Engine/Transmission (1994 - 1998) intermittant Knocking

[Lnwing]

Fuel knocks can be scary! One combine I owned developed a horrible knock when idled down. Turns out a set screw came loose in the injection pump(Simms in-line), which allowed one cylinder to receive WOT fuel while the other five were at idle. NOT recommended! Had the pump pulled and calibrated, which fixed it.



Lynn

 

[Dieseldemon]

When you hang a piston in the bottom of the cyl you will not get excessive blowby out the vent tube and a hung piston could be from a fram or equv bad filter that has plugged up a piston cooling nozzle I just overhauled a 98 with 131000 miles on it that had 3 of the nozzles plugged but only one piston hung #6 A knocking piston is really loud under the truck.

 

[Vaughn MacKenzie]

Any updates Earl?

 

[Earlschultz]

nothing new yet. Dampener looks ok. With the weather changing knocking is quieter when its warmer out. but never goes away . Iam curious what a hung piston is .

Is it when a cooling nozzle falls out ? And if so what knocks because of it?

Wrist pin? It is very loud under the truck.





thanks again guys for all your ideas and thoughts

Earl

 

[Andy Redmond]

Hung piston? I'm guessing seized or stuck. . maybe Jim will chime in if I presume incorrectly?



Piston cooling nozzles are typically made of plastic and allow for oil spray to be directed onto the bottom side of the piston. If this cooling source is closed or restricted by some foreign matter the cylinder will die eventually, sometimes pretty quick.



Damage from insufficent oil cooling could include cylinder wall scoring, piston damage, scoring, seizure, connecting rod, wrist pin damage, etc. etc.



They wouldn't usually fall out they are pressed into a casting.



The oil pan is a big drum. .



Have you done a compression test? Often one or more bad cylinders will show up this way. 350 psi is excellent. 300 is a good target for a used engine, most important is how close all are to a specific reading. Is one 350 and another 260? The low or spreads are often problems.



Your FSM should show the piston cooling nozzles and describe the carnage should they not operate properly or get restricted by foreign debris. Ie oil filter media, foil from the oil jug etc.



Good luck and lets hope its something not major.



Andy

 

[mechanic]

nothing new yet. Dampener looks ok. With the weather changing knocking is quieter when its warmer out. but never goes away . Iam curious what a hung piston is .

Is it when a cooling nozzle falls out ? And if so what knocks because of it?

Wrist pin? It is very loud under the truck.





thanks again guys for all your ideas and thoughts

Earl

I also wondered what he ment by a "hung piston". I would assume it means a galled skirt.

If a piston were hung, the engine would not turn unless the rod on that piston were broken.



What knocks is the piston in the cylinder. When a cooling jet stops working, the piston will heat up to the point of sticking to the cylinder walls, this results in several thousands of an inch of the aluminum piston skirt being ripped away. This makes the clearance increase enough to allow a knock. It can also cause a piston to seize.



As far as I know, the 1st, 2nd, and 3rd generation engines do not fall out, but can stop-up. As I recommended in a previous post, I would check the injectors for a dripper. Then go on to test for more serious problems.

 

[dodge cummins]

i don't know if this helps but issue 25 talks about the difference between the p7100 pumps and the 2nd half 98 24v pumps and it explained that a knocking from the p7100 when cold is normal. the 2nd half of 98 24v pump did away with the pump with the abitilty to advance or retard timing on its own with the temps outside or the temp of the motor. hope its just a minor issue.

 

[Dieseldemon]

What happens is the piston cooling nozzle gets plugged up and the piston gets very hot, hot enough to move metal from the piston to the cyl wall and score the wall bad enough to cause the piston to rock from side to side which is the knock you hear.

If it is scored at the bottom of the cyl it will not have a lot of blow by. I would suspect it is #6 the farthest from the oil pump.

It could happen also from the engine getting hot like losing a belt and not stop on a hill I had one cust that that happened to and he thought he could make it to the top of the hill He did not make it. I hope that is not what it is but it sure sounds like it. If you have to bore the block you can just bore the one hole and deglaze the other ones as the 1/2 and 1MM over pistons are the same weight as the stock pistons from cummins do not buy after market pistons and use your engine # to get the same protrusion.

Good luck If I can be of any help let me know.

 

[Earlschultz]

evening folks



ok what if I picked up a bore scope. Quick check would tell me something?

sounds like I am not getting out of pulling the engine? at this point is a long block in order or do I yank the engine, haul it over to the cummins dealer and tell them to fix it? and if so what does this kind of work go for? will they check it out all over or will they just fix the problem parts and ignore the rest?



thanks for your help

Earl

 

[Andy Redmond]

Needs to be shy of 7mm to go thru the injector hole in the head, bar the engine to get the piston at the bottom and hope the scope is lighted and flexible. The fiberscopes less than a 1/4" might be flexible enough to do the trick.



I have some photos I can email you of what you don't want it too look like. .



Seriously, ck. the injectors etc first, pulling the motor is not loads of fun even when you are compensated, I promise!



Good luck

Andy

 

[Gene Arnold]

Earl—



I don’t know where you live and this probably has nothing to do with your knock, but this happened to me when I lived in Grand Island, Nebraska. I bought a 1969 Mercedes 220D, 4 speed manual, in November, 1969. Shortly after I bought it it started to knock terribly. I took it in to the dealership and they had difficulty diagnosing it for a little while—until the mechanic raised the car. The problem was gravel and dirt in the rear transmission support. On warm days it wasn’t a problem. On cold days (down around zero), especially if I had driven on sloppy roads the day before, the thing froze up and became solid. The effect was to magnify the normal engine noise up through the body—really scary. He cleaned it out, but I had to watch it because it often started to do the same thing all through the seven years I owned the car. Bottom line, could you have dirt and ice in the motor mounts?

 

[Dieseldemon]

If you pull the engine you have already done the hard part the rest of it is not that hard strip it down take it to a machine shop bore 1 hole and deglaze the rest and check the deck to make sure it is flat buy the parts from Cummins I dont trust after market parts for that engine drive out the piston cooling nozzles put in new ones they are made of nylon now and they come with a lower gasket set. Piston cooling nozzles can not fall out they are under the upper main bearings. I have just finished with the 3rd engine 1 with broken front hsg dowel pin fell out 1 with bad block coolent leak into the crankcase 1 with plugged piston cooling nozzles 3 were plugged 1 piston seized or hung whatever you want to call it. If you run into something you dont know you have this forum to fall back on there are a lot of knowledgable people out there that are willing to help I will do whatever I can to help you if you need it tips and what ever.

Where are you located

 

[mechanic]

Earl,

Don't jump to engine R&R untill you know what is wrong. You have gotten a lot of good advise and ideas here. Try the tests that have been recommended and let us know the results and then we can help you go on to the next test or procedure. Take the simple tests/problems first and then the move on to the more complex. From reading the posts, you have several knowledgable folks responding to you. Unless I have missed something, I haven't seen where you have run the tests mentioned and given the results. No offense intended, but try some of the things already posted and then if they don't show the problem, that's the time to talk about and engine taredown and possibly the R&R of the engine. Hope this helps, and hope it is something small.

 

[Vaughn MacKenzie]

Don't remember if this was mentioned but maybe the harmonic damper could be bad and separated?