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Motor rebuild, replace


anthonyyost

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This question should get some responses that will help in my decision making. The 1984 Searay I own has two Mercruiser 205's that are in original condition. Both motors run well and do not use any oil. The hourmeters on both engines were disconnected so I have no idea how many hours are on them, although the starboard motor that has the power steering probably has most of the trolling hours. To be proactive I would like to have both rebuilt or replaced with crate motors. Any thoughts on the pros and cons of each process as well as the cost comparison would be appreciated. Also, where to take to have the work done that would do a professional job first thing in the spring. Thank you in advance..

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I guess the answer depends on what kind of budget you want to work with. Honestly on that year boat you could easily spend more on a couple of motors than the boat is worth. Not trying to talk down your boat but you could be looking at 10 grand plus labor for 2 standard rotation engines. This is what I was looking at for my boat but I am a long way from needing a motor http://www.michiganmotorz.com/vortec-marine-engine-gold-package-19672010-replacement-p-351.html

This one would be cool as well but my boat is not worth much more than the motor costs.

http://www.michiganmotorz.com/complete-engine-package-fuel-injection-sterndrive-p-798.html

but if you ever see me go by at close to 60mph you will know I won the lottery and installed one.

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sad part is it did not say boat on the truck engine and they are different and those were outright new engines so no hoping bubba was awake when he assembled it LOL. Also keep in mind both of those are big upgrade to what you have as they come with electronic ignition and are 100% new parts. I have found in my years of wrenching that aside from what some shops think they are worth for the labor the biggest difference in price is how many old parts are they willing to reuse. I have seen lots of rebuilt engines go bad because they saved money and reused old parts. Or they skipped having the block done because it did not look all that bad. And some of that is no big deal in a truck or car but where we go it is a long cold swim back or a very expensive tow. Also you probably don't need a complete engine I would however recommend the Ignition upgrade as you will love it no more points and much more stable trolling spark.

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Those 4.3 GM marine engines will take a licking and keep on ticking. t sounds like they are in good condition. I'd have them checked out and if all is OK I'd add electronic distributors for about $550 plus labor. This upgrade will make a difference in dependability, performance and economy. A mechanics opinion before doing anything would be wise.:) That link to Michigan Motorz is a good place to buy the distributors.

http://www.michiganmotorz.com/delco-voyager-marine-electronic-distributor-p-121.html

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The Thunderbolts do not use breaker points. I may be wrong but I think this system uses a magnetic pick up device to make and break the current going to the spark plugs. It is one of the earlier types of electronic ignition. It's my understanding that the newer Delco systems are more dependable. I'm sure Jim has a better handle on the old Thunderbolts than I do.:)

The one thing you do have going for you is the twin screws. I'd make sure the engines are sound, and run them. The worst case scenario you limp in on one engine if one fails.

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The motors are very clean, no leaks or rust. They almost look new. They both run excellent, I just noticed this summer that the starboard engine oil pressure seemed to be running a little on the low side compare to the other engine. Neither engine uses any oil, so my first thought is just the hours on the starboard motor is the reason. I would be disappointed if I lost a motor during the season so I thought I would start exploring my options.

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I agree with Frank if they ain't broke don't fix em. Reasonable maintenance will get you around 3000 hours on a gas engine very good maintenance could get in the 5000 plus hours range or better. Do some serious inspections check cylinder balance and leak down test to see if you even have a issue. I have seen several motors that never had a problem till they were rebuilt because the owner thought they would be better. If they pass a thorough inspection run them till you have a problem you might get several more years out of them. The only issue with your Thunderbolt ignition is old age causes the coil windings and pickups to breakdown. Also keep in mind you might just do a long block which would be a great way to freshen up the boat but requires reusing a lot of your parts. Also you need to figure in new Hoses and some new wiring and probably a few cans of touch up paint.

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The motors are very clean, no leaks or rust. They almost look new. They both run excellent, I just noticed this summer that the starboard engine oil pressure seemed to be running a little on the low side compare to the other engine. Neither engine uses any oil, so my first thought is just the hours on the starboard motor is the reason. I would be disappointed if I lost a motor during the season so I thought I would start exploring my options.

Your low oil pressure.......was it at idle or cruising speed?

The first thing I would do is check the compression on all cylinders.

That will tell you if there is excess wear on major components.

If timing is stable and no issues with compression and the lower units are good, I would not replace.

I would really have to love the boat I have in order to replace power plants on that old of a craft.

Personally I would replace the whole rig.

Seems to me Dirty Dog did just that.

hih

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Like was said- those old style 4.3's seem to last forever with little effort on the owner's part. If they're still running strong, just have a mechanic check them out to be safe and keep running them till you have an issue.

If I were going to repower I'd be taking a serious look at a pair of Mercruiser reman's. Rebuilding is a good way to keep cost down, but you just can't beat the amount of precision machining and quality control that they have in that factory.

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just a quick thought what do you consider low oil psi to be because the low psi warning is 7 psi on a GM product. When mine is hot it will sit around 10 psi all day at idle but touch the throttle and you are back up to 30 or better every time. PSI is not that important good flow and volume is, the oil pump is driven off the cam which runs at 1/2 of crank speed what would help the most on boats is a oil cooler since there is no air flow around the oil pan to cool it like you have in a car or truck.

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I guess I can't remember exactly what the pressure gauges read, I think that when the needle on the gauge is straight up it is at 40# which is what the port motor is running at, the starboard is running about 10# less than that at idle but picks up as more power is applied. As far as oil pumps go, can they cause low pressure, or is it that they either work or don't?

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Yep oil pumps can go bad and cause low oil psi if your motors are holding that good of psi at idle I sure can't see a problem. Like I said GM considers 7 psi or more to acceptable. PSI is not as important as maintaining oil flow and coming up with a way to cool the oil.

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Something simple to check and I've seen it on 4.3 GM's is the distributor drive gear & pin. The cam gear doesn't seem to wear but the gear on the distributor does and the retaining pin hole gets hogged out also. I wouldn't think oil pressure would be affected but as it drives the shaft for the oil pump you never know. Just something to look at in the off season that may eliminate a problem on the water.

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