zkeller

iTrader: (9)

I have an interesting issue with a friends car. AFR 205 heads, Thunder Racing Cheater cam, Jesel rockers, 7.4 Comp Cams pushrods and lifter. Pre-load was spot on at .50

Engine completely lost compression on #5 so I removed the valve cover and found that the retainer broke and dropped the exhaust valve causing it to bend. I noticed a few other retainers are ready to fail as the rockers where no longer pushing on the stem but on the retainer cap!

Upon removal of the rocker I see that they all have been making contact at the edge of the retainer cap which I an sure over time caused the failure. What is the root cause of this if preload is good? I can only think that they need to be clearanced at the point where they are rubbing???

I built my car's engine with the exact same parts and do not have this issue.

zkeller

iTrader: (9)

BTW, rub marks are the exact same depth on all of the rockers on both valves.

NXZ28

iTrader: (45)

Did you check the rocker arm tip vs. Valve tip geometry? I have T&D Shaft mounted rockers and I had to shim them up to get the proper contact pattern on the valve tip. What I did was color the top of the valve with a black sharpie. Then I rotated the motor over and few times in order to move the rocker arm up and down on the valve. Once you remove the rocker arm you will see a line across the valve tip. You are looking for the line to be as close as center as possible. Only shimming the rocker arm stands up or down will affect the centerline of the roller tip vs valve tip. Once this is set then you have to measure for the proper pushrod length. Hope this made sense and helps.

zkeller

iTrader: (9)

Thanks, this does help. My curiousity is why I did not have this issue on my engine running the same exact stuff? Should I stay on the high or the low side of the preload specs?

NXZ28

iTrader: (45)

I personally like to stay on the low side of preload specs. I try my best to get it spot on. You can use the adjustability of the Jesels to fine tune it.

I can't answer the question about why they were different from yours even though it was the same setup. I did have the problem of my T&D rocker arms actual pedestal stands not seating all the way because it was contacting the head on the corners. It was not noticeable to the naked eye. I had to file the heads just a little to get them to fit. This was on an AFR head.

zkeller

iTrader: (9)

my Jesel are not adjustable. They are fixed. I will check with them regarding the spacers for the mounting rails.

I do remember him buying the heads used, so maybe the previous owner did some machining for his application?

NXZ28

iTrader: (45)

Are they shaft mounted? The pushrod cups on the rocker arms are not screw in style with a lock nut? They are on my T&Ds and you can fine tune the preload with them.

vettenuts

iTrader: (4)

If heads were worked, valves may sit deeper resulting in a higher stem height relative to the rocker. Do not grind off the material on the underside of the rocker to clear, this could be a fatal error for the rockers and possibly the motor. You need to check the wipe pattern first with your current setup and find out if the rocker shaft height relative to valve stem height is correct.

427

iTrader: (3)

This sometimes happens when guys use +.050 keepers or larger od retainers. If you can remove shims and get the valve tip higher in relation to your retainer the problem may go away. Sounds like your pre load setting was done on the retainer instead of the valve tip. The rocker only needs min clearance in that location, and as much as I hate doing it I have cut the rocker for clearance a few times.

Kurt