Engine Rebuild -- What's Actually Involved
 

Hey Everyone,

I've got a 2003 Mercruiser 6.2, which has apparently lost compression in #2 cylinder, and is in need of a rebuild.

Here's the story:

About a month ago, launched the boat for the first time this year -- my ramp to open lake is about 10 minutes of idling / no wake zone. Boat was idling a bit rough, but figured this was just because it hadn't been run in a while. Get to open lake, try to get on plane, I have no power, and now my engine alarm is going. Idle it back to the ramp with the alarm going, turns out it was overheated -- my water pump was toast. Replaced, no big deal.

Next time out, boat is still running a little rough, and I'm getting a "banging" sound over 4000 rpm -- told it's probably bad gas -- and to take it easy until I can get it down real low, and replace with premium. Couple weeks later, that's done, boat running a little better, but still the banging over 3/4 throttle.

Back to the marina we go, and apparently I have no compression in #2 cylinder, which means engine out rebuild.

The quotes I've generally gotten (without anyone having taken it apart yet) tend to be somewhere between $4000-$5000 Canadian, plus removal & re-installation. My question is -- am I going to get taken for a ride here? I've watched my fair share of DIY car shows, to know all of an engine's moving parts and what they do. Let's say, I've got a bad valve and piston in #2 cylinder as result of some metal on metal contact. When we say rebuild, is the expectation that we're replacing all 8 pistons, rings, 16 valves, springs, rockers, etc? or is it sufficient to simply replace whatever is broken?

Also, if I'm having the engine out and apart, is there much that can be done to these motors to bump up performance, without impacting reliability?

How many hours are on the motor? If your up in the 600-800 area it might be wise just to replace everything. If you are less than 400 probably can get away with only fixing what's broken. Those 6.2's will run a long time. Also depends how long you plan on keeping the boat.

Less than 200.

Probably intend to keep the boat another 3-5 years, but don't want it to be rendered worthless after that.

until the engine is out&apart you don,t really know how much damage you really have.the prices you have gotten are most likley for worst case .if someone quoted you a price for a minor repair and it turns out the engine needs major repair most people would say,BUT YOU SAID 2000 BUCKS,WHY IS IT NOW 5000 BUCKS.my guess is that after you ran it as long as you did while it was overheated a complete rebuild is going to be needed.

Plan for the worst case, hope for the best outcome. Until the engine is out and apart you just do not know.

I see if you could get a bore scope in the # 2 hole to see if there is anything obvious, then pull the valve cover and take a look, maybe the intake, it might be able to be fixed without pulling the engine.

Makes sense.

Perhaps it's as simple as clearly communicating with the engine builder that the $5000 estimate I'll have to agree to assume that pistons/valves/springs/rockers all need to be replaced, when in fact that may not (and hopefully isn't) the case.

The amount quoted could be spot on, a little high, or low...bottom line is you won't really know until it's torn down. With an overheat and a cylinder down there is a fair shot a good rebuild is in order. You likely had an injector lean out and take #2 with it.

Get a good quality Pressure Tester and do a "Leak Down Test". This will tell you why you have no compression, then evaluate/reevaluate the situation. Just MHO.

Yeah -- the marina is doing that this afternoon... why they didn't do that as soon as they found out the compression was gone -- I'm not sure.

Doing some reading, seems like I'm hoping for something in the top end of the motor.

While I'm certainly in no position to debate this assesment (and fear it may be accurate), it does seem a bit strange to me. Even after the overheat, the boat was running absolutely fine, except with more than 3/4 throttle.