Turbo-six Posted December 13, 2017 Share Posted December 13, 2017 Hey guys, I've searched extensively on this top is but haven't been able to find the info I am looking for. I have a 78 280 with an l28et from an 83zx, running a distributorless ignition and megasquirt controlling it with a crank pos. Sensor etc. P90a head and f54 block. I took it apart and my wood wedge failed, allowing the tensioner to pop out so I had to rear down the front of the motor. I reset the cam/crank gears but messed up along the way, when #1 cylinder is at TDC (viewed through plug hole) the front cam lobes are never pointing up. I did try to start it before realizing, wouldn't start of course and turned over like it had no compression. I confirmed all cylinders have no compression with my tester. I pulled the head and expected to see bent valves but the valves appear to be seated properly and the valves and pistons show no markings where they would have made contact. My question is, with the dished pistons on this motor is it even possible for the valves to hit the pistons in this situation? Would the cam being out of sync with the crank cause it to have no compression on all cylinders? Maybe this is because of collapsed lifters? I would think it would still build compression with collapsed lifters though. I'm hoping I can just sync up the cam and crank correctly and put it back together. Thanks for any guidance. Quote Link to comment Share on other sites More sharing options...
rossman Posted December 14, 2017 Share Posted December 14, 2017 7 hours ago, Turbo-six said: Would the cam being out of sync with the crank cause it to have no compression on all cylinders? Yes if the valves are open when the piston is coming to TDC. 7 hours ago, Turbo-six said: Maybe this is because of collapsed lifters? Nope, collapsed lifters would cause the valves to not open all the way but still allowing pressure to build in the cylinder. 7 hours ago, Turbo-six said: I confirmed all cylinders have no compression with my tester. How are you checking compression? Quote Link to comment Share on other sites More sharing options...
Turbo-six Posted December 14, 2017 Author Share Posted December 14, 2017 Thank you for the response. I'm testing compression with a gauge in the spark plug hole while turning over with the starter. I verified that valves are fine and put it back together after putting the crank and cam back where they need to be in relation to one another. I recheck compression at this point and it reads a solid 135 across all cylinders but #2 which is around 75psi. that's the cylinder that pushed out the head gasket. The cylinder wall and piston both visually look fine, still showing crosshatching. I also stripped the threads in the block of one of the head bolts, I had to step away from it at that point lol. So much for being ready for cars and coffee this weekend. Quote Link to comment Share on other sites More sharing options...
TimZ Posted December 15, 2017 Share Posted December 15, 2017 Sounds like the head is coming off anyway, but before you do that, do a leakdown test on #2 to narrow down where the compression loss is coming from. Quote Link to comment Share on other sites More sharing options...
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