5.7 Mag MPI Rebuild or New Long Block?
07-01-2025 | 08:19 PM
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5.7 Mag MPI Rebuild or New Long Block?
Hi, I am new. Enjoyed reading here a lot. I have owned a few boats before. Still had a very nice Wellcraft Scarab 28 Excel up until just a few years ago I sold
Want to ask a question for my Brother who owns a SR Cruiser Boat with a 2008 Merc 5.7 Mag Vortec MPI. The engine took on water from the Risers on the right side facing from front. He was able to get the water out, but the shop still tested Low Compression on all cylinders now after. Trying to help him. We are looking at 2 fix options.
One is to remove the engine and give it to a race shop engine guy who is 40 plus years experience to see if he can tear it down and Rebuild that motor. Would likely do a overbore pistons and small stroker Rod package if so. I do understand it's a Marine engine and would only use Marine engine parts.
The other choice is a brand new GM 5.7 Vortec Marine Long Block. In my mind I feel like the Rebuild would be the way I would go. I would try to rebuild with more durable upgraded internal parts. Including the Rods and overbore pistons.
Anyone had this water in engine situation who rebuilt the existing engine? Also what is a good place to source better upgraded high quality parts like a Piston kits and other that are engine Marine proper parts? Won't really know the full extent of the water damage until torn down. But thinking that piston, rings and internals would def need to be replaced. Any experienced comments would be appreciated. By the way I hung around a Car and Bike engine building shop a while back that built motors from the crank up. Gave me enough knowledge to be stupid dangerous. lol!
Want to ask a question for my Brother who owns a SR Cruiser Boat with a 2008 Merc 5.7 Mag Vortec MPI. The engine took on water from the Risers on the right side facing from front. He was able to get the water out, but the shop still tested Low Compression on all cylinders now after. Trying to help him. We are looking at 2 fix options.
One is to remove the engine and give it to a race shop engine guy who is 40 plus years experience to see if he can tear it down and Rebuild that motor. Would likely do a overbore pistons and small stroker Rod package if so. I do understand it's a Marine engine and would only use Marine engine parts.
The other choice is a brand new GM 5.7 Vortec Marine Long Block. In my mind I feel like the Rebuild would be the way I would go. I would try to rebuild with more durable upgraded internal parts. Including the Rods and overbore pistons.
Anyone had this water in engine situation who rebuilt the existing engine? Also what is a good place to source better upgraded high quality parts like a Piston kits and other that are engine Marine proper parts? Won't really know the full extent of the water damage until torn down. But thinking that piston, rings and internals would def need to be replaced. Any experienced comments would be appreciated. By the way I hung around a Car and Bike engine building shop a while back that built motors from the crank up. Gave me enough knowledge to be stupid dangerous. lol!
