Oh right. That makes sense. Thanks for the pm..
Kubota L4740 Engine "knock" Help?
- Thread starter jshwhite
- Start date
- Views: 40531
-
- Tags
- kubota l4740
Oh right. That makes sense. Thanks for the pm..
jonsstihl
Veteran Member
subscribing since I have the same model tractor and am coming up on 680 hrs. let us know how it all turns out.
Ok, we're making progress, but the I don't think the news is good. I set all the valve clearances. I'll try to do a quick write-up. Leejohn, thanks for pointing out that the timing mark cover would be under the loader mount. Exactly right, and I'd a never seen it if you hadn't have mentioned it. At any rate, nothing was more than .003 out of spec, so nothing major. I set it all to .007-.008.
...and the knock is still there.
So I got to looking around some more...and listening. The more I listened the more it sounded like it was toward the front of the engine, and down low. Then I noticed that the crank pulley seems to be vibrating quite a bit. And I just replaced the front oil seal there. Adding 2+2 makes me wonder. Assuming there's a bearing at the front of the crank, if that went bad and caused a vibration, that could make the seal go bad. And a bad bearing would certainly make some noise I would think. Or worse, a bit of rod slap (especially if it was on cylinder #1) which made the bearing go bad.
Thoughts?
...and the knock is still there.
So I got to looking around some more...and listening. The more I listened the more it sounded like it was toward the front of the engine, and down low. Then I noticed that the crank pulley seems to be vibrating quite a bit. And I just replaced the front oil seal there. Adding 2+2 makes me wonder. Assuming there's a bearing at the front of the crank, if that went bad and caused a vibration, that could make the seal go bad. And a bad bearing would certainly make some noise I would think. Or worse, a bit of rod slap (especially if it was on cylinder #1) which made the bearing go bad.
Thoughts?
TMGT
Elite Member
Have to checked to make sure the front pulley hasn't worked lose since you did the seal? I've had knocking noise from balancers coming lose.
Good thought, but the knock was there the same before and after replacing the seal. I just replaced the seal a couple days ago and the knock has been there for quite a while.
Jim Nelson
Platinum Member
I would think the only bearing at the front, behind the crank seal, would be the front main bearing and it would be a deep, hard, knock.This is just a w.a.g. as I don't know that particular engine. One thing to keep in mind is that sound really travels in an engine and can drive you crazy sometimes.
Yep you're right. I had a look on Messicks at the parts diagram and that's the only bearing I see. There is a collar/sleeve (like a rod bearing sleeve) at the front, so I suppose that could be worn, but maybe that's not the issue.
It's hard to get a video that will show it because of the frame rate of the video (video of airplane propellers is a good example), but I did take a slow motion of it Kubota L4740 crank pulley slow motion - YouTube Hard to tell if it's an inconsistency in the pulley itself, or is actually indicative of something else. Or maybe I'm barking up the wrong tree here.
Based on everything that's been eliminated at this point, rod knock is about the onlything left, am I correct?
K5lwq
Elite Member
- Joined
- Aug 6, 2017
- Messages
- 4,805
- Location
- Mineola, TX
- Tractor
- Kioti LK2554, Branson 4815C, Satoh Beaver, Speedex
That is my fear but can't say for sure. As I said earlier, after hearing your video just at the end it sounded like a rod to me. It is very hard to diagnose noise from a video, for me at least.
Alien
Elite Member
Old mechanic trick.
Get a long screwdriver and push the handle firmly against your ear. Place the other end on various parts of the engine. You can often locate the source by doing this.
Just be careful near the fan/belt.
Get a long screwdriver and push the handle firmly against your ear. Place the other end on various parts of the engine. You can often locate the source by doing this.
Just be careful near the fan/belt.
Jim Nelson
Platinum Member
Boy that video is really a stumper,I don't think there is enough pulley movement there to make that much noise.It's seeming more & more like a rod but the only way to know for sure is to pull the pan and see. Not an easy job as in a lot of cases you have to pull the engine to get the pan off. Depends on how you are set up, shop wise, if you can diy.