electrical1

The Only Thing That Is Reused Is The Oil Cooler. Wondering Now If Checkmate454mag Is Right

cig1988

If the dealer is going to make good on this and give you another engine, this is what I would do. Have the new engine disassembled and the clearances checked. Make sure with the dealer that this will not void warranty. DO NOT mention to the dealer anything about the oil cooler.
What piston is going bad and is it the same one that does?
What exhaust system are you running?
If your running stock mercruiser exhaust, are you using aftermarket risers?
What are the specs on the cam including centerline?

The reason I ask all these questions is that I'm suspecting reversion creating a hydraullic lock. Exhaust is the #1 cause. Although I just came across a problem that was driving me nutz on a reversion problem. Recently freshened up a 454 magnum that had a milkshake problem that never did prior to rebuild. The new "stock" cam that I replaced caused havoc with the reversion problem. Long story short and almost 3 weeks later... it was the design of the aftermarket risers I replaced earlier in the year when I replaced the heads.

Madmax

I've been running the cam out of a 454HO for going on 3 years now. Shouldn't cause any reversion problems. I have prob 150 hours on it with no problems. I'm even running tips with no flappers.

Sounds like something major is going on here. I definately wouldn't have put the 3rd in before figuring out why 2 went South......

bobl

I always disassemble the crate engines and set the clearances. The last 502 I did had only one thousanth piston to wall clearance on one cylinder. It would surely have blown up under load. I feel pretty sure your problems are from improper clearances.

paradigm shift

I do not know if it is normal practice but HP applications call for clearance specs slightly different than a CAR or normal crate motors. Mainly around piston clearance and ring gaps. Many people have just dropped in crate motors with no trouble I think it partly depends on how you drive them and break in time. They way I drive and since I do my own assembly I would tear one down and check everything but that is just me.

electrical1

The Bottom End Of These Motors Still Look Like New. The Problem Is In The Pistons. One Piston Out Of The First New Motor Looks Like Someone Dragged It Along The Road For About 5 Miles. Everything Else Looks Like New. No Cam Problems. It Looks Like A Clearance Problem Some Where

electrical1

As For Exhaust: Running Headers (look Like Stainless Or Some Kind Of Silver Color Metal) Into 4" Polished Stainless Exhaust Tubes To Tips Out Back

jaroot

very likely you may have a clearance issue.. either ring gap or piston to bore clearance.. Marine motors require a larger gap factor for the top rings due to the constant heavy load imposed on them and resulting increased heat. if your end gaps are too tight, especially on the top ring, and it butts under load it may literally sieze in the bore and tear the ring land right off of the piston... the little pieces then go around and all kinds of nasty damage is created on what is left of the crown, valves and combustion chambers...

is the damage mainly around the outer edge of the piston or in the center, or spread evenly across... what does the plug look like, gap closed up, aluminum particles on the insulator, etc? the valves? is the ring land broken from the crown to the top ring? is the bore and piston skirt scuffed extremely bad, especially in one or two given areas which oppose each other (180* apart)?

take a photos if you can and let us see eh...

articfriends

iTrader: (1)

If bottom end still looked good then,no,it did not have anything to do with your oil cooler.If its the same piston in the same motor twice then you will want to check that exhaust manifold. as far as if the piston was too tight,your mechanic should be able to put a dial bore gauge or snap gauge in the little bit of damaged cylinder that piston doesn't run in ,measure it,then measure a good piston and determine if clearence was correct. I would find a new mechanic if this guy told you the 750 carbs caused the problem and convinced you to buy the 800's. Carb sizing will not damage a motor,fuel mixture will,which is controlled by jet size,power valves etc which can easily be changed to a richer setup for minimal investment. If it turns out you had virtually no cylinder clearence on the cyl that became damaged then there must be a coincidental problem on the quality control of the 454's your getting,they would have to be from the same batch,GM doesn't bore cylinders individualy,they are bored 1 bank at a time,i guess it could be possible but you wouldn't be the only one out there with this problem,i hope you find something,let us know,Smitty

HeavyChevSS

Which cylinders are the ones that got hurt? think that may narrow down your search to the problem. GM usually won't stand behind these motors if used in boat but I do know of someone that had one of the ZZ572 grenade within an hour and they did work with him on it so it is worth asking..