Kubota L4740 Engine "knock" Help?

[rScotty]

I'll admit to having been fooled a few times on exhaust noises. Probably would have happened more, but we we don't see much rust of any kind out here in the arid West.

The best way I know of to diagnose exhaust noise is to attach a 25 foot extention to the tail pipe. My favorite extension is a piece of scrap flex-pipe that is just large enough to fit over most exhausts. I run it out the door and around to the side. That moves the exhaust note away and puts just enough restriction on the whole exhaust system to show up any leaks. I don't know of any good way to diagnose a loose baffle. Not something I run into.
rScotty

 

[Leejohn]

Take the temp at each cyl exhaust outlet close to the head and see if one is running colder then the others.

 

[jshwhite]

Well, this sure didn't take a rocket scientist. I popped the side panel off where I could get a good look at the entire exhaust. Major blowby out the rear cylinder manifold gasket. And another spot at the front.

Maybe it has a knock, maybe not. I'm going to replace the gasket first and move from there. Any tips or tricks welcome.

 

[TMGT]

Good chance thats the noise you heard. Nothing special, hit the nuts with penatrating oil and make sure the manifold and head surfaces are flat.

Not sure on that particular model engine, but I haven't seen at lot of manifold gasket failures on the smaller Kubota engines.

 

[CoyPatton]

Well, this sure didn't take a rocket scientist. I popped the side panel off where I could get a good look at the entire exhaust. Major blowby out the rear cylinder manifold gasket. And another spot at the front.

Maybe it has a knock, maybe not. I'm going to replace the gasket first and move from there. Any tips or tricks welcome. View attachment 669818View attachment 669819

Good penetrating oil, small turns to loosen and then tighten back up. Do not remove any nuts or bolts until all have been loosened.
I like to work from center outward.
Another old old mechanic trick is candle wax. Heat the bolt/nut melt candle wax into threads

 

[jshwhite]

Ok, we're making progress, but I've still got a knock. Got the exhaust gasket replaced no problem. It sounds WAY better. But the knock almost sounds worse, now that it's not disguised by the exhaust leak sound. Here's a new video Kubota L4740 knock - take 2 - YouTube

rScotty, you mentioned piston slap due to a faulty injector. Is there a way to isolate which cylinder is the noisy one? Or should I just pull all the injectors out and take them to a shop to get them tested?

Thanks for the help.

 

[CoyPatton]

Do a cheap mechanic stethoscope and listen to each cylinder through a length of pipe. Place it against each high and low on the block. Where it is noisier, gives you more ideal of where it is coming from.

 

[Leejohn]

See post 12

 

[TMGT]

See post 12

Agree,

Does the noise change at all with the clutch depressed?

 

[K5lwq]

It sounded like a rod at the end when you shut it down. Taking temp readings like post 12 is a good idea but I would use a hose or something to listen closely at the bottom end.