i bought the same heads for my boat from summit. i put them on a 496 and guess what? the bastards didn't machine the valve guides on one of the heads. it ran about ten hrs. and the t-chain broke of course u can imagine the damage. my only recourse was thru merlin and they declined to believe me or my machinist. so this is my revenge. good luck.

never had a problem...I have three sets...sorry to hear this, I feel your pain!

Are Merlins made in the US? Judging from the huge decrease in quality at the company I work for since we were ISO certified, I try to find suppliers that do not suscribe to this paperwork form of "quality control". Its the people who make stuff and send it out the back door who have the real control of quality. Its too bad many of our companys have once again shot themselves in the foot by not paying enough attention to this simply concept of responsibility and accountability.

Only have 13 hours on mine so far , but disassembled and checked mine first .

They are made by World Products.....USA??????

They are cheap with the nickel content at the foundry. If you take a gm head and compare the 2 side by side you can tell the differance on the milled/shiney surface. More nickel, more shiney.
On one of my merlin heads, the water passage near the exhaust port corroded and leaked water into the cylinder. Eventually the inevitable happened. I religiously fresh water flushed these engines but still had a problem. Heads were 5 years old.

Kennyo

I ran a set of Merlins for about 7 years without any problem. In fact, I think I used to pass you by on the lake every weekend...ha ha ha ha ha ha ha

just kiddin....you got screwed on those heads.

I'll be back in town in a few weeks. see ya then!

Don't understand how you got Merlin heads to fit a 496, unless you means a stroked 454 Gen 4,6 engine. Merlin heads are a product of World Products, a Bill Mitchell Co. They were being cast by Zeuss foundry out of Pennsylvania until they closed their doors(Bankrupt) last month. World has now pulled their tooling and is taking it to some New York foundry_Good Luck!!
You guys are going to have to be carefullwith cylinder heads, catalogue stuff from Summit and Jegs' etc is not up to the specs required for boat use, valve, springs, casting quality and the like. Stay with head manufactures who will build you a marine specific cylinder head assembly. Old saying" The only thing you get for cheap is cheap!!
By your parts once right not twice wrong!
Raylar