Rough running problem

[Scooter76]

Right now, at idle the engine shakes the whole car and seems too "lopey" when I feel it should be running smoothly.

I know what happened: While you were asleep some Elves came into your garage & slipped a much larger cam into your engine. I just wish they would come to my house & set me up with a 502.
Anyway good luck.

 

[78SilvAnniv]

I'll put cookies, milk and power tools under vette tonight, with a note to head to your garage! :L I'll even tell them you want a 502!
Heidi

 

[cntrhub]

"Right now, at idle the engine shakes the whole car and seems too "lopey" when I feel it should be running smoothly." Well Heidi, I'm thinking the valve adjustment was set out of phase maybe? If that is all you did with the initial fix (i.e. valve ticking), you might want to recheck the valve adjustment? If you have access to look back at my old posts, I have a simple valve adjustment thread for Kenny to look at. If he followed this procedure, or the like there of, then I would assume there is another induced problem upon reassembly? Meaning, a broken spark plug? Wires are out of sequence? Something to that effect.

 

[78SilvAnniv]

Thanks.

I'll check your old posts cntrhub.
Kenny did want to re-do the valves in a more 'scientific' manner than what was actually done. What was done was adjusted them while running, I think. I wasn't actually there. Kenny wants to do something about turning the engine so the valves are at full extension and then adjusting and using something to 'gap' them.
At least that is what it sounded like he wanted to do when he explained it to me.

I think the wires/plugs are okay. We changed cap/rotor/sparkplugs/wires just before doing the valves and I had numbered the cap/rotor and also the top boots of the wires. Wires were replaced one at a time for to prevent confusion.
Heidi

 

[cntrhub]

Sorry Heidi, but that really is not how to adjust the valves. I suggest you find my valve setting procedure I posted not too long ago. If you cannot find it, I will gladly write up another one on this thread. I believe the valves are too tight now and you are losing compression, which will cause a rough running engine.
Look for something about "EOIC" in my posts. This will be my valve adj. procedure.

 

[78SilvAnniv]

Found it!

I found your post and thought I'd copy it to this thread, too.
Heidi

Originally posted by cntrhub
Eventually you are going to have to adjust the pushrods.

Here is a real simple way of doing it. It is one of the most accurate adjustments also. It's an old NASCAR engine assembly trick. Begin with any cylinder you want. Rember to stop turning the crank...."As-Soon-As"....you see one of the pushrods begin to move. This is key to remember.

OK, here we go: EO = Exhaust Opens. IC = Intake Closes.
Lets say, you start moving the crank (pick a cylinder).... now keep turning the crank and watch for the intake's rod (for example) start to close. As soon as you see the slighest movement of the, "Intake Close" (IC)...STOP!
Now set the exhaust pushrod to specs. Say the adjustment calls for one full turn (stock adjustment) from zero play. Without making too drastic of a move to unseat the rod from the lifter, start moving the pushrod up and down. Keep doing this until there is just the slightest up and down movement. Then, begin spinning the pushrod as you keep tighten the rocker nut. When you can no longer spin (a subtle touch as you tighten very slowly) the rod, stop.
Place the wrench at a known starting point, and turn the rocker nut 360 degrees... and stop. One full turn is a standard adjustment for a stock engine. Consult with the performance specs of their adjustments. It might be less or more turns....depending, etc. Solid lifters on the other hand, will take a different adjustment approach.

Now turn the crank, and watch for the exhaust just begin to open (EO). As soon as you see this happen, STOP! Set the intake valve to specs in the same manor stated above. You've completed an adjustment of one cylinder. There are 7 more to go. This is a lot quicker and more accurate (bottom of heel) than finding TDC of each cylinder. Hope this helps.

 

[78SilvAnniv]

Confirmation reached today.

I have Good News, Bad News and Good News.
I also need an explanation.

Good News:
I have found a Chevy mechanic who lives within 3 miles of me that I can trust to do the right thing for me and the 78 who has reasonable prices and will let me watch/help/learn.
Bad News:
I have burned at least one valve, probably more.
Good News:
I'm pricing Vortec manifold/heads.

*the only fly in the ointment would be if the pistons have suffered any damage, but mechanic thinks that is unlikely (5% chance) as I have barely driven the 78 since she started running so awful.

The explanation I need. Heat riser(?) or more about whatever it is the mechanic described.
I'm very tired and not remembering everything mechanic said, pardon my description.

