Poor fuel mileage, BANG! Engine trouble! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

69GMC910 · 12-30-2002, 02:15 AM

Installed a performer plus cam in the 350, performer intake, and performer 600cfm carb also bolted on. Noticed a little power increase, and HIGH FUEL CONSUMPTION. The rest of the engine is stock and previously ran 20mpg using the 4.54 litres=1 Gallon.

So I put about 200-250 miles on the truck breaking the cam in. All is well at this point.

So today I went for a 250 mile road trip. I made it 87 of those miles and had to turn back home.

The engine started sounding rough and when I went to accelerate it would knock REALLY bad. Now I think I may have adjusted the pushrods incorrectly, is this would most of you would assume. I have done pushrods before and been successful, but I don't know about this time.

I had slack in them when they were off the cam lobe, I just hope i didn't have too much slack.

Would improperly adjusted pushrods cause poor fuel economy?

Help, I have to fix this in the morning!!!!

THANX!

FRENCHBLUE72 · 12-30-2002, 02:23 AM

You said knock like bottom end knock or like a lifter went bad did you also replace lifers or did you reuse your old ones????

cableguy0 · 12-30-2002, 02:24 AM

yea when u do the valve adjustment u need to follow the directions that come with the cam. the rocker should be tightened down until theres no more up and down play then another half turn.did u do a proper break in on the cam. u need to let that thing run for about 20 mins at nothing below 2000rpm to properly break in the cam.otherwise its just gonna wipe itself out like ur describing now. im willing to bet that cam and lifters is toast form what u described. dont run anymore until u tear it apart. no need to spew more metal through the motor

mikep · 12-30-2002, 02:29 AM

If your valves are constantly open or open longer then they should be you wont be developing much cylinder pressure and yes you would be getting bad gas mileage. I assume your'e using hydraulic lifters. try readjusting them. Theres some chart you can use to adjust them so you dont have to do each cylinder individually . Phooey ! Bring it around to each cylinders tdc. Heres a tip that will save you a lot of frustration . Invest $25 in a set of polylocks ! I used to have a hell of a time adjusting the hydraulics until I started using polylocs. Nothing could be easier ! Bring it around to that cylinders TDC loosen the loc, loosen the nut and then tighten it with your fingers until you cant tighten it any more . Then tighten it another 1/2- 2/3 of a turn with a wrench. Do the other valve on that cylnder then tighten the jam set screws. Go on to the next cylinder. Its so easy . It works best after the engine has run for a while so the lifters are pumped up.

before you get too carried away drain your oil and see if it looks clean or if its silvery. Cut open the filter. If theres a lot of shiny sludge then your filters packed and you bypassed the filter long enough to wipe your bearings out and probably some crank journals.

69GMC910 · 12-30-2002, 02:29 AM

I had more slack than you have described. I did the 20 minute break-in over 2000rpm. It is definitely a top end knock no questions asked. New lifters came with cam, used all the assembly lube stuff. I am really hoping it is pushrods.

Thanks for the help, keep em coming!

69GMC910 · 12-30-2002, 02:32 AM

When I compression tested it, all eight were between 168-180psi

Blue_71 · 12-30-2002, 03:59 AM

if you can wait untill tomarow i can get you the easy way to adjust them, it invovles getting #1 to TDC compression, then adjusting half of them (certain ones) then turn it 360 degrees and adjust the rest

btw-- ill look around tonight

Hooter · 12-30-2002, 04:04 AM

The way I usually adjust them is as follows:
I have a valve cover that a cut the center out of to keep oil from splattering everywhere.
i start the motor up, loosen off the rocker till it makes noise, then tighten it till it stops making noise then a quarter turn

bigjimzlll · 12-30-2002, 08:44 AM

for US gallons muliply by 3.8

72K10 · 12-30-2002, 08:44 AM

Out of left field, but you may want to recheck your timing and idle fuel mixture screws. Maybe your distributor is a little loose and rotated? Maybe fuel is running too lean? Either will cause knocking on acceleration. Sometimes it's the easy things.

