koutroullos

Hello

I have a Mercruiser 496 Mag 375hp serial 0W035861 (June 2004 with Bravo 3) (base model - not the HO 425hp model).Block castings are D264 12558110. The engine rod broke and created damages to one cylinder plus one piston was detroyed into pieces.
I am in the process of rebuilding it so I took the block to the turner where he bore the 4.250 by 020 (also he had to change one sleeve that had bigger damage).
In the Mercruiser specs I can see that engine is 4.25 bore and 4.38 stroke and manufacturer sells only pistons with rods as one part and sells only 030 for oversizing but again piston with rod as one part.

I came across enginetech MKC496CP kits (without rods) and I want to ensure that the 020 pistons/rings included will be working for my case and I also need to find what rod length should I use.

Also the turner informed me that he will deck the block but it will no be a problem to me because he will remove equal amount of distance from the head of each of the 8 pistons.

Can I have your advice on all these and also do you know the specs of the Pistons and the Rods?

What do others use when rebuilding these chevy engines?

AllDodge

iTrader: (1)

This question needs to be Technical questions and not restro section

Not quite understanding what you have, but the 496 is not a sleeve motor. Once a piston wall is busted, the block needs to be replaced

Ryan00TJ

iTrader: (8)

Correct the 8.1l 496 does not have a sleeved cylinder design. It's a thin wall casting block and can be bored at MAX .040". Your specs on the stock bore and stroke are correct. The factory rod length is 6.693". I don't believe anyone other than GM makes this size rod. Most upgrade to a 4340 6.700" standard pin GM BBC rod. Wiseco makes 4032 forged pistons in different bore sizes that are designed for the 6.7" rod. If I were replacing pistons/rods, I would go forged over the factory stuff.

Search 496 fuel injectors..... Going lean on these setups will turn ugly.

BUP

iTrader: (9)

Something to look at for your new rebuild.. Possible a fuel pressure issue and or the fuel injectors are restricted or the other side of the coin stuck open that might have been an issue ???.

koutroullos

but he said he already managed to change a sleeve and that its ok and that he bore that sleee 020 like the rest of the cylinders. what issues can arrise when sleeving a not sleeved block?

koutroullos

4.250 plus max 0.040 is 4.290 so how they go to 4.340. i mean to use 4.340 i need to overize the 4.250 by 0.090 which is more than the 0.040 which tbe max. is is wise to change the 8 injectors too? what chnages needed to go 6.700 for the rod?
when decking you delete equal distance from the pistons or rod length is affected too and how?

koutroullos

So i must take injectors to an injectors expert to measure them and see if all were spraying correctly just to identify if they were an issue but any eay change them since they are since june 2005 (13.5 years old done about 200 hours)?

Ryan00TJ

iTrader: (8)

There are a few +.060" pistons for the 8.1l. 4.310" bore. I would not try it personally. These blocks are commonly bored +.030". +.040" would be the most I would try. To use a standard 6.7" .990" pin bbc rod, you need to change pistons.

http://www.lgmrnd.com/WIS-PTS524A3-Chevy-8-1-Gen7-2-0cc-Flat-Top-p/wis-pts524a3.htm

The engine is internally balanced. When you change pistons/rods, it all including crank will need rebalanced together.

Decking the block will bring the piston closer to the cylinder head. Pistons/rods are not shaved. Head gasket thickness can be adjusted to get to correct specs.

Have BUP here clean and flow test your injectors. Worth every penny and a necessary maintenance item.
https://www.offshoreonly.com/forums/general-boating-discussion/351552-fuel-injector-maintenance.html

BUP

iTrader: (9)

1000 percent YES. I would be good to KNOW what caused your failure and THAT IT DOES NOT HAPPEN AGAIN.

age can be part of the issue but not really either for injectors. the lower run hours on a engine at times can be worse for the whole fuel system. Old gas leaves deposits - actually fuel from heating and cooling cycles of the engine leave deposits. If you need help with the fuel injectors, I would be able to do it all.

If you ever thought about a new Block look into DART. The marine OEMs are now using the DART block for the 496 - as replacements for 496 boat owners and or repowers

BUP

iTrader: (9)

Ryan THANKS for that above and putting me into the mix about the fuel injector service.