I don't have the piston out of this engine, yet. The heads and valves look normal and the damaged piston in this starboard motor has a similar chunk out of it. Here are pix of the damaged piston out of the port motors. I will have to check the internal flappers on the tips, far as I can tell everything looked fine. Notice the 2 chunks out of the edge. Never did find a defintie answer to this damage. The boat ran 83 mph with no signs of a problem and no noise on Lake Michigan when we test drove it. The only way we found this damage was by a compression and leak down test.

I was told by Merc. Racing that the 525 efi is the most susceptible engine they build for water reversion issues. The blowers motors do well because of the increased exhaust flow. Therefore, when any mild issue such as spark, fuel, injector, header leak, increased back pressure, etc., occurs, problems start to happen. I think in our area, the issues surface quickly due to the warmer water with added salt conditions. I was running the external and internal flappers when mine failed so I don't think this is a cause or resolution. Hope all of our failures down here are just isolated cases. ps: My 15 weeks of downtime research file is too thick to post here. We beat up all lot of possibilites that could have caused this. However, as consumers, I found it to be very difficult to get info. from the engine mfg. or exhaust folks. You can see where my #8 cylinder exh. valve struck the piston in pic. Good luck!

Why would they be any more susceptible to reversion issues than the 525SC, 575, 600's etc. I thought they were all based on the same 502 GM block? Is it the cam lope? Slow idle? Maybe that would be an excuse for blowers?

It was explained to me by an engineer. I'm sure folks on here can explain better than me. But, it has to do mainly with idle. Blower motors normally have less compression inside the cylinder than normally aspirated (efi, carb, etc.) engines so when the boost begins to kick in, you're not over compressing the cylinders where head gaskets would blow, etc. (the 525SC was 7.5:1 where the stock 454 was 9:1) The 496 HO doesn't quite have such an agressive cam profile, so doesn't create as much water reversion potential. You are making more than 1 hp per cubic inch in the 525 efi. One of my earlier boats had a 330 hp 454. I installed a cam, intake, ignition, etc. and it dynoed at 424 hp with all the performance increase parts. The 525 hp is derived from 502 cubic inches. It is a very radical internal set up even though it idles very well. The cam is probably as far as it can be taken and stay just on the edge of not creating water reversion with the CMI's in "new" condition from the factory. I think 75 to 130 hours is creating wear issues on something and that's all it takes to get the reversion or engine failure in warm salt water.

Problem is not limited to 525's as mine are 555's on carburetors with cams with lots of lift, duration and overlap. I think the silent choice just compounds the problem as the water is able to come in through the lower units whereas it has less opportunity to get through at the transom, but as has been attested it can get there through the transom as well. I'm going back with milder camshafts with less overlap and duration and eliminating the silent choice for my own piece of mind but haven't a clue other than the engine builders word that I won't have further problems. I don't know what the cam specs are on the 525's but I would suspicion similar high lift, high duration, and substantial overlap that helps the motors get the performance they enjoy, also help with reversion if water comes back through the headers when the exhaust valve is open, and it doesn't have to be running for an exhaust valve to be open.

I had a similar problem with my headers, a pinhole leak where the 4 pipes meet at the collector. (an easy fix) But I bought another fresh set just because... I run in salt all the time, so I flush with salt away and when I'm done, I unscrew the draincocks and drain the headers as well, so they stay dry when stored. A little over 40 hours on them and no problems since.

I had the same problem on a customers 2001 42 with 525's. The port engine outside pipe started leaking by the mounting flange. I talked with a rep at cmi and they told me this was a problem they had and was caused when the headers were welded and they had since changed the design. I ordered a completely new pipe and it was a little different near the flange. The cmi rep told me they were aware of the problem but would not warranty anything. I heard this guy just lost the starboard motor to the same problem.

I know 3 of the 4 boats down here are not CMI related. Don't know yet about Gerrit's.

Tommy, I spoke with Norm and he said the exhaust valve guides were leaking on his engines and that is why they failed? I don't think anything in his conversation implicated the exhaust system. As you know I also have 525/CMI units in my 42 and knock on wood so far so good, saw an easy 83 mph in Conroe yesterday with the props just back from Mike Hood propshop, and just ran great. But we have been in fresh water all summer. Fixing to bring the boat back to Seabrook for the winter when the water comes back.


So lets itemize the facts here as much as we can. Do we KNOW that the CMI's are a factor? What exactly has been proven? You had bad lifters, right? Whats funny is all these failures happen on both engines at about the same time.

I have one of the newer 525´s (built April 2006) with nearly 160 hours on it, driven hard and fast. I do not have silent choice, but internal flappers, and run clamp on CMI Sound Eliminator mufflers sometimes.

No problems so far from the power unit, although a reoccuring problem (at around 30 hours) with the water supply (s-hose between xr and transom) caused the guardian to chime in and stop the fun when running at full throttle a number of times. This caused the CMI´s to get heated up and turn brown. Once I had found the solution, which was simply to to put some silicon grease onto the s-hose and the belows, there was no further sign of any issues. The water pressure spikes and dips that are experienced when running a relatively small hull at WOT in big waves, were causing the hose to jump as it expanded and contracted under pressure!
The CMI´s polished up good, and the last 100+ hours have shown up no weaknesses at all.

What I´m saying is that I´m impressed with how robust both the motor and the headers have been up until now.

The raunchy sounding idle (created by the hot cam profile) does sound like it is just asking to suck water back into a cylinder, though.