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Mercruiser Rebuild

Old 01-11-2018, 02:00 PM
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Default Mercruiser Rebuild

I should have a few more good seasons out of my 2003 350 Mag Mpi. I have a good bit of experience with auto engine work but have never done a complete rebuild. My idea was to go ahead and get a block and start a rebuild as time and money allow, then when my current engine is ready for a replacement I'll be ready.

I don't want to start a new debate but from a couple of days of internet research the general consensus is that a marine 5.7 block is no different than a truck spec 5.7 GM block. Could someone with some engine building experience suggest some ways to select a good block to use for the build? Thanks!
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Old 01-12-2018, 01:01 PM
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Is yours fwc? Then use that block when it is time. If it is fwc they do last a long time. How many hours?

If u just have a rebuilt block as spare it is still a decent amount of work to transfer everything else. Pumps carb etc

New short blocks are not crazy expensive. Look at Michigan motors etc

If u want to be ready with a straight drop in , buy a complete used mercruiser , , rebuild and have ready. Ebays good for that .
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Old 01-12-2018, 01:08 PM
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I would go with a re manned short or long block , way less headach and faster turnaround on the water.
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Old 01-12-2018, 01:25 PM
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I'll shoot straight with you.

You need this

http://www.mercuryracing.com/sterndr...ngines/1550-2/
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Old 01-12-2018, 07:00 PM
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Thanks for the suggestions guys! Sorry, but what does fwc stand for? Midcap, thats a beauty! I'm afraid my boat and that engine would be a little mis-matched!
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Old 01-12-2018, 07:24 PM
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Fresh water cooled. I would just look for a shortblock or longblock MPI engine. If your MPI is raw water cooled then go for a longblock and get new exhaust manifolds.
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Old 01-12-2018, 10:34 PM
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The blocks are pretty much exactly the same. The cam shaft is absolutely different though and can not be interchanged. They have wider lobe separations.
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Old 01-13-2018, 06:46 AM
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There are other differences, for instance the core plugs in the block are brass not steel (which would corrode if used with raw water cooling) and the head gaskets have to be marine head gaskets (same reason).
If your engine was used in freshwater, it might be fine to re-build, are you seeing any warning signs that make you think you need to re-power in the future? These engines can be good for as long as 3,000 hrs if in fresh water or if in salt with a closed cooling system (FWC). The things that cause them to fail early are not maintaining the cooling system, exhaust system and over-propping so the engine never turns up its specified max rpm. Sometimes all that is needed is a top end re-fresh with a valve job, check the valve guides and new valve seals. If you are an auto tech that is something you can do yourself without too much trouble. Of course this depends on condition, oil consumption, compression, etc.
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Old 01-13-2018, 07:16 AM
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It is raw water cooled but has only been used in fresh water. The engine is running great with no issues. I have 685 hours on it right now and we normally put about 100 hours per season. But if 3000 hours is possible then it looks like I am a little premature.
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Old 01-13-2018, 07:38 AM
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Originally Posted by Holicori View Post
The blocks are pretty much exactly the same. The cam shaft is absolutely different though and can not be interchanged. They have wider lobe separations.
WHAT?? Can't be interchanged?

The OP is kinda over his head already..don't make it worse.
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Old 01-13-2018, 08:05 AM
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Originally Posted by Redeemed View Post
It is raw water cooled but has only been used in fresh water. The engine is running great with no issues. I have 685 hours on it right now and we normally put about 100 hours per season. But if 3000 hours is possible then it looks like I am a little premature.
Yep I'd say you don't have much to worry about unless you have warning signs popping up. Engine temp, oil pressure, oil consumption, etc.
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Old 01-13-2018, 09:48 AM
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Originally Posted by Redeemed View Post
It is raw water cooled but has only been used in fresh water. The engine is running great with no issues. I have 685 hours on it right now and we normally put about 100 hours per season. But if 3000 hours is possible then it looks like I am a little premature.
This. "Don't fix it if it ain't broke". New impellers, oil change...good to go!
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Old 01-14-2018, 08:11 AM
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Originally Posted by billinstuart View Post
WHAT?? Can't be interchanged?

