General Rubuild Questions
 

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 destroyed into pieces. I could see some rust inside that cylinder and above head where head is connecting with the manifold (no 2 inch risers are installed because if they were the engine room wouldn't close but I assume Four winns knew what they were doing when they didnt install risers). I did pressure test to all the parts including block, head, manifold and elbows and all are ok. So my assumption that this maybe the problem was caused by bad manifold gaskets (new gaskets and manifolds were installed before 1.5 years before the damage and engine did only 20 hours since then). Another thing that I would change for sure that might caused the problem is the 2 exhaust flapper valves.

Also there was a small damage in the camshaft but no damage in the crankshaft.

I want to mention that the particular cylinder had lower compression than the others before changing the Aluminum factory fitted manifolds with the new cast irons ones about 2 years ago but it was within the limits Mercruiser states as normal compression deviation between highest compression cylinder and lowest.

My mechanic advice me not to touch because compression was within Mercruiser limits.

Before breaking the Rod the engine was under power for about 40 mins trip and on the return was totally normal but I was returning against 5 Beaufort weather when it broke. Before this engine was a bit difficult to start (first rotation was very slow so I had to change the starter at the beginning of the season which fixed the issue but after it was again hard to rotate at starting). I used it only 3 times this season but I was visiting and starting it once per month.

Another weird thing is that there was no damage at all at the head or the valves but the piston was found in pieces and the rod in bigger ones.

What do you thing? should I check anything esle, or anything else than these could cause the issue and can cause it again?

hydro locked? make sure the injectors are not leaking,had that happen before,,

I do have 496 mag 375 HP camshafts used but in new condition if interested

You need another block

I found camshaft in the kit that I was going to order from enginetech, however didnt order it because not sure if the pistons are correct and also they dont provide connecting rods so I am waiting to clarify these and order. the MKC496CP kit includes the camshaft too.

Why you think so. Can you please clarify so I will avoid spending about 5000 thousands of eur. The experts here in my country didnt advice me that I must change block and that its their part of their everyday job to sleeve a block, bore it and deck it and do adjustment to the height of the pistons and its working as far as they said. Of course even if it does not they will be paid and I will loose about 5000 of EUR but it will be only my trouble...

Up to now mechanic disasseble the engine 600 EUR and turner changed a sleeve and bore the 8 cylinders 020 (there were no sleeves in the existing block). I will need to order parts about 3000 EUR and total labor about 2000 (so I am looking about 5000 at best case).

Why you say I need new block?

Well, I would not have replaced a sleeve in a unsleeved block but know it can be done, have had it done on my bull dozer. I would have just replaced the block, or changed to another motor. Being in europe you have to work with what you have available.

Do you know what caused the rod to break?
I think Ryan00TJ has some good info in the other thread

I wouldn't have a problem with sleeving a block. I think that you have had a problem for some time with that cylinder. I would pressure test the exhaust assembled.