Mechanic commented that there is a system on my 78 that allows for hot exhaust to blow through the heads or manifold (?) to assist with cold start ups and there is a possibitily that it has been stuck open and allowing the hi-temps to constantly flow...which could have been the cause of my damaged valves. The problem valves appear to be the center ones, mostly pass. side. Compression test confirmed damage and sparkplug from #4 or #6 was black.
Heidi

 

[cntrhub]

Heat Valve Definition: A control valve between the exhaust manifold and exhaust pipe on one side of a V8 or V6 engine that restricts the flow of exhaust causing it to flow back through the heat riser channel under the intake manifold. This aids fuel evaporation and speeds engine warm up. A heat riser valve stuck open will slow engine warm-up and may cause hesitation and stalling when the engine is cold. A valve stuck in the closed position will greatly restrict the exhaust system and cause a noticeable lack of power and drop in fuel economy.
Did the heat valve cause a burnt valve(s)? I do not have enough research to know if this is a common problem with a heat valve designed engine?
Was the engine rebuilt not too long ago Heidi? I'm curious.

 

[Bob Chadwick]

Sorry to hear about that Heidi.

I just saw the Vortec heads at Sallee for $242 each. Why the Vortec heads? While they start out cheaper, I think posts here have indicated that they get more expensive due to "other" things that are needed. A search found a lot of posts but this one seems to hit the meat of the question.

 

[78SilvAnniv]

Current engine is a 1997 GM crate engine, 250hp, 4-bolt main. A bit better than the original L48.

As for why the Vortec? That is what the mechanic suggested after questioning me about my driving habits, vehicle care, what kind of performance I expect out of a vehicle and how much of that performance I actually use.

He said the vortech heads and manifold with the existing bottom end, my orig quadrajet and dual exhaust would let the engine breathe better and give me a bit more low end torque and make the engine work less for comparable performance levels I experience now.

Mechanic also advised I could have my heads machined and re-done, but the cost would be comparable to new heads and I'd still have to tear it down...so I think for my money I'd rather have new, with better performance thrown in, to boot. He said "It's broke now, why not fix it better?" So, yes...I would like better performance.

It appears from the thread you linked (thanks, Bob!) that the "extra cost" is the manifold, and the mechanic already advised me about needing the vortec manifold because of the bolt patterns needing to match.

3-4 days of work after getting parts and I'll be up and running again.
Heidi

 

[KOPBET]

Good call matchframe! You nailed it. ;worship

 

[Scooter76]

The Vortec heads are an excelent choice. I read a test a while back & they are the best flowing iron head with intake ports 180cc or less. If you are planning on running the stock cam then they should work fine out of the box. Supposed to be good for 20-40hp. I bought mine upgraded, machined for screw in studs, machined valve guides & dual springs good for .550 lift. because I am running about .470 lift & plan on doing a hyd. roller shortblock in the future. They do cost about 100 a head more in this configuration. As said above you will need a Vortec type manifold & centerbolt covers. I wouldn't get the ones that are drilled for a conventional manifild as I have heard that the ports don't line up very well. With my heads, cam, headers & slightly higher stall converter, my engine changed its whole attitude. It runs like a bear with a bee-sting. I do need to change to a 3.55 or so gear to take advantage of the motor. To sum it up you can't go wrong with the Vortec setup,

 

[Enigma]

Just my 2 cents into the discussion, but a stuck open heat riser valve would have no effect on your valves.
If anything, you might have a rough running engine until the it got up to operating temp.
If you drive the car in a hot climate, you really don't need it.
It's also part of the EGR system on cars so equiped.

Since I drive the car only in the summer months, My mechanic has disconnected that system and the heat riser valve is always open.

Good Luck

Enigma

 

[78SilvAnniv]

I'll try to remember every item I wanted to answer...

Mechanic mentioned the heat riser as a possible problem, we also have many things that are not hooked up and go no-where, and he advised we tie up the 'loose ends' from previous changes.

I have a flexible aluminum-looking ducting connected from the driver side valve cover to the air intake duct on my air cleaner...perhaps this is my heat riser? The item mechanic seemed concerned about was on the passenger side near the middle to rear of the engine. Came up on a long tube and had a head on it that looks like a water-tower with a vaccum connector.
(maybe I need to take a picture to show what I'm talking about)

78 is driven year round with the exception of ice, snow or torrential rain.

