OK...before I go pulling the front cover and timing chain...AGAIN...I want to run something out here..

My car was CRACKING back through the carb. Which to me means that I have a INTAKE valve remaining open during the plug firing. I pulled the plug wires and found the offending valve (number 6)...pulled the valve covers, and number 6 intake valve is only moving a LITTLE bit...maybe .25"...rocker is not loose, and pushrod is snug...(never adjusted it...)

All the rest of the poss. have been tried...wires, plugs, timing chain..

Here's my thought...If the cam/lifter is worn, wouldn't that keep the intake valve from opening? ...not closing should mean a bad spring?

Am I right here? Or am I missing something. How do I check for a bad spring?

Help me out before I waste another weekend...

thanks

Jim

 

A non-opening intake valve will not cause backfiring through the carb. A non-closing one will, but will make the engine produce essentially no power at all, might not even be able to run.

Sounds to me like you have a rolled cam lobe. It's cam & lifters time. Check carefully for a blown head gasket too (between #4 & #6, where they always blow) while you're at it.

 

Sorry...I meant

"keep the intake valve from CLOSING"

but doesn't the vavle spring CLOSE the valve? What is the cam doing or not doing that is preventing the valve from closing?

Jim

 

That's just it. The cam won't do that.

It's possible that the spring is simply broken, which woul dkeep the valve from closing. If that's the case, the rocker should be ridiculously loose; or if you had readjusted it to take up the slack, the nut would be like ¼" farther down the stud than the others.

Are you sure it's the intake valve, and not the exhaust valve? Is it the 5th one back from the front of the motor, or the 6th one?

 

Thanks for the help...The rocker is not loose, and has never been adjusted...I will check the operation again, but I was certain it was the 6th one...plus a exhaust vavle wouldn't cause it to crack back through the carb...could it...

ANY and ALL help apprecaited!

Jim

 

One other thing...it didin't seem to crack ALL the time...just under load...but when I pulled the wires of the number 6 cylinder it didn't do it at ALL...barely ran though...I was thinking of just calling it a V7 (267 CI)javascript:smilie('')
big grin

Thanks again

Jim

 

Anymore Comments...?

 

Pressurize #6 through the spark plug hole with compressed air, and see where it's leaking to.

You may find you have 2 problems: blown head gasket for sure, maybe a cam lobe down.

 

Blown head gasket? Why? And I still don't understand your logic on the worn cam lobe? I am NOT argueing...just confused...

The cam lifts the valve...the spring closes the valve...if it is NOT closing...it must be the spring? How does the head gasket get in here?

Thanks

 

Put compressed air into the #6 spark plug hole and see where it comes out. That will tell the tale. Either air will appear in the #4 cyl, in which case the spitting back through the carb is caused by a head gasket leak; or it will appear in the #6 intake runner, in which case you have some sort of problem with the #6 intake valve; or it will stay put, in which case both of the #6 valves are closing & sealing properly and the head gasket is OK, and you have a rolled #6 exhaust valve, and you've just mis-counted and think it's the intake.

Just do it and let us know what you find. The symptoms you have described are not consistent with each other.

If a valve isn't closing for whatever reason, and you haven't adjusted the valves, you'd have a rocker flopping around in the breeze. There's no way you could have failed to notice that.

Once again, your current info is not internally consistent. No one defect can possibly account for all the symptoms you are reporting. We need more info.

 

Will do...thanks for the comments! Looks like I have more work to do this w/e...

Jim

 

Perform the leakage test as RB suggests.

And not to confuse the matter, but a bent valve will also not close completely, even if the spring is intact.

 

Is the rocker stud pulling out? I think it is time for a cam and lifters too. You did say the travel on that one valve appeared different than the others. Like RB said, an intake valve still open or not closing during firing will cause it back fire through the carb. The other logical thing it could be is a burnt or bent valve or a valve that is not seating properly. You could always measure the lift too on the cam lobe and compare to the other intake valves. www.cranecams.com has great instructions and a list of tools you would need to do this

 

I've seen a broken valve spring (82 4wd Blazer, 6.2 liter oil burner) cause problems while still (varely) closing the valve. Until it broke in a second spot. It was broke under the cap that sits on top of the valve and the Chevy garage didn't notice it when they replaced the broken rocker arm shaft it caused. The next year the rocker arm shaft broke again and while doing that one myself I saw the valve spring was broke just below the cap. When I replaced it I found it was also broke inside the cap and by the wear patterns I could tell it had been broke a long time at the upper break. This was on the #6 cyl. exhaust valve. It caused lots of black smoke and a hard knocking sound out the right pipe until the engine warmed up (ran like that for 2 years before it broke the rocker shaft the first time). When the spring broke in the second spot it broke the replaced rocker shaft real quick.

 

Thanks for all the help on this one...I pulled the lifters, and number 6 intake was damaged (dished out by .063")
M
One the positive side, I went to the annual flea market at Maple Grove this weekend, and picked up a new cam/lifters/covers/gaskets/front cover all for less than $60...

Nice to save a little cash...well I am gonna pull the cam tomorrow night.

I did check the compression, and the cylinders are fine (150 on both sides of number 6)...so it looks like I can save the head gasket for another time...

Thanks again...now anyone want to help me get a 3/8 hex bolt out of the oil pan in my olds 455 in my 70 442...after it dropped down the valley...

If it is not 1 thing it is 10...But at least it's SPRING!

Jim

 

Well I pulled the cam, and as expected, it was missing a lobe...almost completely gone. Put in new cam, lifters, and began reassembling...but the damn intake bolts wont line up. Looks like the gaskets I got are 4 times as thick (1/8") as the steel orignals. I guess I could open the holes a little in the intake, but MAN what a PIA...now I have to wait MORE time...Any comments on gaskets...???

Thanks again!

Jim

 

I got the Victor Reinz gaskets at NAPA they lined up perfectly. I wouldnt rape the intake for gaskets. Gaskets are cheap get the right ones. The gaskets I got at NAPA were far better than the felpros I used earlier. Thats just my opinion though

 

Well I replaced the cam/lifter/timing chain/gears, put in new intake gaskets, se the valves, and started the car. but NOW I get a LOT of white smoke out of the exhaust, plus the oil is brown...and it will barely run...sounds like a head gasket..PIA...!

Fortunately, i have another set of heads (601) already done and ready. But from what I've read on the board, I may have problems getting them off.

I already have the a/c compressor and condenser and all of the plumbing pulled off (it was empty when I got it), but the case attached to the firewall is still in place. All the top of the engine is off, and all the access and air pump.

I have an extra set of exhaust manifolds with the AIR tubes in, so I was thinking of cutting the tubes on the ones in the car, and pulling them off. The heads have never been off the car. Can you normally get the manifold bolts off from up top or below.

ALL help appreciated!

 

You should be able to take everything off from the top. I didnt have a problem taking the heads off you wont either. If it is stripped down like mine hehe no emissions it can be done in a day or 2. what ever you do dont run it anymore the coolant will destroy bearings. Just pray it is a gasket and not a cracked block good luck.