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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: bigben5054 on May 03, 2020, 08:38:43 am
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Sorry for the long post, but I don't always know what details are important to include.
I recently rebuilt the 350 in my 1979 K20. Last weekend I got the cam broke in. I didn't pay a lot of attention to where timing was at, my focus was on getting it running and keeping it at 2,000-2,500 RPM for 20 minutes. Every so often I slowly revved it up to 3,000. It ran fantastic, right up until the last 10 seconds or so when I noticed a signifiant drop in RPM and it started running really rough. So rough that I suspected it lost more than one cylinder. But, happy to have the cam broken in I shut it off to wait for another day to really dial it in. As I thought about it over the last week, I convinced myself that the distributor (which wasn't bolted down very tight) probably just worked its way so far out of time that this is what caused the sudden change in behavior.
Yesterday I got back at it. First, I still have a miss or two. I know this because of how rough it runs and also I have a squirt bottle of water that shoots a real fine stream and I hit each header pipe right off the head one at a time. When a cylinder is firing, that water sizzles and evaporates within a few seconds. If a cylinder is not firing, there is little to no sizzle and the water drops will last much, much longer. Sometimes, its hard to tell exactly - I know there are probably better ways. But I am almost positive I lost #1, maybe #7, maybe #2. Seems like the middle cylinders on both sides are fine.
So I ignored this problem while I set the timing. I put it right around 10* BTDC at idle with vacuum advance disconnected and plugged. Engine had fully warmed up. Now here is the fun part. When I shut it off and went to start it back up, I have this problem where the starter tries to start it, but then sounds like it kicks back. Sounds horrible. Sometimes it pushes past this and cranks a couple times, sometimes it just kicks back and stops or freewheels. I had this exact same problem before I pulled the old engine. I did reuse the old starter but don't think that is the problem because before I set the timing to 10*, the starter worked wonderfully and there were no kickback problems. Everything else is new - harmonic balancer, valve train, distributor, spark plugs, wires, timing chain, etc. When I assembled the motor I checked and at TDC #1, the 0* mark on the balancer lined up perfect with the 0* mark on the timing tab. By the way, I had to advance the timing (I turned the distributor counter-clockwise...I think that means I advanced it) to get to 10*, so when breaking in the cam and when everything worked perfectly, it was probably closer to 0* or even ATDC a little, if that makes sense.
Everything I have read when searching for stater kickback problems says it is because timing is too far advanced. But I know for sure I am dead on that 10* mark. But, I suppose every engine is different and if mine wants to behave better at 8*, 6* or even 4*, do I just give it what it wants? Or am I putting a band-aid on a different problem?
Another possible culprit that comes to mind is a grounding issue. My battery is grounded to the frame and that is it. I know I need to ground the block to the frame, and maybe the block to the body. I will do that later when the parts store opens. My hope is that this is why I don't have all cylinders firing and why the starter is acting up, but I am not hopeful because of how everything worked fine initially. But it needs to be done anyway. Or...maybe the battery drained enough while breaking in the cam that it just doesn't have enough juice to give it the spark it needs....can you tell I'm thinking out loud here?
I also think that if not a timing issue, maybe the cylinder(s) that are not firing are loading up on fuel that isn't getting burned and it is hydro locking when trying to restart. Obviously, if this is the issue, getting all the cylinders firing properly fixes everything.
Thanks for reading, and please let me know if you have any helpful tips or suggestions!
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By the way...if I take my timing light, and hook that little clamp around each spark plug wire one at a time while its running, this would tell me whether I at least have spark going to the spark plug on that cylinder, right? (if the strobe light pulses, you have a spark).
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I'm not sure it will solve your problems if you improve the grounds, but you definitely need to make some additions.
This is what I have on my '75 GMC, and I think its fairly original. There may be more that I didn't think of.