The rockers DID coincide with the bad valves. I don't recall him saying anything about that. He asked what initially happened and who did what to it afterwards. (Implying...who has fiddled with it and possibly made the problem of fixing it worse.)

Still looking forward to the Vortecs, thanks Scooter for the positive feedback about them.
Heidi

 

[Bob Chadwick]

Don't get me wrong Heidi, the Vortec is a good head. There are just some hidden costs that make them a little more expensive than they seem, ie., the intake manifold and the valve covers. This needs to be priced in as well.

One of the way valves cool, especially exhaust valves, is contact with the valve seats in the heads. I would suspect that the problem with the rocker studs were not allowing the valves to be closed long enough to transfer heat from the valve to the head.

 

[matchframe]

I wish it were not burnt valves, but when I heard the symptoms, sounded much like what I have experienced in the past.

You will end up with a better power producing engine, and will forget the tough times!

Bill

 

[78SilvAnniv]

Re: And for me....

Ref: valves not opening fully or transferring heat properly.

If in your position, my concern is why wouldn't your mechanic immediately recognize this as the primary factor & advise you accordingly?

I don't know. Maybe he thought he would confuse me with the explanation? Maybe he did say something and I didn't process it?
I took the 78 to him at about 3:30pm, hadn't had lunch and was begining to deal with blood sugar problems so I have probably forgot quite a bit that we discussed...

Arguendo, if you decided to merely do a valve job with no concern for pulling/weak rocker studs, you button it all back up & have the same exact problem when the next stud(s) pulls out... ten miles later.

I'll certainly bring up the weak rocker studs...and anything else anyone can mention that should also be checked.
Aren't the rockers in the head, and won't those be changed with the new head?
Heidi

ps, was planning on the new intake in addition to the heads. Valve covers will need to be priced...but I have a friend at the speed shop.
Still looking forward to the vortec change, but I also want to be sure I am doing everything I can to ensure a reliable engine.
h

 

[bossvette]

Vortec heads are a good choice, they will require a different Intake and centerbolt valve covers and possibly rocker arms, if the mechanic suggested them and has done the conversion before he can tell you what is needed. You would have to replace most of these things anyway to properly rebuild your heads. I did not read thru the whole thread, but summized that somehow you have burnt some valves and have decided to go vortec

 

[billagroom]

I don't know much about this stuff but how hard would it be to upgrade to L82 heads. I'm sure some one around here would have a set they might part with cheap. Then you have more power and your still sort of stock.
Bill

 

[78SilvAnniv]

Advice from a trusted individual...

email message from Chris
You present a difficult question. Yes, the Vortec complete combo would be wonderful. You would pick up a bit more power, and get your car back running. However, without changing the cam, exhaust, carb, and ignition system over to a matching combo of higher flow/performance parts.....I just don't think you will notice all that much difference in performance.
You might be a bit disappointed in the final outcome with just heads and intake.

The question is......does this make the most sense right now?

There is more to doing this swap than just changing the basic parts.
The two intakes will have different things that will cause you to have to chop/cut, re-route some of your vacuum and brackets and emission stuff that is part of the stock 78 system. You also run into hood clearance problems using the stock aircleaner if your manifold is taller than the stock one in the least amount.

So, a simple head/intake swap turns into a major project with limited benefits when done alone.

My suggestion. Have your stock heads rebuilt. Clean and detail it all up and slap it back together as is. Save your money for a crate engine swap at a later date. That way you get all new pistons, cam, crank...etc, and you are not putting a "high performance" patch job on an older lower performance bottom end.
If you get a crate swap motor, you will need a taller hood, as the C3 won't allow you to run a decent intake and carb without one. There is less overall labor involved as well in a basic engine swap, vs. a top end rebuild being done in the car!

Just my .02 for you to chew on.

The comments highlighted in italics and bold are the ones that have swayed my thinking. Everything Chris says makes perfectly good sense.
Now, will good sense win out...or my desire to have a "better engine"? A dilemma every gearhead must face.

Since I had been very happy with my 78 up until this problem, I think I will stick with only changing the heads for ones that will swap right in.
Does anyone have any L82 heads collecting dust they would like to part with? Exactly what are L82 heads and what do I need to look for when trying to locate a pair for purchasing new and ready to go in? Should I check my GM dealer?
Heidi