Mercruiser 496 base model - Pistons and Rods
 

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?

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

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.

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 ???.

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?

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?

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)?

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

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

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

kout - I dont know where you are the US or Europe but it isnt unreasonable to find these blocks or engines that have been pulled out on Craigslist. I am in Florida so there are typically both boat engine 496/8.1 and truck 496/8.1 on craigslist. At one point during my rebuild, I had salvaged 3 off craigslist in my shop. Maybe get one off eBay hand have it shipped? Or you can even buy a short block from Raylar for $6000 and have it shipped.

So correct me if i am wrong.
1.Sleeving 1 of the 8 cylinders and over sizing it all 8 of them to 4250+020 will not be an issue even if this block has no sleeves> New Pistons and rings will be 4.270 and I can use the 4340 series of pistons. He already bored the block to plus 020 and if I ask him to do it 030 I assume he will ask double money for doing 2 times the job.
2. All parts (block, head, manifolds and elbows will be pressure tested).
3. Additionally Manifolds with turbolator and elbow must be pressure tested as one complete part all together.
4. After decking the pistons will not be shaved but head gasket that will be used will be thicker by the size of the removed surface from the block decking (if 0.5mm removed then gasket must be 0.5mm thicker)
5. The existing rods are 6.693 and it will not be a problem to use any 6.700 rod without any other change??? What about the 2 hole sizes, screws of the rods (should they be specific size or type)?
6. I must take all 8 injectors to a professional to clean them and measure their flow and if anyone has issues I must replace it with new (no need to replace all 8 of them???)
7. Since the rods, pistons will not be standard I must rebalance the crankshaft to work smoothly with the new pistons and rods.
8. The camshaft that has a damage must be replaced with a new one exactly as the original
9. I must replace all bearings of the camshaft and cranckshaft
10. I must replace oil pump
11. I must replace exhaust flappers
12. Replace crankshaft position sensor who broke while turner tried to deck the block

Can you recommend me any model for piston 4.270 4340 series? Should I care about anything else like the pin type or something?
Can you recommend me any model of 6.700 rod that will be ok to use with the new pistons and existing crankshaft?
Is there any way to check the work done by the turner? is there any tool that I can use and see if they did correct work before installing thousands of dollars of new parts back to where they worked?

Thanks and merry Xmas!

More explanation
 

When the boys on this forum are talking about 4340 rods, that is the material that the connecting rods they are recommending are made of. This material is much superior to the OEM rod material. The pistons are not 4340 style/make or anything.

People often put in 6.700" length rods (4340 material) with .990" (std) bore small ends so that they can use more easily obtained forged Big Block Chevy (BBC) pistons. Most BBC pistons use .990 wrist pins whereas the oem Merc pins were 1.004" I believe. The Enginetech pistons you are referring to are the 1.004 pin size and correct compression height (CH) 1.34 for the oem stock rods. I suppose you could get 6.7 rods re-bushed to 1.004, but why would you = Enginetech pistons are hypereutic material and nowhere near as strong as the forged pistons.

If you go 6.7 rods and forged pistons they are not likely off the shelf and will be somewhat custom = more money, but you are upgrading the motor at that point. People use the forged pistons because they are stronger and more tolerant to a " less than perfect" tuning situation, not a fix for ignoring the tuning\fuel injection issues though.

Turner = Machinist to us in N.A.

Are you sure the cylinders are finish honed to size? and what are they bored for, piston material wise? 4.270 is a +20 over stock size for sure but the finished size is dependant on the material the pistons are made of: forged 4032, 2618 or Hyper all have different finished sizes for the +20 oversize. The "turner" needs the pistons in hand before they hone it to final size or it is a guess.

I hope this is more clear.