Re: Need help reinstalling head on Mercruiser
just about any head will have bolt tighten sequence from center moving outward. Like this:<br /><br />---8---4-----1-----5----9<br />--7----3-----2-----6-----10<br /><br />reason behind this is even clamping force and it spreads the gasket outward from center so there is less chance of it crumpling or binding in the middle. Same principle can be applied to any gasket- intake manifold, exhaust manifold, etc. Usually it's not as critical with those as it is with cylinder heads.<br /><br />I don't remember what tq specs are exactly for 7/16" vs 1/2" bolts. I think it's 90 lb-ft for 1/2"x20 which you probably have. But some GM heads have smaller 7/16x20 bolts which have a tq value around 70 lb-ft lubed. You will have either one of those for head bolts. Bolt tq is primarily dependent on the bolt material and thread size, and is something like 75% of it's yield strength- all that means is 75% tight before bolt snaps. I know the merc manual #26 for my 2002 3L says 90 lb-ft. That's with the bolts lubed with 30 weight oil, and they are 1/2x20 I believe. If you use something like ARP thread lube or other fancy thread lube then the tq value is reduced even further. ARP fasteners have a good website last I checked and explain the science behind it all (very simple). Typically you make 3 passes tightening the bolts. If you went 90 lb-ft in one pass, then that's more chance for things to bind up. It's in rough even increments, like 30-60-90 for pass 1-2-3 tightening bolts in order like I showed above from 1 to 10 folr a head having 10 bots holding it down.<br /><br />Do you need help adjusting the rockers too?<br />If it's a GM 3L block, then you most likely have standard adjustable rockers with hydraulic valves. Proper preload is set by 3/4" turn (270 deg rotation) of rocker nut down from zero lash. That's based on the rocker stud thread pitch. 3/4 turn will give you 0.030" preload. websites like crane cams or comp cams have good writeups how to set lifter preload, or tightening rocker arms. Centuryperformance.com has some good tech articles too, but it's 3/4 turn down from zero lash.
