5ksev Posted February 22, 2015 Report Share Posted February 22, 2015 Hey guys, just chasing some advice, iv got a few years experience building these k motors but I'm a bit confused at the moment. From the top, built a 4k Cam, carb, head decked to 9.8-1, double valve springs Got over it after about a year, so i purchased a 5k in parts The build consisted of the following. Pulled down my 4k for parts, 5k block, Brand new shallow dish 5k pistons approx 7cc instead of the 28cc? That the standard D dished pistons are. ( youl see why soon ) Brand new rings Brand new bearings through out New graphite 5k head gasket New sump gasket ( 4k sump used ) Crank & conrods are from my running 4k My worked 4k cam Brand new 202 solid lifters New 4k double timing chain Used but straight Datsun a12 pushrods 4k solid rocker setup Used double valve springs from my 4k Brand new plugs Points type dissy from 4k as it didnt come with a dissy. Note- i used shallow top pistons and the decked 4k head, to have high compression, 4k being flat top piston and chamber in the head, wqith 5k the other way around, flat head and dish piston. So by my 4k being 9.8-1 i was thinking the iv got 7cc extra in the piston dish + the bigger bore, my compression ratio would still be quite close? So i built the engine and put it in, got it running yesterday to find it has a small knock ONLY AT IDLE AND WHILST WARM and also today i d given it another go and it has a miss when under load? It still pulls quite well, all the way through the rev range, but with a small miss. What could it be? Also its struggling to turn over with a chaarged battery? Ill list a few things iv done / tried *drained the tank of all old fuel, and filled it with 98 *New fuel filter *checked cam timing is correct *Used timing light and set it to 15*adv *checked valve clearences and set them *checked plugs which are black and dry *charged battery *jump started from d40 navara Anyone have any ideas??? Quote Link to comment Share on other sites More sharing options...
GJM85 Posted February 22, 2015 Report Share Posted February 22, 2015 The knock at idle is likely bottom end. Possible the big ends have bit to much side to side action on the crank journals. My set up is almost the exactly the same. I also have knock at idle that disappears once revs increase. As for the miss fire or stumble, I'd say carby and ignition timing. What carb do you run? Is you dizzy graphed to suit the camshaft? Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted February 22, 2015 Report Share Posted February 22, 2015 If its struggling turn over the ignition might be too advanced. Mark 35deg or so on the pulley with some white paint and use the timing light to see where that is at 3000rpm with no vac advance. If you have to retard the timing you will have to wind up the idle speed. Then you know you have the right total advance, and you can look at idle and mid-advance separately. If you have less than 10deg at idle it might also get rid of the knock and if you're lucky, the missfire if its under 3000rpm. You should calculate the compression ratio, I'd do it but I don't have the head volume for that flat 5K one. Quote Link to comment Share on other sites More sharing options...
Taz_Rx Posted February 22, 2015 Report Share Posted February 22, 2015 6cc Quote Link to comment Share on other sites More sharing options...
5ksev Posted February 22, 2015 Author Report Share Posted February 22, 2015 I'm using 4k head, not 5k And ok ill check that method with the timing! Nd no dizzy wasnt regraphed for the cam, altho it did all work perfectly in the 4k shitter Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted February 23, 2015 Report Share Posted February 23, 2015 Ok, so the compression will be about the same. If you use 5K pistons in a 4K the shallow dish removes the extra compression from the 1500cc. Another answer for idle knocks is, sadly, a broken compression ring. It doesn't hold the piston firmly so you hear the piston knocking at TDC. Other than that, just go over it all carefully and see what you can find. Quote Link to comment Share on other sites More sharing options...
tojo2 Posted February 23, 2015 Report Share Posted February 23, 2015 dynamic compression wont be same if 4k was worn and 5k is fresh Was head cc ever measured ? Quote Link to comment Share on other sites More sharing options...
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