Help!! Backfiring after re-doing top end

NotchJohnson · 04-16-2003, 11:26 AM

Did you make sure you set the rocker arms correctly? If your heads are miled .035, the point in which you reach zero lash is going to be different than on an untouched engine. Pull your valve covers off and loosen your rockers. Put the engine at O degrees TDC. Make sure the dist. is pointing to the number one plug. Slowly tighten the rocker arm, while spinning the pushrod al the while between your fingers. Whenever you feel the slightest resistence on the pushrod, stop, youve reached zero lash. Now tighten the rocker to 20 ft. lbs. If it takes you more than one full turn to reach 20 lbs, you need shims. Thick shims represent one full turn, and thin shins represent 1/2 turn. Ive gone through this before when i did my head swap, and all my rockers need .090 of shims! The motor was backfiring like crazy, but I forgot to check the rockers. Here is the exact procedure:

Get engine to tdc, make sure dist. is pointing to #1. Tighten the following rockers to zero lash, then to 20 ft. lbs. (make sure you note how many turns it takes)
cylinder #1 intake and exhaust
#3 exhaust
#4 intake
#7exhaust
#8 intake

Now rotate the engine 360 degrees, so it is at tdc again, repeat the procedure for:
#3 intake
#2 exhaust
#7 intake
#6 exhaust

Now rotate it 90 degrees and do:
#2 intake
#4 exhaust
#5 intake and exhaust
#6 intake
#8 exhaust

I am willing to bet money you are gonna need shims, the only place i found them was through jegs. Try that and keep us informed what you find out.

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04-16-2003, 11:26 AM	#2
NotchJohnson Registered Member Join Date: Oct 2001 Location: Florida Keys Posts: 593	Did you make sure you set the rocker arms correctly? If your heads are miled .035, the point in which you reach zero lash is going to be different than on an untouched engine. Pull your valve covers off and loosen your rockers. Put the engine at O degrees TDC. Make sure the dist. is pointing to the number one plug. Slowly tighten the rocker arm, while spinning the pushrod al the while between your fingers. Whenever you feel the slightest resistence on the pushrod, stop, youve reached zero lash. Now tighten the rocker to 20 ft. lbs. If it takes you more than one full turn to reach 20 lbs, you need shims. Thick shims represent one full turn, and thin shins represent 1/2 turn. Ive gone through this before when i did my head swap, and all my rockers need .090 of shims! The motor was backfiring like crazy, but I forgot to check the rockers. Here is the exact procedure: Get engine to tdc, make sure dist. is pointing to #1. Tighten the following rockers to zero lash, then to 20 ft. lbs. (make sure you note how many turns it takes) cylinder #1 intake and exhaust #3 exhaust #4 intake #7exhaust #8 intake Now rotate the engine 360 degrees, so it is at tdc again, repeat the procedure for: #3 intake #2 exhaust #7 intake #6 exhaust Now rotate it 90 degrees and do: #2 intake #4 exhaust #5 intake and exhaust #6 intake #8 exhaust I am willing to bet money you are gonna need shims, the only place i found them was through jegs. Try that and keep us informed what you find out. __________________ 89 notch-finally not stock!! ported gt40's, ported cobra intake, 65mm tb, 75mm maf, mac cai, lt's,prochamber, fms 1.6 rr, 125 shot.