Considering re-powering

RUN from Daddy-o's. RUN. I have heard many horror stories about their rebuilds, which basically they take a worn out engine only replace some components and re-use many of the old components and have many failures.

I would go with Marine Powers with a 2 year warranty, a little more expensive but all new components and peace of mind with a warranty.

Unless a reputation is impeccable always deal with someone close enough that you can reach out and grab them by the throat if they do a shoddy job.

How much different are marine blocks from automotive? I didn't think there were any differences in the block itself. 2500ish will get Dart's aftermarket performance blocks that will be considerably stronger. Maybe you should look into performance automotive engine builders. A good one will built to your needs, and have way better pricing than most marine shops.

Wouldn't these old original engines be counter rotators? I don't think automotive engines were available in either rotation.

It's just a camshaft, oil pump, starter and a few other little things to change. Not a big deal. A good performance shop can also do a more precise balance than most crate engine will offer.

Crankshafts are sometimes different due to oil passageway drilling locations.
For those engines to which this applies, and I do not have extemporaneous knowledge of all of them, this is a critical issue. Just reversing a crankshaft's direction of rotation is not as simple as it may seem.

Ralph: The position of a connecting rod journal's oil hole exit on the journal's surface is typically phased approximately thirty degrees Before Top Dead Center (BTDC) for each cylinder's rod bearing. This is due to the need to phase (time) oil flow to the connecting rod journal region of the crankshaft
where and when it will be most highly loaded, which is during air-fuel combustion and expansion. Combustion typically begins approximately fifteen degrees BTDC, with gas pressure forces during the expansion stroke developing a maximum connecting rod compressive force load at approximately fifteen degrees ATDC. If a given crankshaft design is rotated in a reversed direction, the connecting rod oil hole location would be incorrectly phased with respect to Top Dead Center. Instead of thirty degrees BTDC it would be phased thirty degrees ATDC, thus not properly oiling the most heavily loaded region of the connecting rod journal when the oil is most needed to support the combustion gas pressure compressive loads in the connecting rod.

The practice discussed above is common in left hand and right hand rotation piston engine aircraft, some, not all of which do incorporate opposite rotation engines. It is also incorporated in older, Detroit Diesel Two-Stroke engines which were available as either left hand, or right hand rotation. I cannot state with certainty which gasoline marine engines have, or have not utilized the practice of oil hole location phasing. I can state that oil hole location phasing has become the norm throughout the field of pressure lubricated piston engine design, irrespective of the field of application.

Hi,

That is a good post there Ron, thanks for sharing your knowledge.

I have seen them like that too. I've seen one engine driving from the flywheel and the other driving from the balancer as well.

Ahh, I was thinking GM 427. The op mentioned converting to 454's, so I made that assumption. Dart does make ford blocks as well.

Thank you KIWI.

Good information. But on gas inboards, Mercruiser, Cruisader etc, nothing is done to the bottom end in regards to the crankshaft oil holes, rod bearing oil holes etc. They are in a standard location for both RH and LH rotation which is typically at top and bottom dead center on your typical chevies and fords for both the rod and main journals. As to the other specifics, it's been so long since I dealt with rebuilding or dealing with them I forget exactly what is different to make it turn backwards. I know the camshaft is different, (I have seen timing gears to reverse the rotation), firing order change and few other parts. Of course freeze plugs are bronze instead of steel on the marine motors. On the early (1980's etc) gas inboards many things were different based on HP level, like most Mercruisers always had 4 bolt mains and forged cranks etc.

To the OP I would get a set of crate motors (454's or 8.1's etc). I would absolutely not go with some weird Chryslers where finding parts to fix them will be a nightmare, and someone who understands them is a nightmare. With 454's you can find parts ANYWHERE and EASILY and you have a 2 year warranty with a company that will stand by it. Also, ALL components on the motor are new. At least down here, anytime I see a gas inboard with 1000 hours the motor might run great, but all of the accessories are a rusty crusty mess that are ready to go at anytime.....starters, alternators, brackets, etc.

As to how different are marine motors from truck/automotivce, usually not much. HOWEVER sometimes something really small is a huge thing. When the 350 vortec motors were initially marinized, they used a typical truck cam in them. Well what happened is it took them 1-2 years to find out that the cam had too much overlap and the engine would actually ingest water back in from the exhaust valves while it was running and you'd end up with a little water in the oil and the motor led sometimes a very quick death. I put a Marine Power 350 vortech in a 18' Donzi classic and this happened and was outside of warranty and turns out it ingested just enough that it spun the main bearings and etc.

The oil hole is usually placed so that it is out of the way by the time max cylinder pressure occurs. The reason for that is the hole itself reduces bearing area and best bearing life is obtained when the highest loads are not imposed on the area of the journal which is missing part of its load bearing surface.

Another issue is that the load on the crank and the piston pin at TDC is inertial, the big end is loaded at the bottom because the rod and piston is trying to depart the engine. This provides a relatively large gap for the oil to fill and provide hydrodynamic separation as the journal rotates.

There has been a lot of experimentation with the location of oil holes, Detroit Diesel claimed to have increased minimum oil film thickness 83% by tweaking the oil hole location on 92 series engines.

As far as I know, there is no difference in the stock cranks for the marine version of the 427 regardless of rotation though I have seen cranks that had 2 oil holes that appeared to be about 30 degrees apart. That might have been a technique to optimize lubrication in an opposite rotation.

Part of the aircraft engine lube issue comes from the condition in which the prop can "drive" the engine at high rpms. The unloaded condition reverses the location of maximum force on the bearings. This was a source of failure for fighters and dive bombers and even transport aircraft doing steep power off descents but part of that problem was solved by adding silver to the bearing shells along with changing the location of oil holes to keep the bearings flooded.