5.7 vortec in 72 c10 issues - The 1947 - Present Chevrolet & GMC Truck Message Board Network

lanehicks76 · 08-02-2015, 07:35 PM

Hi guys. This is my first post, but I have been reading through this site for some time now. I recently bought a roller 72 c10 long bed. I had a 98 5.7 vortec from a truck that I put comp cams magnum 280, comp cams bee hive springs with required hardware, aluminum dual plane intake, holley 750 vacuum secondaries, hooker super comp 1 7/8 headers and jegs quite flow fuel pump. I installed cam straight up as per comps tech line. IM having trouble with backfiring through carb and exhaust. It acted like the valves were to tight, but I just ran them again to zero lash plus 1/4 turn. Also I have played with timing and all the same. Has anyone had this popping, backfiring issue. Thanks in advance . Oh yeah all parts are new and the long block was running strong before it was pulled.

geezer#99 · 08-02-2015, 07:44 PM

What method did you use to run the valves?
The spin the pushrod or the wiggle the pushrod method.
It's likely you have a couple valves hanging open!
http://www.crankshaftcoalition.com/w...raulic_lifters

lanehicks76 · 08-02-2015, 08:55 PM

Hi there. I first set them on stand. Then I ran then with engine runnin .

geezer#99 · 08-02-2015, 10:06 PM

What are you running for timing?
Have you proven your timing tab/balancer are accurate?

lanehicks76 · 08-03-2015, 01:41 AM

Yes it doesn't matter where timing is. Initial set at 10. Then total 38. Then moved dist. Around. No changes with backfiring

cadillac_al · 08-03-2015, 06:57 AM

Running the valves with the engine running is pretty fool proof imo so they must be adjusted close enough. If you are positive that you don't have a spark plug wire crossed, then you must have a cam/lifter problem and will have to have a closer look. I crossed a couple plug wires a few years ago and it ran pretty decent until I got on the throttle and I got nice machine gun backfires. I ran it like that for a couple weeks because I was positive the wires were on correctly and an old dog like me couldn't make such a rookie mistake.

fleetsidelarry · 08-03-2015, 07:14 AM

x2 on the crossed wires, especially 5 and 7. could be a bit much on the total timing for a vortec

lanehicks76 · 08-03-2015, 08:41 AM

I'm gonna change cap when I get to the shop if no good I will measure all valve travel. Thanks for all replies.
Posted via Mobile Device

geezer#99 · 08-03-2015, 09:19 AM

Look for coil bind too!
Vortec's don't like more than 32 degrees too!

BossHogg69 · 08-03-2015, 04:22 PM

I know you said it's a '98 block, but is that magnum 280 a hyd flat tappet or hyd roller?

cableguy0 · 08-03-2015, 06:49 PM

Did you break in the cam properly and use plenty of assembly lube? Did you use a zinc additive during break in. If that cam is a flat tappet cam I really hope you didn't fire that engine up and let it idle while you attempted to adjust the valves. The first 20 minutes of a flat tappet cams life is the most important. If you didn't do proper break in I would suspect that you wiped the cam out.

08-02-2015, 07:35 PM	#1
lanehicks76 Registered User Join Date: May 2015 Location: Rotan TX Posts: 13	5.7 vortec in 72 c10 issues Hi guys. This is my first post, but I have been reading through this site for some time now. I recently bought a roller 72 c10 long bed. I had a 98 5.7 vortec from a truck that I put comp cams magnum 280, comp cams bee hive springs with required hardware, aluminum dual plane intake, holley 750 vacuum secondaries, hooker super comp 1 7/8 headers and jegs quite flow fuel pump. I installed cam straight up as per comps tech line. IM having trouble with backfiring through carb and exhaust. It acted like the valves were to tight, but I just ran them again to zero lash plus 1/4 turn. Also I have played with timing and all the same. Has anyone had this popping, backfiring issue. Thanks in advance . Oh yeah all parts are new and the long block was running strong before it was pulled.