69GMC910 · 12-30-2002, 10:12 AM

Okay, it's morning here, I'm gonna go pull the pushrods and see how they look. I'll get back to you if I have time for an update!

Thanks !

69GMC910 · 12-30-2002, 01:00 PM

Okay all, here's the scoop.

Pulled the valve covers off and found that #5 exhaust lifter was crooked, removed rocker and pushrod, pushrod bent, top of valve is rounded off.

My dad thinks he is joe mechanic and he wants to file the rounded part flat on the valve. I say it needs a new valve.

Opinions and a reason why this would happen would help me a lot.

Thanks!

69GMC910 · 12-30-2002, 01:22 PM

Back to the top!

69GMC910 · 12-30-2002, 02:10 PM

Just spoke to an engine rebuilder and he told me that the fix for this problem is new style rockeres that have some sorta rails that prevent the rocker from sliding off the valve. Whaddaya think???

Thanks

69GMC910 · 12-31-2002, 12:00 AM

we put on the new style rockers and replaced the bent pushrod,we set the valves as hooter suggested and the 350 ran just fine. then the young fellow headed out on the 250 mile road trip and made it with no problem. thanks for all the advice. joe mechanic

Jwill41 · 12-31-2002, 09:38 AM

I always go 3/4 turn after the ticking stops. (1/4 at a time) Have I been wrong all these years?

12-30-2002, 02:23 AM	#2
FRENCHBLUE72 PROJECT 7DEUCE Join Date: Dec 2002 Location: GRANTS PASS OR Posts: 21,606	You said knock like bottom end knock or like a lifter went bad did you also replace lifers or did you reuse your old ones???? __________________ GO BIG GREEN GO DUCKS MEMBER #6377 72 k-5 daily driver 6'' lift 35'' 350-350-205 slowly getting rust free. Project "7DEUCE" check out my build http://67-72chevytrucks.com/vboard/s...d.php?t=267665 Tim Powell..R.I.P EastSideLowlife..... R.I.P..

12-30-2002, 02:24 AM	#3
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	yea when u do the valve adjustment u need to follow the directions that come with the cam. the rocker should be tightened down until theres no more up and down play then another half turn.did u do a proper break in on the cam. u need to let that thing run for about 20 mins at nothing below 2000rpm to properly break in the cam.otherwise its just gonna wipe itself out like ur describing now. im willing to bet that cam and lifters is toast form what u described. dont run anymore until u tear it apart. no need to spew more metal through the motor __________________ 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.

12-30-2002, 02:29 AM	#4
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	If your valves are constantly open or open longer then they should be you wont be developing much cylinder pressure and yes you would be getting bad gas mileage. I assume your'e using hydraulic lifters. try readjusting them. Theres some chart you can use to adjust them so you dont have to do each cylinder individually . Phooey ! Bring it around to each cylinders tdc. Heres a tip that will save you a lot of frustration . Invest $25 in a set of polylocks ! I used to have a hell of a time adjusting the hydraulics until I started using polylocs. Nothing could be easier ! Bring it around to that cylinders TDC loosen the loc, loosen the nut and then tighten it with your fingers until you cant tighten it any more . Then tighten it another 1/2- 2/3 of a turn with a wrench. Do the other valve on that cylnder then tighten the jam set screws. Go on to the next cylinder. Its so easy . It works best after the engine has run for a while so the lifters are pumped up. before you get too carried away drain your oil and see if it looks clean or if its silvery. Cut open the filter. If theres a lot of shiny sludge then your filters packed and you bypassed the filter long enough to wipe your bearings out and probably some crank journals. __________________ No truck :-( Last edited by mikep; 12-30-2002 at 02:32 AM.

