View Full Version : Need Info On 502 Chevy Crate Motor

01-20-2005, 09:43 PM
A friend just blew his jet boat motor and is looking at one of the new chevy 502's to replace it. He was concerned about a note that said (not recommended for marine use). Has anyone run one of these motors and if so which one? Theres several to choose from. :confused:

01-21-2005, 02:14 PM
get a MARINE 502 block the cratemotors GM sells arent designed for prolonged High RPM use... Redline, MarinePower, and others build Good Replacement Jet power get a hold of a Pump dealer and they can direct you to a good MARINIZED block to replace the old one with

BTW to keep reaming down to minimum i simply named the names off the top of my head.. there are many manufactures to choose from and those named are the ones I see on a daily basis in my area.

01-21-2005, 03:43 PM
Thanks for the info. I'll call him and let him know. He needs to get something that will last for that kind of cash.

triple dude
01-21-2005, 04:25 PM
Thanks for bringing up that question. I've seen that disclaimer also and always wondered what the difference was. The 454 in my jet is from Hardin Marine.

01-21-2005, 04:48 PM
A friend just blew his jet boat motor and is looking at one of the new chevy 502's to replace it. He was concerned about a note that said (not recommended for marine use). Has anyone run one of these motors and if so which one? Theres several to choose from. :confused:

1, the camshaft needs to be changed if he's going to run a wet exhaust,it's not the best grind either (zz 502)

2. Head gaskets suck......need to change those

3. Put a better oil pump in it, along with a bigger pan.

4 inconel exhaust valves.

triple dude
01-21-2005, 06:09 PM
Some cam concern is duration. If not careful, you'll suck water up thru the exhaust. Another suggestion--if he doesn't already have it, tap the oilpan for a fitting/hose to drain the oil. The old suck the oil out thru the dipstick tube is for the birds.

01-21-2005, 10:05 PM
I've got a pair of 502 crate motors that came from Merc. I really can't tell any difference between them and what GM sells over the counter EXCEPT: the Mercs have an almost plastic like coating on the outside of the block in place of paint, the Mercs have brass freeze plugs (all the other GM stuff may very well have that now also), the Mercs had intakes that had the bronze inserts in the water passages. The head gaskets seemed identical to the over the counter GM low horse 502 although I haven't compared part numbers. (both of my 502's were the early version Mk IV blocks, so some of this could have changed)

I'm suspicious that most of the differences are for protection from salt water. In the case of the lower horse 502 which I THINK GM rates at somewhere around 450, I think it's virtually identical to the marine version. Like the marine version it has rectangular port heads and a mild camshaft. If you're talking the higher horse GM 502's, the obviously the camshaft may come into play, and they have alum. heads.

01-21-2005, 10:37 PM
I had heard years ago when I had a jet boat bearing clearances were not the same on Jet Boat motors as on car motors. I would be interested to know what the real differance is between a marine engine as compared to a car crate engine. I think your right on the corrosion protection Raceman. I'm thinking probably a marine cam and upgraded parts too.

01-22-2005, 09:31 AM
Triple Dude Had a buddy with a Hardin Marine 454 back when I had my jetboat it was a good motor never had any problems. My Olds blew up twice in 2 years always had problems. They were rebuilt car motors by a guy that was supposed to now how to build jet boat motors. (Yea right)! Could have been the oil pan as Capt. Insane-o mentioned. I think he's going with a marine application for sure.

01-22-2005, 10:33 AM
The jet boat motors need more piston to wall clearance. Usually in the area of three thousands give or take depending on piston type. The block doesnt come up to temperature like it does in a car and the cylinder walls dont expand as much. That way you prevent cold seizure.

triple dude
01-23-2005, 02:23 PM
You're right on the temperature. If my temp guage starts moving, I know i"ve sucked up some weeds. On the earlier Olds versus Chevy comment. My Advantage boat is a 1991 which I've had since 1995. As far as I know, the motor has never been apart. I've replaced a counter rotating starter and fuel pump. The American Turbine pump was rebuilt just before I bought the boat. I think the receipt says $1500. All in all, I certainly can't complain.

01-25-2005, 12:24 PM
The clearences are different, most marine engines have roller rockers and roller cam, The bottom end is built for the stress of High load High RPM use intakes are different to allow for Raw water to pass through (brass or other coatings) all marine enginges are 4 bolt main berrings even small blocks. Marine engines also seem to run different compression ratios because of their cooler thermostats and higher operating loads.

Head gaskets are copper or copper clad not the standard aluminum felt that car blocks get (or at least should be)

better flowing heads for high RPM use

NO emmission controlls( thats changing though)