Hello,
As my boating season is nearing to an end, North East, I have lost a cylinder in my Merc 500EFI. The engine had 460 hours without work, so I am not surprised, just sucks with the timing. It is my first week of ownership and I was planning to send it out this winter. Any recommendations on reputable shops selling rebuilt 500 EFI race motors ready to go out the door. I plan on sending mine back my for a core. The boat is a 2000, 29' Fever that was kept up very well with a brand new XR drive. This is not my first choice, but it would give me a month of Fountain pleasure. Thanks

Unless there is a reputable builder on here that has an excellent takeout, I would probably just call it a year and move on. Depends on the thickness of you're wallet and length of you're season.
Good luck with whatever you decide to do.
Edit,. REPUTABLE, IS A THE KEY WORD.

Have u determined what the cause of the failure is?

Could be broken valve spring.

The boat was started for a second with the throttle lever bumped up. Immediately turned the key off as it started to rev up. On the restart there was a slight knocking and a loss of power out of the hole and top end speed. The knocking went away, all temps were normal. Boated home and pulled the plugs. One cylinder plug tip lost its gap slightly and that cylinder has zero compression. Took off the valve cover and everything seems normal and spun the motor over all valves look to be working properly. Will pull the motor out on Sunday but does't seem to make sense to pull off the heads as the damage may be into the piston. At this point talking to a few shops that can do an in house rebuild.I trust the previous owner that the current block was not beat. My fault not paying attention on the restart. So part of me feels better sticking with my block and parts rebuilt than buying a drop in unit ready to go. We'll see, like I said it is a timing thing. Did I mention it was my first full day with the boat. Oh well. I don't have the angst of cutting out on work to use the boat so I guess that 's the one positive. It will have about 5 coats of wax by the time it get wet again.

Call everyone and see how their schedule looks, could rebuild one quickly if you just want to go back like it was.

Eddie Young
Ron Sporl
Precision Marine
Boyd's
Potter
Retter
Etc...

Man i remember hanging out in north conway .its 105 here right now ,dont even want to go outside..
oso member BHD is from north of boston and involved in offshore racing i would see if he can plug you in with someone in that area . If it just has a bent valve ect could be a quick fix . Would do a quick leakdown on all 8 and go from there

Thanks for dropping names everyone, I really appreciate it. The internet is full of them, but recommendations always work out better. Been making some phone calls, I have realized that if it is sitting in a crate somewhere ready to go, it probably sounds too good to be true. I will pull the motor out tomorrow and hopefully have it packaged and heading out somewhere this week. Yes North Conway has been a hot one this week, unfortunately it never last long. The Fall is upon us soon enough. Hence the rush for an engine, but you can't rush quality. The motor is due, so I rather get it done right so next summer it is trouble free. Just hard to go back to a pontoon boat after listening to a Big V8 skimming across the lake. Has anyone heard anything about Butler Macmaster Performance in Maine, it would be a quick drive? Seems like they do Marine and Auto. It would save some time and shipping costs but.....

Give Carl @ CNC Blocks a call he is in Maine.

Go to a reputable well known RESEARCHED marine engine shop. We dont want you having to make a post that says " HELP!! I had my motor rebuilt Jimbo's machine speed and pizza and its blown up 3 times in the last 3 weeks"