Knocking 454/B&M 250 - Cig Bullet
 

What's happening everyone?!

A couple of weeks ago, my buddy's Bullet developed a loud/sharp knock while being flushed after coming out of the water at our marina. The oil pressure was still good so, and after listening to video off my phone, it sounded like a rod knock (sounds different listening on my PC). I was not on the boat the day things happened, but I understand that the engine(s) overheated some due to running in some very low water. He cleared the problem, then proceeded with the rest of the day. On the way back, he ran WOT to the marina (about a mile, maybe two), came in and docked the boat. There was no indication of a knock prior to docking, but he usually docks on the starboard side so it may have been missed. I'd post a video of it running, but can't get it uploaded (figures).

We removed the engine from the boat.

Got the manifolds off and attached are some pics of what we found. It looks like maybe number four started to let go. Is it evidence of water or a piston giving up the ghost? We have a new short block coming so this is only for informational purposes. He's limited on tools so getting it apart might take some time.

Engine is a 460 CID BBC mag (per what we know... engine was in the boat when he got it over ten years ago), B&M 250 with a single 850 Holley, Crane cam, V6 module with MSD 6M-2, etc. Exhaust is Stainless Marine with 4.5" risers that are dry to the transom. The engine has run well over the years, and this is only time we've run into a problem.

Thoughts on what went?

Pressure check those manifolds

When taken apart, it was evident that the manifolds were leaking at the riser joint.. I think that was causing some nasty reversion.

New short block coming. I assume those heads are not going back on as-is? We know it wasn't a rod knock, cuz it woulda let go in that full throttle run...

been getting water in for a while looks like, very easily could have spun a rod bearing...would have to throw a rod..keep running and thats another story

No, they're going to be redone at Magnum Machine over here in Chesapeake.

Never any sign of water in the oil. It could be that the heads started to eat through... that happened on his starboard motor eight years ago (leaking out of the exhaust port).

We still need to get the engine apart. It's still on the hoist in his garage.

think about replacing them. Salt rots thru end exhaust valve guide. You take heads in and say fix em, easy 800 bucks. At that point buying 1500 set of upgraded heads is mucho easier to justify...

Agreed.

He's got the one head off.... I'm a little confused on what's in the boat... appears to be a low compression 060 over 454... 525sc-ish. 7.75:1 with open chamber heads.

Mine piston is burned up pretty bad from detonation (number 4 that all the deposits in the exhaust). Number 2 shows some detonation damage, but minor. Anyway, its toast.

One big thing here is making sure that the engines are relatively even. He doesn't have the funds to replace both engines hence trying to keep the heads and such close. The short block that he has his eye on is a 8.75:1 Mag set up; it'll be better with the 250, but I'm pretty positive the starboard engine is a flat top (it's been years since we put to together). Will the differences cause a huge issue?

Very little. And that second engine will need done sooner, rather than later. Upgrade this engine to what you want in the long run. Live with the diff in throttle settings for the time being. Then, when the second motor needs done, you have engines upgraded instead of same old stock stuff that you already gad. Think about 502's instead. They look the same...