- Battery terminal has a large gauge cable running over to the alternator bracket, grounded to a bolt on the top of the bracket
There is also a smaller wire on the battery terminal and it runs over and grounds to the radiator support
- Low down on the engine block, ground wire from engine to a bolt into the top of the frame near the fuel pump
- Passenger side, back corner of engine - ground wire bolted to the block and running over to the firewall. I think the A/C relay and heater resistors also ground to this point.
- Ground wires (black) from each headlight assembly to the radiator support
- Ground wire (white) in the back of the truck up above the license plate area, to ground the rear lighting circuits
- Black ground wire running from instrument cluster over to a post on the emergency brake pedal mechanism
Bruce
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Regarding grounds: scroll down to the inventory of standard ground connections in the technical article, "Vehicle Ground (http://)." This list augments Bruce's post.
The location of factory timing marks migrated over the years of engine production. Although the balancer is new, verify that the timing marks actually line up on zero with the #1 cylinder at TDC. If the timing marks don't correspond at TDC #1, the timing is set incorrectly.
Yes, to your question on using the timing light to verify spark to individual cylinders.
Did you install a stock or near-stock profile camshaft using factory valve springs or is it a performance profile using higher pressure springs? Did you use ZDDP enriched mineral oil during camshaft break-in? Once you have established the proper ground connections and verified ignition timing, if the symptoms persist, remove the valve covers and verify the rocker motion (lift) for each and every valve.
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By symptoms you mean it starts but runs poorly, right?
He has a lot of symptoms... :(
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Update: I feel really stupid. I don't know how to use my timing light (http://forum.73-87chevytrucks.com/smforum/index.php?topic=38055.0). Turns out, it's a bit fancy and you can set the advance right in the light. So...I had the engine set about 28 degrees initial advance...duh. Once I figured that out and set it at 10*, the starter issue went away. Oh, and I fixed the ground.
I still have a miss and I think it is on cylinders #1 and #7. I do have spark and they are new plugs, so I am going to pull the valve cover and see if maybe a rocker worked loose or something. I recall the rocker nuts feeling a bit "loose" when setting the valves. Probably should get new ones.
Another issue I have is that with timing set at 10*, vacuum advance disconnected and plugged, it starts fine now. But when I hook the vacuum advance up, it doesn't want to start. Acts like it has too much advance. I think that is because I hooked into a port on my Holley that has full vacuum. I know it is supposed to go to the timed port on the metering block, but for some odd reason my metering block doesn't have that port. I don't think there is any harm in running without vacuum advance, but it probably would idle a little smoother with it properly hooked up. As it is, it really smoothes out around 1,500 RPM. Maybe that's when the mechanical advance kicks in and helps it out.
To answer some other questions raised: It's a new cam (SUM-K1103) and I would consider it fairly mild. They are Vortec heads that came pre-modified from one of the online big parts stores. Supposed to be machined and springs good for up to .500 lift. My cam is below that. I did use special break in oil with the ZDDP (its actually still in there, but I'll get that changed out soon).
We will see what lies beneath the valve cover. Thanks for all the help guys.
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Everything under the valve cover looks fine. Would a vacuum leak cause a miss at idle, then go away at higher RPMs? I’m going to pull the spark plugs and look them over too.
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Spark plugs, 1, 3, 5, 7 left to right. Wasn't quite what I expected. Hard to get a good pic, but 1 and 7 look halfway normal (those are the ones I thought were not firing), 3 looks charred and 5 looks brand new. Now I am really scratching my head.
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Everything under the valve cover looks fine. Would a vacuum leak cause a miss at idle, then go away at higher RPMs? I’m going to pull the spark plugs and look them over too.
Absolutely a vacuum leak can cause a misfire condition
Sent from my XT1254 using Tapatalk
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Do a compression test, don't forget to tie the carb throttle to wide open during the test.
It also looks like your carb is not delivering evenly.
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Compression test is a good idea. It will have to wait until my next trip to the parts store to borrow a tester.
