OT Cummins N14 engine knock

I enjoy all the things posted on here and I know there is a lot of knowledge about diesels on this forum so here's the problem with my road TRACTOR hehe

Engine is a Cummins N14 in a 99 Freightliner. I bought the truck with a knock in the engine. Found the problem to be a galled piston and cylinder liner. I put a new liner, piston, rings and gaskets in it. Just to be safe I cleaned out the piston cooler nozzle and it did have a piece of gunk that could have been restricting oil flow to that cylinder. I cleaned it out and reinstalled.

Today I got the engine together and started it and it still has a slight knock. It is not nearly as bad as the noise was before and the noise can be heard the most through the breather. If you put your hand on the outside of the breather it is like someone is beating the breather with a hammer. Engine runs smooth and doesn't miss.

Does anyone have any ideas? I am thinking maybe the injector on #5 is dumping too much fuel into the cylinder and that is what caused the problem in the first place? Let me know what you all think... Thanks in advance, Morgan

Look at the exhaust smoke, cold start and when it warms up. This might tell you more. You can alway test the injectors to elimate them.

You may have more than one piston with a scuff. The easiest way to check is to remove the oil filter, cut it open and check for piston material. It is normal to find some metal but if it is full of metal you have another problem.

Be sure and check the top ring groove in the piston, It has a steel alloy that Cummins had a problem with debonding on engines built during this era. I doubt if this is your problem as it ran this long.

Odds are the engine was operated with low coolant, has a water pump or radiator or thermostat problem. Some engines built during this era had a system called low flow cooling. They had two thermostats. One was normally open and the other was normally closed. The thermostats switched from open to closed and vise versa as the engine warmed up. Engines with the low flow cooling systen used radiator hoses about the size of radiator hoses. Temp drop across the radiatoe while at operating tem was about 30 deg. F.

Engines with traditional cooling systems will have a temp drop of about 10-15 degrees F at operating temp.

If you have to drop the oil pan again I would remove and cleam all of the piston nozzles. Would also remove and flush the oil cooler on the oil side to remove and foreign material.

The bottom line is something caused your piston(s) to scuff and you have to find out what it is. I am assuming your overhead is properly adjusted. If you can't tell I worked at Cummins in Field Service when theses engines were being produced.

Hope this helps.

Bill.

You could have an accessery drive bad. It will make an intermitant knock,though.Turn engine off and pry accessery drive pulley forward and backwards, if it moves replace with recon.IF the noise is steady, consistant,look at valve train or piston, rod knock.If noise is at idle but goes away as you slowly increase rpm,it may be normal:the electronic injectors can make it sound like a knock, especially in the freightliner chasis.Also engage the engine fan to run at idle(unplug the fan solenoid,usually on left firewall)It will put a small load on the engine and posibly change your noise/knock; if noise gets better it probably is ok/normal.
MARK

watch valve operation while running--reminds me of one I worked on once with bad cam roller on exhaust--valves won't allow exhaust out fast enough, giving that constant pop thru air cleaner---

(quoted from post at 15:32:19 03/11/12) watch valve operation while running--reminds me of one I worked on once with bad cam roller on exhaust--valves won't allow exhaust out fast enough, giving that constant pop thru air cleaner---

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Thanks for all the responses. I think I will check out the valves to make sure they are all opening as far as they should first and then check the injectors. I will keep everyone posted as to what I find.

Thanks!
Morgan