Engine Issues

[bigben5054]

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!

[bigben5054]

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).

[75gmck25]

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

[bd]

Regarding grounds:  scroll down to the inventory of standard ground connections in the technical article, "Vehicle Ground."  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.

[JohnnyPopper]

By symptoms you mean it starts but runs poorly, right?

He has a lot of symptoms...

[bigben5054]

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.

[bigben5054]

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. 

[bigben5054]

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. 

[Poppy 87]

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

[JohnnyPopper]

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.

[bigben5054]

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.

[bd]

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?

[bigben5054]

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?

[bd]

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.

[bigben5054]

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?