Elite Marine

Is there a tru advantage to buying a Gen 5 or 6 block over a
Gen 4. I've read through Dennis Moores book, I see the physical differences, but is there any real advantage to one over the other?

Raypanic

Mark 4 and gen 5 use flat type lifters gen 6 use roller lifters with larger lifter bores. Also the timing covers are different. Performance wise both I think are equal, you can put roller lifters in the gen 5, and I thin mark 4 too. Also the gen 6 uses a serpentine belt whereas the older versions use V belts. Fuel pumps are belt driven on the gen 5 and prior (off water pump) Gen 6 use electric fuel pumps. These are compairing Mercrusier engines. I think the Gen 6 is better looking because of the belts but some may use this difference to determine if it is an "old" engine or "new" engine. For resale I would get the Gen6

Elite Marine

The pulleys can be changed, I plan on reusing my Gen 6 pulleys. All the accessories bolt up. I've been informed that the Gen 4 blocks are a little more stout than the Gen 5 and 6. Other than the 2 pc. rear main seal, is there any other performance issue regarding the Gen 4? The Gen 6 is newer and difficult to find.

I'm still looking for a Gen 6 454 bare block, standard bore cylinders. Does anyone have a source for one?

Thanks

Brad Perry

Gen VI also uses a one piece oil pan gasket and o ring timing cover. It has a thrust plate on the cam nose. With that said, it is common to put a gen 4 crank in a 6 block and use an adapter kit to use the gen 4 rear main seal. I'm also running a modified front cover that allowed the use of a double roller timing chain from gen 4. It won't fit under a 6 cover. That made me use a gen 4 cam and button, since I could no longer use the thrust plate. Also had to use aftermarket lifters anyway. Some people even re drill the front of the block to use a gen 4 cover. Nickerson is the only one to my knowledge that uses the 6 cover. See the advantage of a 6??????????????

If I started with a 4, I would have lost the aluminum timing cover with oring, and the nice oil pan gasket, but all else would have been the same or cheaper. I think the only time you would really want a 6 is if you were going to use stock lifters, gen 6 cam and timing set. Then it MIGHT be less $$ and less time.

I bought my block from a Lubbock texas dealer called Scogg and Dickey. They cost about the same as a Merlin II block (4).

Also a gen 6 doesn't really have a hi-vol pump. I'm sure the stock one is fine, but I went with a teague gen 4 blue printed pump and had to modify a main bolt to get it to fit.

Brad Perry

BTW, my original stock mercruiser gen 6 had v-belts. There were a few leftover 300hp 454s out there..

formula31

And one piece oil pan gaskets are available for Mark 4 too.

Elite Marine

What about block integrity? I believe the Gen 4 block is stronger and thicher than the Gen 5 or 6.

I know about the pan gasket, crank gasket and timing chain cover. These items are easily replaced, but strength and block integrity are not formed by bolt on parts. Right???

Dennis Moore

The Gen V and Gen VI have certain advantages over the Mark IV

The oiling system is better with priority feed.

The one piece rear main seal is less prone to leaking.

The cooling passages are better because;
The fuel pump boss removal helps the #2 cylinder run cooler.
The redesigned oil filter pad helps the #7 cylinder run cooler.
Using the single row timing chain gives more room at the front of the #1 cylinder for a larger coolant passage.

These are just some of the things I learned writing the book (that I can think of off of the top of my head).

Sincerely
Dennis Moore

bobl

They now make double row roller timing sets for the Gen VI blocks and step nose cams. They fit under the stock timing cover.

Elite Marine

Thanks to all of you...I'm rebuilding the motor with a Gen Vl block!!!