General rebuild question

[skibum]

As a guy who has been involved with at least 10 car engine rebuilds over the course of my life, I sit here reading about $5K+ engine overhauls wondering why the heck they are so expensive.

Once the engine is stripped down to the short block and heads is there any reason why an automotive machine shop couldn't do the necessary work? I assume that the basics are the same, hot tank to clean, shot peen & magnafux the connecting rods, grind, polish, and balance the crankshaft, hone the cylinders, align bore and press in new cam bearings, etc.. Heads generally just need the springs checked, valves lapped (or replaced), new valve guides, and hot tank to clean.

All of the machine work mentioned above usually runs in the ballpark of $300-$400 if you take the heads & short block to them.

The replaceable items inside of the engine like rings, crank bearings, cam bearings, valve guides, gaskets, oil pump, etc. usually run another $200-$300. This assumes that they did not need to bore the cylinders larger due to wear, in which case you need new pistons, or if valves or springs need to be replaced you can add a couple more hundred.

My last 3 engine rebuilds cost about $800 - $1000 in machine work and parts. The 496 Magnum in my boat is basically a GM truck engine. If I ever need a rebuild, I figure that I could do it for about $1300-$1500 once I got it out of the boat.

Has anyone on here ever rebuilt their own boat engine using an automotive machine shop?

Thanks,
Michael

 

[keokie]

My dad and I did the 502 EFI in his boat. That motor had (and we used again) all forged components. The 496's don't use forged components which is why I can't help but feel my 502 is a much more appropriate marine motor. Anyway, you also have to remember the vlavetrain uses more durable components in any marine motor. Because of the demand, you really should balance it as well. Even marine gaskets and freeze plugs are different. And don't let a car guy near that camshaft. In short, the job should be done by guys who specialize in marine motors, if you ask me.

 

[fwebster]

The head gaskets are stainless steel and freeze plugs are brass. The cam is not an automotive grind, so you need to go to Mercruiser or a custom cam grinder who is experienced with marine engines for that. The biggest single difference is going to be preparation of t he engine block. Simple vatting won't get the corrosion and sediment out of the block. Then the valve train is usually corroded and pitted which means its not just checking springs, but replacing valves and sometimes valve guides and seats.

The precess is a little more involved than "freshening up" a street motor.

 

[PlayDate]

As a guy who has been involved with at least 10 car engine rebuilds over the course of my life, I sit here reading about $5K+ engine overhauls wondering why the heck they are so expensive.

Once the engine is stripped down to the short block and heads is there any reason why an automotive machine shop couldn't do the necessary work? I assume that the basics are the same, hot tank to clean, shot peen & magnafux the connecting rods, grind, polish, and balance the crankshaft, hone the cylinders, align bore and press in new cam bearings, etc.. Heads generally just need the springs checked, valves lapped (or replaced), new valve guides, and hot tank to clean.

All of the machine work mentioned above usually runs in the ballpark of $300-$400 if you take the heads & short block to them.

The replaceable items inside of the engine like rings, crank bearings, cam bearings, valve guides, gaskets, oil pump, etc. usually run another $200-$300. This assumes that they did not need to bore the cylinders larger due to wear, in which case you need new pistons, or if valves or springs need to be replaced you can add a couple more hundred.

My last 3 engine rebuilds cost about $800 - $1000 in machine work and parts. The 496 Magnum in my boat is basically a GM truck engine. If I ever need a rebuild, I figure that I could do it for about $1300-$1500 once I got it out of the boat.

Has anyone on here ever rebuilt their own boat engine using an automotive machine shop?

Thanks,
Michael

Michael,

There is no question that if you have the experience you can do it. The bigger question is the condition of the block and heads as a starting point.

1) A raw water cooled block that has been in salt water for it's life is a bad idea for both the block and the heads. The internal corrosion creates serious rebuild issues. You are far better off getting a new long-block assembly since you have the skills to move the remaining parts over.

2) A raw water cooled block that has been in fresh water for it's life is workable. Same goes for a fresh water cooled (antifreeze)engine. Marine parts are typically more worn than their automobile relatives. So expect work on the crank, rods and block. As Frank mentioned, marine parts are more expensive.

The final consideration is the value of your own time. Even though my engines are fresh water cooled, I would probably opt for new longblocks to shorten the amount of downtime.

-John

 

[skibum]

That's what I was thinking, John.

As to the cooling system, my 496 Mag uses the closed cooling system with antifreeze in it. I shouldn't have any corrosion issues above and beyond what a car engine would experience.

I assume that the assembly sequence is the same. If the tolerances and torque specs are published, I still remember how to work plastigauge :wink:.

I guess the big question in my mind is if I take the short block and heads to an automotive machine shop, will they be able to machine it just like a car engine, or will they look at me and :smt017?

Michael

 

[PlayDate]

That's what I was thinking, John.

As to the cooling system, my 496 Mag uses the closed cooling system with antifreeze in it. I shouldn't have any corrosion issues above and beyond what a car engine would experience.

I assume that the assembly sequence is the same. If the tolerances and torque specs are published, I still remember how to work plastigauge :wink:.

I guess the big question in my mind is if I take the short block and heads to an automotive machine shop, will they be able to machine it just like a car engine, or will they look at me and :smt017?

Michael

No problem at the machine shop with your engine. Just take the Mercruiser engine manual with you for the specs. The heads are regular big block heads. I would probably have them assemble the short block since they have all the equipment to check the clearances, gap the rings etc. unless you have a really clean place to do it.

Make sure you get a camshaft with the same specs.

-John