The OP is kinda over his head already..don't make it worse.
I mean...yea sure...you can insert an auto cam in there and it would run...yes. But its going to run like shit for marine purposes. Automotive cam setup is for ... well, automotive use. Which is generally lower rpm's below 2,000. Where you have the complete opposite when running a boat that usually runs at 5500 or so.
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Old 01-17-2018, 07:42 AM
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Originally Posted by Holicori View Post
I mean...yea sure...you can insert an auto cam in there and it would run...yes. But its going to run like shit for marine purposes. Automotive cam setup is for ... well, automotive use. Which is generally lower rpm's below 2,000. Where you have the complete opposite when running a boat that usually runs at 5500 or so.
You're digging the hole deeper. Not much difference in cams. No inboard runs 5500 rpms.
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Old 01-17-2018, 08:53 AM
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I have 2200 hrs on a 1990 fwc carbed 5.7 that has only seen the salt. I hope I can get a few more years out of it. Like LouC says 3,000 hrs is certainly possible. With the proper maintenance you chould, at the rate you use your boat, get another 20 years out of that engine. I sure hope I did the math right.
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Old 01-17-2018, 05:42 PM
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A FWC (closed cooled) GM Marine inboard for sure can go even more than 3,000 hrs as long as the exhaust system (manifolds and risers if its a half system, or risers if its a full system) are maintained, the heat exchanger is cleaned out when needed and the engine is propped correctly so it does not labor when pulling the engine up on plane. These are the important things that get overlooked. I know of a guy on iboats.com who had a nice reman engine about 10 years old. It had full closed cooling too, used in salt. But, the exhaust risers failed and filled the cyls with salt water. So he wound up having to rebuild it again, but since it was closed cooled from his first use, it was worth the rebuild. DO NOT neglect that exhaust sytem. 5-7 years in salt! I have followed this rule and never had an exhaust related problem in 15 years of salt water boating. I'm on my 3rd exhaust system, the first 2 were the original OMC bat wing one piece units, the latest one is a Volvo style center riser system (Barr aftermarket, with Volvo 90* elbow adapters to adapt the 4" riser hose to the 3.5" OMC Y pipe....)
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Old 01-19-2018, 07:53 AM
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Hello, it is surprisingly difficult to kill a chevy V8! That motor is based on the 350 small block, as old as the hills, as others said some parts are not interchangeable, head gaskets, freeze plugs, starters and alternators, the main enemy is corrosion and neglect plus poor laying up and winterising, the odd water pressure sensor or map or IAC but not the end of the world, serviced regularly and the cast iron exhausts changed at the intervals recommended and it will last a long long time. Hope this helps.
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Old 01-20-2018, 07:34 PM
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Originally Posted by billinstuart View Post
You're digging the hole deeper. Not much difference in cams. No inboard runs 5500 rpms.
You've clearly already buried yourself in your hole bud!

So let me break it down for you why marine cams and automotive cam's are different and not interchangeable. That way when I make it clear as day and night, everybody else will understand just how much of a dumbass you are.

Automotive cams: Have been designed to try to be as efficient as possible. The cam lobe separation angle is tighter together. This means that when the piston is on its exhaust stroke (pushing the exhaust gases out of the exhaust valve) that the intake valve actually starts to open when it reaches the end of the exhaust stroke. Also, the exhaust valve stays open for a short duration while the piston is moving down on its intake stroke. So for a moment, while the engine is on its "intake" stroke...while it is SUCKING air in...BOTH intake and exhaust valves are open momentarily.

Marine cams: Have a greater cam lobe separation than automotive cams. This is to prevent the exhaust valve from being open at the same time the piston is SUCKING air in (disclosure since I know you like to put my post under a microscope to find every little thing wrong.....Im not 100% sure if they completely prevent both valves being open at the same time, or just reduce the amount of time it is open simultaneously). The reason for this, is because immediately after the riser (where the bellows are) the water and exhaust gases are mixed. So it is possible for water to actually be SUCKED in through the exhaust valve while the piston is on its intake stroke. Once this happens, you end up hydro-locking your engine and its a catastrophic failure.

