Need advice from the engine wizards [message #281789] |
Thu, 09 July 2015 22:44 |
kerry pinkerton
Messages: 2565 Registered: July 2012 Location: Harvest, Al
Karma: 15
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My 403 has a problem. I had a burned valve and low vacuum. Found the bad valve and had the head done by a local shop. Put the engine together last week and the motor has issues:
- Low vacuum at idle 10 inches of mercury.
- A random miss that you can hear in the carb and at the exhaust pipe. Very noticeable at 2500 RPM.
- Motor acts lean. Slight improvement in the miss if the choke plate is closed a bit.
Compression runs from 200 to 188 PSI. Pretty dang good.
My car buddy neighbor has been working with me on it. He's more knowledgeable than I am and I'm OK...not great but OK. I've built a few engines and done my own tuning for 50 years.
Our first effort was to find the vacuum leak. We did all the spray test and nothing. Pinched off all the vacuum lines...no change. Finally decided the leak had to be in the intake manifold or a cracked manifold. Pulled the manifold and noticed it was an EGR model. Plugged the holes in the intake runners with brass pipe plugs. No change. Thinking the intake was cracked, I found an aluminum factory manifold and got new gaskets. Some work to drill and tap a couple things but it fit fine and was much, much easier to handle. We used silicone on the gaskets and got a good squish. The crossovers are blocked with stainless plates and the Mr. Gasket gaskets are cut out for the plates and a good bit of silicone holds them in place while the intake was set. We're confident the gaskets are good. We used modeling clay to verify the manifold fit the heads and also checked for straightness on the mating edges. I had high hopes this would solve the problem...no change. I am running a brand new Patterson carb and swapped it out for my old original carb...no change. Changed the distributor cap, coil, module and even the pickup coil...no change.
At this point we were both stumped and slept on it. Today, we verified the harmonic balancer (which is relatively new) is correct. The timing is set to 11 degrees. Vacuum was ported but we discovered it ran a bit better with a little more advance so we're currently on manifold vacuum and switched back to the new Patterson carb...no change. Pulling the spark plug wires one at a time from the distributor results in a noticeable change in sound and drop in RPM Getting a good spark about an inch long as the end of the wire gets close to the distributor cap. Vacuum doesn't change much. Today we removed ALL the vacuum lines, replaces the brass fittings with new one and plugged all the holes....no change. Made sure the spark plug wires are separated. Currently vacuum is about 12-13 and the needle swings rapidly 10-15 at idle. Observed the same readings on three separate vacuum gauges.
I talked to Jim Hupy and he said that if we can hear it in the exhaust (you can feel the flutter too), it is an exhaust valve or spring. We had previously pulled the valve covers and observed the valves working. While we did not measure them, they appear to be operating normally and consistently. Jim suggests a leak down test. Tomorrow I will borrow or buy one and perform the test. I will probably also swap out the Patterson distributor for my original, plug wires and all just to eliminate things.
We've been grasping at straws and eliminating possibilities for the last 10 days and the straws left to grasp at are getting pretty sparce. ANY ideas and suggestions are welcome and encouraged. As it stands now the coach is not running well enough to go the the Dixielanders rally in a couple weeks and the boss is getting frustrated also.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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Re: Need advice from the engine wizards [message #281799 is a reply to message #281789] |
Fri, 10 July 2015 07:28 |
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SeanKidd
Messages: 747 Registered: June 2012 Location: Northern Neck Virginia
Karma: 4
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One last thing, reading back to Jan? You replaced your timing gears, did you ever resolve your cam timing? Sounds like late timing, low vacuum, and resulting in burned valve....
Sean and Stephanie
73 Ex-CanyonLands 26' #317 "Oliver"
Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD Honda 6500 inverter gen.
Colonial Travelers
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Re: Need advice from the engine wizards [message #281800 is a reply to message #281799] |
Fri, 10 July 2015 07:39 |
kerry pinkerton
Messages: 2565 Registered: July 2012 Location: Harvest, Al
Karma: 15
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SeanKidd wrote on Fri, 10 July 2015 07:28One last thing, reading back to Jan? You replaced your timing gears, did you ever resolve your cam timing? Sounds like late timing, low vacuum, and resulting in burned valve....
Yes, the timing gears are back to stock and my buddy and I both laid eyeballs on it to make sure it was right. Can't explain why the other head reads a bit higher than previously but that is what it read earlier this week. I measured and my buddy cranked the engine, held the gas pedal down, and cranked the engine. The previous readings could have been a bit lower because I didn't have the gas pedal pressed down.
I agree it sounds like late timing but everything checks out....
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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Re: Need advice from the engine wizards [message #281805 is a reply to message #281789] |
Fri, 10 July 2015 08:13 |
jhbridges
Messages: 8412 Registered: May 2011 Location: Braselton ga
Karma: -74
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What would happen if an exhaust valve was sticking open slightly, occasionally?
Optionally, build an altar at the garage door, get a kid goat from your neighbor, and at midnight on the first full moon........
