bad cam shaft?

[camjck89]

so today i went by to drop off my mirrors at the glass shop and on my way home i stopped by a little shop a co worker told me about. i wanted him to take a look at my quadrajet and tune it , due to the bogging issue when i hit the gas too hard.after listening to him bash the carb rebuild done on my quadrajet he said that it was the least of my worries, said i need a new motor, that this motor had a intake valve leak, and that the valves were possibly tightened too much that could cause the motor to pop back through the carburetor. then he said that the motor probably had a ton on miles on it (the inside of the valve covers are spotless. and it was family owned and told it hadn't even turned the odo over so they ere origional miles, 87235) and the camshaft lobes were most likely worn. so i diddnt know to believe him so i ask you guys, it this fixable through a new camshaft and pushrods and valves? if not what, is the motor just better off being rebuit?

[Lee H]

Wow, your truck must have a hard time getting around with that diagnosis! Does your ride run badly, (except for the bogging), missing, back firing, burn oil, stalling, hard starting? Second opinion is in order and a leak down test is highly recommended before rebuilding. The bogging is probably due to a bad accelerator pump. The accelerator pumps in most kits these days are not compatible with ethanol blends. I'd start with this: Get a good A pump from Sean Murphy Induction or Cliff Ruggles (simple google search). Verify rocker adjustment. Dial in distributor and dial in carb.

[LONGHAIR]

I would do a little more investigation before jumping off of that bridge.
A "leak-down" test can tell you a lot. Removing the valve covers and visually inspecting the rocker arm movement would be good too.

If in-fact the cam has lost a few lobes, it is going to take a total rebuild to fix it. Do not let anyone tell you that the rest of the bottom-end will be "ok" and just cut corners into a top-end job. When a cam goes flat, even on just a few lobes, the oil circulates all of those metal particles through everything. It take a total rebuild to get that cleaned out. If you don't it will happen again, much more quickly.

[camjck89]

Lee: the truck runs like a champ, sounds great (other than the exhaust leak) starts up every time, never misses a beat. and if i have the pedal pushed an 1/8th of the way down and go to 3/4 it will straight up move. its just that you cant hit the gass from a stop. thats why i went to get it tuned in the first place. doesnt burn oil or stall

[Fitz]

Originally Posted by camjck89

Lee: the truck runs like a champ, sounds great (other than the exhaust leak) starts up every time, never misses a beat. and if i have the pedal pushed an 1/8th of the way down and go to 3/4 it will straight up move. its just that you cant hit the gass from a stop. thats why i went to get it tuned in the first place. doesnt burn oil or stall

Sounds like the guy at that shop is about to start mining your wallet for a major chunk of change. If your engine really had all of the problems he claims I doubt that it would idle well or accelerate at all. Walk away from that shop as fast as you can. If you're curious, do a leak down test as Lee suggests. That should tell the story and this is something you can do yourself. I think Auto Zone will rent you a leak down test guage . then all you need is a compressor to pressurize the cylinders.

[RIA69]

If its a bad cam you will be able to hear it. especially when you take your foot off the gas.It makes a very loud popping noise almost like backfiring but worse. I just had this issue with my old 307. The cam had four (4) flat lobes on it and did not make it happy. I find all this out buy the way during a 1200 mile trip driving the truck from UT to KS. It made it but with a lot of issues. ANYWAY sorry. ya as stated above it will need a total rebuild. besides it will be worth it that way you KNOW what the condition of the engine is and can build it up your way. I got a full rebuild kit from summit racing for around $126. Just my opinion and thoughts.

[camjck89]

ok so say i do that test and hear something out the tailpipe or the carburetor is that something that can be fixed by swapping out parts or no? and if its not the valves then what could it be

[coloradosean2009]

Originally Posted by camjck89

Lee: the truck runs like a champ, sounds great (other than the exhaust leak) starts up every time, never misses a beat. and if i have the pedal pushed an 1/8th of the way down and go to 3/4 it will straight up move. its just that you cant hit the gass from a stop. thats why i went to get it tuned in the first place. doesnt burn oil or stall

Sounds like the accel pump, as a previous poster has stated.

[camjck89]

aye i believe im going to address that soon, but however would the accelerator be sending compressed gas back through the carburetor?

[coloradosean2009]

Originally Posted by camjck89

Lee: the truck runs like a champ, sounds great (other than the exhaust leak) starts up every time, never misses a beat. and if i have the pedal pushed an 1/8th of the way down and go to 3/4 it will straight up move. its just that you cant hit the gass from a stop. thats why i went to get it tuned in the first place. doesnt burn oil or stall

Originally Posted by camjck89

aye i believe im going to address that soon, but however would the accelerator be sending compressed gas back through the carburetor?

If your accelerator pump is not discharging a small squirt of gas at the exact time the throttle valve opens, the mixture becomes very lean. The lean mixture will cause the engine to "back fire." Sometimes this is accompanied with flames! Looks cool, but bad for the motor and a quadrajet. One backfire will blow out a powervalve on the QJ (or so I am told).

