406 sbc build

R

Robert Miller

Member
I have a new 406 sbc build, that developed 2 dead cylinders #7 and #4 tried new plugs, wires, went back through the valves, started engine and sprayed water on headers bye the heads and that's how I found the problem, it's a new dart block, forged rotating assembly, 13.1 pistons has a solid roller cam and lifters with afr220 heads, 1.6 roller rockers, engine has been started maybe 6 times since built, I'm stumped and need some advice on what it could be. Thx in advance.
 
I know this is silly to suggest, but having seen this issue before I have to ask??
did you install a 4/7 swap cam and not correct the firing order to match?
or forgot the change was required?
if you used a 4/7 swap cam and still use the 18436572 ignition firing order it won't work???
BTW your not alone if you did, I know a couple guys in FLA who spent hours trouble shooting before one remembered they ordered a 4/7 swap cam
 
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if not, return to the basics,
got compression?
got spark?
are you getting fuel?
verify the firing order?
verify the ignition timing?
look for vacuum leaks?
 
Yes it's not a 4/7swap cam, I'm going to look more into it tomorrow, I had to walk away I was frustrated, I'll let you know how it goes, Thanks
 
I wish I was local, things like this can be fun to diagnose and find a cure for :like:

personally Id pull both valve covers and get a breaker bar on the crank /damper bolt and bring the engine up on TDC watching the rockers on #1 , and rotate the engine watching the firing order and very carefully watch the rockers move and verify the rocker movement verify's the firing order and that there's not a worn cam lobe or two
yeah I know you, and every other person on the planet,(including myself for a few years ,)
think or thought why bother, you can do something similar using the starter,
....its just not nearly as easy to spot trouble issues..
trust me that's why I suggested the breaker bar and moving the crank about 45 then 90 degrees and checking rockers until the full 720 degree cycles checked
and yes it helps if theres TWO people and ideally your dampers marked every 90 degrees


yeah it helps if its not in gear, up on jack stands and youve removed all the spark plug
thus the engine spins far easier AND
SO YOU CAN DO A COMPRESSION TEST NEXT

verify you don't have a 4/7 swap cam timing even though that's not what you think you've installed
watch the intake rockers firing order how the rockers move or just try swapping the 4 and 7 wires on the distributor cap and see how it does or does not run

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Thx again for the information, I've tried different plugs and wires with no luck, I'm leaning towards something internally because I took the headers off and looked in exhaust ports on all cylinders and #7 #2 looked like they were not firing, compared to all other's, they had no carbon of any color on valves or exhaust port's, when plugs were pulled from those 2 dead cylinders they looked brand new, had no signs of fuel on them. Engine just sounds so healthy, can't imagine what it is going to be on all 8 when I find the problem, compression test is going to be done today and I will let you know. Thanks again for all the advice.
 
I'm back, I did a compression test on all cylinders and to my surprise they were within 5,lbs difference they were 180 to 185 let each cylinder set up to 5 minutes with barley any bleed off at all, started chasing wires and nothing noticeable, I getting to the point I'm going to contact Bullet cams and see if some how they sent me a 4,7 swap cam by mistake, the cam card does not say 4,7 swap nor did I order that when Bullet and I were working together for this cam, Time will tell.
 
everyone occasionally makes mistakes, it won't hurt a damn thing to test!
why not just swap the #4 and #7 plug wire on the distrib cap and see what happens when you start the engine as a fast simple test??
they may or may not have used the wrong cam billet, but if you swap ignition wire locations on the distributor cap and those cylinder's start working you'll know, if there's no change then you look further?
 
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