Kubota L4740 Engine "knock" Help?

[jshwhite]

I'm back, and we're making progress. Honed the cylinders yesterday with a dingleberry hone and got a nice crosshatch on the cylinder walls. Got the crank mains on, crank installed, pistons in and rods attached. All torqued down. Next up is putting balancer shafts, valve cam, fuel cam etc. And I have a question..maybe a dumb one??

Supposed to set 4th cylinder to TDC on compression stroke, then put all the shafts in and line up the timing marks on the gears. But how do you know whether it's on compression stroke or exhaust? There's no cam in, no valves (no head). Does it not matter? Just set the 4th at TDC and when you put it all together with timing marks aligned it becomes the compression stroke? Sorry if that's a dumb question. Thanks!

 

[dodge man]

I would say it doesn’t matter. With no cam in the rest of the engine wouldn’t know if it’s compression or exhaust. Once the cam is in that would determine it. Keep in mind I’m not sure of my answer but it makes sense.

 

[TMGT]

You've got it right, cam determines what stroke its on, so set piston to tdc and install cams.

 

[ruffdog]

Cam runs 1/2 crank speed so half the time it is comp stroke, half is exhaust.

 

[jshwhite]

Thanks guys. Yeah that makes sense. I guess for extra security one could just make sure the lobes are down on the cam for cylinder #4. But I think if all the timing marks line up it should be correct.

 

[jshwhite]

Made some more progress this afternoon. Everything went smoothly.

To put all the shafts and gears in, first set cylinder #4 to TDC,
- Slide the balancer shafts in. Put the mounting bracket and torque those, as there's one bolt hidden behind the cam gear.
- Slide the cam in and line up the timing mark to the balancer shaft.
- Install the fuel cam.
- Bolt/torque the idler gear mount, then slide the idler gear in, lining up all timing marks.

Note: make sure to put the valve tappets in BEFORE the head. I almost forgot and was just about to torque the head down.

I forgot to put the tappets in order of how they came out, and noticed it said in the service manual not to swap them around. Oops. Hopefully since it's a pretty new engine it won't matter. I'll double check all the valve clearances before running it.

Note 2: There's a little lever (governor??) that's part of the fuel cam assembly. When you put the injection pump in, you have to push it back out of the way of the rack pin on the injection pump before you bolt it down. See the pic with the red arrow. I missed that and tightened it down with that lever under the pin. It bent the lever but thankfully I was able to straighten it out.

Hoping to get it all back together in a few days here. Will be nice to be able to blow snow!!

 

[dodge man]

It’s coming along. I went back and reread this thread, I had forgotten some of the history. Do you have an opinion on what caused the problem.

 

[jshwhite]

It’s coming along. I went back and reread this thread, I had forgotten some of the history. Do you have an opinion on what caused the problem.

Well, as best I can figure, something caused an oil starvation issue on the front end. Basically every bearing toward the front end was at least somewhat worn. The main crank bearing took the hardest hit for some reason, and the resulting vibration destroyed the gears, which caused yet more damage. The question of course is what caused the oil starvation? I don't know. All the oil passages were clear as best I could tell.

I suppose it's possible that something messed the gears up, and as they self-destructed the pieces made their way through the system and destroyed the bearings, as well as causing some oil starvation from clogging. But that doesn't make complete sense because it was the front bearings that were worn. General oil starvation would affect the entire engine, not just the front. And what made the gear get messed up to begin with?

I guess it's hard to say which came first, the chicken or the egg, but in my opinion the oil starvation issue came first.

Would love to hear ideas from others on here.

 

[rScotty]

Well, as best I can figure, something caused an oil starvation issue on the front end. Basically every bearing toward the front end was at least somewhat worn. The main crank bearing took the hardest hit for some reason, and the resulting vibration destroyed the gears, which caused yet more damage. The question of course is what caused the oil starvation? I don't know. All the oil passages were clear as best I could tell.

I suppose it's possible that something messed the gears up, and as they self-destructed the pieces made their way through the system and destroyed the bearings, as well as causing some oil starvation from clogging. But that doesn't make complete sense because it was the front bearings that were worn. General oil starvation would affect the entire engine, not just the front. And what made the gear get messed up to begin with?

I guess it's hard to say which came first, the chicken or the egg, but in my opinion the oil starvation issue came first.

Would love to hear ideas from others on here.

I would like to see a lubrication diagram for this engine. Do you have one? My assumption is that engine oil under pressure is forced everywhere that there is a passage open under approximently the same pressure. It's a fairly low pressure at best - in the 20 to 50 psi range I'd guess. So I realize that pressure doesn't mean flow is happening.
And from what you've seen it does sound like something starved the front of the engine. So the first guess would be something clogging the oil passages to the front.

But you've checked that path to the front. So could it be that one of the other oil pathways passages suddenly opened up too much for some unknown reason and all of the oil flowed to the easier path?

Here's a thought....If all the oil was being forced to flow in a low resistance path, wouldn't it show as an overall drop in oil pressure on the gauge?

If true, then I think that I'd be tempted to see if I could put a couple of extra pressure taps into various places in the oil flow.... and maybe some extra gauges. They don't cost much. And then keep a close eye on them for awhile. Keep in mind that most taper tapped holes in Kubota blocks (oil & water) are British Tapered Pipe Thread rather than Metric or SAE. That's so common with Japanese engines that most hardware/auto stores have the required thread adapters.
luck,
rScotty

 

[TMGT]

Well, as best I can figure, something caused an oil starvation issue on the front end. Basically every bearing toward the front end was at least somewhat worn. The main crank bearing took the hardest hit for some reason, and the resulting vibration destroyed the gears, which caused yet more damage. The question of course is what caused the oil starvation? I don't know. All the oil passages were clear as best I could tell.

I suppose it's possible that something messed the gears up, and as they self-destructed the pieces made their way through the system and destroyed the bearings, as well as causing some oil starvation from clogging. But that doesn't make complete sense because it was the front bearings that were worn. General oil starvation would affect the entire engine, not just the front. And what made the gear get messed up to begin with?

I guess it's hard to say which came first, the chicken or the egg, but in my opinion the oil starvation issue came first.

Would love to hear ideas from others on here.

I'd tend to lean towards either something going through those gears or the gear failing and a tooth/teeth jamming between the gears.
The high pressure of that could damage/deform the front bearing enough to allow excessive clearance and essentially pound itself lose. This could also explain the excessive wear on the adjacent main bearings, partly from excessive play but also from reduced oil pressure from the extra clearance in that front bearing.

Thats my theory at least, its hard to tell from a few pictures online, but I have seen foreign material take out timing gears before, however in those instances the valve timing was thrown off enough that the engine shut down preventing further damage. The bearing journals did show signs of damage from the high forces of the gears, even from just the initial damage and the engine spinning down.

I'm also curious about the oiling circuit, being that the pump is front mounted I'm guessing that the 1st or 2nd main is getting fed first and mostly likely it has priority main oiling system.