Engine Miss After Rocker Issue
 

General question. I had a rocker lock nut break on HP500 on the exhaust valve hole #7. Tech replaced lock, checked push rod and all was ok. Fired it up and no noise and seemed to be hitting on all 8. Started it this week and it is miss firing and is not accelerating on the muffs smoothly. What are the potential issues? Was going to pull plug to see if it is fouled, do a compression check, maybe the rocker is adjusted too tight or loose. Any suggestions appreciated.

Loose would probably tick, tight would probably miss. How and why did the lock nut break, are there more ready to go.

Maybe another nut broke?

This thread has some info on a BBC rocker nut breaking. It'l doesn't appear to be a common event compared to rocker studs breaking.

https://www.hotrodders.com/threads/r...agnose.148710/

I don't think there is any others broken, no weird noises just missfiring. I am considering replaceing all of them on both engines. Question is, who makes the best ones out there? ARP?

It's hard to beat the availability, quality, and price point of ARP hardware.

Need to be careful buying aftermarket, the Merc ones are shorter to clear the stock valve covers, all my years Ive never seen one break

I'm not familiar with that exact motor, what brand rockers are they and are they aluminum ?

If they're stock it should have Crane gold aluminum rockers, but so many have been changed out over the years

I was just curious, aluminum rockers have a cycle life.

the poly lock nut broke not the rocker

Talked with builder yesterday. He gave me some extras to change if needed. Explained everything to him and he said it is adjusted to tight and hanging the valve open causing the miss and to pull the plug, it is likely fouled. If I can't get to it today, he will himself or send one of his guys out to correct it.

BTW, thanks to everyone for your input. I will update once it is looked at and hopefully fixed.

Sorry forgot to update the latest. Builder came out to my garage and took a look see. Found the rocker was set correctly but they used a taller poly lock, and he found a witness mark on the Valve Cover. Probably from when the first one broke or the taller lock. Put the correct one on and adjusted to base circle I guess, Pulled the #7 plug and it was fuel fouled. Replaced the plug and it fired right up. So far so good. Not back in the water yet, still finishing up sea pump impellors, trim pump reservoir and clean up all the spilled stuff in the bilge. Should finish up tomorrow and will be ready to re-launch and put back on lift. Oh and add a bunch of fuel.