CAT 3208 new knock

Hi everyone, I bought my Californian 34 the first week of May. It's powered with twin Cat 3208NA engines w/ twin disc transmissions. Both had fuel leaks from the throttle shaft seal, which I was told could wait but should be fixed sooner than later. I even had a CAT mechanic that was in town come take a look and he said everything looked good but I should think about replacing those seals. I have since used the boat a lot with the family- trolling, cruising, sometimes pushing it to learn about the boat, learn how the trim tabs work, etc. Tuesday we were all packed and ready to take the kids for the family-only fishing and playing adventure we were all so excited about. I got the motors started up, they were running fine. Went to the fuel docks, filled up, and started up again to hit the "road." I noticed the stbd engine smoked when I started it, I thought it was white but now I'm second-guessing myself that maybe it had some blue in it. I thought it was odd but just decided to get going and pay more attention to it en route. 20 minutes later after we got out of the harbor I decided to give it some extra power to try to make up for some lost time and shortly after that I heard a very obvious, very loud, and very new knocking sound from the stbd motor. We shut it off and just went around the corner to anchor for the night before limping home the next morning on one motor. Today, I fixed the fuel leak but the knock still showed up after running for just a minute or two. When I started it, it smoked a lot out of the exhaust but then seemed to become more intermittent, maybe related to just a particular cylinder? I don’t know but I have very limited resources here right now becuase the fishing fleets, understandably, take the mechanics priority this time of year. Any thoughts on how to diagnose, where to start, etc are greatly appreciated. Thanks,

Rob

Could be a bunch of things. First thing is check blowby flow out the rocker cover vents that lead to the air cleaner. Or just take oil fill cap off with engine idling and see if air/vapor is "puffing" in sync with one cyl firing. compare to other engine.

Next is take rocker covers off and look for anything amiss, like bent pushrod, broken spring, missing valve, etc. Check valve lash 0.015" intake, 0.025" exh. Need a 1.5" socket to bar engine over. Note any valve that is more than a few thou different than spec. When cyl is at tdc, spin pushrods looking for a wobble.

Start with the above.

Ski in NC said:

Could be a bunch of things. First thing is check blowby flow out the rocker cover vents that lead to the air cleaner. Or just take oil fill cap off with engine idling and see if air/vapor is "puffing" in sync with one cyl firing. compare to other engine.

Next is take rocker covers off and look for anything amiss, like bent pushrod, broken spring, missing valve, etc. Check valve lash 0.015" intake, 0.025" exh. Need a 1.5" socket to bar engine over. Note any valve that is more than a few thou different than spec. When cyl is at tdc, spin pushrods looking for a wobble.

Start with the above.

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Is the lash measured hot or cold?

Cold. But engine temp does not affect it much. I've set them with warm engine and checked after it cooled, readings did not change perceptibly.

Thanks- it's the task of the afternoon.....

Thanks Ski, I removed one valve cover and didn't see anything obvious, but I'll measure all of the valves today and inspect everything closer. If there is puffing that's in sync with one cylinder, what does that mean?

does it knock a all idle speeds? Is it rpm dependent. In or out of gear make any difference?


If the injectors are accessible loosening each tube in turn while listening for the knock will identify a bad cylinder. No change is good because it means it is somewhere else.

Neutral or in gear and rpms don't seem to make a difference. I have the valve covers off now and when I'm done I'll start it again to make sure I'm remembering correctly. As soon as I hear it, I shut the motor down for fear of something else developing from whatever the knock is, but I'll let it run a little more and see how it goes

When you say "loosening each tube" are you talking about the nut where the fuel line enters the where the valves are on the outside of the motor?

3/4" nut right where fuel line fitting goes through side of cylinder head.

Can you make a recording of sound and post?

Hopefully that works. Having a hard time getting a video loaded

I've adjusted the valve lash, most of which didn't need any adjusting. I've loosened each tube and did not notice any change in sound. The only thing I have left is that I was told if I run the engine and use a temp gun on each injector at the exhaust manifold, if one of the injectors is bad, it might be a lower temperature. Before I go out and buy a temp gun (which I've wanted to do for a long time anyway but am sick of spending money right now!) I'm worried to run it too long and cause further harm. If it is an injector, what can happen if I keep it running for an extended period? Thank you all for the help

Sounds like it is in the valve train. Have you checked lash since it started to make the noise, or did you check it before? You can run the engine with the covers off, easier to zero in on the source that way. Also push down on all valves and check for one that is sticky. The springs are firm on these, so it takes a good push to open a valve. A sticky one will defy your efforts to push it open. But piston will smack it closed and you will get that sort of sound. Also check that rocker shaft bolts are snug and all adjusters snug too.

thanks Ski, I'll go back tonight and try again. The benefits of 20 hours of daylight I suppose. If it is a stuck valve, what's the fix for it?

Narrowed it down to the number 8 cylinder, but don't know where to go from here. I rechecked the lash on all valves, verified rocker shaft bolts were tight and everything looks fine. I had a guy that's done a lot of work on diesels (not cats though) take a look and he seems to think it's inside the cylinder, either the sleeve or piston. I have another guy that can come to look at it Thursday if he's finished with the job he's on now. I'm not sure I want to try to go any deeper into it until then, unless there's a very compelling reason to. I think the next step would be remove the head, right? Thanks for all the help

#8 valves not sticky?

Were any valves far off from spec?

