B7610 engine knock

[Stoweski]

Just had my 7610 in for service yesterday... only 7.1 hrs on it. I had been using it on Sunday and in the afternoon I started it up and throttled up to about 1800rpm. All of a sudden I heard this god-awful knocking. I immediately shut it down because I didn't want to damage it. I checked all the fluids and around the engine for lodged sticks or something and found everything to be ok. I left it for a couple of hours then tried it again. The same knock occured again. I drove it back to the garage for the night and noticed a decrease in power. Also, since I back it in to the garage I stopped, paused, and then proceeded in reverse. Just as I stepped on the pedal a few heavy puffs of blue smoke billowed out of the engine.

The guy who took it in noticed the 'unidentifiable' knock when he started it but then it went away. At the shop they checked it over and ran it but couldn't find the problem. They returned it today and I used it for about 1/2 an hour. All sounded normal.

As a first time tractor owner I was very concerned about this. Now I'm just puzzled (and feel like an idiot for asking for service on a machine that works fine). I hope for my sake it doesn't happen again. A friend suggested that water might be in the fuel/cylinder and it's misfiring. Until it all burns out it will keep knocking. Is this a possibility?

Anyone know what may have caused this 'hiccup'?
Thanks for the help!
Keith

 

[DanR67]

Keith -

I have a copy of the B7610 "Workshop Manual" - going by your descriptions - here are the symptoms in the engine troubleshooting table that best match your descriptions:

Engine Revolutions Not Smooth:
a) Fuel filter clogged or dirty
b) Air filter clogged
c) Fuel leak due to loose injection pipe retaining nut
d) Injection pump malfunctioning
e) Incorrect nozzle injection pressure
f) Injection nozzle stuck or clogged
g) Governor malfunctioning

> a, b and c seem the most likely candidates here

With respect to either "White or Blue exhaust gas is observed:
a) Excessive engine oil
b) Piston ring and cylinder worn or stuck
c) Incorrect injection timing
d) Deficient compression

Granted these all sound fairly nasty - all but a) would be unusual for an engine with just 7 hours on it...but right below it in the troubleshooting chart is:

Either Black or Dark Grey Exhaust Gas is Observed:
a) Overload
b) Low grade fuel used
c) Fuel Filter clogged
d) Air filter clogged
e) Deficient nozzle injection

> b,c and d seem like they could be related to "Engine Rev's not Smooth"

**********************************************

Keeping to the old "K.I.S.S." principle - I'd look at the simple things first: fuel filter, air filter, double check your diesel.

I once found a mouse / chipmunk nest in my SUV's dashboard fan system - any chance somethings' gotten into your air filter?

Also - do you get the impression - assuming the "knock" comes back again (hoping it doesn't for your peace of mind!) - that ONE cylinder is acting funny - or all three?

For example does it go:

putt-putt-KNOCK-putt-putt-KNOCK etc

--> this would point in my opinion to a single cylinder problem (ex clogged injector), whereas if it goes:

KNOCK-KNOCK-KNOCK-KNOCK-KNOCK....etc.

--> Then this suggests that ALL cylinders are having the same problem --> more likely a fuel / air filter etc. that affects the entire engine.

Don't feel like an idiot - unfortunately not everything is 100% perfect. You have informed your dealer - and they at least heard it too - so they know you weren't making stuff up.

If it comes back - I'd just call up the dealer and have them pick it up again until it's resolved - you ran it for @ 7 hours so you know how its supposed to sound - and also how its NOT supposed to sound.

For future peace of mind regarding fuel (ex. water contamination) - you may want to pick up a "Mr. Funnel" - website here - then you at least won't have to worry about water in your fuel again.

Hope that helps - keep us posted.

Dan

 

[john_bud]

Wow, that's two words you never want next to each other (engine and knock!).

I could be water in the fuel. Easy to check. Take out and clean the fuel filter. See if the fuel bowl has any water in it. You can also add some fuel additive like primrose or powerservice. DON'T get the stuff for water in the fuel, just the normal white or silver bottle (if you use powerservice). I really don't think it's going to be water, unless you got some total junk fuel. Oh, for a new tractor owner you did all the right things. Including checking for sticks - smart.

What were you doing when the knocking happened?

jb

 

[Egon]

Shut it down and call dealer.

Don't even attempt any home diagnosis!!

It's still under warranty isn't it?

Egon /forums/images/graemlins/frown.gif

 

[Stoweski]

Ok, so I took the tractor out for about an hour today. Decided to 'play around' for a bit before dark. In the little bit of time it was running I did not hear anything unusual. Even opened the hood and listened closely (almost got a hair cut too).

