502MAG EFI motor freshen up
 

I have my 2000 502MAG EFI motor out of my Baja 272 ans sitting on the shop floor. Motor has weak compression (120# in 6 cylinders and 90# in 2) with 450 pampered hours on it. The question is this should I do just the heads and slap it back together or should I roll the motor over and get into the bottom end...rod and main bearing and rings also?
I would like to keep a little more than stock HP but I really don't want to get in changing the computer and messing with the fuel map. Any thoughts?

502mag efi
 

i too am doing a freshen-up on my 94 502.i have 465hrs on the engine and was told that around 400hrs the heads should be remover and serviced....springs,retainers,seats,etc.my engine guy told me that the bottom is probley ok,and that it is not much you can do w/the motor being efi,as you know this.my only concern is my oil is realy black.have changed oil serval times and is still jet black.my be rings worn and blow by.not sure yet.good luck w/your motor.

I had 640 hors on my 99 502 with a side mounted whipple and finally blew a head gasket. Upon tearing apart the motor everything looked great. My engine guy (LJ Engines) who built over 80% of Gary Teagues motor in the last 10 years did in awesome job rebuilding mine for half the price.

If you change from the oem cam specs or increase compression you will have to reprogram your ECM (big pain in the butt). I would rebuild the entire motor and have a good valve job with some porting and polishing to increase some flow on the heads.

I would have figured you would have gotten more hours than that.. I know a few guys that put 750 + hrs on their 502 before selling their boats with no issues... I have 215 pampered hrs on my 99 502, and hope to get alot more. I dont have an answer to your question, but you will get answers on here, there is a world of knowledge on OSO.....

Do a leak down and see where the loss is to determine if you need rings and a full rebuild or pull the heads and check the condition of the bores. Most likely you only need a top end rebuild.

You can't add HP without recalibrating the ECM.

At 500hours mine had low oil pressure along with low compression.
I would recommend rings, bearings, oil pump, and new timing chain for the bottom as a minimum. Full rebuild on top with new exhaust and she'll be ready to rock for another 400-500...
If you do decide to swap the cam, consult who ever is going to recal the computer first.

If it's out do it all.

Also replace the coupler since its out.

I agree, if its already out might as well do the entire thing.

If you need to bore it I have some used JE .030 over pistons cheap!

what bore are the pistons,30 over?how much $$?

Stock bore is ø4.470inch.
Don't go .060 over unless you have to.

High end main bearings - $100
High end rod bearings - $100
cam bearings - $40
Refresh at machine shop $150
Set of high end rings - $100
Timing chain and gear set - $75

Total $565 for a brand new bottom end on your engine using the best parts available.

Peice of mind that you don't have to touch it for another 450 hours. - Priceless

By the way. THat is using the best of everything. You can probably put it back stock for less than half that and still be ok.

Vavle job and springs should only be another $300 a side - max.

Moral of the story, if it is out of the boat, you might as well tear it down.

I assumed the 502 was a 4.5 bore. these are .030 over stock size. I have to make sure they don't hurt them pressing the pins out. Probably take between $150-175 for them.

I totally agree with the other responses, while it's out, do it all. I think Jeff's number are a little low for the refresh. Parts numbers are correct. The biggest problem I have seen is that the vast majority of the 502's won't go back standard bore with 400 hrs. They run very little piston to wall clearance. By the time you hone the cylinders and get them round again, you have opened the bore to much. GM recommends no more than .0045 clearance. If you run to much clearance, you will break a piston skirt because of their high silicone content. DO NOT put new rings in a cylinder that is not honed to perfectly round. They won't seal worth a damn. I would not put it back without doing the bottom end while it is out, that just seems like a waste. Hope this helps and good luck, Eddie.

Bore to 4.5, stroke it to 4.25 and make a nice 540. If you find you need a new crank for some reason, probably not, go 540.

You can get a complete rotating assemblie for the bottom end using all high end stuff (good to 1000hp) for under $2000 delivered.

My prices earlier didn;t include labor, but I was just trying to make a point.

Good luck with your project.

I was on that bubble last week until I figured in the $$$ for a bigger cam, pushrods, the lifters, etc.. Easily another $2000

how come you are using pressed in pins?why not floating.had bad luck w/spral-locks before?

Stock GM rods are a press fit. Has nothing to do with the piston. Also doesn't make sense to put bushings in stock rods for what you can buy a set of aftermarket h-beam rods with bushed ends and cap screws.
Eddie

We have a whole kit for that engine upgrade with the ecu upgrade. crockettmarineengines.com. It will add 100 HP.

Old thread but I have a question.
So does everybody replace the oil pump with a full refresh? Or if the gears look good and everything is clean just reuse?