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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Re: Need advice from the engine wizards [message #281808 is a reply to message #281789] |
Fri, 10 July 2015 09:54 |
JohnL455
Messages: 4447 Registered: October 2006 Location: Woodstock, IL
Karma: 12
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Vac leak to the inside? Not likely with manifold swaps. I know you checked but be sure 5 and 7 are not swapped. Good comp so valves are closing but are they all opening properly? Observe valve opening action on all 16. At cranking speed cyls may fill to give good comp but have week output due to bad fill/ evac at speed.
John Lebetski
Woodstock, IL
77 Eleganza II
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Re: Need advice from the engine wizards [message #281815 is a reply to message #281808] |
Fri, 10 July 2015 11:20 |
Carl S.
Messages: 4186 Registered: January 2009 Location: Tucson, AZ.
Karma: 13
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I'm not an "engine wizard", but the first thing I thought of was mentioned by John (above) that the #5 and #7 plug wires are crossed up. I'm sure you've already checked this, but it just seems like the obvious problem.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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Re: Need advice from the engine wizards [message #281816 is a reply to message #281789] |
Fri, 10 July 2015 11:29 |
Bullitthead
Messages: 1411 Registered: November 2013
Karma: 5
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Something basic is off here, something is giving you wrong information...like the timing indicators or something. What happens if you ignore the marks and advance the ignition timing farther than 11 static? Does it become drivable without pinging? Does it smooth out or develop any more vacuum?
Is it possible that the timing gears are off due to erroneous marks and you have made up for the difference with the distributor/ignition timing but not the valve timing?
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
[Updated on: Fri, 10 July 2015 11:32] Report message to a moderator
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Re: Need advice from the engine wizards [message #281823 is a reply to message #281789] |
Fri, 10 July 2015 13:07 |
mercdave
Messages: 45 Registered: May 2014
Karma: 2
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I'm not an engine wizard but your symptoms and thorough troubleshooting lead me to think that your machinist did not set the valve stem installed height correctly on one or more of the exhaust valves or you may have one or two push rods that are not standard length from a previous repair. If the height was close the valve might be closing under the low oil pressure of cranking (no loss of compression) but when the valve warms up the valve might be unseating. head gasket thickness and head milling will also change the effective pushrod length.
Dave L
Lynnwood, Wa.
1976 GMC 26' Edgemonte Rear Twin
1973 GMC 23' Rear-Ended, Totaled
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Re: Need advice from the engine wizards [message #281824 is a reply to message #281789] |
Fri, 10 July 2015 13:31 |
roy1
Messages: 2126 Registered: July 2004 Location: Minden nevada
Karma: 6
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When I installed my cloyes timing gears the timing marks were not correct. Fortunately I used a degree wheel to confirm the cam was not set properly otherwise I would have had a nightmare trying to figure out what was wrong. Set it back a tooth and all was well.
Roy Keen
Minden,NV
76 X Glenbrook
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Re: Need advice from the engine wizards [message #281828 is a reply to message #281789] |
Fri, 10 July 2015 14:19 |
jhbridges
Messages: 8412 Registered: May 2011 Location: Braselton ga
Karma: -74
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Geez, I can measure stem height without pulling the head off. What am I doing wrong? I can either keep air pressure on the cylinder to hold the valves closed, or stick some nylon rope in through the spark plug hole and run the piston up to hold the valves closed. Now, if the height isn't correct, I'm probably gonna have to yank the head off.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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Re: [GMCnet] Need advice from the engine wizards [message #281835 is a reply to message #281830] |
Fri, 10 July 2015 15:43 |
James Hupy
Messages: 6806 Registered: May 2010
Karma: -62
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Senior Member |
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Hydraulic lash adjusters as used in the Olds and many other GM products
have a maximum preload of .080" + or - a few thousands of an inch. That is
how much lash they will absorb at the rate of oil leak down in a stock
engine. If the oil does not leak down fast enough, the lifters are said to
be "pumped up" and do not allow the valves to close on their respective
seats. If they leak down too quickly, they do not take up all the lash
present and you will hear a clattering sound from the valve train. Neither
one of these conditions are good. That is why you want to have the static
preload somewhere near center of the range of preload. In this case .035"
give or take. Head gasket thickness when crushed affects this, as does
block and head surfacing. When you grind valves and seats, the end result
is that the valve sits deeper into the seat, and the stem along with the
keeper groove also move farther away from the spring seat, and lessens the
load on the spring, also uses up some of the preload in the lifter. The
combination of all this can be holding the valve off the seat. A big no-no.
Simple, right? Stock is good.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Jul 10, 2015 1:07 PM, "A." wrote:
> Johnny Bridges wrote on Fri, 10 July 2015 14:19
>> Geez, I can measure stem height without pulling the head off. What am I
> doing wrong? I can either keep air pressure on the cylinder to hold the
>> valves closed, or stick some nylon rope in through the spark plug hole
> and run the piston up to hold the valves closed. Now, if the height isn't
>> correct, I'm probably gonna have to yank the head off.
>>
>> --johnny
> No need to be sarcastic. I have been perusing the MM to figure out how it
> says to adjust lifter preload and haven't found it yet. I did find this:
>
> http://gmcmotorhome.info/HEADS.html
>
> I figured Kerry had that nailed down before he turned the key the first
> time.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> Upper Alabama
> After all is said and done, a helluva lot more is said than done.
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