Ticking from my GT40 @ GL

79, p/allen, Keith, Alan, and whoever else.....took my boat to the marina and they called and said my #2 cylinder is way down (35) on compression. Lifters are good, rocker arms are good. I trust these guys a lot, as they have done good work for me in the past, but they're saying the inside of the cylinder wall is pretty scored. I haven't had a chance to go look at it yet, but they said they talked to PCM, and there is a service bulletin out describing pretty much what is happening to mine....they call it "shrunken piston". The marina says they won't know what's going on exactly until they tear off the heads. They also said worst case will be $2500 to $3000 for a rebuild, but, again, they haven't got it all apart yet.....just ruled out the simple things. Does this sound right to you guys? Or do you think I'm getting jerked around? I'm probably going to bite the bullet and take it to MCC for a second opinion. About 75 miles away, but probably worth it.


For those of you not at GL, my 97 SNOB with the gt40 suddenly developed a tick at idle that I, and pretty much everyone who listened to it thought that it was a lifter.

Thanks...
Rob   

Sorry to hear of your misfortune to cap off a wonderful weekend. Why would the piston be ticking . I also would think it would smoke.Maybe you have a stuck or bent valve that would make aticking noise, lower youre compression and not smoke.I'm not an exspert but that is my thinking. Keep us posted good luck . If their is a service bulletin out , is there a recall?

Pat

Rob,
What a bummer...I think Id at least talk to another CC dealer to find out more info?
Good Luck and keep us posted...

If your valve is not seating properly, the compression will not be normal. For example, on my Solid Lifter Cam, if the lash is not properly set the compression is less than 80 or about 1/2 that of normal.

Ticking lifter and low compression in one cylinder gives the first impression of a bent pushrod or valve and not a rebuild, but I'm just guessing since I'm not in the boat. Remove the valve cover, loosen the rocker and pull the pushrod out...takes about 10 minutes.

That rebuild price seems high to me.

I would try disconnecting the spark plug wire to that cylinder and the noise should change pitch or go away all together. Try the other cylinders as well one at a time incase it's not the #2. If the noise does go away or change pitch/tone then it could be a piston issue. If you still hear the noise then it's most likely in the valve train somewhere and not a piston.

By removing the spark it should lessen the forces against the piston so that it does not bang or flop around inside of the cylinder and is just floating so to say.

Doesn't sound good either way keep your fingers crossed.

Tim D wrote: How do they know the walls are in bad shape with the heads on?

you remove a spark plug and run a scope through the hole to see. I would say he picked a pretty good mechanic. He seems to have the right tools for the job.

Running WOT you get the highest piston temperatures, highest piston speeds, and most thermal expansion. You also have a lot of water flow through the block since your waterpump is spinning fast as well. Piston scuffing is usually caused when something gets too hot. That can be caused by lack oil, running lean, insufficient water flow, etc.

A WOT run will bring all of these items to the surface faster than any other condition.

I scuffed 2 cylinders in my '79 during a WOT run a couple summers ago. The engine had 25hrs on it after a rebuild. Turns out the machine shop set the piston to bore clearance to automotive specs, which is too tight for a marine engine. There was no failure event, she just started ticking.

AWhite70 wrote: Running WOT you get the highest piston temperatures, highest piston speeds, and most thermal expansion. You also have a lot of water flow through the block since your waterpump is spinning fast as well. Piston scuffing is usually caused when something gets too hot. That can be caused by lack oil, running lean, insufficient water flow, etc. A WOT run will bring all of these items to the surface faster than any other condition. .

I agree but I hope they can diagnose the cause before they just go ahead and fix it. Rob's motor sounded fine before that and it was a very short bust of WOT cause of the chop. If it went bad that fast there is something else wrong that caused it. I guess it's possible that he picked up some weeds and ran it hot for a short while cause the lake did have a bunch of weeds in the shallows but he never mentioned anything like that.

OK guys....bad news. I went to the marina last night and tried the spark plug removal as 79 suggested. The noise got a lot softer with the plug removed. They showed me the extent of the scoring on the piston wall through the scope, and said they would put money on it being a piston. I called MCC today and they said it sounded like a piston to them, so I told the marina to go ahead and take off the head to see how bad it was. I went back today at lunch to see how bad it was, and I couldn't believe my eyes. Pretty deep scoring at the 5 o'clock and 7 o'clock positions, as well as a valve that looks pretty charred. I took pics of both, but the ones of the cylinder wall didn't turn out (cell phone pics).



As you can see.....not good. There were also metal shavings in the exhaust valve, probably from the piston. Not the news I was looking for after a great weekend at GL.

I did talk to MCC again later in the day, and it sounds like they are going to go to bat for me with PCM, since this is a known problem. They said not to hold my breath, but they'll see what they can do. Hopefully, they'll help out a little, otherwise I'm probably done until spring. Wish me luck

That sucks SO MUCH. I am right there with you on this one. On the positive side, you'll have a boat with a new (or basically new) engine. I would never imagine an engine could run so smoothly with that much damage.

AWhite70 wrote: When a cylinder scuffs frequently the piston skirt will collapse slightly creating more clearance with the bore. Then when the cylinder fires the piston can rock back and forth and slap against the bore creating the ticking sound.

This is EXACTLY how the marina explained it to me.....good call Awhite70.

At least I didn't do anything bad to cause this. I would feel worse if I had neglected it, but the marina and MCC both said it was "bad luck". The boat only has 277.3 hours on it. That's why I'm hoping PCM may step up to the plate...especially since they know of the problem.

Hey guys.....
PCM isn't really willing to help me out too much (no big surprise there). Tom from MCC (the guy who was at GL) has been terrific to work with on the phone, and he told me to get the boat to them and they'll try to give me the best deal possible on the labor and parts. He also said PCM said to "resleeve" that cylinder. That seems to me to be more of a band-aid than a fix. What if 10 hours down the road another piston lets go? What do you guys think?

Rob

I agree with your thought process, Rob. One cylinder down today, maybe two next week. I bought a rebuilt engine for mine with a warranty. I had four bad pistons. I only had 567 hours on my original '86, 351. Now, I'm in great shape, $5,500 installed with lots of replacement parts.

Good luck,

Ken

Thanks guys....I've think I've decided to bite the bullet and just go for the long block. I found one for $3550 plus $200 shipping. Marina wants $700 +\- in labor, so with tax, I'm at $4800 +\- out the door. Unfortunately, having just paid for our 250 person wedding, my wife and I don't have that money to plunk down right now. So, this season will be cut sadly short, and we'll hope to be back in full swing in the spring with no worries. Everyone says the gt40s are bulletproof, so maybe the next one will be.

This underlines a need for another smaller CC gathering so we can get Rob out skiing this summer.