ZackeryNM Posted March 4, 2014 Report Share Posted March 4, 2014 Not sure how to make this long story short. Head gasket was blown between cylinders 3 and 4. Took the head off and found it scorched there as well. Took the head in to have it arch welded and machined. They cleaned it, ground the valves and set the lash. Here I am with a new head gasket kit on. The whole deal and a new thermostat to boot. We're all put together now. No vacuum leaks. No draw on the electrical system. Brought the engine up to operating temperature. Used the timing light and adjusted the dizzy until the timing showed 3° like the hood sticker points to. Here is the main issue. It's throbbing/shaking/chugging and it sounds like a flippin subaru flat four. I can't get it to time right. Any thoughts guys? Quote Link to comment
ggzilla Posted March 4, 2014 Report Share Posted March 4, 2014 Very common when the firing order spark plug wires put on clockwise. 2 cylinders will still be right ... Quote Link to comment
ZackeryNM Posted March 4, 2014 Author Report Share Posted March 4, 2014 Very common when the firing order spark plug wires put on clockwise. 2 cylinders will still be right ... So to be clear, I've got them on backwards? Quote Link to comment
ggzilla Posted March 4, 2014 Report Share Posted March 4, 2014 Maybe. Check it out. Quote Link to comment
CorAce Posted March 4, 2014 Report Share Posted March 4, 2014 Are you absolutely sure you got the timing chain was set correctly? And 3 deg sounds to low, I normally shoot for 10-12. Quote Link to comment
banzai510(hainz) Posted March 4, 2014 Report Share Posted March 4, 2014 Corace its a z series 2 plug head motor its usually closer to 3-5 on these I think. L series yes you would be right. Z series has a before and after spark Quote Link to comment
ZackeryNM Posted March 4, 2014 Author Report Share Posted March 4, 2014 I have the chain set properly double checked with pics I took before taking it off. I labeled the spark plug wires as I took them off and all of those are in the right place. Hood sticker says 3° B.T.D.C. So three degrees before top dead center. I'm not sure what exactly I'm missing here. Quote Link to comment
datzenmike Posted March 4, 2014 Report Share Posted March 4, 2014 Now that it's warmed up set your own valve lash, never assume that it was done for you correctly. 0.013" for in. or ex. And 3 deg sounds to low, I normally shoot for 10-12. Dual plugs light the fire in two places, and like burning a candle at both ends, it's burns twice as fast. A shorter burn time means that you need to light the fire much later to get the maximum pressure from the expanding gasses pushing down on the piston at the proper place after TDC. The shorter burn time also reduces the time that heat is absorbed into the combustion chamber and the piston tops, (quench) allowing more to be used to do work pushing the pistons. There is also less time for oxides of nitrogen to form. Quote Link to comment
ZackeryNM Posted March 4, 2014 Author Report Share Posted March 4, 2014 Ill crack into that. Quote Link to comment
CorAce Posted March 5, 2014 Report Share Posted March 5, 2014 Corace its a z series 2 plug head motor its usually closer to 3-5 on these I think. L series yes you would be right. Z series has a before and after spark Now that it's warmed up set your own valve lash, never assume that it was done for you correctly. 0.013" for in. or ex. Dual plugs light the fire in two places, and like burning a candle at both ends, it's burns twice as fast. A shorter burn time means that you need to light the fire much later to get the maximum pressure from the expanding gasses pushing down on the piston at the proper place after TDC. The shorter burn time also reduces the time that heat is absorbed into the combustion chamber and the piston tops, (quench) allowing more to be used to do work pushing the pistons. There is also less time for oxides of nitrogen to form. I should have read what he was driving, I assumed it was an L series. That's cool info though, I didn't realize that's what the dual plugs were for. Quote Link to comment
datzenmike Posted March 5, 2014 Report Share Posted March 5, 2014 Solely for reducing pollution but inadvertently the NAPS system is rather detonation resistant when the timing is that short. Also hemi head and cross flow so the exhaust port does not heat up the intake air too. Quote Link to comment
