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Discussion Starter · #1 ·
I'm refreshing the 4bt before throwing it back in the expedition. It's got less than 40k miles on the rebuild. I'm concerned about the rod bearings and what I would consider excess carbon on the pistons.

The crank is/was a brand new chinese casting. The pistons were .040 over PAI brand, that the local machine shop puts in all their rebuilds. The ring end gap is pushing the limits, but I don't think that would make this car on build up.

As far as the rod bearings, I have not measured anything yet. Maybe the rods need resized? Tomorrow I'll measure stuff up and throw in some plastigauge and try to figure this out. The crank still looks really good. I am running ARP rod bolts....and I did not realize them when i put the bolts....supposedly it's advise.

Any input on this stuff would be great.


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Has this seen any heavy towing or lugging?
What oil are you running?
Pistons do not look too bad, maybe a little oil getting past the rings.
Any pic's of the piston crown?
Cheers Steve
 

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Discussion Starter · #3 ·
Here's a semi-cleaned up piston. A little tarnished where I let it sit in cleaner to cut the carbon. Looks like the injector is shooting outside the bowl a bit?


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Discussion Starter · #4 ·
Has this seen any heavy towing or lugging?
What oil are you running?
Pistons do not look too bad, maybe a little oil getting past the rings.
Any pic's of the piston crown?
Cheers Steve
No towing at all. I would say i lug it a little, but don't think it's overkill. Too much vibration to really lug it.

Always ran Rotella t4 15w-40 in it.

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I am running ARP rod bolts....and I did not realize them when i put the bolts....supposedly it's advise.
Supposedly eh?

I suppose then if you found out that your big ends weren't round anymore because of the fastener change you wouldn't be surprised?

Upgraded fasteners do vastly more harm than good if you don't use them correctly. Rod and main bolts require machinework to correct the distortion they induce.

The carbon looks typical. Those early pistons don't have an upper ring land relief so they get extra cruddy like that. The standard solution is to relieve the upper land about .015" down to the steel insert. That makes for a real good piston that won't scuff a bore. Those frequently scuff if you run them without relieving.
 

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Discussion Starter · #7 ·
Supposedly eh?

I suppose then if you found out that your big ends weren't round anymore because of the fastener change you wouldn't be surprised?

Upgraded fasteners do vastly more harm than good if you don't use them correctly. Rod and main bolts require machinework to correct the distortion they induce.

The carbon looks typical. Those early pistons don't have an upper ring land relief so they get extra cruddy like that. The standard solution is to relieve the upper land about .015" down to the steel insert. That makes for a real good piston that won't scuff a bore. Those frequently scuff if you run them without relieving.
Thanks for the heads up on the distortion. I'm going to measure the big ends and see how they spec and report back. Im not opposed to having them machined.

Do you have a pic of this newer style piston so I can duplicate this relief area?? I do like to machine my own stuff. I could bore the big ends of the rods after I surface ground the cap, but couldn't finish hone them. I'm going to research how resize the big end.

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Big ends are not bored ! Resizing the bearing end is not something you can do at home as it take a machine that measures the center to center length of the rod to keep the compression height correct ! If you intend to do it right in a Diesel. If you grind the caps the bore will be distorted and require honing to round and the bearing crush must be corrected. Also with the wear showing here, you should also check the wrist pin bushings and pins for wear. I've seen engines with over 200k looing better than this. Carbon AND bearings. If your ring end gaps are wide, this really makes me question the mileage figure you posted. The only way this can be, is you have an engine with more than 40k on it or old parts were installed in a shop. My first thought would be a timing issue doing this to the bearings, that would also result in carbon deposits outside the bowls. The only other thing that might be a reason is the wrong injectors discharge angle. This a fairly common issue with Cummins engines you know little about, unless you have exact knowledge of which nozzles are installed. Relieving the pistons isn't a big deal, just don't take out too much as this allows added heat to reach the top ring which causes gap clearance issues, more heat more expansion and less gap which means broken rings. It's better to have a slight taper above the ring insert and not a simple reduced piston head diameter straight down. If there isn't any scuffing I wouldn't worry about it as much as I would cracking of the pistons at the top of bowls. As for the cranks NO Cummins cranks are Cast, they're all forged. The wear you are seeing here is as I said likely from advanced timing ! You need to measure the bores to be sure they are not tapered, out of round and not worn. Like I said, look at the wrist pins and bushings and measure the piston pin bores. This is not normal bearing wear for any Cummins ! Not with only 40K along with wide ring end gaps.
 

