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50 HP Mercury Compression Question

D

domercam

New member
I have a 2000 50 Hp 2 Stroke Mercruy that I bought new. I had random starting problems with the motor recently and I had it towed into the marina 2-3 times. It would run fine and then just randomly not start. There was water in the gas from a gas cap not sealing properly at one point last year. We drained the tank and reinstalled. The marina is saying there is unbalanced compression in the cylinders 110-90-80 now and they are 80% sure that the problem is bad compression. They are saying in 2000 Mercury used a foam core head and it cannot be repaired, only replaced? Does this make sense? Are there any other procedures to check or other options to be 100% sure before I make a decision? Spending $3500 on buying a head and repairing a motor on a pontoon that is only worth $4-$5000 seems crazy.
 
If that's what it has left for compression, you'll need a new power head, or get that one bored out and rebuilt (too expensive to consider).

Sorry.

Jeff

PS: Like most Mercs, the cylinder heads don't come off.
 
Those models are also know about the sleeves turning in them, thatwhy I pin them when I rebuild one of these series. The run fine and then just randomly not start issue is not compression related.
 
..."pull the head and inspect the cylinder walls and head/gasket. "

To reiterate. there is NO head gasket.

Jeff
 
Right! I run the old Merc triples on my little boat and would really love it if the head came off (so I could port the beegeebers out of it and then mill the head to get the compression back). Some (like me) have been so "desparate" to be able to do this that they've converted a Merc V-6 into a three by using only one bank! They pull three rods and pistons out, seal the cylinders with epoxied-in PVC pipe, and run on three! Motor supposedly does not vibrate, even though it's not rebalanced.

Jeff
 
Some (like me) have been so "desparate" to be able to do this that they've converted a Merc V-6 into a three by using only one bank! They pull three rods and pistons out, seal the cylinders with epoxied-in PVC pipe, and run on three! Motor supposedly does not vibrate, even though it's not rebalanced.
Click to expand...
Yep...That was the SST-70 class if I remember right and the blocks were highly modified with porting and block offs, and you could run the factory 2 barrel carb on each cylinder in certain class races!!! I aint worked on one of those in years.....
 
You actually worked on one! Wow. I'm amazed that they didn't vibrate like crazy with half the rods and pistons removed.

Jeff

PS: One guy claims that, after blowing a cylinder, he pulled the bad piston out between heats and finished the race on 5 cylinders!
 
I have seen the Merc Race truck at the St Louis races pop the front intake remove all 6 pistons and rods, raise the exhaust port and blow out shavings with air,reassemble ,drill ECU so have access to adjust pots and put back in water in about 10mins between heats!!!! This was on Bill and Tim Seebold engines along with Chris Bush when he ran Mod-VP.
 
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