If you don't already have it, attached is the manual for twin disk MG502:

http://files.twindisc.it/tdfiles/disc4/MG502 MG502-1 1015924_0382_CD.pdf

In a quick scan, I didn't see a prohibition against free wheeling, but i may have missed it. From their description I wouldn't be surprised though since it relies on high pressure lube oil for lubrication, cooling and clutch engagement. That's a question for the manufacture.

Sounds like you isolated the knock to one cylinder, which is what it sounds like. The knock could be a lot of things. Eliminate the easy ones first, bad injector, lifters, push rods, rockers. After that you're probably looking at pulling a head. Time for a mechanic familiar with 3208's.

I didn't think a 3208 had liners, as they refer to them as "throw away blocks." So probably not a good idea to run it anymore than necessary until you determine the problem.

I hope it's something simple. . . .

Thanks, I searched for that manual and found others but for some reason couldn't find that one, or when I did, it wouldn't open up. I read in a different twin disc manual that it shouldn't freewheel, but in another it sounded like it was ok except they used a different term for it that I can't remember now. That's when I decided I'll just make some phone calls Monday. I'll go through this manual thoroughly, thanks again.

Regarding the No. 8 cylinder, it looks to me like the knock is in sync with the exhaust valve but it's hard to tell with certainty. I tried to push down on it and it didn't seem any more difficult than the others, which were all very difficult. How much are am I supposed to be able to push it? None of the valves seemed far off spec, and I went through all of them again so the lash should all be good now if it wasn't before.

Is there a way to inspect the injector, lifters, push rods, and rockers without removing the head? I did a visual and didn't see anything obvious or different from the other cylinders, but I also don't really know what I'm looking for. The injectors have to be tested in a shop, right? Or can that diagnosis be made, or even strongly suspected, by removing it? I have it in my head that I have to remove the head to remove an injector, is that not right?

I don't know about the liners, the guy that looked at it admitted that he wasn't sure and he isn't very familiar with cats. The mechanic coming Thursday has done a lot of work on 3208s and hopefully will figure this out. Otherwise I buy a plane ticket and pay for a room for a cat-certified mechanic to come from Juneau at $150/hr and that's really not something I'd like to do. Once the fishing season is over, there will be other people available but not until after the summer. It's pretty defeating, I have to admit. We paid a lot, by our standards, for something turn-key-ish. Or so we thought. And my wife is growing increasingly exasperated and stressed out with boats at this point. I should have just stuck with the free, wooden skiff we got last year! Thanks for your help

not sure if that shows anything more than the other one, but here it is without the valve cover on

Do you have access to a bore scope? Or a small inspection camera? If you have a bore scope you can look through the injector hole. Harbor freight sells a cheap inspection camera that you might be able to get it past the exh valve when its fully open. You probably have to remove the exhaust manifold to get where you want.

Even if the hole is damaged. The block can be repaired. It won't be a cheap or easy repair but it can be done.

I will go ahead and embarrass myself here attempting to add to the list of possible diagnoses.
Piece of number 8 injector tip break off and sitting on top of cylinder? I would think more of a miss than I heard in the video unless nozzle itself intact.
Sounds like more of a rap than a slap but wrist pin broke?
Seems like at least the head on that side and the pan are going to come off to get much further?

Crack the injector line it on #8, if the knock stops get a rebuilt injector from your Cat dealer and swap it out. I've heard fuel knocks on several engines over the years but never a 3208. If it's not a fuel knock remove the oil filters and cut them open and remove the media and and check for any metal shavings. If there is metal you will most likely have to rebuild the bottom end.

A mechanics stethoscope or a long screw driver (touching the handle end to your ear) will help you isolate the noise. Just start slowly touching each item under the cover until you find it or not. It truly does to me also sound like a valve train issue.

Another trick is to rev engine to like 1500rpm, then hit stop button or turn key off. Listen to engine as it coasts down to a stop. If tick persists during coast down, then it is not injector or fueling related, as no fuel is being injected. Cheap and easy test.

Oooooo! That's a really good one, Ski! I'm gonna remember that one.

3208 are a parent metal block not replaceable sleeve type. With that said if the block is damaged a good engine machine shop can bore the block and press a sleeve in to repair damaged holes.
You might try pulling number 8 injector and swapping it with the one on the opposite end of the same head. If the noise moves the injector is a problem. If not then it is a cylinder problem

thanks for the replies. I was able to check the temps on the exhaust manifold to try to find the guilty injector, if that's the problem. Temps were all about the same though, so that didn't help much. I took it easy today and will get up early and try the screwdriver stethoscope as well as revving it up and shutting it down to see what happens. I found out I can get parts here on the same day if I order them early enough from the Juneau CAT shop using one of the small airline companies that services around SE AK. Thursday I was able to order some gaskets and had them in hand just a couple hours later. Unfortunately, most of them were the wrong gaskets, but at least things can get here quickly when they're in stock

Did you check blowby for puffing?

Ski in NC said:

Another trick is to rev engine to like 1500rpm, then hit stop button or turn key off. Listen to engine as it coasts down to a stop. If tick persists during coast down, then it is not injector or fueling related, as no fuel is being injected. Cheap and easy test.

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Awesome trick! Just goes to show you the great information obtained here? Thanks Ski!

Rob,

You may wish to join boat diesel.com, there are several post of cat 3208s with similar issues. I have found this forum helpful.

Ken