I am really suspicious of an intake vacuum leak. I'm going to put it back together and spray carb cleaner along where the intake meets the heads. I saw a video online where a guy talks about a problem of constantly blowing intake gaskets on Vortec heads until he started using a certain type of intake gasket that had some sort of steel center.
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It's a new cam (SUM-K1103) and I would consider it fairly mild. They are Vortec heads that came pre-modified from one of the online big parts stores. Supposed to be machined and springs good for up to .500 lift.
If the heads are advertised to handle 0.500" valve lift with the springs provided, spring pressures are significantly greater than stock and significantly greater than the pressure required to control the valvetrain with the camshaft you installed. Unless you substituted break-in springs during the initial break-in, the cam lobes may be wiped. It only takes a few minutes to wipeout the lobes if high-pressure valve springs are used during the break-in process. The symptoms you described fit that scenario. Are you certain that the valve lifts, cylinder-to-cylinder, are correct?
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Yikes. I did not use break in springs. Lift on this cam is .444/.466. I thought that was a pretty good match for springs good up to .500. Is checking this as simple as watching the rocker arms while I turn the motor over to make sure they they are all moving, or can it be more subtle than that?
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Two things you can do. 1) Collect a sample of the motor oil. If it has a pearlish sheen, drag a magnet through it. Ferrous metals will adhere to the magnet, inferring one or more wiped lobes. 2) Warning - this next method is messy as engine oil will fling from the rockers. Remove the valve covers, one at a time, and start the engine. Watch the rocker motions as the engine idles. When cam lobes wipe out it usually happens unequally valve-to-valve. Wiped lobes should be readily apparent due to the visible inconsistencies in rocker motion/valve lift. A more precise method (and cleaner, if tedious) is to use a 1" dial indicator resting against each valve retainer, in turn, with the indicator anvil oriented parallel to the axis of the valve stem while barring the engine over to measure valve lift. All of the exhaust valves should measure the same and match the advertised exhaust valve lift (assuming 1.5:1 ratio rockers). Similarly for the intake valves.
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Well, it's one of those good news/bad news deals. Good news is I found the problem. Bad news is that I think its a big problem. I pulled the rest of the plugs from the passenger side bank and they all looked ok. I pulled the driver's side valve cover and all looked fine. I then moved on to a compression test. All were between 155 and 170, except #6, which was 0. I pumped a little air into the cylinder and could hear it coming out the exhaust. I pulled the passenger side valve cover and the rocker arm on #6 was off to the side. As I looked closer, I could see that #6 valve is stuck open. I would assume a bent valve, but not sure. I was planning to pull off the header and see if I could see anything obvious looking into the exhaust port. Anything else I can do or check before pulling the head? And if it's a bent valve, what causes that?
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The pushrod is bent too. Slightly, but obviously bent. And it looks like the rocker arm was cutting into the side of the rocker stud on one side.
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That's a bummer! A few possibilities that could cause a valve to hang open are a bent valve, a lubricant starved (dry) valve stem*, insufficient valve guide/stem clearance*, a dislodged press-in valve seat, a dislodged press-in valve guide, or something trapped between the valve face and its seat. Removing the exhaust manifold to peer inside the exhaust port is a sound next step. Peering through the spark plug hole may be telling but the view is limited. In both cases, a small head borescope might benefit. Look at the top of the piston too if you can.
*The valve stem may have seized in the guide.
How high did you rev the engine during break-in?
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Thanks Rich. I'll see what I find when I pull the header. For breaking in the cam, I had the idle set to 2,000. Every once in a while I would slowly rev it up to 2,500 or so. I don't think it ever went over 3,000.
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just pulled the header and didnt see anything obvious - although I couldnt get a real good look in there. I dont have a borescope, so I'll have to see if I can find one. Thing is, with the valve stuck open that far, it had to have been smacking on the piston, right? I cant imagine a scenario where I dont have to pull the head. Just hate dealing with the antifreeze. Where is the best place to drain it from so I dont have that extra mess?
