Engine Rebuild Advice

[HotRodr56]

One of the projects on my Z-33 is rebuilding the port engine. It was supposed to be a 454 Magnum with a bad valve. Upon disassembly I find a Mark 4, 454 4 bolt main, cast crank, std rods with 3/8" bolts, cast pistons, rectangle port heads with roller rockers and 2 bad valves, a cracked cylinder wall, and badly worn main bearings. My thoughts are someone replaced the mag with a 330 hp short block at some time, all measurements check out as standard-no overbore or turning. My engine builder says the block is fine and has sleeved the cylinder. He has done a valve job and replaced the bad valves so the heads are good to go. The crank needs .010 on the mains but a cast crank scares me a little. The rods and pistons have to go in the spare parts box. I have decided to replace the crank with a new forged 4130 steel std 4.00 stroke, rods with 4340 steel 6.135 std length pressed pin with 7/16" bolts and TRW forged pistons 8.7 compression. If anyone has better recommendations or sees a problem with this combination let me know before I start spending money. I am not after ultimate horsepower so much as bullet proof durability. I want to run 5000rpm with no worries on the bottom end. I haven't checked the cam specs yet but I am betting it is the 330hp profile. If I change cams does anyone have a recommendation on a nice hyd that is not too radical to use with the stock springs but gives good performance? Lastly my engine builder says the sleeved block will be plenty strong, second opinions or practical experience is welcome.
Thanks, HotRodr56

[TREYSTJOHN]

I have a complete Mark IV rotating assembly, 1053 GM crank, 7/16 dot rods, TRW 2399 .060 over pistons with flywheel and balancer (assembly is ballanced and ready for install. Comes with all new bearings. All you need to do is put in a block. I also have the same setup at .030 over with the block ready for assembly. Decided to go with 515 Dart based engines for my Fountain, thus all the new spare 454 stuff.

As far as cam, best cam for your setup provided you have 049 oval port heads or 990 square port heads is the Crane 278 9PART #133801, install at 112 degrees and it will idle at 700rpm and pull until 5,000. Also install a 1" spacer under your carb. With this cam no need for jetting changes provided same exhaust is used. Call me at 410-761-1337 if you have any questions.

Trey

[Rodger]

I have a cylinder sleeved on my 468 BBC turbocharged engine running 11 PSI boost. Over 1000 hours on the setup. I don't think you need to worry about it. Good luck!

[HotRodr56]

Thanks guys.:smile: My heads are the rectangle port 990's. I looked at the cam and the numbers on the back end are 3848 either 075240 or 975240 can't tell for sure and 13-35-97. None of these numbers match anything I can find in books so if someone recognizes this let me know what I've got. If all else fails I will measure the lift and see if I can determine what it is. I mentioned running at 5000rpm but is this the range I should shoot for? What rpm range do most of you with big blocks run at WOT? Also thanks for the offer on parts Trey, I am actually looking at the TRW L2399 pistons but I like the idea of stock bore with more material left in the cylinder wall. If you wanted to part with the crank and rods that might be a different matter.:wink: Any other engine gurus got suggestions on doing this the right way the first time? Cams you've had good luck with? Brands to avoid? Anything to watch out for?

Robert

[TREYSTJOHN]

Did you machinist sonic test block to determine wall thickness? If it is below .125 anywhere, I would not use it for raw water marine application.

Not interested in breaking up the assemblies since they are balanced.

The cam you have is very similar to the Crane 260, by going to the 278 you will not need to change valve springs as you would with the Crane 228/312 which was the OEM cam for Merc 420. We have installed many many 278 Cams in the old Merc. 370 and newer 365 Mag. The difference in performance is night and day. We picked up 7 mph on a 25' 1989 Single 365 mag Checkmate with a 278/1 " spacer and prop change. On average, by installing a 278 and a 1" carb spacer, you can expect 400-415hp using stock exhaust. With the 278, the power does drop off rapidly at 5,000, we usually prop for peak rpm at 4,800-5,000which in you case should increase your 3,500 rpm cruise speed by about 3-7mph.

Do not get caught up in "race car engine builder mentality". In most cases, these guys over cam marine engines which leads to slower than stock performance and no idle. Remember a boat is always running uphill.

I would also recam the other engine to match performance.

Hope this helps.

[Pismo]

Check out

http://www.offshoreonly.com/forums/forumdisplay.php?f=20

there is a ton of this type of info on this subject.