Pat McPherson

Call Summit, they will tell you what those pistons are.
Maybe you have dome pistons?
Oval port heads are not stock from GM on a Gen V 502.
If you send 7K maybe you got new after-market heads?
A stock rebuild on a 502 should cost no more than $3500.
Hell, you can buy a new one for under $6000.
Good Luck,

meis1

All factory marine 502's have rectangular port heads. Either your shop is wrong, someone changed them or it wasn't a 502 MPI.

You can pull a spark plug and look in the hole to see what the pistons are for sure, it honestly doesn't matter that much in this case.

FYI...the piston in the pic has been HOT.

Stock compression is 8.75:1.....put a supercharger on it and yes I happen to have a 250 setup available, both carb and efi.

sleeper_dave

Why do you say it's been hot?

The color on the underside of the piston is because there is some oil pooled there. But yea... the oil did hit 300+ degrees at some point. Burned the paint off the oil pan and it sucked into the oil pickup.

They're not new heads. they did a valve job on the ones i had.

Why is $7k so outrageous? When i was looking, i couldn't find a new one for that price. And that price includes removing and installing the engine, as well as reconditioning the prop and replacing the lines on the external steering. And a new oil pan, without paint on the inside. I don't have a hoist to pull the motor myself, so i'm stuck paying someone. Actual cost of the rebuild was 4200 on the reciept.

pullmytrigger

you need to figure out how fast you want to go......65 or 80......man!!!......you need a methodical approach.......one documented modification at a time or you'll never know what did what........have you borrowed a Bravo1 yet........??????

sleeper_dave

I want to go a gazillion miles an hour. But really, i'd be fine running 65.

I want a blower, but i don't have the money, and i don't have the money to go through drives or motors. And from searching the site, i see at least a few references to "stock JE700 pistons" in a 502, so i'm thinking they're stock.

When i'm done for the season, i'm pulling off the intake. I'll get a better one because that's pretty cheap. Probably a carb too.

Friend has a 23 pitch 3 blade he's going to loan me. I'll see what that does for me. I figure i'll see what that prop does to it now, then do intake and probably carb, then see where i'm at with the 23 pitch and decide what pitch prop i want to buy.

I haven't found a local place that will loan props.

pullmytrigger

it is normal for them to ask for a credit card deposit worth more than the price of the prop so they make sure you comeback......post your location......maybe one of the board members can lend you one or can tell you someplace that will

sleeper_dave

I'm in Harrison Twp., MI. Problem is i'm usually out of town during the week so i don't have time to call around and find a good place for props. I don't have a problem leaving a deposit, i would expect to. I would figure they would sell the prop then allow me to return it, possibly with a restocking fee. That seems like the best way, unless they have a large assortment of lightly used props that they can just loan out like "demo" cars.

I called JE about that piston. That's a special line of pistons that they make for Mercruiser, and only for mercruiser. He couldn't tell me exactly what size dome it has, because there are a few different ones, but if it says JE700 on the bottom it has to come from Mercruiser. Since this is a 502 MPI block, i'm betting it's a stock 502 MPI piston.

I'm still trying to verify what size carb it is. It's probably a 750, but i want to double check that.

I will pull the intake off when i'm done with it for the winter and try to verify what kind of heads it has. They're probably stock Mercruiser, but the shop that installed the motor said they're oval port, so i don't know. Maybe a previous owner put on performance heads with a larger chamber volume than stock to lower the compression ratio for a blower. If that's the case i can probably just have them shaved down a bit. Where would the casting numbers be on the head?

sleeper_dave

I tried a different prop today. I borrowed a Mirage plus, 23" pitch 3 blade. With 6 people on the boat it wouldn't get on plane. With 3 people on the boat it got about 4000 RPM and went 56 mph, 2 mph down from what i was running with the 19" prop.

I need to check the timing and see where it's at. I don't think i'm making as much power as i should be and so far i can't find anything that isn't as it should be. Except maybe the carb but i can't seem to find any way to check that.