GM crate engines

[SleekPanther]

Does anyone know why I shouldn't put the 502/502 GM crate engine in my jet boat as is? GM says "not intended for marine use" is it corrosion they're worried about or something else?
Thanks,
Paul
.

[rivercrazy]

The cam that comes stock in that motor has some exhaust valve timing overlap. This could cause some water reversion through the exhaust into the combustion chamber.

[gnarley]

Wouldn't that happen with only a few types of exhaust & not all?

[BBC502]

Hey SP,
I have a 502/502 in my boat. It's been in for 2 seasons and I haven't had any problems. I believe they say not for marine use due to the add ons-Non Marine carb, ignition and starter.The cam profile could be a little better to keep from having a reversion problem. I'm running water injected headers with a valve thus I haven't had that problem. I would suggest buying the long block version and adding your own ignition, carb. and starter. Also, if your concerned about the cam, change it. With a little head work, the right cam and carb, the 502 will make close to 575-600 hp and tons of torque....Bill

[BBC502]

Also you may have to change the oil pan like I did(may be to deep).

[powerplay230]

Panther,
I did almost this exact swap.Went from a 454 to the 450hs/502 it is the exact same longblock as the 415/502 mercruiser sells. I got one from Scoggins-Dickey few things I had to change: oil pan, intake manifold (if salt water cooled), starter, water pump, used flywheel off 454, had to switch to electric fuel pump, make sure head gaskets are composite or stainless and maybe a few other things but due to the 454 being a Mark IV. Don't know if the 502/502 has a different cam or not if so reversion might be a concern but can always buy the Stainless marine exhaust with long risers. Best Change I ever made, of course still not fast enough... :cool: eek!

[DUCKY]

They just say that to keep from getting sued. The one guy is right about the cam, but if you run a manual shut off valve for the header water,and kill it at idle or run logs or lightning style headers, it won't be a problem.

[Maverick]

[QUOTE]Originally posted by SleekPanther:
[QB]Does anyone know why I shouldn't put the 502/502 GM crate engine
Every tech article I have read sez - cam will have risk of water "reversion" - be careful valve or motor damage could occur.
MAV

[SleekPanther]

I've heard some say that clearances for pistons, rings, bearings should be set different for a marine engine, usually wider. I'm OK with the reversion issue, it does have a fair amount of overlap in the cam. Open engine so I'm not worried about marine specific starter, ign and alt. I think I'm going to do it! Anyone interested in a tired 2 bolt 454 with 049 heads and tunnell ram with NOx? Cheap.
Thanks to all those that responded,
Paul
.
PS BBC502, what oil pan did you end up with?

[gnarley]

I'm just a little curious as to what makes their cam specs so different than a marine cam??? There are subtle differences right? But how would that create reversion as to a "marine" cam not making any???

[powerplay230]

If you read mercruiser bulletins about these engines they reccomend not idling under 1300 rpm for any amount of time because reversion may occur. Someone with knowledge of GM could confirm this but I would have a hard time believing they build the same short block with different clearances for diff' uses. Also marine cams are usually ground on a different centerline to have less overlap?

[tsnave]

I have a '96 502 shortblock for sale with less than 25 hours on it. $3150.00 to closest Yellow Freight terminal. E-mail me at taevans@swbell.net if you are interested.

[Nubbs]

Does anyone know why I shouldn't put the 502/502 GM crate engine in my jet boat as is? Yes, because you should put one of these motors in your boat instead.
http://www.sallee-chevrolet.com/Sneak/Previews.html
I have a GEN V 502 in my boat and I really like it.
Good luck.

[Craig]

gnarley:
I'm just a little curious as to what makes their cam specs so different than a marine cam??? There are subtle differences right? But how would that create reversion as to a "marine" cam not making any???The marine cam will typically not have as much overlap. Overlap is the time both the exhaust and intake valves are both off of the valve seat some amount. Basically the exhaust is still letting out spent gas but the piston has started back down on the intake stroke with the intake valve open. So if you have some residual water hanging out in your exhaust header and it's close to the exhaust port, the vacuum generated by the downstroke of the piston can draw some of that water back into the cylinder through that still open exhaust valve. That's why a lot of the race headers dump the water further down the riser then a standard set up. While a small amount of water can cool the charge and surpress detonation, ala water injection, water is one of the few liquids that does not compress. Piss it off and try to compress too much of it and the loser will be your connecting rod eek!
Craig
[ November 28, 2002, 07:40 AM: Message edited by: Craig ]

[230Stingray]

I've run the 502/502 in my boat for three seasons now. It has over 200 hours of use on it and no sign of trouble. Running Gil Offshore manifolds and full MSD ignition. 16 degrees initial advance and 39 degrees total timing. Boat runs at 5200 rpm all day long. I like the idea of the 572 and may consider it when pricing is released next month. If its reasonable I might have a 502/502 for sale.

[Rayhill]

I looked at the crate motors last year and also was curious about "Not intended for marine use". I emailed them " http://www.paceparts.com/default.htm" (http://www.paceparts.com/default.htm) and asked if they offer any marine engines. They replied "No we do not offer any marine engines, but we sell engines to boaters everyday!" I ended up getting a sweet deal on a SBC from http://www.zigourasracing.com/

[BBC502]

SleekPanther,
Sorry took so long to get back to ya-gone over Thanksgiving week. I used a Milodon pan that was 7 3/4" deep.The stock pan was 1/2" to deep. This pan gave me 1/2" clearance. I bought it through Jegs. Used ones are hard to find for the Gen 5 and 6 engines..........Bill :)