I know some people have used Chevy crate engines as an economical alternative for marine applications, even though they are not designed for that purpose by Chevrolet. To get them to live, some clearances need to be opened up, but I can't remember what they are. As I recall, one may be the exhaust valve guides. Anyone have some experience here?

Michael

First and foremost, sadly, GM crate engines AIN'T WHAT THEY USED TO BE! Most now are assembled by subcontract companies to GM that are trying to be the cheapest price supplier to GM to get the contracts. Under these conditions some of these suppliers are starting to use some parts that well lets say are a bit suspect in terms of GM's original parts quality requirements. Couple this with not the best machining and assembly consistency and as many can now tell you these engines can be even hit or miss in the automotive performance aftermarket, let alone the marine performance market.
The other items that need to be checked I believe that need to be checked are all internal clearances, especially, rods, mains,ring end gaps, and valve guide clearances before just ploping one of these in a boat for marine performance use.
That being said, some of the crate engines such as the GM HP crate engines tend to be better but those must have brass freeze plug upgrades and camshaft upgrades to make them beginning base marine engines.
Its kind of a ticklesh situation in that none of the crate engines are warrantied for marine use other than the marine engine replacement engine programs so the warranties that buyers believe they may have will become non-existant when they try to make a real claim. Even with the marine crate engine replacement pieces we hear many times about new engines right out of the crate having problems and issues. THE BEST MARINE ENGINE WARRANTY= AN ENGINE THAT DOES NOT BREAK!
If one is careful to get the right base crate engine, get the clearances, fittings , camshafts, valves, etc. in line they can be a good source of a base engine. Just remember when all is done that should be done they are not always as CHEAP as they first appeared.

Best Regards,
Ray @ Raylar

I do not know much about their contractors or assembly process, but based on their specifications, the HO crate engines with the rect port heads are basically the same as the 454 mag and 502 mag. (cam is just slightly different) They will need a 30lb oil filter bypass valve instead of the 11lb and the alum dual plan intake that comes on the engine does not have brass inserts on the water passages. They come with a 6 quart oil pan instead of the 8 quart that comes on the mag motors. Other than that you just need to add the marine parts like alternator, raw water pump, etc. They also come with brass freeze plugs.

why a 30lb bypass instead of 11 just curious.

Also remove the relief valve in the center, or plug them both so oil is always going to the filter.

You will find several threads on this topic.

I have a brand new 502 mag marine cam (Gen 6) with springs, locks, and retainers.
Send me a PM if interested.

The 11lb bypass valve will make it too easy for oil to bypass the filter and cooler on cold starts are during warm up. I'm not so sure about the center relief valve. If someone can give more details about that one, it would be much appreciated.

Ray, don't some of these clearances need to be opened up for marine use, and, if so, which ones?

Michael

What's the point of buying a crate engine and then have to rear it down, do alot of machine work, change some of the hard parts and then re-assemble? For all that expence and trouble you can re-build what you have or start from scratch and build exactly what you want in the first place. With probably better quality parts.

ZZ502 comes with brass freeze plugs. Quick checklist:
1) Install 30lb. oil by-pass relief valve
2) Install marine oil pan to your boat needs (V or Cat)
3) Install single plane intake to your choice
4) At a minimum, lock-out the distributor and install a rev limiter
5) Install marine alternator
6) Install "quality" marine exhaust manifolds or headers
7) Install marine remote oil filter system
8) Install marine remote oil cooler
9) Install your merc marine sea pump/fuel pump combo (if that is what you have)
9) Install marine flame arrestor

Optional:
1) Install an RMbuilder cam
2) Install an MSD marine ignition box
3) Install an HP950 Holly 4150 based mechanical sec carb
4) Install 1.7 roller rockers
5) Install marine intake and exhaust valves
6) Install Hi volume oil pump
7) Install marine valve covers (needed with the rollers)

Hmmmm. Did I miss something?

Something else that I believe that has been overlooked are the head gaskets. Regular automotive engines have a standard steel gasket while a marine engine has a stainless head gasket, in a fresh water environment or cloosed cooling it might be ok, but in brackish and/or salt water a standard head gasket will not last long. Spark plugs also need to be a marine grade to prevent rusting up, and exhaust valves should be changed.