skyknight789990 Posted September 7, 2012 Report Share Posted September 7, 2012 i dono what it is but something is telling me i cant drive me truck at all i think it hates me been through 2 motors 1 tranny just did the head gasket on it an also a new diff now my cam snapped on me an i was only cruising at 60 just relaxing when it happened dose anyone know what would cause this to happen Quote Link to comment
Draker Posted September 7, 2012 Report Share Posted September 7, 2012 Poor lubrication in the head.. or poor oil condition causing excessive heat build up in the head/cam. Or a bent cam.. and on an on.. Quote Link to comment
skyknight789990 Posted September 7, 2012 Author Report Share Posted September 7, 2012 damn well i dont think its a oil problem when me an my buddy rebuilt the motor we did alot to make sure it was oiling perfect. well what should i get for a cam i do want a bigger one but nothing to crazy i only have a downdraft weber an 2 1/4 exhaust Quote Link to comment
Draker Posted September 7, 2012 Report Share Posted September 7, 2012 Did you unbolt the cam when doing the head gasket? If so did you loosen and tighten it in the correct sequence? Quote Link to comment
skyknight789990 Posted September 7, 2012 Author Report Share Posted September 7, 2012 no i didnt i always make sure to do it all in the right sequence Quote Link to comment
Draker Posted September 7, 2012 Report Share Posted September 7, 2012 :confused: I dunno man! Quote Link to comment
Stupid_fast Posted September 7, 2012 Report Share Posted September 7, 2012 During the rebuild, did you shim the cam tower? Most of the time its because the cam towers are shimmed improperly, AFAIK! Check and make sure the shims are identical spacing across all four cam towers. Quote Link to comment
skyknight789990 Posted September 7, 2012 Author Report Share Posted September 7, 2012 nope no shims my head didnt need milling an my timing chain was tight Quote Link to comment
flatcat19 Posted September 7, 2012 Report Share Posted September 7, 2012 NismoDr had a cam snap on him. His was machined incorrectly. Don't know about yours. If you source a new(to you) cam, resurface rocker arms prior to install. Or take the ones from that cam, and keep them in order with the lash pads also. GL! Quote Link to comment
datsunaholic Posted September 7, 2012 Report Share Posted September 7, 2012 Lots of things can cause that to happen, but it would help knowing where it broke. Then look at the cam towers and see if one or more are discolored. When you take the remains out, look at the bearing surfaces of the cam and towers, Look to see if the cam is discolored near or behind the break. Other than that, the common problems are already listed- Bent cam, poor or no oiling to the cam towers, incorrectly aligned com towers, bent head. But some of these cause the cam to break in different places. Quote Link to comment
skyknight789990 Posted September 8, 2012 Author Report Share Posted September 8, 2012 ill post pics soon Quote Link to comment
skyknight789990 Posted September 8, 2012 Author Report Share Posted September 8, 2012 there is no blueing at all i took the front plate off to move the cam to see everything Quote Link to comment
bananahamuck Posted September 8, 2012 Report Share Posted September 8, 2012 take all the valve gear off that touches cam and stick new cam in it should spin freely .. Quote Link to comment
datzenmike Posted September 8, 2012 Report Share Posted September 8, 2012 i dono what it is but something is telling me i cant drive me truck at all i think it hates me been through 2 motors 1 tranny just did the head gasket on it an also a new diff now my cam snapped on me an i was only cruising at 60 just relaxing when it happened dose anyone know what would cause this to happen This is interesting as these things rarely happen at random. I would ask you why you had to change the head gasket??? Did the old gasket blow? Did it overheat? this can cause the head to warp. How did you check for warpage? Is it possible that the oil jet in the block was blocked when the gasket was changed? Quote Link to comment
datzenmike Posted September 8, 2012 Report Share Posted September 8, 2012 I've pulled lots of valve covers off and never seen one so dry. Usually it's swimming in oil. Isn't the cam usually filled with oil??? Wouldn't it at least be wet??? Quote Link to comment
skyknight789990 Posted September 8, 2012 Author Report Share Posted September 8, 2012 my truck is parked on a steep driveway so the truck is not level an it has been there for lil over a week an the head gasket was done due to something bouncing under my truck on the freeway cutting my rad an ended up having water in the 2 an 3 cylinders i took a straight edge to it on an checked for warp Quote Link to comment
72240z Posted September 8, 2012 Report Share Posted September 8, 2012 You said you always tq'd in sequence so that means you HAVE removed the cam towers? What work has been done tot he head that you know of? Also you cant use those cam followers* as is in order or not as advised earlier, because they are worn into the cam thats broken. You need new or resurfaced followers with the next cam. I can see the head being that dry if it sat at angle for a week. If lack of lube caused it there would be a good deal of blueing imho. 1 Quote Link to comment