Anyway, thanks for the advice on what to check. I'm in the process of looking for a workshop manual... and when I get some time I'll clean the fuel filter. Guess it could very well be the fuel. I'd check the injection nozzle but the book says to consult a Kubota dealer. Anyone have info on what to do with the injection nozzle? How to check? I like reading up on this kind of stuff... just in case.

As I recall the knocking sound was more of a putt-putt-knock. I checked the air filter for mice and other contaminants before calling the dealer.

To answer JB's question, I have been clearing an area next to my house. I'm down to leaves and sticks to move out of the way. I wanted to clear an area to plant some trees. I started the tractor (it had been off for about 20 minutes), backed it up, stopped, then throttled the engine. That's when the knocking started... just as I throttled up. About 2 hrs before that I was moving the firewood and some pretty good sized logs... with chains. Again, nothing too strenuous for this tractor.

Funny, before I purchased the tractor I did a ton of research and sat in the background on this forum absorbing all of the valuable info. A lot of it has helped so far. I've been very happy with the tractor... despite the knocking... and with this site. The tractor has more power than I'll ever need. Oh, and Dan, your site was one of the reasons I went with the 7610. Originally I was looking at a BX model. The rock pictures sold me. Since I had a friend cut a few beech trees (between 2-3' diameter) I've been hauling tons of firewood around. The bucket has been nice... and the bucket hooks have been even nicer!

Thanks again. I'll definitely let everyone know if it happens again.
Keith

 

[kevincook]

Does this only happen when you increase the engine rpm? Air in the fuel system can make the engine run very rough and vibrate quite a bit. Could that be it? I would expect that to continue until the lines were bled though. Maybe some type of vapor lock from sitting idle after being hot?

I am just throwing out some thoughts. Good Luck.

Kevin

 

[john_bud]

Stowski,
The dealer gave the OK to use the tractor, right? (Just wanted to clear that up, explicitly). Sounds like it is working well, that's a good bit of news.

Checking the injectors takes some expen$ive equipment. Snap-on sells a good one. Not that you will do it, but basically, you have to take out the injectors, put them in a test fixture, pressurize them to determine the pop off pressure (1991-2133 psi). Your tractor will be smoother if all injectors pop off at the exact same pressure. Also note the spray pattern. It should be uniform and develop a fine mist. There is also a spec for leak down when holding pressure just short of the pop off. Bring pressure up to 1849 psi and hold for 10 seconds. There should be no leaks. If there is no adjustments needed, it's 20-30 min test time per injector. R&R time for the injectors is where the bulk of the expense lies. If you do this test, be cautious of the pressurized fuel, it will cause gangrene and can even kill you if injected into the skin.

Water and alcohol in fuel will lay waist to injector seats. Check the fuel bowl for water!


jb

 

[dholly]

My first inclination was towards a fuel-related issue as well. Did this knocking happen to coincide with a recent fuel-up? Did you try draining your fuel filter? My B7610 came with a cross-threaded (and leaking) fuel filter at no extra charge!

Hey Dan - those new 'spill-proof' nozzles on the 5-gal Blitz cans are a real PITA with a Mr. Funnel now. /forums/images/graemlins/mad.gif

 

[Stoweski]

Yes, he did tell me to use it. I gotta be honest, I was very hesitant on increasing the throttle on it this time. Almost half expecting the thing to start knocking again.

The knock occured whenever the engine was running. It increased in speed when the rpm's increased. It definitely sounded like a single cylinder problem.

I did fill the tank with about 2 gal of fuel but that was around 5 hrs. Now at 8 the gauge reads 3/4 more or less. The book says to wait until 1/2 tank to remove and clean the fuel filter. I got more chores to do... it's a nice afternoon... think it's time to play!

Just to reiterate... I have not heard anything since getting it back from the dealer. /forums/images/graemlins/smile.gif

Keith

 

[btolle]

I hate things like this on new machinery.

I think sometimes it is just new stuff getting settled in.

I bought a brand new Jeep Liberty in 2004. It had about 2,000 miles on it and suddenly started hesitating to go into gear when I shifted it from Neutral to Drive. Also made a "racheting" sound from the transmission area.

I happened to be close to the dealer I bought it from so I took it straight to the Service Manager. He came out and tried it and sure enough, hesitation and noise. Check trans fluid, it was OK.

Svc. Mgr. said to bring it in the next morning. I did and it was OK on the way home (60 miles) and on the way back. They tinkered with it for about 2 hours and it never acted up again. 21,000 miles later it is still OK.

Maybe you had a stopped up injector that finally flushed itself out and will be OK. As long as the dealer wrote it up and told you to run it I would not worry about it. Get out there and use is so that if it is bad it will do it while still under warranty.

Bill Tolle