If you are having backfires through the carb, you better not jump to the accelerator pump conclusion though. More common cause of ultra lean condition is big vacuum leak. If you have ball of fire, cause is likely wrong firing order.

what was the last thing you did before the motor had the "bogging" problem?

[camjck89]

Originally Posted by coloradosean2009

If your accelerator pump is not discharging a small squirt of gas at the exact time the throttle valve opens, the mixture becomes very lean. The lean mixture will cause the engine to "back fire." Sometimes this is accompanied with flames! Looks cool, but bad for the motor and a quadrajet. One backfire will blow out a powervalve on the QJ (or so I am told).

If you are having backfires through the carb, you better not jump to the accelerator pump conclusion though. More common cause of ultra lean condition is big vacuum leak. If you have ball of fire, cause is likely wrong firing order.

what was the last thing you did before the motor had the "bogging" problem?

its never not had the problem i bought it got the QJ rebuilt and hei put on and driven it its always had this problem

[Blue Rat]

Originally Posted by LONGHAIR

I would do a little more investigation before jumping off of that bridge.
A "leak-down" test can tell you a lot. Removing the valve covers and visually inspecting the rocker arm movement would be good too.

If in-fact the cam has lost a few lobes, it is going to take a total rebuild to fix it. Do not let anyone tell you that the rest of the bottom-end will be "ok" and just cut corners into a top-end job. When a cam goes flat, even on just a few lobes, the oil circulates all of those metal particles through everything. It take a total rebuild to get that cleaned out. If you don't it will happen again, much more quickly.

I agree a total rebuild is the way to go. Peace of mind is worth a lot.

[camjck89]

not exactly what i hoped to hear but. so other than the rebuild kit i need a camshaft and new........pushrods and valves, maybe rockers, any thing else?

[rsavage]

You really need to diagnose the problem before jumping to the conclusion that you need to rebuild your engine.
Pull your valve covers. Disconnect the coil wire from the coil or cap ( take the 12 volt wire off the side of the HEI if you are not running a points distributor. Have someone crank it over while you check to make sure each valve is opening and closing (you will be able to see the rockers going up and down, being pushed up by the pushrods by the lifters that are riding on the cam lobes, and, in turn pushing down on the valve stems that are surrounded by the valve springs. If the rocker isn't pushing down on the valve (and providing that the rocker arm is adjusted properly) the lobe which should be egg shaped has been worn round on that particular valve.
If all the valves seem to be working correctly (appearing to open and close) you should adjust the lifters to insure that one hasn't been cranked down too far which would hold the valve open. Each cylinder should be at its top dead center when you adjust the two lifters at a time for that cylinder (piston at top of cylinder and both intake and exhaust valve closed meaning that the rocker won't be putting pressure down on the valve stem. Adjust them so there is no lash or slop. If you do it while it is running, you actually loosen each rocker, one at a time, until it begins to click, tighten until the clicking stops and then go a little further 1/4 to 1/2 turn. Specs probably say 3/4 turn but on an engine with some time on it I've found it is maybe a little too much. Only have one valve cover off at a time if you do it while it is idling as a lot of oil goes over the lip of the head. It can get messy and you have to work quickly (5/8" socket, ratchet and extension will be needed). If you adjust it not running (static) I just take them to the point where there is no lash when you grab and try and move the rocker up and down when the cylinder is at TDC.
If the cam is good and the lifters are adjusted correctly, button it up and check your point dwell setting them to 30 -32 degrees at 600-800 rpms, then time the engine with a timing light at 6-8 degrees BTC with the vacuum advance hose off the distributor and plugged at about 600-700 rpms. Mark your balancer slot and the spot on the timing tab with chalk first so you will be able to see it with the timing light. You will need a 9/16" open end wrench to slightly loosen the distributor hold down bolt if it is necessary to adjust the timing - just so that you can move the distributor. Move it a little and check with the light to see if you are heading in the right direction.
Make sure your plug wires are routed to the correct cylinder, that they are in good shape, and that they are not laying against the exhaust shorting out. Check your spark plugs. If they are old change them making sure to correctly gap them.
Change the small filter in the Qjet inlet and your inline filter if you have one and it is older.
Now, if you have tuned the motor as above, you have eliminated other possible causes of hesitation and you can get into the carb if necessary. It might be something as simple as it needing a cleaning and a rebuild kit with a new accelerator pump but you have to diagnose first.
Good luck and Keep us posted.

[piecesparts]

Agree with all of these guys..... Do a little diagnosis first and then make plans or assumptions from that info.

If the truck has a stutter or miss in it's performance, then I would consider a bad cam as a possibility. If there is backfiring, then it could be a valve. The leak down test will tell you a lot about the cylinders and the upper end of the engine. Since you say the truck starts easily and runs quite well, then I would not be too scared yet.

Rebuild or replace the carb and see what happens there---You know that it needs to be worked, so after the diagnosis, do the carb first and then plan any other investments later.

[camjck89]

hmmmm. thanks r savage looks like ill have to bust out the other truck while i do check all those variables. or untll i get time to.