MikeRL411 Posted March 5, 2014 Report Share Posted March 5, 2014 "Dual plugs light the fire in two places, and like burning a candle at both ends, it's burns twice as fast." To quote the poet "My candle burns at both ends. It will not last the night! But oh my darlings and oh my friends, it makes a pretty light!" 1 Quote Link to comment
xsdg Posted March 5, 2014 Report Share Posted March 5, 2014 Where is your truck from? For a California truck, an MPG (Z22), or a Cab and Chassis, you need to disconnect and plug the vacuum advance before you set timing. In that case, you'll set the timing to 3deg +/- 2, and when you reconnect the advance, you'll probably see around 12deg btdc (if I did mine right, which I didn't necessarily do :o) For a non-California, non-Cab-and-Chassis Z24, there is no advance at idle, so there's no need to disconnect the vacuum advance. Quote Link to comment
datzenmike Posted March 6, 2014 Report Share Posted March 6, 2014 The MPG or Mileage motor was a Z20. Disconnect vacuum advance to set timing? I would doubt this very much. The lack of advance at idle is key to reducing NOx emissions so I don't think California would do this at all. Besides the MPG wasn't available in California it had 9 to 1 compression. Quote Link to comment
ggzilla Posted March 6, 2014 Report Share Posted March 6, 2014 Almost every repair manual instructs to plug the vacuum advance when setting timing. It won't hurt to do it in any Datsun. Quote Link to comment
xsdg Posted March 6, 2014 Report Share Posted March 6, 2014 Mike: here's my factory under-hood tune-up sticker: https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-prn1/t1/1622097_10100234766218418_912052555_n.jpg It's a 3/1985 California 720, RWD with a Z24. It definitely shows advance at idle with vacuum line connected (as mentioned, I believe it sits at around 12degrees BTDC). When I pull the vacuum advance, it drops back down to 3degrees BTDC. Quote Link to comment
ggzilla Posted March 6, 2014 Report Share Posted March 6, 2014 "Ignition timing is checked with vacuum line removed" Quote Link to comment
datzenmike Posted March 6, 2014 Report Share Posted March 6, 2014 I wonder if that is only California? It's my undestanding that there is no vacuum signal at idle Quote Link to comment
xsdg Posted March 6, 2014 Report Share Posted March 6, 2014 It's the specific ones that I mentioned. It's all in the table at the bottom of page EF&EC-60 of the FSM (I have the '86 FSM). Page subtitle is "Spark Timing Control System (Except M.P.G. and Camper models)" The table caption doesn't mention California by name, but the table contents do. (PS: ggzilla, thanks for the assist) Quote Link to comment
datzenmike Posted March 6, 2014 Report Share Posted March 6, 2014 I have the '84 FSM. '86 would be Z24i with throttle body injection and crank angle sensor then? Quote Link to comment
ggzilla Posted March 6, 2014 Report Share Posted March 6, 2014 It says California, 1985 Quote Link to comment
datzenmike Posted March 7, 2014 Report Share Posted March 7, 2014 Yes but he said an '86 manual. I believe all 720 Z24i motors were throttle body after April '85 making all '86s TBI. (except the Z20 and diesel) Quote Link to comment
ZackeryNM Posted March 7, 2014 Author Report Share Posted March 7, 2014 So. The lash was correct. The timing is correct at 3°. I'm getting spark. Dizzy looks fine. Did a compression test... 1- 125 2- 0 3-132 4-120 Looks like I have a bent valve. Only way I can think of this happening was if it was mashed when I torqued the head down. Being that the head went straight on without rocking or any odd contact kinda confuses me. Everything was in the right place. Quote Link to comment
ZackeryNM Posted March 7, 2014 Author Report Share Posted March 7, 2014 Yes but he said an '86 manual. I believe all 720 Z24i motors were throttle body after April '85 making all '86s TBI. (except the Z20 and diesel)And if I didn't specify, I have a carbed z24. Quote Link to comment
datzenmike Posted March 7, 2014 Report Share Posted March 7, 2014 I found the Spark Timing Control section for the '84 FSM. Vacuum hose not mentioned. Quote Link to comment
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