CAT 3208 new knock

[Busterbrown]

The piston I replaced looked similar. It had similar discoloration from the high temperature. The third pic from the top it looks like the skirt of the piston has wear? I was told when a aluminum piston gets too hot it will change shape. How did the crank journal look? If it is in good shape be careful not to scratch it during reassembley. How dose the cylinder wall and Rod bearing look? Hopefully good. Remember I've done this but still consider myself a rookie.

[BruceK]

There are devices with a camera at the end of a flexible tube(I`ve seen one but no idea what they are called), you can view on a screen in the head unit areas you cannot see into. Do they take pics, I don`t know, at least you`l get to see the crankshaft. Try ebay.

[BruceK]

This type of camera should get you a look at the crankshaft. 720P HD Inspection Camera 3 5 Inch Wireless Monitor DVR Recording SD Card | eBay

[FF]

"I was told when a aluminum piston gets too hot it will change shape."

Piston mfg understand this , so pistons are machined oval, and expand closer to round under normal operation.

The piston skirt that is in contact with the cylinder wall in line with the rod provides most of the anti rocking , so has the most contact.

[Baker]

That piston is toast!!! But that connecting rod looks fine....and that is my very ignorant opinion!!

[sdowney717]

Connecting rod looks ok, but it could still be bent or twisted which will wear the bearing shells, piston, cylinder wall.

One way is use plastigauge. If bent, the plastigauge wont be evenly compressed all the way cross the journal face.
If a rod is bent even a tiny amount, the developed thrust will cock the piston and cause accelerated wear, combustion creates huge pressures which will be transferred at odd angles not straight down to the crank.

But, yes, it is most likely ok.

[Capt. Jon]

Is that a 3 ring piston? If so I've never seen a 3208 with a 3 ring piston. All I've ever seen had one compression and a oil ring. Aftermarket? Has someone been in the engine before?

[bayview]

bad injector spraying too much fuel????

[Ski in NC]

Three ring piston. Most 3208's have two ring pistons, not sure of the 210. Might be aftermarket?? Rod could very well be bent. Either have it checked at a machine shop, or replace it. Dimensionally checking rods is not super easy unless set up for it.

How is cylinder bore?

[Capt. Jon]

Originally Posted by Ski in NC

Three ring piston. Most 3208's have two ring pistons, not sure of the 210. Might be aftermarket?? Rod could very well be bent. Either have it checked at a machine shop, or replace it. Dimensionally checking rods is not super easy unless set up for it.

How is cylinder bore?

Just looked up the part numbers for NA pistons in my old parts book. Looks like all the NA and turbos use the same piston. They are all 2 ring pistons. Rebuilt my port 375TA the end of last year. Used all CAT parts with a rebuilt rod exchange. Cost for a rod exchanged was around $275 each. If you are planing on doing a replacement in frame then I would just do the rod exchange. If not then when you pull it down a good rebuilder should be able to do an exchange or re-work with warranty for less.

Bottom line IMO someone has been in that engine before. I would be curious if all the other cylinders have 3 ring pistons or just that one? Maybe that cylinder has had issues before?

[Ski in NC]

Cat does make three ring pistons and I think those are fitted in 435hp, but those use lower comp ratio than lower hp machines. Some folk when rebuilding a lower hp 3208 will chose to put in three rings from Cat. Less blowby.

This is where it is very good to be nice to a knowledgeable marine Cat parts guy. The good ones can sort out what to get.

[robs523]

yes, it's a 3 ring piston. Which apparently makes it harder to replace. I contacted a diesel shop in Tacoma and they're supposed to be looking into it and calling me back. The engine was rebuilt in '03-04 and the only I thing I could find about it says it was rebuilt back to stock.


I found the only "machine shop" we have here, and he's not sure what to do with a connecting rod to make sure it isn't bent or twisted, but said I could go ahead and drop it off next week and he'll check it out.


I was wondering about the injector too, but the only guy in town that can pop test them says he's too busy. It will probably be months before he could do it, so I might try to find someone in Seattle that I can send all of the injectors to for testing just to make sure.

