Beware of merlin heads
 

Purchased 2 sets of merlin heads new from merlin,1st set 2 vavles hung an hit piston called bill mitchel racing and he said ill replace heads sent back old ones they sent new ones and same thing after 30 minutes of run time hung 3 vavles.hit pistons i took heads to machine shop they said they were machined wrong and honed the guides put them on my bb motor they are perfect now .so after all the labor and gaskets plus the $550.00 charge for machine shop sent bill to brad at merlin an they admit i was correct they wouldnt even pay the machine shop bill .. Nice huh ? Ill buy dart for now on;motor is a 572.cu everything standard ...........thanks for nothing brad at merlin factory bill mitchel ill always do business with you but never buy merlin products again

Sorry you had issues, there's been other threads about different companies with off the shelf heads with to tight tolerances, hind sight tear every thing down and check it.

How much time do you have on the heads now? I had the same issue years ago. What were the measurements from stock setup? How much were they opened? Did you buy the heads from Bill to begin with?

I though everybody knew to double check off the shelf heads before running them

Apparently not. That`s a costly mistake.
Has nothing to do with Merlin, put a set of AFR heads on you`ll get the same thing

My engine builder said the same thing, check all heads, they are set up for street use. I buy my heads bare and check everything first then add my preferred parts. I have AFR heads and the guides had to be honed. Wouldn't put to much faith in Dart either, my engine builder had a set with bad guides. They were too soft and wore our in a very short time. He checked the hardness and there was a wide variance in the bronze guides on the same head. Worst part is they wouldn't stand behind them. He had to put new guides in and eat the cost and labor to R&R both motors.

I always buy bare , my guides , my seats , my valves , my clearances. It saves money in the long run.
Never trust a ready to run head , they are production run to huge tolerance ranges for speed of production.

Anyone whos been in the game a while or reputable builder will tell you, always pull heads apart to check guides and valve seat/face mating

thks guys i guess your never too old to learn.just dont go buy what the manufactor says. i spoke directly to merlin an they said they were good to go no need to check nothing SHAME ON THEM,,,dumbass me

sorry
 

Even AFR was going through some rough times with seats 0.007" out.

Guide sizing is an engine dependant tolerance, and should be checked. No different than rod and main bearings.

If you're cutting seats, it's good practice to touch up the seat with a fine valve stone by hand to true it up and cut down any micro chatter marks etc.

I don't think OP is still on this site and I don't think he built his own engines from what I read. I bought AFR heads and their site says specifically that if these are used in a marine environment you need to adjust them to suit your needs. I also called them and told them I bought them for marine use and they said they were "good to go as is". They make it YOUR responsibility to make sure their product works for your application. We will never know what actually happened between OP and Merlin. We only get one side of the story here. I think it was pretty generous of them to send him a replacement set of heads. It is beyond my comprehension as to why he didn't have the new set checked before install?? "Fool me once, shame on you, Fool me twice, shame on me" You have to take responsibility for YOUR actions. From what I have read on this site, most of you that actually build engines for a living (and some others) either order heads bare or disassemble a complete head and check everything. In my case, I supplied all of the "Top End" stuff and my builder simply installed it. No checks other than what was necessary in his opinion. I know he checked p/v clearance for example. I'm pretty sure he built 2 automotive engines for me but he also told me to run 10w30. I think you guys building for marine use run 20w50 for the most part. With your tolerances, could you even run a 10w30? With the advancement in oil protection over the years, do you really have to run a 20w50? Did this guy hang valves because he didn't warm up the engine before stomping on it? Would he have had this problem if he ran a thinner oil?

Many merc engines specify 25w-40, some older a sae40, so there’s that on thin oil in marine :)

My go to is mobil 1 15w-50 and valvoline vr1 20w-50 conventional depending what motor i’m dealing with.

15w50 synthetic is what GM says you need to run on the Corvette engines at the track.

Not sure now, but 0w40 was not a Dexos approved oil. It's pretty hard for a multiviscosity oil spread so far apart. As the oil shears...it gets reduced to its base viscosity. Large timings chains on DOHC engines have a massive shear factor on oil.