Powerhead Rebuild


A few tips on the 2.5l EFI rebuild...

So it begins...With the arrival of the 1994 used 2.5l Mercury powerhead, I began to disassemble the 2000 powerhead.  I cant stress enough how important it is to take dozens if photos of the block as you remove each item! Label each wire and hose as you disconnect them. The 94 powerhead is almost identical as the  00' with a few easy modifications.

I called around to many shops, the prices ranged from $6000+ for a new crate powerhead (minus all the bolt on's) To $3500+ to have the power head #2 cylinder re-sleeved and welded & crank polished. Not having any luck finding any used '00 powerheads, I located a decent used '94 in Florida and bought it for $380 shipping included! (upper, lower block & crank). The parts needed to complete this task are;  #2 piston, connecting rod, piston ring kit, #2 rod bearings, crank bearings, crank rings, #2 reed valve & engine gasket kit. The crank will be sent to Harrys Machine in Northborough to have the #2 journal polished.

At first I was told that the engine was believed to be fine, that the only repair required was in the jet drive... Then after close inspection, I determined that the engine was blown, not the jet drive. I figured the engine failed due to overheating caused by no water being circulated through the powerhead due to the boat being run while beached... However, upon disassembling the block, I found the reason the engine failed was due to a damaged oil pump gear on the crank **see photo** which in turn caused the engine to run on straight gasoline which caused the #2 cylinder to fail. (Makes you wonder if the convenience of having an oil pump is worth it...I think I'd rather premix the oil & gas and bypass the pump just to make sure this wont happen again!)

With a little patience, creativity & balls, I plan on saving thousands of $$ doing this rebuild myself. At the end of it all, I plan on having a $13,000 20' Challenger for only $4500 (and that includes the purchase of the boat!)


*** Please bare with me in regards to the proper names of each item, I have ordered the shop manual but have yet to receive it. Corrections will be made as the project continues.***

Each part is placed on a sturdy rack, with it's corresponding hardware in a zip-loc bag.

From the top looking down. '00 on the left / '94 on the right.

The first modifacation I noticed was to swap the solid brass plug from the damaged '00 block to replace the "tree" plug in the '94 block. **See arrows in photo**

The '94 powerhead on the left / '00 powerhead on the right

The next mod... you'll need to remove the fittings on the side of each cylinder, Vise-grips and a good twist will pull them right out. You'll then have to drill & tap the hole. I used a 1/4" tap and brass plug.

Here you'll see the '94 crank on the left & the '00 on the right. The gear that's completly stripped on the '00 is the oil pump drive gear. Why Mercury uses a composite meterial verses an alloy is beyond me! But this was the cause of the failure. You can also see just above the gear, is the #2 journal that needs to be polished.

'94 crank on left / '00 on right.

The next mod... The only real differance between the 200hp '94 & the 240hp '00 is the exhaust ports. The '94 is about 1/4" shorter then the '00. The mod is an easy one... All that's required is to shave the bottom of the '94 ports to match the '00 ports. Everything beyond the ports is the same. Only the aluminum block is thicker at the bottom. Some delicate dremel routing worked nicely here. Then give it a good polish and presto!

The next mod... You'll have to remove the diaphragm and spring from behind this cover since the '00 powerhead dosn't use it and the '94 does.

A view of the structurally sound '94 block.

The '00 block with holes punched through the bottom of cylinders #1 & #2. The cost to weld these holes, buy a new sleeve and have it pressed in is up in the thousands of dollars, compared to the structurally sound '94 block at $380!!!

Before using 3 - 5/16" bolts and a 3 leg puller to remove the fly-wheel, I marked the # 4 piston at 14* TDC.

Fly-wheel removed...

Make sure you take note where all the linkage is. The block has wires & linkage coming out of it everywhere! God bless digital cameras!

You'll need to be careful when trying to remove the crank seal, I used a rubber mallet and a putty knife to start it, then I gently pried it out working it around with the screwdriver. Its really in there...

The front bearing & seal removed...