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Discussion Starter · #9 ·
Big ends are not bored ! Resizing the bearing end is not something you can do at home as it take a machine that measures the center to center length of the rod to keep the compression height correct ! If you intend to do it right in a Diesel. If you grind the caps the bore will be distorted and require honing to round and the bearing crush must be corrected. Also with the wear showing here, you should also check the wrist pin bushings and pins for wear. I've seen engines with over 200k looing better than this. Carbon AND bearings. If your ring end gaps are wide, this really makes me question the mileage figure you posted. The only way this can be, is you have an engine with more than 40k on it or old parts were installed in a shop. My first thought would be a timing issue doing this to the bearings, that would also result in carbon deposits outside the bowls. The only other thing that might be a reason is the wrong injectors discharge angle. This a fairly common issue with Cummins engines you know little about, unless you have exact knowledge of which nozzles are installed. Relieving the pistons isn't a big deal, just don't take out too much as this allows added heat to reach the top ring which causes gap clearance issues, more heat more expansion and less gap which means broken rings. It's better to have a slight taper above the ring insert and not a simple reduced piston head diameter straight down. If there isn't any scuffing I wouldn't worry about it as much as I would cracking of the pistons at the top of bowls. As for the cranks NO Cummins cranks are Cast, they're all forged. The wear you are seeing here is as I said likely from advanced timing ! You need to measure the bores to be sure they are not tapered, out of round and not worn. Like I said, look at the wrist pins and bushings and measure the piston pin bores. This is not normal bearing wear for any Cummins ! Not with only 40K along with wide ring end gaps.
You gave me a lot to process here, I appreciate that.

First, I'm 100% sure the engine has less than 40k on a rebuild. It was bored 40 over at the time, and as I recall it was on the outer ring gap limit at that time.....to get previous wear cleaned up. When I got this engine, it was in pieces, completely disassembled. I then had it hot tanked, block decked, bored, etc. I had also had 2 VE pumps to reseal and try out that the engine came with. I actually took the worst looking pump to reseal first and try out. I didn't seem to have any issues with it operating. I also didn't cross reference the pump part numbers to make sure the pump was suitable for the common cpl858(my tag is gone).

For timing I set it per the specs out of the gate for timing. I set the timing with #1 at TDC per dial indicator and also mounted a dial indicator on the pump piston and rotated the pump to get the proper lift, iirc 0.040". Initially I ran the engine with new DAP 5x14 injectors, I bet I ran those for 30k miles. I was never happy with their performance for a DD. I then downsized to a 5x12 from DAP. The injectors were pop tested on my tester and shimmed to spec. I too have suspicions that injection timing has played a factor on these bearings, as my pistons did show signs of spraying on the top of the piston.

The rods are currently being resized at the machine shop....big end and small end.

Is there a sure fire way to confirm pump timing on these things? I've really thought about getting diesel timing light.

Again, thanks for your input.

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The VE camplate lift spec only works for the given camplate it's for.... They vary in lift and lobe form.

The diesel timing light sounds like a good idea in this situation.
 

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Discussion Starter · #11 ·
Ok. I'll check out my pump numbers and maybe charr or someone can tell me more about them. They may both be the same pump, I can't remember.

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Since the block has been bored, with high ring wear, another issue way have been bore finish. If the bore is or was not finished correctly your rings can wear faster. Cat engines are factory assembled with a bore finish that is very fine and everything is factory burnished and disassembled for a final inspection to insure all clearances and parts are within specs before any sub assembling is done for the final assembly. As I said earlier, I have been around Cummins and Cats, and other Diesel engines that have had far higher use and seen better conditions. One Cummins 6BT i knew about had just a few miles under 1Mil and the only thing that was out of spec was 1 EX valve stem. As for rod bearings, they are factory service scheduled for 250K and mains at around 500K I think. So you definitely had something not right.
 