[dadsworktruck]

i always have a moto. do the simple things first, such as how old is the gas, how long has it been since a fuel filter change,is the fuel all gumed up and blocking the fuel lines,so many things, so easy to armchair quarterback on here too, but one thing is for sure there has been a butt load of people suckered into engine rebuilds for a 2.00 part so be careful, and good luck..

[beautimus]

OK dude, it honestly sounds like you are being suckered to me.

1 how indepth did this mechanic friend of yours go in his diagnostics?

If he spent 15 minutes with your truck and gave you all these diagnosis, then i would suspect that he either A. Is about to do needless repairs.
Or B. doesn't have a clue what the problem is, but feels that he can solve the problem by rebuilding everything.
or C. doesn't know his butt from first base and is about to screw up your truck.

If the guy spend several hours, pulled the valve covers, ran a compression check on all eight cylinders, and did a check on vacccuum. he may have some idea of what he is talking about.
now a word about worn camshafts. If you camshaft is original and has lots of miles on it then it may be worn down enough to cause a problem. but try readjusting the valves, it may be normal wear. not a big problem, If it doesn't clear it up do a cam swap, with new lifters and change the oil frequently for a few thousand miles you will be fine.

the Advise you were given about bad cam lobes causing major issues is sound but, thats only in casses of faulty camshafts and lifters that grind the lobes of the cam extremely fast, as in big chunks, not microscopicly (as in normal wear).
Cams that were installed without proper lubrication, not breaking the cam in properly, valves set to tighly cause these problems.
I suspect that in your case thats not the issue, because if you were driving this thing around continually , you would notice the engine deteriorate noticably in a short period of time. Go get a second opinion before you lay down your money. Just my 2 cents worth

[Lee H]

Originally Posted by camjck89

Lee: the truck runs like a champ, sounds great (other than the exhaust leak) starts up every time, never misses a beat. and if i have the pedal pushed an 1/8th of the way down and go to 3/4 it will straight up move. its just that you cant hit the gass from a stop. thats why i went to get it tuned in the first place. doesnt burn oil or stall

From the limited info you have told us right now I would suspect a timing issue first, then carb. Make sure the mechanical advance is free and the vacuum advance is working. These two things are critical to drivability. Set timing to 12-14 advance at idle with vac disconnected and try it out. Next off to the accelarator pump. Then fine tuning time on both.

[BLACK AND BLUE 67-72]

I suspect timing or a carb problem, check and recheck timing!! If you get the timing perfect and it still does it try putting a different carb on it, if it still does it then start doing the tests as stated above!!

[70BLAZERX2]

today's motor oil does not have "ZINC" in them anymore wich is vital for camshaft life.. summitracing sells the additive for older engines..

I had 2 cams go out in the last year..on motors with less than 10,000 miles on them..valve were adj. right..

It is just another way for them to kill old engines..one at a time.

If you can get an upgrade roller cam..kit..The oil wont hurt them.

[LONGHAIR]

Originally Posted by beautimus

now a word about worn camshafts. If you camshaft is original and has lots of miles on it then it may be worn down enough to cause a problem. but try readjusting the valves, it may be normal wear. not a big problem, If it doesn't clear it up do a cam swap, with new lifters and change the oil frequently for a few thousand miles you will be fine.

the Advise you were given about bad cam lobes causing major issues is sound but, thats only in casses of faulty camshafts and lifters that grind the lobes of the cam extremely fast, as in big chunks, not microscopicly (as in normal wear).

Not so, this is the exact advice I caution against. "Worn enough to cause a problem" means virtually any wear at all. Cams and lifters are "case hardened" which will stand for almost no wear at all. This is why that "failures" are sudden and seemingly fairly extreme. Once a cam makes it through the break-in process and is at least adequately lubricated, it will last a very long time. Once the wear "starts" it goes very quickly, the case hardening is very thin. Think of it like chrome plating on a bumper, one you get through that outer layer, it's just raw steel.
You will not get "enough wear" to cause a performance issue until the castastropic failure. At that point, as stated before, it needs a major rebuild. Hot tanking the block and starting from the ground up. Trying to "refresh it" with a new cam will result in a quick failure.

[raycow]

A bad cam doesn't require black magic or esp to diagnose. If you take off the valve covers you can SEE it.

Ray

[LONGHAIR]

Originally Posted by raycow

A bad cam doesn't require black magic or esp to diagnose. If you take off the valve covers you can SEE it.

Probably in more than one way. You may see the silver metallic sludge before even turning the engine over to watch the rocker-arms.

[4LUG39]

Originally Posted by ria69

if its a bad cam you will be able to hear it. Especially when you take your foot off the gas.it makes a very loud popping noise almost like backfiring but worse. I just had this issue with my old 307. The cam had four (4) flat lobes on it and did not make it happy. I find all this out buy the way during a 1200 mile trip driving the truck from ut to ks. It made it but with a lot of issues. Anyway sorry. Ya as stated above it will need a total rebuild. Besides it will be worth it that way you know what the condition of the engine is and can build it up your way. I got a full rebuild kit from summit racing for around $126. Just my opinion and thoughts.

^2