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I agree, a borescope is optional and won't provide escape from the inevitable. Nonetheless, Harbor Freight markets a couple of compact head models (8.5 mm) that may serve your purpose, 61839 (https://www.harborfreight.com/automotive/diagnostic-testing-scanning/digital-inspection-camera-61839.html) and 61838 (https://www.harborfreight.com/high-resolution-digital-inspection-camera-with-recorder-61838.html).
Regarding cylinder head removal: first, drain the radiator into a clean pan. Second, there are 1/4" NPT plugs threaded into the water jacket on the left and right center flanks of the engine block, a few inches above the oil pan gasket rail. Typically, the plugs are threaded VERY TIGHT into the block. If you are patient and diligent, you may be able to loosen and remove the plug to drain the water jacket on the offending side so the head can be pulled w/o coolant flooding the cylinders and floor. If residual sediment is caking the base of the water jacket, you may need to probe the hole with stiff wire for coolant to drain effectively. Replace the plug with a brass draincock for future service needs.
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bd's analysis is good but makes me wonder...
Do you think anything would bend the push rod except an obstruction?
I guess at the moment the rocker went sideways it could have bent. :-\
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Just an outside thought here: Did you use sealant on the head bolts when you installed the heads?
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Ok something weird is going on here: i go to Utube and this just happens to pop up on my feed:
https://endosnake.com/products/endosnake-viper-3-9mm?gclid=CjwKCAjwqdn1BRBREiwAEbZcRxpnxL9cvW7WVEVvDhtvflkwr32bxZiaFZqDhTAz_C4tG-k-E9tedhoCENsQAvD_BwE
Can google "read" what you are reading and analyze it?
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Yes, I sealed the head bolt threads. And yes, I think anything you do online is tracked these days. My guess is it didn’t necessarily pick up on the plain text, but the Harbor Freight links that bd posted.
I haven’t gotten any further. Just sitting here thinking through what could have happened and what the damage could be. When I put the heads together I lubed the stems with motor oil. Not sure what I could have done wrong there. In order for a valve to hit a piston, I think you have to over rev and get into valve float. I don’t think I did that either. The mystery persists for now...
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Did the heads come bare? Did you assemble the valves and springs onto the heads?
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I bought the heads slightly used and they were assembled. Just for good measure, I took them apart to wire wheel the valves and put new valve seals on them.
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Well, reaffirming what you already know, the next steps are removal, disassembly and thorough inspection.
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Bent valve. From the naked eye, it looks to me like the valve and piston just gently kissed once. I pulled the lifter out and it came out no problem and looks fine. I took the valve spring off and the inner and outer spring both look fine. I tried to pull the valve out by hand and it wouldn't budge. I used a wood block and rubber mallet to gently tap the stem and it would move maybe 1/4 inch is all. So its not seized completely in the guide. So...what happened? My list of possibilities is:
1) wiped cam lope, caused slack in valve train and allowed rocker to slide off to side and pushed the valve at an angle
2) rocker just worked loose and slid off to side, pushed valve at an angle (not likely - rocker arm nut was still installed about same as all others)
3) I got bad info re valve springs good for .500 lift cam, and the valve springs can't handle this cam and allowed valve float (I'm not sure how this works exactly)
4) ???
Attached pics of the piston and valve. Also attached pics of #8 showing some oil on the intake valve. There was also a little oil in #8 cylinder. #8 compression test was 150, others were 155-170. Think there is an issue on #8, or just needs a little more run time to break in the (moly) rings?
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Correction: That is #2 with the wet oil and #2 was at 170 lbs. So all good there as far as I am concerned. Going to take the head to a machine shop today and see if they can fix and and give me some ideas on what might have happened. I'll have them test the valve springs too so I know if these are truly appropriate springs for this cam. I was thinking, perhaps I should not be so fast to rule out seizing. I suppose it could have seized when hot, caused the valve to stick, piston hits it and does the damage, then after it cools down it frees up again. Does that happen? Or once they seize does the valve and guide basically weld together?