08-02-2015, 07:44 PM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,731	Re: 5.7 vortec in 72 c10 issues What method did you use to run the valves? The spin the pushrod or the wiggle the pushrod method. It's likely you have a couple valves hanging open! http://www.crankshaftcoalition.com/w...raulic_lifters

08-02-2015, 08:55 PM	#3
lanehicks76 Registered User Join Date: May 2015 Location: Rotan TX Posts: 13	Re: 5.7 vortec in 72 c10 issues Hi there. I first set them on stand. Then I ran then with engine runnin .

08-02-2015, 10:06 PM	#4
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,731	Re: 5.7 vortec in 72 c10 issues What are you running for timing? Have you proven your timing tab/balancer are accurate?

08-03-2015, 01:41 AM	#5
lanehicks76 Registered User Join Date: May 2015 Location: Rotan TX Posts: 13	Re: 5.7 vortec in 72 c10 issues Yes it doesn't matter where timing is. Initial set at 10. Then total 38. Then moved dist. Around. No changes with backfiring

08-03-2015, 06:57 AM	#6
cadillac_al Registered User Join Date: Oct 2013 Location: Maine Posts: 2,375	Re: 5.7 vortec in 72 c10 issues Running the valves with the engine running is pretty fool proof imo so they must be adjusted close enough. If you are positive that you don't have a spark plug wire crossed, then you must have a cam/lifter problem and will have to have a closer look. I crossed a couple plug wires a few years ago and it ran pretty decent until I got on the throttle and I got nice machine gun backfires. I ran it like that for a couple weeks because I was positive the wires were on correctly and an old dog like me couldn't make such a rookie mistake. __________________ 76 Chevy K20 76 GMC K15 77 Chevy C10 77 Chevy K10

08-03-2015, 07:14 AM	#7
fleetsidelarry Senior Car Nut Join Date: Jan 2008 Location: shellman bluff, GA Posts: 1,411	Re: 5.7 vortec in 72 c10 issues x2 on the crossed wires, especially 5 and 7. could be a bit much on the total timing for a vortec __________________ Larry

08-03-2015, 08:41 AM	#8
lanehicks76 Registered User Join Date: May 2015 Location: Rotan TX Posts: 13	Re: 5.7 vortec in 72 c10 issues I'm gonna change cap when I get to the shop if no good I will measure all valve travel. Thanks for all replies. Posted via Mobile Device

08-03-2015, 09:19 AM	#9
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,731	Re: 5.7 vortec in 72 c10 issues Look for coil bind too! Vortec's don't like more than 32 degrees too!

08-03-2015, 04:22 PM	#10
BossHogg69 motor exploder Join Date: Mar 2009 Location: Pittsburgh, PA Posts: 2,346	Re: 5.7 vortec in 72 c10 issues I know you said it's a '98 block, but is that magnum 280 a hyd flat tappet or hyd roller? __________________ Adam 1969 Chevy CST/10 stepside, DART Big M/TREMEC Magnum Extreme/3.73's w/Detroit Truetrac 1965 Chevy Bel Air Wagon (daily driver), 327/TH350,10 bolt w/3.08's 1961 Chevy Bel Air Sport Coupe, ZZ454/M21/9" rear w/3.50's & Detroit Truetrac 2005 GMC 1500 ccsb 2wd, 6.0L/4L65e/3.73 G80 2006 GMC 2500HD ccsb 4x4, DMax LBZ/Allison 6spd/4.56's w/Detroit TrueTrac Use the SEARCH function on this forum - it is your friend!!

08-03-2015, 06:49 PM	#11
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	Re: 5.7 vortec in 72 c10 issues Did you break in the cam properly and use plenty of assembly lube? Did you use a zinc additive during break in. If that cam is a flat tappet cam I really hope you didn't fire that engine up and let it idle while you attempted to adjust the valves. The first 20 minutes of a flat tappet cams life is the most important. If you didn't do proper break in I would suspect that you wiped the cam out. __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.



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