Help me identify my motors!

I have read a lot of information on OSO about how to identify Gen 4/5/6 motors, mine are definitely not Gen 4s but they don’t totally fit the description for a Gen 5 or a Gen 6. To add to the confusion when you check the serial numbers in the Mercruiser database it says they are 1997 7.4 Bravos (not magnums) however only the parts from the 454 Magnum Bravo of the same year match. The motors have rectangle port heads, high rise intakes, roller cams, roller cam retainer, forged popup pistons (part # for Magnum), 7/16 dimple rods, 4 bolt mains, forged cranks, one piece rear seals, and aluminum timing chain covers.

The cylinder head casting number is 14097088, which were used on 91 and up Gen 5, 454/502 HO are rectangle ports and 118cc open chambers.

The block casting number is 10237297, which it says are 96 and up 454, 4 bolt mains vortec 7400 L-29. Interestingly behind the timing gear cast into the block is MK-VI.

The Crank casting number is 14097044, which is 454/502 forged 1053 steel, 1pc rear seals, 4.00” stroke used in Gen 5 & 6.

I would appreciate any help in determining whether these are Gen 5s or Gen 6s.

Gen VI blocks are '91 and up, I bet that Mercruiser used Gen VI Block (You found a Mk VI on your block - some people use the term 'Gen' and 'Mk') and mix matched some Gen 5 and Gen 4 parts on your engine.

If I'm not wrong Gen 4/5/6 stands for the Big Blocks and Gen 1/2/3 stands for the Small Blocks no matter if were made from Iron or Aluminium.

Gen V blocks were 91-95 if I'm not mistaken, Gen VI was 1996 and newer!
You can tell for sure if it is a GenVI if you only have six timing cover bolts on the block.
The fact that it is stamped GENVI on the block is a sure sign!!
If you have rectangular port heads you have a Magnum!!
Also, on the side of the block, the liters are cast in, either 7.4 or 8.2.

Andrea & TomR,

Thanks for your replies. I checked the number of bolts in the timing cover and it is definately 6. On the side of the block it has 7.4. I also noticed that with the block turned over you can see where it has 7.4/8.2 L cast in to the cam area.

To complicate things I had ordered a pair of Crane cams custom grinds for my two motors. I just got of the phone with them confirming that they will not work because they are for a Gen V block which doesn't have the cam retainer. So now I have to send them back and see I can get the correct ones.

you can eliminate the cam retainer but you have to change the timing gears,just use the mk4 style timig set,the only problem is the stock timing cover wont clear all of the timing chains,you have to use either a heavy duty single roller or get a aftermarket timing cover,I think edlebrock makes one!

CayFormula,

If these are roller cams, and crane is willing take them back & work with you ($$), I would have them grind the cams for the GEN VI.
If you use a roller cam ground for a GEN IV or V , you will have to use a cam button instead of the retainer plate, along with other things such as timing covers and gears! No sense undoing a good thing!!
One of the improvements of the GEN VI over previous versions was the addition of a roller cam, and it is a very good design!
The retainer plate is a much cleaner setup than a button!

Thanks guys, I just packaged them for shipping back to Crane to see what they will do. I really want to go for the Gen VI cams.
They were very helpful so far, so I am hoping they will work with me on it. I think we both made mistakes with the cams as I told them Gen Vs but I explained that it had the factory roller cam with the retainer and he actually gave me the part number for the OEM style roller lifters.

I thought the Gen V heads couldn't be used on the Gen VI blocks but I guess this is not so unless I have managed to come across some Gen 5.5s. I have the new Gen 5 head gaskets that I ordered and they match the old ones.

I have been doing some more research on the mercruiser part numbers and I notice the part number is the same for the rectangle port heads for the Gen V and Gen VI motors in 96 and newer. The part numbers for the cam is also the same for both Gen V and Gen VI in the 96 and newer.

Ian T.

You can use Gen V heads on a Gen Vl block. Its Gen lV heads that you cannot use on Gen V or Vl blocks.

Dennis Moore has a great book on this subject. ven if you have someone else do the work, its a great resource to have. Try Amazon.com.

Thanks Pantera, will look for the book.

Ian T.