skyknight789990 Posted September 8, 2012 Author Report Share Posted September 8, 2012 when the motor was rebuilt the cam towers where done when i did the head gasket i didnt take the towers off before the motor was built i resurfaced the head that was it head wise the valves whereglassbeaded an did a 3rd angle cut on them this is after the the valves where put in n Quote Link to comment
72240z Posted September 8, 2012 Report Share Posted September 8, 2012 when the motor was rebuilt the cam towers where done when i did the head gasket i didnt take the towers off before the motor was built I'm sorry I still dont understand if they were or werent touched. Confusing typing in this post lol. In any event if they were at some point loosened or removed I would say that and or a bent cam was the cause. Looks like a stress fracture and there arent any signs of rotational distress. That I see anyway.... Have the towers line honed by a machine shop before installing another cam. Since you have to remove the head to do that have them confirm the head isnt warped as well. Straight edge check or not having previously blown a head gasket the option of a warped head is still on the table imo 1 Quote Link to comment
skyknight789990 Posted September 8, 2012 Author Report Share Posted September 8, 2012 ok ill talk to some people an see who can check it out for me Quote Link to comment
datzenmike Posted September 8, 2012 Report Share Posted September 8, 2012 Easy to check yourself, just stick a cam in without the rockers.... it should spin easily by hand if the towers are lined up. If the cam was getting lots of oil but the towers were high or low in the middle, the cam would be turning while forced into a banana shape.... it would definitely fracture, yet not necessarily show heat or wear damage at the towers or cam bearings. Quote Link to comment
72240z Posted September 8, 2012 Report Share Posted September 8, 2012 No its not that easy to check I'm sorry to disagree with you. From the factory they are line honed and the fsm clearly states not to loosen/remove them or it will need to be done again. Its not the kind of tolerance you can feel out just by spinning a cam in there. It could be out a fraction of a hair and cause crazy stress at high rpms. Misaligned towers can def cause a fracture. I think weather or not it would show in the bearings or journals is up to how many miles it was occurring. What do the followers look like? If they were set up with perfect patterns across the board and the cam was bent then the adjustments or wipe patterns would follow suite. 1 Quote Link to comment
Sealik Posted September 8, 2012 Report Share Posted September 8, 2012 No its not that easy to check I'm sorry to disagree with you. From the factory they are line honed and the fsm clearly states not to loosen/remove them or it will need to be done again. Its not the kind of tolerance you can feel out just by spinning a cam in there. It could be out a fraction of a hair and cause crazy stress at high rpms. Misaligned towers can def cause a fracture. Line honed or bored? If the cam towers are removed and installed with due care..... torqued accordingly at 5/10/12 lbs Can't see an issue..some machinists remove the towers to do head work anyways. Even the "How to keep your Datsun Alive" book states.."Datsun tells you not to remove them under penalty of death. But don't believe it...." Done it many times....no problemos Quote Link to comment
datzenmike Posted September 8, 2012 Report Share Posted September 8, 2012 No its not that easy to check I'm sorry to disagree with you. From the factory they are line honed and the fsm clearly states not to loosen/remove them or it will need to be done again. Its not the kind of tolerance you can feel out just by spinning a cam in there. It could be out a fraction of a hair and cause crazy stress at high rpms. I definitely would avoid removing them if at all possible. That said, if I did remove I would take care to put them back in the same order and torque carefully. If they spin by hand good enough for me. Quote Link to comment
72240z Posted September 8, 2012 Report Share Posted September 8, 2012 Line honed, it means something completely different then bored. Honestly you guys can eye ball it all you like, and you may get by, but its completely incorrect. Every bolt on a car has a tq spec right? How many actually use a tq wrench for each bolt? No one lol. I personally dont feel out valve train, its incorrect and unprofessional. Thats the result you get too, backyard mechanic fail. Its extremely important the towers be honed not just for engine life but performance as well. You can site a self proclaimed "idiots guide" if you like but I can site "how to restore your datsun z car", "How to modify your nissan/datsun ohc engine", as well as the FSM for every L series engine made. The cam tower on a proper rebuild are to be line honed. Not doing so can result in a broken cam, improper wear, ruined journals etc... There is no reason to remove them ever, unless you shim them in which case they need to be honed professionally. I know people who rebuild motors with stock bearings every time and get away with it long enough for the car to leave the shop. Does that make it right? "Done it many times" Doesnt override factory specs. Whats the point exactly on cutting the corner and feeling it out? A machine shop will do it for under 100 bucks. Slapping shit together home owner style is one way of doing things but its not the way I go about it. To each their own though I guess, pay now or pay later..... 2 Quote Link to comment
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