Stingray69

The oil bypass valves for automotive motor are about 10lbs; the ones in Merc motors are the 30lb ones, so that the extra restriction of cooler and lines do not cause valves to open in and of themselves. If you don't switch to th e30lb ones, the oil will bypass the oil cooler, causing heating and filtering issues.

the duke

One of the first things to do on a 502 build is take ALL the stock oil lines and throw them in the trash. Then replace with -12 an lines and fitting. The stock system is useless. I gainned 10 lbs of pressure with just that switch.

Pismo10

"the rest" ??? There are about 1,000,000 merc ignition systems out there, you forgot about those. There are many threads on OSO regarding the reliability of marine MSD systems, many not very flattering. Corrosion issues I hear, thats why they work so well in cars.

the duke

I'm talking about the MSD boxes, not the basic iginition system that is on a standard GM/Mec engine. If you buy a marine MSD, its totally sealed, and it doesn't get moisture in it. I'm aware that there are many threads on OSO about the MSD box. That was my point. With the years of being made, and the thousands of boxes out there, MSD is sure to have more issues than the Crane box that has not been around anywhere near as long as the MSD has.

GoCiggie31

I respectively don't agree to set to std auto clearances. The reason is that If you look on JE's website (also stated by wompom above post) AND the actual build instructions that come in the box of pistons ( I just pulled it from my box of pistons) it states "marine applications may require an additional " 002"-004" clearance (vs the std bb app of .0030 to .0035)" see www.jepistons.com.
I followed these guidelines on my 454 build 10 years ago and was still running strong till I sold it over 200 hrs of WOT and synthetic oil. So, needless to say, I feel comfortable following OEM suggestions.

Crazyhorse

The shortblock he is considering has the same clearances as a new Merc engine would have.
I prefer to run the piston-to-wall clearance a little on the big side but that's my personal preference. JE pistons run just fine in a natural-aspirated marine application at .0035 to .004 clearance.
Rod and main bearing clearances work just fine at .0015 to 0025 and I prefer to run them at no more than .002 but again, that's my preference.
The 502 is a nice upgrade and doesn't require a lot to marinize it.
As several people have mentioned the steel core plugs should be replaced with brass.
Don't rule out rectangle-port heads. They work very well on the 502 and are an important consideration if you plan to look for more power in future upgrades. Pro Topline cast iron heads look like a nice item and are very cost-effective, about $850/pair bare.
You might consider buying a Hurricane intake. It's the best deal out there (about $159 each on Ebay) and they work very well. I installed two on my 509 engines when I removed the superchargers last spring.

the duke

You misread my post and misread again where you quoted it. Rods and mains are NOT pistons. when I stated pistons, I stated do what JE says to do.

Crazyhorse

The operative phrase here is "may require". Extra clearance would be advisable on a supercharged application. Probably not if the engine is targeted to make 500-600 horsepower.

GoCiggie31

Duke and Crazyhorse,
I appologise for misreading your post-
reading some of your post you have much experience in this engine application and I didn't intend to challenge your approval in using a create 502 for marine application.

I guess i am gun-shy (not much marine experience) as my background has been aircooled engines 4-6 cyl in the 70's.
Recently one of my marine experiences after i retire from twisting wrenches was to installed a create 454 in a 30' Challenger hull (heavy slug) for a friend and had problems with piston to wall clearances in my playground outside the SanFrancisco Bay-ugly place to get stuck and was an expensive error I made in trusting the create engine.
So my last 2 marine engines I have taken precautions similar to my aircooled days with going with extreme conditions by lineboreing, flex honing if nec and just going back to full bacis and not trusting production assys using the 'higher tolerances' guidelines. Maybe I will regret this one day with the extra time and work but I am still learning every day from pros like you 2.

Forgive me, I retract my earlier statements and carry on.

GoCiggie31

the duke

Believe me when I tell you, that this is years of learning from other people. Their mistakes and mine help us all learn, which is whats important. I couldn't begin to tell you what piston to wall clearance is, which is why I trust SRP to tell me, as they are the experts.

The most important thing that you have done, is found a problem area., and corrected it. It seems that your correction works well, so thats a VERY good thing.