time, nothing specific from the 5th one. Nothing alarming I found rotating the engine without compression, no hard point, no strange noise.
Well I'll should have started from that, I made a video of the 5th cylinder noise. You can hear the difference with the injector turned off in the middle of the video. You need a good speaker as it's a low-pitched noise that isn't heard well with laptop speakers. The .mov file is on google drive.

IMG_3635.MOV

drive.google.com

Do somebody has already heard that noise?
Thanks for your help and have a good day!

 

[North Idaho Wolfman]

Hi all,
Small update on the work.
I removed the glow plugs and turns the engine by hand. I got only some squeezing noise coming from every cylinder from time to time, nothing specific from the 5th one. Nothing alarming I found rotating the engine without compression, no hard point, no strange noise.
Well I'll should have started from that, I made a video of the 5th cylinder noise. You can hear the difference with the injector turned off in the middle of the video. You need a good speaker as it's a low-pitched noise that isn't heard well with laptop speakers. The .mov file is on google drive.

IMG_3635.MOV

drive.google.com

Do somebody has already heard that noise?
Thanks for your help and have a good day!

OK now that sounds like a baffle noise in the exhaust manifold.
I'll listen to it again later on the big computer with full sound.

 

[libertairegv]

OK now that sounds like a baffle noise in the exhaust manifold.
I'll listen to it again later on the big computer with full sound.

Thanks for that! I hope you are right!

 

[North Idaho Wolfman]

Thanks for that! I hope you are right!

Listened to it on the big computer with full sound and it really does sound like a baffle /cavitation in the exaust manifold.
A wrist pin or a rod bearing issue does not sound that deep.
If it was mine I would pull the injector and look at it, if it looks odd or wet then I would do a compression test on it.

 

[libertairegv]

Ok thanks a lot for your help.
I already changed the injector with a new OEM one and the old one looks quite OK to me (1500h since the last injector setting check).
I think the cylinder is fine, maybe so deposit in the exhaust manifold. I removed the exhaust manifold for the last time 2000h ago. But I think I had this noise since a very long time. I don’t heard it when I am not in the engine room.
Anyway thanks again and have a good day!

 

[North Idaho Wolfman]

Yep that looks good to me too!