C-2 L79 Engine problem

[Ron Still]

Need some advice. My engine has developed a significant knocking sound that sounds like it's from the area of cylinder 5 or 7 (left bank). Now it is burning oil (blue smoke) from left bank and you can smell engine oil in the engine compartment. There are no leaks I can see. I have not checked spark plugs or anything else yet (too upset at moment!). The engine was rebuilt 13 years ago with the cylinders bored .030 over and new pistons and valves installed. It probably has less than 200 miles since then as it took me that long to finish the restoration. The little bit I did drive the car last 2 summers the engine ran great. I have not contacted the person who did my engine work yet but I'm looking for ideas on what may be the problem(s). Could it be a stuck ring, broken piston, or what?? Where should I look 1st? I don't want to run the motor anymore for fear of doing more damage ( it is the original engine). Any ideas???

Thanks!
Ron Still

[Bill M.]

Re: C-2 L79 Engine problem

Ron
i had the sound you are describing many years ago and it was a spun crank bearing. Drain all of your oil and check for metal and inspect your filter. if all clear then remove the valve covers and see if you dropped a valve. also do a compression test. remove all of the plugs and turn the engine over using the harmonic balancer nut and a breaker bar. This will tell you if the piston or rings are damaged
Bill

[Ron Still]

Re: C-2 L79 Engine problem-update

OK, just pulled valve cover and found #5 intake rocker arm completely off the pushrod and barely still attached to stud. That's easily fixed, but why would this cause oil burning? Do I still have another problem?

Ron

[dave sly]

Re: C-2 L79 Engine problem-update

Likely, if it was an intake valve that was stuck closed (due to the missing rocker arm), then the engine was sucking air (with oil) through the valve stem seal. Likely that no damage is done.

[Ron Still]

Re: C-2 L79 Engine problem-update

Dave, that makes sense. I am breathing easier right now! I have Posi-Locks for the rocker arm nuts, do you know what the procedure is for adjusting the rocker arms with these?

Thanks

[Dave Sly]

Re: C-2 L79 Engine problem-update

Yes I do. First thing is to make sure that the posi-locks are installed the correct side up. The nut should be at the top (not at the bottom in the rocker (or interference could happen).

Then you'll need to ensure that the valve you are adjusting has its lifter on the base lobe of the cam. Follow the service manual with regards to which lifters are on the cam lobe base, when the crank is at compression on cylinders 1 and 6.

Next, for the lifters that are on the base of the cam, turn down the posi-lock until the lifter's plunger just starts to move (or all of the play is taken up vertically by the pushrod - no play). Then turn down the posi-lock 3/4 of a turn and lock down the set screw. Make sure the set screw is tight.

After setting all of the lifters, it is highly recommended that you manually turn the engine over a few times to ensure that there is no valve-piston interference. Then, as an added check, I do a static compression check on each cylinder, to ensure that all of the valves are sealing correctly.

Then you're done.

Good luck

[Joe L.]

Re: C-2 L79 Engine problem-update

Ron-----

If this is a more-or-less stock engine with stock-type rocker arms, I would not use the posi-locks, at all. I would use the stock GM self-locking lock nuts. I would change all the nuts on the engine to these. Then, adjust the rockers per the instructions in your factory service manual. That procedure will work perfectly with the engine off.

By the way, the stock GM nuts are GM #12557390. However, you should be able to get basically the same thing from auto parts stores under other brand names like Dorman, etc.

[Clem Z.]

Re: C-2 L79 Engine problem-update

posi locks will not hold well unless the top of the stud is machined flat and stock chevy studs are not. you should set the lash .003/.004 loose, tighten the locking set screw and then adjust the lash the rest of the way by just turning the nut. this will lock the set screw into the top of the stud BUT as i said before this only works well with studs that are machined flat on the top like ARP. you can have the stock chevy studs machined flat on the top

[Duke W.]

If it works, don't fix it!

With the exception of the weak OE connecting rods there is NOTHING on a small block that needs to be "re-engineered" with aftermarket parts. If fact it's the guys with the aftermarket parts that seem to have all the problems.

In particular the valvetrain (including OE camshafts and the 3911068 valve spring) is bulletproof.

