Age Old Question?

[Dr. Dan]

:pimp: How old is the 502 vs 454? When did Merc and whoever come out with the 502 Block...and other than displacement...what are the primary differences?

Thanks....just trying to get a feel for my new power and where it all originated?

Doc :smash:

[Dr. Dan]

ttt

Doc

[gcarter]

Dan, I think the first time I saw one for a boat was at the 1988 Miami boat show, so I guess the development goes back to the mid eighties. My memory may be faulty, it goes with the age. :lookaroun

George

[marcdups]

George, according to my mercruiser parts catalogue they started in 1990, earliest ser #OC878221, but am not totally certain.

[gcarter]

And I'm probably operating from a faulty memory!!!

George

[RickR]

The 502 has Siamese cylinder walls for stability. Most 454s do not.

How is the project coming?

It might throw a rod tommorrow, but for now the 502 in Genuine Risk is runnung GREAT! :biggrin.: Still not dialed in and already exceeding my expectations!

[rayjay]

:pimp: ...and other than displacement...what are the primary differences? - Doc :smash:

My good Doctor, There are differences between all BBC's based on Gen series; i.e. IV, V, and VI; whether they are 454's or 502's. But the biggest overall difference between a 454 and a 502 is the siamesed bores which allow the (approx) 4.5" bore over the 454's 4.25". I have not seen or heard of any cooling problems directly due to this but I have been warned about head gasket problems between the cylinders under high compression or high boost. Later 502 blocks and all Bow Tie blocks are supposed to have a thicker casting in the deck area to alleviate this. I am talking about Chevy blocks and not aftermarket blocks. Some aftermarket blocks are cast thicker there and some aren't, check with the manufacturer. I have a Gen VI 502, which I believe you do also, which has the thicker casting and have been advised by friends to run an FE head if I want no problems or if I want to run an AL head to make sure I get one cast with a really thick deck surface. Also I am to make sure the head and block surfaces are dead flat and to use a real good head gasket. I am also running studs instead of bolts to hold down the head just for better sealing.

If you are using a stock Mercruiser engine you really shouldn't have any problems especially since you seem to be very good about maintaining your equipment. I don't think you will have anything to worry about until it is time for a re-build, And then your biggest problem will be the same thing I am going through now, what to do to the engine. Do I leave it a 502 or go up to a 540 or a 554... (etc.) (LOL) :rlol:

rayjay

[BigGrizzly]

Rajay, has done his home work and as usual he is correct. There are other changes like Roller lifters which cures an age old oiling problem that affected the old 454's. I wouldn't wory about the 502 block it is stronger and better then the 454. My engine is a genV and I am not worried, blower closed coopling system and 650+ Hp. I don't even have studs.

[rayjay]

... I don't even have studs.

Oh, I don't know. I remember your riding from almost 30 years ago (yikes!)!!

454's, especially Gen V's and VI's and late Gen IV's, usually do not require studs even when bored to within an "inch" of their life because of the heavier deck. Check the block weight. Newer BBC blocks and Bow Tie blocks are (usually) heavier with metal added in certain areas like the deck or cylinder walls for added strength. I added the "usually" as there were Bow Tie blocks for racing that were cast to be lighter than normal to save weight. They sound like a good idea but do not stand up for very long on the street or in the water as they were only meant to last to the end of a race.

The bigger bore of the 502, 4.466" v. 4.25", or approx +0.25", significantly reduced the distance between the edges of the bores by the same 0.25". The first time I saw a 502 block I thought someone had made a mistake and over bored it too much. Strong (thicker) decks on the block and the head, plus perfect clamping force with a good head gasket are important if you really want to run a built up 502 that will live for any length of time. A friend's wife has a 632 in her grocery getter Monte SS Aero (yes, you can get groceries through the trunk lid of an Aero, but that's about all!!). Merlin tall deck with 9.75:1 and AL heads. Has just over 50K on the motor with no problems (except with her license or the license of anyone who drives it) and still runs strong. If it's well thought out, put together right, and then well maintained it will stand up to (ab)use for a long time.

rayjay

[MOP]

Slightly off track, early 502's had a oil problem does anyone know what the cause was? I have heard it said if building a 502 make sure you get the block with no fuel pump provision with boss cast shut that these later blocks did not have the problem.

Phil

[rayjay]

Slightly off track, early 502's had a oil problem does anyone know what the cause was? I have heard it said if building a 502 make sure you get the block with no fuel pump provision with boss cast shut that these later blocks did not have the problem. - Phil

If I remember correctly it was not enough oil to one of the middle cam bearings. Different oil passage sizes and a change to roller lifters are supposed to have fixed this. GM's overall casting techniques seemed to improve significantly in the Gen IV period. Late Gen IV blocks are supposed to have the thicker decks and the correction for the oiling problem, but I am no expert in running stock engines. It always pays to throughly go through your oiling system, make sure you match any components that have oil passages such as lifters and bearings to the correct generation of the block, and investigate (but not necessarily do) any fixes such as oil restrictors that the racers are doing. Better oil pump and better pans go without saying.

rayjay