Cummins Engine Cylinder Failure

Harry Babb · Post by **Harry Babb** » Dec 4th, '06, 22:54

Recently I purchased a pair of 300 6BTA engines that were listed on our Swap & Sell board. I bought these engines knowing that they had about 5400 hours on them and that the port engine had serious blow by on the #6 Cylinder.

As I disassembled the port engine I was looking for something that caused the failure. I think that the engine should run for a lot more than 5400 hours before failure. The #6 piston suffered from stuck top ring and the blow by destroyed the second compression ring and the piston itself.

I sent the injector pump and injectors out for inspection and overhaul. I expected that the #6 injector may not be atmozing correctly but I was wrong. The pump and injectors were functioning properly and not the cause of the piston failure.

Yesterday I disassembled the Turbo and the exhaust elbow and WALLLAAA there was the problem. The inner part of the elbow was coroded or eroded thru and I belive that water got back in the exhaust manifold and settled in the #6 cylinder causing corrosion, rust and eventually the piston failure.

I post this so that you Cummins guys might want thourghly inspect your exhaust elbows (shower head) this winter and possibly save your engines from serious damage.

If you are like me........I would rather take a beating than screw with exhaust.........and its going to be difficult to disconnect the 6" hose to inspect the elbow but I am sure that you will agree that it would be worth it to save your engine.

I would like to know if you guys find a problem with your exhaust elbows and the age of the elbow.

Harry Babb

scot · Post by **scot** » Dec 4th, '06, 23:40

Sorry to hear that Harry, was the corrosion at the 6 o'clock position in the jacket?

Harry Babb · Post by **Harry Babb** » Dec 5th, '06, 08:46

Scot
I purchased the engines fully aware of the problem with the port engine and more specifically the #6 cylinder. The other parts of the engine are Okay.

The exhaust elbow is corroded out at 6:00 as well as 12:00 and the holes in the inner elbow are quite large. I will bead blast it later and try my hand at getting some pictures posted.

I was happy to find the problem with the elbow.........now I have the confidence that I can rebuild the engine and know that I have corrected the root cause of the failure.
Harry Babb

scot · Post by **scot** » Dec 5th, '06, 09:06

I sure miss having a machine shop, we had a Pangborn Roto-blast shot blaster and a sugar sand bead blaster. tape the flanges and get after it. I think machine shops were taylor made for boat owners.

I wonder if a fresh water flush after each run would prevent that scenario? If the corrosion was only at 6 o'clock I feel fairly certain that the salt water sitting in there for prolonged periods (at the dock) did that, but the 12 o'clock has me puzzled??

Scot

JP Dalik · Post by **JP Dalik** » Dec 5th, '06, 10:25

Harry,
Were these the stock stainless exhaust elbows or something different. 5" or 6".

Harry Babb · Post by **Harry Babb** » Dec 5th, '06, 10:32

I BELIEVE that these elbows are stock but I am not totally sure. The engines came out of a boat that spent its life on Long Island in New York.

I do know that they are a welded stainless steel fabrication and they bolt directly to the turbo and the exhaust hose clamps onto the other end. I will measure the hose diameter when I bead blast them.

Harry

Ryan · Post by **Ryan** » Dec 5th, '06, 10:59

Exact same thing had happened to a guy in my marina with the exact same engines, around a 90-92 vintage. He only had about 2,500 hours on his. He wound up getting a re-man short block and new elbows for both engines.

In Memory of Vicroy · Post by **In Memory of Vicroy** » Dec 5th, '06, 12:32

Cummins used to offer several exhaust elbow options ranging from cast iron to cupro-nickel. I got lucky and mine came with the cupro-nickel ones that are pretty much bullet proof. I looked at both of them within the last couple of years (engines built Nov, 1989) and they both look like new inside. The fact that AJ mostly lives in fresh water obviously don't hurt none......The welds in the stainless ones are suspect......See if you can locate a set of cupro-nickel ones.

UV

Capt. DQ · Post by **Capt. DQ** » Dec 5th, '06, 14:05

Had a friend build me a set of stainless steel for mine 5" which mine have the shower collar wrapped at the end with 1/4"-3/8" holes around the outside of the main exhaust pipe. Should last me for a while on this set.

R,
DQ

Harry Babb · Post by **Harry Babb** » Dec 6th, '06, 20:22

Okay guys let try this
This link to Photobucket shows the pictures of the Exhaust Elbow that is the cause of the #6 cylinder failure on a 6BTA engine.

The exhaust hose size that fits the elbow is 5"

Ryan you hit the nail on the head........these engines are 1992

http://s147.photobucket.com/albums/r289/chip51maker/

Harry Babb

scot · Post by **scot** » Dec 6th, '06, 21:16

That's odd Harry, looking through the holes the exterior shell appears uneffected? All of the corrision seams to be in the exhaust flow path, upstream of the water entry. They must have used two different materials and married them (welded) at the outlet weld. One worked, one did not.