12-30-2002, 02:32 AM	#6
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	When I compression tested it, all eight were between 168-180psi __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

12-30-2002, 04:04 AM	#8
Hooter My other Love Join Date: Aug 2001 Location: Castlegar B.C. Canada Posts: 4,085	The way I usually adjust them is as follows: I have a valve cover that a cut the center out of to keep oil from splattering everywhere. i start the motor up, loosen off the rocker till it makes noise, then tighten it till it stops making noise then a quarter turn __________________ Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life

12-30-2002, 02:15 AM	#1
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	Poor fuel mileage, BANG! Engine trouble! Installed a performer plus cam in the 350, performer intake, and performer 600cfm carb also bolted on. Noticed a little power increase, and HIGH FUEL CONSUMPTION. The rest of the engine is stock and previously ran 20mpg using the 4.54 litres=1 Gallon. So I put about 200-250 miles on the truck breaking the cam in. All is well at this point. So today I went for a 250 mile road trip. I made it 87 of those miles and had to turn back home. The engine started sounding rough and when I went to accelerate it would knock REALLY bad. Now I think I may have adjusted the pushrods incorrectly, is this would most of you would assume. I have done pushrods before and been successful, but I don't know about this time. I had slack in them when they were off the cam lobe, I just hope i didn't have too much slack. Would improperly adjusted pushrods cause poor fuel economy? Help, I have to fix this in the morning!!!! THANX! __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

12-30-2002, 03:59 AM	#7
Blue_71 Bloo Join Date: Feb 2001 Location: Barren County Kentucky Posts: 6,283	if you can wait untill tomarow i can get you the easy way to adjust them, it invovles getting #1 to TDC compression, then adjusting half of them (certain ones) then turn it 360 degrees and adjust the rest btw-- ill look around tonight

12-30-2002, 08:44 AM	#9
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	for US gallons muliply by 3.8 __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

12-30-2002, 08:44 AM	#10
72K10 Registered User Join Date: Dec 1999 Location: New York Posts: 288	Out of left field, but you may want to recheck your timing and idle fuel mixture screws. Maybe your distributor is a little loose and rotated? Maybe fuel is running too lean? Either will cause knocking on acceleration. Sometimes it's the easy things. __________________ RLTW 70C10 72K10 72K10 Cheyenne 72C10 Cheyenne Super

12-30-2002, 10:12 AM	#11
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	Okay, it's morning here, I'm gonna go pull the pushrods and see how they look. I'll get back to you if I have time for an update! Thanks ! __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

12-30-2002, 01:00 PM	#12
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	Okay all, here's the scoop. Pulled the valve covers off and found that #5 exhaust lifter was crooked, removed rocker and pushrod, pushrod bent, top of valve is rounded off. My dad thinks he is joe mechanic and he wants to file the rounded part flat on the valve. I say it needs a new valve. Opinions and a reason why this would happen would help me a lot. Thanks! __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

12-30-2002, 01:22 PM	#13
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	Back to the top! __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

12-30-2002, 02:10 PM	#14
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	Just spoke to an engine rebuilder and he told me that the fix for this problem is new style rockeres that have some sorta rails that prevent the rocker from sliding off the valve. Whaddaya think??? Thanks __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

12-31-2002, 12:00 AM	#15
69GMC910 MOTORHEAD! Join Date: May 2000 Location: Devon AB, Canada Posts: 849	we put on the new style rockers and replaced the bent pushrod,we set the valves as hooter suggested and the 350 ran just fine. then the young fellow headed out on the 250 mile road trip and made it with no problem. thanks for all the advice. joe mechanic __________________ 82 GMC High Sierra VortecPro 496 12 Bolt, 3.42's AFR 265 Holley 850 Performer RPM Air Gap Hooker 2455's TCI Turbo 400 Super Street Fighter TRRC 12 Bolt Eaton Posi Mark Williams Axles Cal-Tracs Hoosier 30x10.5 Radial Slick Full weight long box pickup Current best- 11.33@117mph

12-31-2002, 09:38 AM	#16
Jwill41 Registered User Join Date: Aug 2002 Location: Farmers Branch, Tx Posts: 1,009	I always go 3/4 turn after the ticking stops. (1/4 at a time) Have I been wrong all these years? __________________ http://www.picturetrail.com/jwill41 67 1/2 ton GMC short step side 68 1/2 ton Chevy long fleet side 72 1/2 ton Chevy Suburban 99 1/2 ton Chevy Suburban founder (and only member) of the primer/clearcoat club



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