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Dropped off the head today. Chatted with the guy at the machine shop for a minute before I left. He quickly dismissed the idea of the valve springs not being sufficient. I guess a .444/.466 lift cam isn't impressing anyone! He seemed most concerned about a wiped cam lobe. I haven't checked that yet, but should be pretty simple with the intake off.
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Went out tonight and turned the engine over by hand several times, watching the lifters. They all seem to come up all the way. Cam is good.
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Well that's a relief!
The pic that showed the valve open didn't look bent.
Sounds more like it seized in the guide.
Look forward to more news, and THANKS for keeping us updated! Means a lot.
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Maybe it was a bad picture, but it was bent for sure.
I have not heard back from shop yet, but I have a new theory. What if the gas was really old and it gummed things up enough to cause the valve to hang open and that is how it got smacked by the piston? Embarrassingly, I don't know what kind of gas is in the truck or how long it has been in there. I do know its the same gas from when I bought the truck in September 2018. I have no idea how long that gas was in there before I bought it. I also know that when I took the intake and carb off (just recently I mean), I turned the carb upside down and drained the fuel bowls. The gas looked darn near red. Needless to say, I need to figure out how to empty these tanks and get some fresh gas in there, but do you suppose this could be the culprit?
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Machine shop called. He said the guides on the exhaust side were too tight, causing the valves to seize. In addition to the bent valve, he said he had to replace 2 other exhaust valves because the stems were galled up so bad. He suggested I pull the other head and bring it in, so I'll be doing that when time permits.
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I suppose bad gas can have an effect, but will wait till others weigh in... Caustic gas?
One would think that modern guides are designed to work with the lack of lead.
These were rebuilt, right? Have you checked with the supplier?
There may have bee a bad run of parts and they are experiencing the same thing on other heads they've sold.
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Machine shop said bad gas would just make it run bad. I bought the heads off a guy that said he bought them new from one of the online places like Summit or Jegs. Said they were supposed to be good for .500 lift cam. He had them on his motor only briefly, but never could get motor to run right so he bought a crate motor and was selling these (and some other parts).
Now, I don't like to buy such critical engine components used from strangers, but I thought I was pretty careful about these. No visible damage and they looked consistent with what he was saying as far as them only being run a little bit. On top of that, I could see for myself that the guides and spring pockets had been machined (like they have to do on Vortec heads to get them to accept bigger valve springs). And they only reason to do that machining work is to allow a higher lift cam. The other thing the machine shop guy said was that he had to re-grind the exhaust seats because they way they had been done, the valves weren't even sitting on the 45*. Makes me wonder about where these big parts stores source their heads from. I wouldn't be surprised if they are being reconditioned and machined in Mexico or something by people that might not have any business doing that work.
I wonder if my problem was a combination too little clearance and letting it get too hot on start up. I had posted about the motor overheating on me when I was trying to break in the cam. First time it ran about 5 minutes before I noticed the water temp gauge had pegged. Second time it did the same thing, but I caught it faster because I was looking for it. But she got pretty hot before I figured it out. When I did my third run, it kept cool - never over 200 - and ran great for the 15 minutes or so I ran it. It was right towards the very end of that long run when I heard it drop a cylinder. I think the timing was pretty retarded when I did that too, which I understand causes excessive exhaust heat because of the late-burning fuel.
Anyway, its nice to have an answer. Hopefully get it back together soon!
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...My problem was a combination of too little clearance...
...and insufficient lubrication.
...I bought the heads off a guy that said he bought them new from one of the online places like Summit or Jegs. Said they were supposed to be good for .500 lift cam. He had them on his motor only briefly, but never could get the motor to run right...
