So i rebuilt the standard 4.0 Straight six engine in my jeep and just finished installing the head ,lifters,rods and i ran into a problem ... the fricken bolts that go through the rocker arms just snapped.... the holes are clear and they are deep enough for the bolts so no bottoming out and the torque is 19 ft lbs which i torque in two steps 10ft lbs then 19 ft lbs.....i Snapped one and then i replaced it and snapped two more including one i replaced....at 10 ft lbs......Im thinking is has to do with the position of the cam meaning one of the lobes is pushing the rods up against the rocker arm..... but im unsure ...so heres the question .to prevent to bolts from breaking is their something i can do like turn the engine inotherwards moving the cam which would also move the lifters relieving pressure on the rod which would allow me to fully bolt on the rocker arm...? anyone got any suggestions ?

vehicle specs :
87 jeep cherokee xj , 4.0, automaic. everything is stock

 

1) The screws may have corroded or gotten heat-soaked, and lost their strenght.

2) These may be replaced with standard items - I don't recall which size, but they're either 5/16"-18 or 3/8"-16, about an inch and a quarter long. Flange heads would be preferred, if you can find the - SAE5 or SAE8 quality pieces should work. You may also use socket head capscrews. Good-quality socket head capscrews are usually H&T to SAE8 specs (if you can't find anything locally that you're sure isn't from China, order them. You should have a catalogue from MSC Direct on your shelf anyhow - www.mscdirect.com, catalogue is free. Lots of useful stuff in there, I get one every four or five years.)

3) The FSM doesn't say so, but I've always turned the engine to make sure the valves were closed before I torqued them (you can probably do it with the valve open, but I've never trusted torque values with tension present in the system.)

I know that, if you ride them like a borrowed mule, the Chinese can actually do some decent work. Left to their own devices, I've noted that their "SAE8" screws can usually be considered counterfeit, and roughly equivalent in strength to glass-filled 6/6 Nylon.

If you have a local Fastenal, check them out - their supplies are usually good. Consider just about anything outside of China to be made fairly well, with a preference to US, Europe (both Western and Eastern Europe,) or England. Taiwan, Hong Kong, and Japan are acceptable.

 

I am rebuilding my motor too!! I dont think I am at the part you are though... Still waiting to get the crankshaft back from the mach shop...

But to try and answer you question, I would make sure the pistons are at TDC before tighting them up. Make sure you check the push rods for play as well.

 

This is an old post, but I can attest that the bolts will break if you attempt to torque them without taking the tension off the pushrods (TDC). I checked the manual again also, it said nothing about it. I broke one of the bolts off flush, tried everything in the world to drill it out, ended up damaging the threads on the pedestal. Had to take it to a machine shop, sat there 2 weeks and cost me $90 to repair. i guess thats common sense, but the only heads I've ever dealt with in the past were OHC ones and I never had an issue. I hope this will save someone else from going through this ordeal, but unfortunately chances are they will be searching AFTER the bolt has broken.

 

The fact that your bolt broke had absolutely nothing to do with cam position.

 

Always verify that the rocker bolt holes in the pedestals are free from any oil before applying the 21 ft/lb torque to them.