HyFive578

iTrader: (3)

The 525 is a great motor and there are plenty of guys out there that have run them for 100's of hours. But there are weaknesses and if you are educated and aware of them, you can prevent the major issues from occurring. My reversion issues are a combination of the silent choice exhaust setup and the 525's cam characteristics. My center engine is just fine..

I'm not sure why you say the compression test passed with new plugs... the plugs should be out of the engine when a compression test is being done. If the buyer replaced the plugs just before the survey, that would be a red flag to me... As a new 525 owner, you MUST, MUST, MUST pressure test those headers... aside from that, read these threads; they will tell you what you need to know about the other weaknesses..

imartin

Thanks, I just clarified my post. Plugs pulled, comp test performed and passed, new plugs installed....

thirdchildhood

iTrader: (6)

Eddie, isn't that "dam" a complete circle and a little longer than in your sketch? This is my set-up and it has been trouble free. The top of the downspout is nowhere near the water line. Since my headers never get hot I did not remove the restricters. Wouldn't removing those increase the volume of water being dumped into the tail?

brian41

iTrader: (1)

Carl the dam Eddie is talking about is made into the diverter itself, yours are there and in good shape. I have serviced several 525 EFI's and Carl is right about his being in excellent condition with perfect bleed down #'s and zero sign of reversion or any type of abnormal wear to valve train. I discussed doing the Isky conversion from the start with Carl but as they say "its his boat" and I have to agree with him that for him it has worked and held up very well. By the way Carl we were shorted 1 keeper that might show up today.I always lay out and count parts before I start.....thank god this time or there would have been an engine teardown looking for the missing keeper.

HyFive578

iTrader: (3)

First, the "dam" Eddie is referring to is an anti-reversion cone. If you look down the tailpipe from inside the boat, you will see what looks like the end of a trumpet. It is a tapered cone that has a hole at the end. This is designed to prevent the water from creeping up the pipe into the collector.

Second, I don't think you are understanding the reversion problem correctly.. The issue has nothing to do with the water line. The exhaust water enters the tailpipe through the bung on the tailpipe end of the jumper hose. Inside the tail, there is an inner assembly (a "swedge") that is pressed up against the inner wall of the tailpipe and it carries that water down the tailpipe and it exits at the end of that swedge. Because of the Silent Choice, the tail has a hole where the water and exhaust go down the "Z" pipe to the "Y" pipe on the transom. Because of that hole, the swedge ends very close to the collector. Look at your picture.. the water is entering the exhaust stream only a few inches from the collector... this is where it gets sucked back in.. Without silent choice, that swedge can end much closer to the transom putting it far away from the collector.

Third, with respect to the restrictor. You need to leave the restrictor in the top bung connected to the jumper hose from the header. This is important to maintain good water pressure in the header. What you need to do is remove the bypass hose that is running from the end of the header to the underside of your tailpipe. Plug the tailpipe bung with a SS 3/8" NPT plug and plug the header with a SS 3/4" NPT plug. This is the Mercury Service Bulletin to maintain better pressure in the header. The bypass hose allows too much water to escape too fast. Maintaining strong water pressure is ABSOLUTELY essential with these headers. Keeping them cool is the most important thing you can do.

Young Performance

I have never seen a dam that is a full circle. They have all been just less than half a circle. They are also about 4" long or so. The dam ends before the point at which the water enters.

You will increase water volume by removing the restrictors, but you may drop the pressure too low. The PCM has a window programmed into it that dictates what the water pressure must be. If it's not in that window, it will send it into power reduction. There is really only one way to find out and that's by removing them. Another thing to consider before removing them. That additional water would be great to keep the headers cool, but it may also be too much for the tails and could potentially cause some reversion. If it's worked fine for this long, I think I would leave it be.
Eddie

Young Performance

I just noticed the bypass hose is still there on the rear of the header distribution tube. You want to remove that and plug the hole in the end of the tube and tail. That allows too much water to bypass the header, which can cause them to get hot and crack. Mercury put out a TSB on that a few years ago.

thirdchildhood

iTrader: (6)

Thanks for all the info. I feel my headers often and they never get too hot to hold my hands on them and that's why I've left it the way it is. I understand about the longer tails and water being introduced further back but I paid a lot of money to keep the silent choice. It was either buy those new diverters or have CMI make custom tails. Anyway it's been trouble free so I'm hesitant to change anything. I'll discuss removing the by-pass hoses with my mechanic, Brian.

Thanks for the update, Brian. No hurry on the boat. I'm enjoying the extra garage space! Will you put on a new fuel filter while it's there? I'll call you. Carl.