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In A Recent Thread, I Explained How I Went Through 3 Motors On My Boat Due To My Oil Pan Being Sucked Dry After About 15-20 Minutes With The Motor 3000-4000 Rpm. It's Been 2 Different 350 Block With The Same 400 Heads. Everything Was Done Properly.

I Have Just Now Discovered That There Are 2 Different 400 Heads Being Used On This Motor. One Head Has 5 Long But Narrow Oil Drains Above The Pushrods And 1 On Either End Of The Head. The Other Head Has 4 Fairly Large Squarish With A Curved Top Oil Drains Above The Pushrods And The 2 On The Ends Have A Deeper Recess. Obviously, This Head Will Drain Oil Faster Than The Other.

Can Someone Tell Me The History Of These 400 Heads And Why They Are Different? Also, Would Running 2 Different Cylinder Heads Cause Oil Drainback Problems?

Thank You In Advance For Your Help.
 

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stock drain holes in any casting would be more than adequate

have they been screened ?

are the heads filling up with oil and not draining that yu know of for sure? ?
what kind of oil pump?



an HV one?

if so then i would try OEM replacement ones instead
 

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Discussion Starter · #3 ·
No screens. New stock Melling oil pump each time. Engine runs outta oil after 3000-4000 revving in a boat for 15-20 minutes.

First time was the rear main bearing. Second time was #8 connecting rod bearing. Haven't taken the motor apart for the third time but it is definitely a bearing.

I'm fairly positive that it is running out of oil. I stopped the engine immediately last time and checked the oil. None was on the dipstick for quite awhile.
 

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If I even suspected that the oil was congregating on top of the heads, I'd be doing some surgery to the valve covers and the top side of the oil pan, installing fittings and hot oil rated hoses to drain the oil back to the pan externally, like maybe one on each corner.
 

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Does this engine have a larger capacity marine oil pan on it or a standard car pan??

I would suspect cavitation/foaming is causing the problem, not lack of drainback, SBC's have no problems with drain back. If you had a drain back problem it would show after less than a couple of minutes, the fact that it takes longer tells me that the oil is getting all foamed up, and then it won't drain back too well. Think of pouring warm Coca-Cola into a glass of ice, a little liquid becomes a lot of foam.

Just like sustained circle track running, I think a larger capacity pan and a windage tray/baffle are needed in this case.

You could plug all the drain holes except the rear one in an SBC head and still have enough drain back unless the oil has become full of air.
 

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I agree with Eric, his answer makes good sense. I`ve never had a small block with drain back issues, even ones that had some stopped up passages.
I learned a long time ago engines that run at a constant high rpm need a oil cooler and a windage tray. Due to the high constant RPM the whipping action of the crank turns the oil into foam just as Eric said, when that happens it gets to the point most of it`s foam and the oil pump picks up some air and the ball games over. I would add a oil cooler and a windage tray, and I would do some drain back mods to the block. Look in the lifter valley, you`ll see 4 humps, 2 on each end and they are right below the drain back holes in the heads, these should be ground down and smoothed. Now look in the rear of the lifter valley right by the distributor hole, you`ll see the oil drainback hole, but it`s rather small and looks rough, take a carbide cutter and open it up and smooth the entryway. Doing these mods greatly aids oil drainback at the rear of the engine. Since the engine often sits at a lean and is at a lean during operation in a boat this would be of great asset as it cuts the amount of oil dropping on the crank so more returns to the pan without turning into foam. This link will show the areas I`m referring to, You won`t need screens so you can overlook that area:
http://www.stockcarracing.com/techa..._engine_block_upgrades/oil_gallery_plugs.html
 

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Oil Drainback Issue

Hey Friend, I didn't catch your first thread but after reading this one something isn't adding up. I have run both 350 and 400 sbc in my boat with stock automotive pans and high volume pumps without sucking the pan dry. I'm not so sure that the pan, pump or the drainback is your issue. I run my boat for extended periods of time 15-20 minutes at 5000rpm without chewing up bearings. 3000-4000rpm is loafing along(the speed my wife likes to run at). I do agree however with the other posts that improvements to the oiling system as a whole greatly improves the longivity factor on marine engines as well as any high performance engine. As already stated, oil foaming is an issue on these marine engines. Most, if not all factory marine engines have windage trays to help with this as well as oil coolers. Now back to the engine problem in question. I can give you feedback on what I've witnessed with mine. When running the 350(car engine,car pan,no windage tray,melling hv pump) I did see a drop in oil pressure after extended high rpm run, but never enough to cause a bearing failure. When I upgraded to the 400 engine I used a 7 quart pan with a crank scraper built in, added a high capacity remote oil filter(fram hp1) and a oil cooler, guess what, oil pressure still drops when you run it extended high rpms. My point is, neither motor has had a bearing issue at 5000rpm, so maybe you need to look at your bearing clearance or your crankshaft grinder/engine builder. The only small blocks I've ever chewed a bearing in were due to insufficient clearance and or a improperly ground crankshaft. By the way, I use the 2-3 rule, .002 on the crank,.003 on the rods. Hope this gives you some food for thought. Good luck cause as they say "A boat is a hole in the water that you throw money into." olnolan :thumbup:
 
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