I think the cylinder bore will be ok, but I'm going to try to have the mechanic that's been helping me some take a look for a 2nd, and educated, opinion.

What happens if I put a 2 ring piston on and the rest are 3 rings??

[Ski in NC]

You could put a two ring piston in and you won't see any effects. But try to find the Cat three ring. Try to avoid aftermarket parts.

[Edelweiss]

I'm not a CAT owner and this may be the wrong piston, BUT. . . . If you go to Amazon.com and search 3208 CAT Piston, this is one that comes up and it says it's OEM CAT. There are other sellers on there too which you can search as well.

Looks like it may be a 3 ring or may not even be the right piston, but worth a look anyway. $55 + $14 shipping

CAT PISTON 7e4729, 7e-4729 CTP Model#3208

https://www.amazon.com/gp/offer-list...0449333&sr=8-5

[Capt. Jon]

There maybe some weight difference between a 2 ring and 3 ring piston. May not really make much difference. However you will need to use a bore gauge or measure the existing piston to determine what size over it is.

Ski might correct me but my memory tells me that there are different rods for different pistons and wrist pins. I could however be way off base. As for the rod, like I said earlier it might be best to just do an exchange with CAT. It's not worth the cost difference to make sure it's ok.

Look on top of the front cover ( under the coolant tank) for the engine build tag. You at some point will need the serial number and the series number to facilitate getting most parts. I would sure try and find a good CAT parts guy who can help you locate the proper piston. May take him/her a few days but it would sure be worth the wait to find a match. Keep us posted on you outcome.

[FF]

but the only guy in town that can pop test them says he's too busy

Most ANY injector repair shop can test an injector.

A truck, farm place or industrial engine repair will be fine.

3208 is ancient , they have all done them.

Just take it there , it will be faster for the shop owner to test it than make out paperwork and have you wait.

[robs523]

Originally Posted by FF

but the only guy in town that can pop test them says he's too busy

Most ANY injector repair shop can test an injector.

A truck, farm place or industrial engine repair will be fine.

3208 is ancient , they have all done them.

Just take it there , it will be faster for the shop owner to test it than make out paperwork and have you wait.

Thanks, but we don't have those places here. We are a small, remote fishing town with very limited resources and somehow only one diesel shop in spite of the number of boats here. Kind of blows my mind, but it is what it is

I found the guy in Washington that did the rebuilds and called him this morning. As soon as I told him what it was, he knew what I was talking about. Sounds like it's an aftermarket part, which I'm not thrilled with but it will match the rest of them and should be available from what he said. He's going to get some info for me and call me back. He also said he and can test the injectors if I mail them down to him. Hopefully this will all still have a happy ending and I can get back on the water in the next couple of weeks

Thanks again everyone for the help!

[MYTraveler]

I would pull at least one other piston, from the other end, and make sure it is also 3-ring. If not, I would pull all and replace all with factory spec.

[Ski in NC]

Rob can you get some clear, in focus pics of some of the cylinders including pistons? Include the problem hole.

Some good pics of the top of the failed piston and the bottom of the head on that hole.

Pics will help figure out what happened.

I prefer Cat over aftermarket, but unless you want to replace all of them, probably best to go back to the same brand.

Kudos on finding the guy that built the motors. Be nice to him as he will be a wealth of info. Including whether bore is std or oversize. Offer to pay him for his time, it will be worth it.

[fijigone]

I am do not know much about 3208 but found this

The pistons shown are all three-ring pistons. Caterpillar produced a three-ring piston only for some turbo application but never for a naturally aspirated engine. Instead, two-ring pistons were used in these versions. The two-ring piston was only available as a conventional type ring groove while the three-ring pistons use a top Keystone ring (see illustration).

Use the three-ring piston as your choice of piston: it’s a superior replacement for the two ring and you’ll never use a two ring in place of a three ring. Naturally aspirated pistons come with three different compression ratios: 16.5:1, 17.5:1 and 18.2:1. Turbo pistons primarily have a compression ratio of 16.5:1, though there are some lower horsepower turbo engines for California applications, which have a 17.5:1 compression ratio.