...The other thing the machine shop guy said was that he had to re-grind the exhaust seats because the way they had been done, the valves weren't even sitting on the 45*.
It would cause me to question the real reason the seller sold the heads. And, were valves replaced after-the-fact to hide the truth - w/o fitting or machine work. Caveat emptor!
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I bought the heads slightly used and they were assembled. Just for good measure, I took them apart to wire wheel the valves and put new valve seals on them.
Sounds like you had the valves out- did you notice unusual tightness in the exhaust valves?
What blow my mind is it ran great until the end of the break in period, like 19 minutes, then the valves seized, 6 got smacked and bent, and poop ran downhill.
bd what accounts for the lack of lube? He used break in oil. No mention of overheating at this point either...
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Dissimilar metals expand differentially as they heat. If there is insufficient clearance between the stem and the guide, there is also insufficient lubrication because of diminished space, which increases friction and heat, which decreases lubricity, and so on, until lubrication fails and one or both of the metals begin to gall. At that point, there is zero clearance and the stem seizes. Essentially, machine work and setup was lacking before bigben acquired the heads. -JMO
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So far, we only know of the one exhaust valve that was bent. He replaced two other exhaust valves because of galling on the stems. I have to pull the other head and take it in, so we'll see what he finds there. Compression test 1-8 was 170, 165, 170, 160, 170, 0, 155, 150. So I am not expecting any other bent valves, but wouldnt be at all surprised to find more bad valves due to seizing/galling.
I did have them apart and I did not notice any anything tight or unusual. But I didnt measure it and we're talking about thousandths of an inch. So probably not something I could tell by feel or eyeball.
I'll file this away in the "lesson learned" drawer and consider myself lucky that the heads weren't cracked or otherwise complete junk.
Question: How are the valve stems lubricated once a motor is put together and running? The valve seal should be preventing lubrication from the top side, right? Another question, when I pull the other head, do I need to remove the block plug on that side to drain anti-freeze, or did removing the one on the other side drain them both (worked awesome by the way - not a drop of antifreeze anywhere up top).
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Quick update - yes, you have to pull the block plug on both sides (got darn near another gallon out this side). No bent pushrods or visible damage on this side. Will take it in to machine shop later today.
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The valve guide seals don't block oil from reaching the stems, they meter the amount of oil that draws down the guides due to negative pressures in the cylinder head ports while the engine is running. They also limit excess oil from migrating down the guides due to the pull of gravity while the engine rests. Generally, I recommend Viton positive-stop seals used in conjunction with the square-cut o-ring stem seals that seat into the spring retainers. Talk with your machinist.
The coolant jackets in the left and right halves of the cylinder block are physically isolated except through the water pump, cylinder heads, and intake manifold coolant passages. So, yes, each jacket must be drained independently.
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Negative pressure on the intake valves right?
Exhaust valves are pressurized. Wonder how they get any oil except for gravity...
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Read up on exhaust scavenging...
Exhaust Backpressure and Cylinder Compression (http://forum.73-87chevytrucks.com/smforum/index.php?topic=24561.msg205069#msg205069)
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Thanks for the info guys. Very helpful.
Machine shop had to replace 3 valves on the other head and grind the seats. All together, $185.
Back when I was planning this engine rebuild, I briefly looked at brand new, aftermarket, name brand, made in the USA aluminum heads and decided $1000 was too much to spend on this budget build. So instead, I did this:
Bargain find, barely used Vortec heads: $400
Required Vortec intake and gaskets: $205
Centerbolt valve covers (another bargain find - nice tall aluminum ones): $75
Machine work to fix bargain find Vortec heads: $185
New set of intake/head gaskets: $100
TOTAL: $965
Can I have a do-over?
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You're still ahead 415.00 in costs, but definitely upside down on labor. :(
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Not sure if the pic will be good enough quality to see because of the upload size limit, but here's what a galled up valve from seizing looks like in case anyone is curious.