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You gave me a lot to process here, I appreciate that.

First, I'm 100% sure the engine has less than 40k on a rebuild. It was bored 40 over at the time, and as I recall it was on the outer ring gap limit at that time.....to get previous wear cleaned up. When I got this engine, it was in pieces, completely disassembled. I then had it hot tanked, block decked, bored, etc. I had also had 2 VE pumps to reseal and try out that the engine came with. I actually took the worst looking pump to reseal first and try out. I didn't seem to have any issues with it operating. I also didn't cross reference the pump part numbers to make sure the pump was suitable for the common cpl858(my tag is gone).

For timing I set it per the specs out of the gate for timing. I set the timing with #1 at TDC per dial indicator and also mounted a dial indicator on the pump piston and rotated the pump to get the proper lift, iirc 0.040". Initially I ran the engine with new DAP 5x14 injectors, I bet I ran those for 30k miles. I was never happy with their performance for a DD. I then downsized to a 5x12 from DAP. The injectors were pop tested on my tester and shimmed to spec. I too have suspicions that injection timing has played a factor on these bearings, as my pistons did show signs of spraying on the top of the piston.

The rods are currently being resized at the machine shop....big end and small end.

Is there a sure fire way to confirm pump timing on these things? I've really thought about getting diesel timing light.

Again, thanks for your input.

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I'm concerned with the clear star pattern of the spray from the injectors outside of the bowl.. That would say the injectors are wrong... or.. its out of time... if out of time you'll see carbon build ups .. I'd think it has delayed timing.. at least on that cylinder with the star pattern outside of the bowl.. Is that injector sticking ????? Just My observations.. and out of time might give you the bearing marks too...
 

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I'm concerned with the clear star pattern of the spray from the injectors outside of the bowl.. That would say the injectors are wrong... or.. its out of time... if out of time you'll see carbon build ups .. I'd think it has delayed timing.. at least on that cylinder with the star pattern outside of the bowl.. Is that injector sticking ????? Just My observations.. and out of time might give you the bearing marks too...
Delayed injection on any Diesel should emit white smoke, atomized unburned Diesel fog, smell like unburned Diesel fuel, show wet exhaust pipe. As the piston is retreating in bore from TDC, the temperature in the chamber is cooling down and the fuel will not ignite, going out the exhaust. In such a case since there is no or very little combustion pressure transferred to the bearing, it is not likely to be that which caused ABINORMAL wear. Also power level is extremely LOW with late timing. So in this case it is left to improper discharge nozzle angle for the piston design or advanced timing and leaking injectors will have advanced timing! Mechanically timed verses actual timing are not the same ! By setting the pump timing you only have the effective position of the cam plate. If the injector is leaking, low injection pressure, spray pattern marks might be manifest and since the piston is compressing, the temperature will be rising enough to ignite the fuel. The visible indications of pattern could be from wet fuel depositing on the piston and burning which would leave the marks. I've had more experience with 7.3 Fords as far as engine internals, with injectors and burned/cracked pistons then with Cummins as they're so much better built engines, and other engines. When fuel is being injected correctly in the cylinder, it should start burning as it exits the nozzle thereby not depositing on the piston before igniting. Either way the injectors should be pulled out and checked. There are nozzle discharge angles of different degrees. For starters I think there are some injectors/parts of injectors that will interchange from an International DT 466 to the B series Cummins, I may be wrong, it's been awhile. Some suppliers sell injectors built from matching parts from one app to another. Go to dieselworldmag.com for a good read about building injectors. Carbon buildup is certainly a consideration. When fuel is properly burned, particulates should be at the lowest levels unless there is crankcase oil being leaked into the chamber. Either way, if oil is burning, injector condition and timing are not going to make much difference. With turbocharged engines bad intake guides are much less of a problem and exh guides will be tell tail with wet heavily carboned ports, not carbon in the bores. It has been my experience one can tell timing issues simply by the way the engine starts and stops, if the timing is late it will be hard to get it started, if the timing is advanced, the engine should fire instantly, especially with the VE pump, if the pump head pressure is good, when the key is turned off the engine stops very abruptly, it does not spin down.
 
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