pete6583 Posted July 19, 2019 Share Posted July 19, 2019 Help! I'm in the final stages of rebuilding a 72' 240Z. The Cam timing sprocket bolt has now come loose for the second time. The first time I pulled the head and had two valves replaced. (Also got a good bit of hazing about proper torque...) Replaced everything and torqued the cam bolt to 105 ft/lbs. Two short test drives, everything just fine. First longer drive, she stopped running about two miles out and when towed home, the cam bolt has loosened again. (Cam stopped spinning, pinged the top of several pistons, now need to remove the head and get valves inspected/replaced... again) Any thoughts on why this keeps happening? I don't want to continue fixing the same thing if something else is the root cause. (Definition of insanity...) 72' 240Z Original engine and E88 head Original intake and SU carbs (rebuilt by Z-Therapy) Aftermarket electric fuel pump (with flow gage to check and adjust the flow) Aftermarket exhaust 3/2 exhaust header 280X Non-Turbo Distributor Original AT (Rebuilt locally) Thanks, Chris Quote Link to comment Share on other sites More sharing options...
HuD 91gt Posted July 19, 2019 Share Posted July 19, 2019 Are you sure the sprocket is sitting flush on the cam, not getting hung up on the alignment pin? Quote Link to comment Share on other sites More sharing options...
pete6583 Posted July 19, 2019 Author Share Posted July 19, 2019 Yes, the sprocket was sitting flush on the cam and the pin was seated completely in the #1 hole... Quote Link to comment Share on other sites More sharing options...
zbloke Posted July 19, 2019 Share Posted July 19, 2019 Can you check to see if the bolt is bottoming out in the camshaft before its actually pulling up against the cam sprocket? Quote Link to comment Share on other sites More sharing options...
grannyknot Posted July 19, 2019 Share Posted July 19, 2019 It could also be that it was over torqued in past and the bolt is now stretched. Quote Link to comment Share on other sites More sharing options...
pete6583 Posted July 20, 2019 Author Share Posted July 20, 2019 (edited) zbloke, great idea, but the threads in the cam as so trashed, I'm pretty sure it won't tighten now if I tried... However, The sprocket wouldn't "wiggle" after it was torqued down, not that the tolerances we are discussing could be felt by hand... Thanks! Edited July 20, 2019 by pete6583 Clarification Quote Link to comment Share on other sites More sharing options...
pete6583 Posted July 20, 2019 Author Share Posted July 20, 2019 grannyknot, is there a way to check the bolt? Also, Helicoil the end of the cam, or new cam? Not sure which is best. Which brings me back to my original concern, could something else be creating this issue? thanks! Quote Link to comment Share on other sites More sharing options...
zbloke Posted July 20, 2019 Share Posted July 20, 2019 If the threads in the end of the cam are trashed I personally wouldn't want to reuse it or even attempt to Helicoil it either Same for the bolt, if its threads are anything like the threads in the end of the cam again I personally wouldn't reuse As for an underlying issue causing the problem, do you know any history of the engine prior to the bolt coming loose? was it a running engine when it came to you? have you completely rebuilt it or part rebuilt it? left it untouched and just got it running? Quote Link to comment Share on other sites More sharing options...
grannyknot Posted July 20, 2019 Share Posted July 20, 2019 Just contact Nissan and buy a new bolt or Z Car Source and get a good used one, same for the cam, new or good used. Quote Link to comment Share on other sites More sharing options...
pete6583 Posted July 20, 2019 Author Share Posted July 20, 2019 The engine was running when I got the car. Completely disassembled (except the head). Machinist said cylinders still had factory cross-hatching, and head looked recently rebuilt. Rebuilt engine with new bearings, rings, seal, gaskets, hoses, timing chain kit, ss bolts. I have no other info on the car or the engine. I'm waffling on new cam or have the machinist helicoil. He's got almost 50 years experience and thinks it will be just fine... New cam means new lifters and springs as well to do it right... Thanks for your thoughts and the information! r, Chris Quote Link to comment Share on other sites More sharing options...
zbloke Posted July 20, 2019 Share Posted July 20, 2019 2 minutes ago, pete6583 said: The engine was running when I got the car. Completely disassembled (except the head). Machinist said cylinders still had factory cross-hatching, and head looked recently rebuilt. Rebuilt engine with new bearings, rings, seal, gaskets, hoses, timing chain kit, ss bolts. I have no other info on the car or the engine. I'm waffling on new cam or have the machinist helicoil. He's got almost 50 years experience and thinks it will be just fine... New cam means new lifters and springs as well to do it right... Thanks for your thoughts and the information! r, Chris I might be massively wide of the mark here but, the bit I've highlighted in red combined with the issue you're having would lead me to believe the engine had this bolt coming loose problem before coming into your possession or if the head had recently been worked whoever had done it had overlooked something, the result being the bolt coming loose Quote Link to comment Share on other sites More sharing options...
Canadianz Posted July 21, 2019 Share Posted July 21, 2019 I had the cam gear spin on my L28 once. In that case, the bolt did not seem to have loosened appreciably, but it was the dowel pin that wiggled out far enough for the gear to spin on the end of the cam. I ended up swapping the cam to a different head, and shimmed behind the pin to prevent it moving again. This might be a different problem from yours though, as it sounds like things really came apart on you. Quote Link to comment Share on other sites More sharing options...
grannyknot Posted July 21, 2019 Share Posted July 21, 2019 On 7/20/2019 at 6:14 PM, pete6583 said: I'm waffling on new cam or have the machinist helicoil. He's got almost 50 years experience and thinks it will be just fine... Well if your machinist really is experienced then it might be worth it, he probably won't be using a Helicoil, more likely he would use a Time-sert, get your machinist to re seat the dowel pin as @Canadianz mentions above, if it wiggles out you're in for bent valves. Quote Link to comment Share on other sites More sharing options...
tioga Posted September 7, 2019 Share Posted September 7, 2019 Time-sert as grannyknot says. Make sure you get a insert that goes as deep as possible but still allows the expander to be used. The inserts come in many different lengths. I would be looking at bolt length and proper washer as mentioned above. Put the bolt in with no washer and make sure it goes in deep enough that when the washer is added the bolt definitely does not bottom. Quote Link to comment Share on other sites More sharing options...
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