When is it time to rebuild a motor I have twin Mercruiser 470

[max2fastboat]

Hi all I have been on here with a bunch of stuff this year, electrical and starts. Well both engines are running but this winter looks to be a
rewire winter with new gauges. But with all that I have been thought this year maybe I should just bite it and rebuild the motors.
The starboard engine has a rap on start up but once she warms the rap stop (maybe the oil pump). the port engine runs fine....but
she has a small leak from the old alternator. And it would be easyer with the motors out to strip and rewire the engine compartment.

So heres the question, When do you rebuild? or do I do something to keep them running for another year and find different type of engins to rebuild and install. What would be a good engine to change out with?

I know lots of people hate the Merc 470 but should I just rebuild them????????

Thank for any help

 

[stonyloam]

Re: When is it time to rebuild a motor I have twin Mercruiser 470

I would do a compression check on both engines and see what that looks like. That should give you an idea of the condition of the rings. If the compression is OK you may not need a full rebuild. If you are going to pull the engines, you might consider reconditioning the heads, valve job, hardened seats new guides and seals. You can pull the pans and Plastigauge the bearings to see if all is still in spec. Best bet is stick with the 470s IMHO.

 

[Bamaman1]

Re: When is it time to rebuild a motor I have twin Mercruiser 470

+1 on above. If compression is good, try not going into these engines. They're not normal engines, with different water pumps, water cooled voltage regulator and a strange alternator. Bearings and heads are from a big block Ford 460 engine. The wiring harness is pretty simple, and relatively easy to remove with the engine in the boat.

I still have a 470 motor in parts after never getting around to assembling 10 years ago--including a complete gasket set.

 

[elkhunter338]

Re: When is it time to rebuild a motor I have twin Mercruiser 470

Are these motors fresh water cooled?
If not have they been used in salt water. The blocks might not be in good enough shape to rebuild.
Hows the oil pressure, that will give you some idea of the condition along with a compression test.
Use a manual oil pressure gauge with the engines up to temp and warm, see if they meet min idle oil pressure.
The other suggestions give are good.

 

[dollarten]

Re: When is it time to rebuild a motor I have twin Mercruiser 470

Are these motors fresh water cooled?
If not have they been used in salt water. The blocks might not be in good enough shape to rebuild.
Hows the oil pressure, that will give you some idea of the condition along with a compression test.
Use a manual oil pressure gauge with the engines up to temp and warm, see if they meet min idle oil pressure.
The other suggestions give are good.

that rap , you here from one of the engines is a piston that is fitted a bit to loose from the factory and a little wear brought it beyond spec until it warms up . In this case it is best to leave mean slepping dogs rest . This is a complaint with many moderen day engines using low tension pistion rings that will not hold a piston square in it's bore

 

[alexr254]

Re: When is it time to rebuild a motor I have twin Mercruiser 470

I decided to rebuild both 470 engines in the boat i purchased.
I just made sure before i got the boat the engines were repairable. The blocks were in great shape, and i didnt notice any corosion around the water impellor.

The reason i did this is because no matter if its running now, its used and it will have problems later, and usually at the worst time possible. When you buy a used boat the sellers will usually make it look as nice as possible to sell it. But its still old and used even if its clean. When we opened up the engines the bearings on the crankshaft were in bad shape, the seals on the camshaft were in bad shape... The only way to know your in really good shape is to do a rebuild. I am glad we did because even though they would run in the shape they were in, we could have broken down at anytime, at a bad time.