Indy

I either need to get rid of my PowerPlay or sink some $$ into the engines so I have faith running them. I have stock twin 502s in my PowerPlay (1996 serial number 0K021726) that have approximatley 450 hours on them. I've heard stories about head/valve failures that have caused major overhauls on the engines and manifold/exhaust issues causing same. I don't run them hard nor do I go far anymore because I know they're ready for some sort of rebuild.

I don't have unlimited funds so I need to make my $$ work as hard as it can for me and still have some comfort that the updating I have performed will give me some reliability. If it is too much $$ for reliability I have to sell. I don't want to half-a$$ the job and throw good money after bad, I'd rather get rid of the boat and buy something else in a few years. Am I better off looking for a pair of low hour 496s??

If you have any ideas about how much these updates will cost that would be great.

Also, I live in CT...is there anybody in the NY metro area that does this type of work?

hoozeyurdaddy

Oh thre will be a lot of people get in on this one, but here it goes, I would suggest a basic bottom end overhaul, a good one but not over the top, a set of edelbrock aluminum heads with ss intakes and inconel exaust valves, a good cam to fit your boating style, something that comes in early and tops out around 5200 rpm, or depending what you are running it up to, install new timing chain and gears and go boating.

MILD THUNDER

iTrader: (3)

I would freshen the bottom ends, new rings, bearings, and oil pumps. I assume they are carb 502's. I would install a crane 741 or 731 cam, have heads freshened with new guides, seals, etc. Go with some HP500 intakes and holley 800 carbs. Then maybe some good exhaust manifolds. I would think with this combo, you should make around 500-550HP or so on the dyno. I dont think the cost of going to aluminum heads will be worth the HP gains.

Contact JC performance engines, he is not too far, and does great work I hear.

KAAMA

iTrader: (1)

Your 502's should have all of the good forged parts...rods, cranks, pistons. I am assuming these 502's are the carbed version? You might be able to retain the Rochester carbs or may have to swap them out for some Holley 750-800cfm carbs. Depending on the cylinder bores, you might be able to get away with just a cylinder hone job, and keep the same pistons depending on how well they check out (whoever is doing the work will be able to tell you) and have the shop use a torque plate during the honing process and make sure the mains are checked for proper alignment/clearances.

Also, check the heads for cracks between the seats---the GM rectangle port heads are notorious for this and then have them mildly bowl/pocket ported with some short side radius work done to them. This will give you about 20-30hp or so of additional power (results will vary depending on the kind of exhaust system you're running). If you are running a stock Merc exhaust system then it might be a good idea to stay with the stock GM dual plane intake manifolds. This would also be a good time to install/upgrade to a hydraulic roller cam/lifters. Cam options can vary depending on the exhuast system you are/will be using---actually, the type of exhaust system you plan on using will or SHOULD determine what components should be used. Have a good valve job done, rings, bearings, and add some Crane Gold roller rocker arms and new ARP rod bolts---you may even need some new stainless steel valves.

Also, it is just as important to find the CORRECT precision machine shop that is familiar with machining with the correct tolerances/clearances to make an offshore marine performance engine to live and perform well---this is where most unsuspecting guys get themselves into trouble by choosing the wrong guy/shop to do the work. That is when you will be spending good money after the bad so, make sure you ask other customers and get some good references first. Even then it still can be very difficult to judge when a shop is being honest with you. Get a quote on paper and ask for a labor sheet for each machining operation, etc. Just make sure the shop you choose has an excellent reputation when it comes to marine offshore hi-perf engines.

I am sure others will chime in with some good input.

Westcoast

Do a comp. ck and a leak down-Replace the exhaust since it is 11 years old. If every thing looks good why overhaul...those engines could have alot of life left in them...If you are still worried take some oil samples. that will show a wear pattern.

MILD THUNDER

iTrader: (3)

Would a 1996 502 already have a HYD roller cam already?

Indy

Thanks for the responses so far...502 MPIs, not carbs.

Turbojack

I will second this. You could redue the motor & a part can still fail. Two years ago I had a valve that was not sealing when I did a leak down test. I was just going to redue the Heads but a friend said while you are at it have the motor gone thru. I did. When I went to pick up the motor the shop thanked me for bring in a perfect shortblock to be rebuild.

Griff

If they have been well maintained and not pushed hard more than about 20% of total time and for less than 10mins or so at a time, then leave them alone. They should be fine.

Either way, bottom end should still be fine for 700-800hrs. To be on the safe side, get a valve job and new springs, and maybe lifters as well.

Pat McPherson

Leaky cast iron exhaust is the #1 reason for failure.
Buy yourself some good aluminum manifolds, I like Stainless Marine, and swap them now. The new exhaust is also needed if you deside to up the HP during a rebuild.
Then in the off season you can do a top end rebuild or complete refresh...

My 1997 502MPI started loosing oil pressure at a little over 500hours.
I did the rings, bearings, oil pump on the bottom. Valve job with new springs, retainers, and locks. New lifters, timing chain with the same cam. Last thing was a new oil cooler.
I'm in my 3rd season and she's running great.
Knock on wood...