So no...no marine cams aren't interchangeable.

Yes, you can INSTALL an auto cam on there. It will even run. It will probably even run for 100hrs. But it only takes 1 time for water to get in the cylinder for you to blow it. So while you think just because you can "install" it, doesn't mean its ok to interchange them.

I mean hell, why dont we just put steel plugs in? And use auto distributors/starters/alternators, etc! It fits and it runs!! Hell lets install Ford pistons in a 350 with dodge crank! I'm sure as long it fits it's interchangeable!



And by the way....My truck cruises on the highway at 1900 rpms. Boats cruise around 3500-4500. So yea, the rpms are different there too dumbass.


Now, I've clearly laid it out for you. You haven't offered a damn bit of advice or contributed anything to this post or to the OP. You have only gone after me and my post; which apparently required more common sense than you have. So, from now on, how about actually providing something useful or helpful...or at least stating facts about your argument. Otherwise, Id ask that you just please, politely, shut the fuck up. Have a great day!
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Old 01-20-2018, 08:26 PM
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For what it's worth I replaced the engine in my '82 Wellcraft 248 Offshore a Mercruiser 260 hp with a reman engine purchased from a local rebuilder. Only thing I changed were
the freeze plugs. A set of brass plugs from NAPA cost me $25.00. I ran the boat over 300 hours before selling it. Performance was good. Maybe if I had spent 10 times more it might have been better. I will never know.
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Old 01-22-2018, 10:56 AM
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Originally Posted by Holicori View Post
You've clearly already buried yourself in your hole bud!

So let me break it down for you why marine cams and automotive cam's are different and not interchangeable. That way when I make it clear as day and night, everybody else will understand just how much of a dumbass you are.

Automotive cams: Have been designed to try to be as efficient as possible. The cam lobe separation angle is tighter together. This means that when the piston is on its exhaust stroke (pushing the exhaust gases out of the exhaust valve) that the intake valve actually starts to open when it reaches the end of the exhaust stroke. Also, the exhaust valve stays open for a short duration while the piston is moving down on its intake stroke. So for a moment, while the engine is on its "intake" stroke...while it is SUCKING air in...BOTH intake and exhaust valves are open momentarily.

Marine cams: Have a greater cam lobe separation than automotive cams. This is to prevent the exhaust valve from being open at the same time the piston is SUCKING air in (disclosure since I know you like to put my post under a microscope to find every little thing wrong.....Im not 100% sure if they completely prevent both valves being open at the same time, or just reduce the amount of time it is open simultaneously). The reason for this, is because immediately after the riser (where the bellows are) the water and exhaust gases are mixed. So it is possible for water to actually be SUCKED in through the exhaust valve while the piston is on its intake stroke. Once this happens, you end up hydro-locking your engine and its a catastrophic failure.

So no...no marine cams aren't interchangeable.

Yes, you can INSTALL an auto cam on there. It will even run. It will probably even run for 100hrs. But it only takes 1 time for water to get in the cylinder for you to blow it. So while you think just because you can "install" it, doesn't mean its ok to interchange them.

I mean hell, why dont we just put steel plugs in? And use auto distributors/starters/alternators, etc! It fits and it runs!! Hell lets install Ford pistons in a 350 with dodge crank! I'm sure as long it fits it's interchangeable!



And by the way....My truck cruises on the highway at 1900 rpms. Boats cruise around 3500-4500. So yea, the rpms are different there too dumbass.


Now, I've clearly laid it out for you. You haven't offered a damn bit of advice or contributed anything to this post or to the OP. You have only gone after me and my post; which apparently required more common sense than you have. So, from now on, how about actually providing something useful or helpful...or at least stating facts about your argument. Otherwise, Id ask that you just please, politely, shut the fuck up. Have a great day!
stock 929 Chevy cam..195/202 duration, 112 degree lobe center. Chevy stock marine, 200/212 duration, 110 degree lobe center. tighter lobe center, wider cam lobes=MORE overlap.
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