Replace any rocker nuts that don't have at least 10 lb-ft of breakaway torque or tweak them with a hammer.

Duke

[Ron Still]

Re: C-2 L79 Engine problem-Thanks to all

Thanks to all for your responses. I can't remember when/why posi locks were installed (probably over 30 years ago!)but I am taking Joe's advice and replacing with stock nuts. I don't think the studs were ever machined flat and really don't see the need to "re-engineer" this! It is a stock motor. Thanks again everyone!

Ron

[Joe L.]

Re: C-2 L79 Engine problem-Thanks to all

Ron------

For me, the self-locking nuts are preferred over all other types of rocker stud nuts.

As a matter of fact, because I am using roller rocker arms with the "ZL-1", I have to use posi-lock-type nuts (with ARP studs, of course). However, I tried MIGHTILY to figure out a way to use self-locking type nuts with the roller rockers. The problem with all roller rockers is the available clearance between the rocker body and the nut. It makes it virtually impossible to use anything other than a posi-lock nut. I searched HIGH-AND-LOW for a self-locking type nut that was of such a configuration that I could use it with the roller rockers, even with the thinnest wall socket I could find. I came up totally "dry". If anyone ever comes up with a self locking-style nut that can be used with roller rockers, I'd "junk" my posi-locks that very day.

[John D.]

Re: If it works, don't fix it!

Duke etal, Last winter our Pittsburgh chapter had a technical seminar. Kimball Midwest Fastener company was nice enough to send out two quite knowledgeable individuals who demonstrated to us why we should not be using our old original nuts and bolts over again. Each time a nut or bolt is reused it looses its strength as you well know. They also pointed out various problems in the industry with a lot of graded hardware that is foreign made. We got to see how much torgue it took for a particular fastener to fail after each use. Our junior members got quite involved with this demonstration. It was quite interesting and a little scary thinking that some of us are driving around in our old Corvettes worried about the proper logo of the fastener when in fact we could end up with a life threatening situation if one of those antique bolts or nuts failed.
As far as the rocker arm nuts go we always said they were a one time use only.
Clem used to preach that all the time and still does. JD

[Clem Z.]

Re: If it works, don't fix it!

i used to add a "pal" nut as a lock even with the GM locking nuts. most likely over kill but i never had one come loose even in race engines. john is correct i always used a new GM nut if i had to R&R one.

[Duke W.]

Re: If it works, don't fix it!

"Each time a nut or bolt is reused it looses its strength as you well know."

No, I don't "know" that, and, if fact, I don't agree with the statement.

Most fasteners are designed so that the material is stressed within the elastic range. Some, typically head bolts on some modern engines, are designed to be stressed into the inelastic range when torqued to specification, and these often are one time use, but some can be reused until as long that their overall length is below a specified amount.

I see no problem with reusing conventional fasteners that are not stressed beyond the elastic range. At some point thread wear can be an issue, but critical fasteners are usually not removed and replaced that often.

Severely corroded fasteners should be replaced and the replacement fastener should be of the same strength class.

Also it is not necessary to "upgrade" fasterners unless there is clear evidence that the joint has insufficient clamping force. For example, using a Grade 8 fastener where a Grade 5 was used is of no use unless the torque is increased above the specified torque for the original Grade 5 fastener. Otherwise, clamping force is unchanged and the "upgraded" fastener does nothing, but drain your wallet.

As far as rocker nuts are concerned, even new nuts sometimes have little preload. The fix is to peen the nut as you have done, and in some cases the problem may be the stud threads.

Duke

[John D.]

Re: If it works, don't fix it!

Duke, Kimball Midwest Fasteners had quite an elaborate setup on the stage in front of our chapter and guests. Even a brand new fastener took less torgue to break it each time it was used. This machine had a gauge on it and it register how much torgue it took for a bolt or to fail. The noise from the fasteners breaking definitely woke up the guys sleeping in the audience.
Repeat: each time a bolt was used over it took less and less to snap the thing. It was quite an impressive display.

Dave Kitch if you are looking in help me out here as you were at the seminar.
That's all I know Duke. I am guilty of using original fasteners over on my cars. You have much more experience that I do. I was just showing our audience that it is not safe to reuse critical bolts over and over according to KMF. JD