Am I mistaken, isn't the heavly corroded interior dry in the elbo?..short of a salt fog as the water exits downstream. But no water sits there when not operating. The water exit ports look fine?

Scot

Harry Babb · Post by **Harry Babb** » Dec 6th, '06, 21:35

Scot
The exterior shell and the "Shower Head" are still in great shape. The corroded area should always be dry........the water is injected down stream thru the small holes drilled in the face of the shower head ring.

My thoughts are that if the inside part of the elbow cracked or developed a leak then the corroded area that we are discussing will then be wet. I wonder if salt water started leaking upstream of the water injection then the situation simply deterioated from there.

Anyway...........thats the worst elbow that I have ever seen.

I stated earlier that the injection pump was just fine and today I talked in detail to the Injection shop and he told me that there is a device (cannot remember what he called it) that prevents the fuel rack from opening up to full throttle until the turbo boost comes up and that device was not working very well and the engine probably was experiencing low power. I wonder if for some reason this caused high exhaust tempetures and acclerated the corrosion inside the elbow. Long time ago in my Mack Truck days that device was refered to as a Puff Limiter.

Harry Babb

bob lico · Post by **bob lico** » Dec 6th, '06, 22:32

those are absolutely pre 1992 elbows.maybe part #3914717 deleted by cummins in 1992. well from your decription you have cummins cpl 970 engines.this was cummins first shot at 300hp from the 6bta.the problem is the cylinder head(3927288) have two design flaws.the first is no exhaust rotators in the head and the second is the injector size.if you overprop even slightly you will pop #6 or the slighest overhead. you must treat these cpl 970 as 250hp. every single part of that engine but the block was deleted as of 1995.you can live with the pump and exhaust manifold (watch for cracks on exhaust port to #6) but the heads must be treated like a baby.make sure you do not have welded aftercooler.DO NOT USE!!!
e-mail me and i will help you the best i can--bob

IRGuy · Post by **IRGuy** » Dec 6th, '06, 23:03

Bob...

Are you saying that after 1995 the 6BTA engines did not have this problem? My engines (315 HP) were made in late 1995, and identified by Cummins as 1996 models (CPL 1928). If this is a chronic problem and my engines are suspect I would certainly like to know so I could plan on changing the elbows.

scot · Post by **scot** » Dec 7th, '06, 09:24

Harry,

I'm just getting started with the marine diesels, what is the cost of the Pyro gauges? If temps were up they would have been warning you. Are they big money? I here a lot of talk about them on the boatdiesel.com board.

As for the corrosion, I feel like that is a metalurgy issue. Based on the fact that everyone seems to know the years that this stuff occurred they had a problem. The interior metal should not have corroded like that.

As with most boating problems "when all else fails...throw money at it"

Good Luck with the new pieces.

Scot

bob lico · Post by **bob lico** » Dec 7th, '06, 09:57

irguy you have a completly differant engine.about the middle of 1994 cummins came out with the diamond series built around the best of the best 7100 series pump.present day heads.redesign exhaust manifold and after cooler etc.that being said possibly jp could sent a post a picture of the new style 6" exhaust elbows i sold him and this would clear up all issues they are 316 stainless and the "shower head" is internal .ir guy there are no issues with your diamond series just keep a eye on the water temp, the raw water pump impellar has to be maintain--------off season remove and coat with vegetable oil ----NO grease or any other petro. derivitives.

IRGuy · Post by **IRGuy** » Dec 8th, '06, 12:11

Bob Lico..

Thanks for the reply. My engines seem to have been made just before the Diamond series hit the market.. as I said above they were built in Dec 05 and left the Cummins factory as 1996 models. They don't have the word Diamond anywhere on them. I had Tony Athens of the Boatdiesel forum run the serial numbers and get some warranty history for me a few months ago, but no mention of them being Diamonds. If pictures are posted of the exhaust elbow I might be able to compare them to what I have. I will check back here to keep updated.

I really appreciate your help!

Harry Babb · Post by **Harry Babb** » Dec 8th, '06, 14:36

Good afternoon Bob
I just checked the data plate on the 6BTA engine that we are discussing and you are correct the CPL number is 970. The serial number is 44645256 and the date code is 19910725. I stopped by the engine machine shop yesterday and got the news that the cylinder head is cracked on every cylinder between the valve ports and the crack runs down into the valve bowl area. The engine did not have valve rotators. The injectors have the 7 MM nozzle tips which as I understand is the small size(instead of the 9MM nozzles)

Attached here is a pic of the defective piston.

Rawleigh · Post by **Rawleigh** » Dec 9th, '06, 16:20

Bob really nailed that one didn't he!!!

bertram31.com

Cummins Engine Cylinder Failure

Cummins Engine Cylinder Failure

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