Rebuild or Crate Engine?

deafwish · **Posted:** Sun Mar 01, 2015 6:35 am

Starting to think about a winter project for my Horizon RS180's Volvo Penta 5.7GL...
It has the flat tappet, swirl port head (TBI heads) with a Holley 2300, 500cfm carb.
After plenty of homework, the only real upgrade is to go for Vortec Heads, matching intake manifold, 4BBL carb and ideally a cam upgrade.
While my current engine has only 330 hours and runs perfectly, is it better to fit the above parts to my current block, or look for a complete Vortec long block?
Would I need to re-ring my Pistons?
Could I re-use my existing mechanical fuel pump, circulating pump, oil sump and other random ancillaries?
Please note that Vortec crate engines are a good 30% more expensive in Australia than the USA, if that assists in your response?!

Cheers!

pickledboater · **Posted:** Sun Mar 01, 2015 12:55 pm

DW,
Would you be doing the work on the motor (other than machine work on the heads) if you were to do a rebuild? If so, that would be my option, simply because you will know exactly what all went into; and the condition of all parts of the motor. I would for sure do piston rings, main and rod bearings and gaskets while you were at it. With your low hours, a quick hone and once around with a ridge reamer, the cylinders will be like new. In my opinion, you'll end up with a better product, because it will be built by you, someone who cares, and not a production worker on a bad Monday.

deafwish · **Posted:** Sun Mar 01, 2015 9:31 pm

My mates & I would do some of the basic bolt-ons, but would likely have critical things done by a trusted, local engine builder.
Generally speaking, given this is a raw water cooled 1997 engine, might I be throwing money at an old & potentially corroded block?

LouC · **Posted:** Sun Mar 01, 2015 11:01 pm

How many years has it been used in the salt?
Most mechanics here do not rebuild raw water cooled engines because of the difficulty of getting them apart, and clogged cooling passages. However, I know people who have done valve jobs, replaced head gaskets and been able to get the boat back on the water. Its more risky though because you never know what shape the cooling passages will be in, or if it will even come apart.
That said if the boat is running well I'd just run that engine till it starts acting up or develops other problems and when I re-powered, then go with a new long block with for sure closed cooling at least the half (engine only) system.

meinmelb · **Posted:** Mon Mar 02, 2015 2:05 am

Mate at 330 hours that motor is still very young. The rule of thumb we have used is to multiply the hours by the average speed of a car (approx 75km/h) and you get about 25 000kms... not an exact science but puts it into perspective. If you have flushed after salt water these motors last a long time and as we all know the exhaust is the real trouble spot..

I have seen the insides of a pair of 5.0L mercruisers that have come out for a 40ft cruiser and while they were rusted, they were not as bad as expected after 20 years in salt water. These had about 900 hours on them and were running fine with power and compression all with in specs. They were replaced with twin turbo diesels.

If you are concerned about the motor, do a compression test / leak down test, but from the research I have done recently and from experience, you should not need to work the pistons / bottom end. Many ski schools will run boat motors to 2000+ hours with just oil changes and they run perfectly ( yep mainly fresh water)

I agree that changing to vortex heads, better cam profile, better intake manifolds and a refreshed carb should give you much bigger bang for you buck. There is little value in pulling the motor apart or even a long block swap over unless yours is shot. You are not going to see any more resale value, or better performance, or in my opinion any greater reliability / longevity.

My 2 cents...

rpengr · **Posted:** Mon Mar 02, 2015 11:49 am

I agree with meinmelb here. No need to pull apart the bottom end to do bearings or rings, unless you see wear or a step in your cylinder walls when you remove the heads. At 330 hours, they are likely to look very good.

I also agree that the block does not get anywhere near the rust that the manifolds get. My 1987 OMC was used in salt water and fresh water, until I sold it in 2012. That's 25 years. While I never had the heads off, looking under the thermostat housing the rust in the block was not that significant. It was only the Exhaust Manifolds and Thermostat housing that would get badly rusted because they don't remain full of water.

I would suggest your plan of Vortec Heads, Manifold, and CAM. Least important would be the carburetor, as a 5.7L theoretically draws 500cfm at 4937 rpm and you can't run an I/O much higher than that anyway.

ric · **Posted:** Mon Mar 02, 2015 2:01 pm

The Vortec block doesn't have the manual fuel pump hole, so if you're manual fuel pump now you'll have to switch to electric.

www.iFourWinns.com

Rebuild or Crate Engine?

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