| Compression check try number two [message #255151] |
Sat, 12 July 2014 10:15  |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Gentlemen, the folks who helped me last week.... I tried the compression check again and have the following readings: 8-133, 6-135, 4-133, 2-132, 1-138, 3-132, 5-140, 7-133. It took awhile to get that high though. Certainly wasn't fast. Also, my vac gauge readings were 15-20 main port in front of carb jumpy readings (vac leak?), vacuum advance to distributor 0 at idle and steady eddy on dial as you increased the throttle. Got to a max of 20 and steady at a high rpm. Back port 13/14 (air cleaner port) and fairly steady. My timing is set at 13 degrees tdc at a slightly high idle. Any thoughts on jumpy vac readings and compression readings would be greatly appreciated.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Compression check try number two [message #255157 is a reply to message #255151] |
Sat, 12 July 2014 10:38  |
lotsofspareparts
Messages: 726
Registered: May 2014
Location: Arlington, WA
Karma: -9
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I know that a tick that repeats itself over and over on a vacuum gauge while running at idle can be indicative of a burned valve.
Jared
Jared & Tina Lazaron + 14yr old Daughter.....
77 Eleganza II "Recherché".....
73 Canyon Lands 230 "Elephant"
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| Re: Compression check try number two [message #255167 is a reply to message #255151] |
Sat, 12 July 2014 13:07 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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budworks521 wrote on Sat, 12 July 2014 09:15Gentlemen, the folks who helped me last week.... I tried the compression check again and have the following readings: 8-133, 6-135, 4-133, 2-132, 1-138, 3-132, 5-140, 7-133. It took awhile to get that high though. Certainly wasn't fast. Also, my vac gauge readings were 15-20 main port in front of carb jumpy readings (vac leak?), vacuum advance to distributor 0 at idle and steady eddy on dial as you increased the throttle. Got to a max of 20 and steady at a high rpm. Back port 13/14 (air cleaner port) and fairly steady. My timing is set at 13 degrees tdc at a slightly high idle. Any thoughts on jumpy vac readings and compression readings would be greatly appreciated.
As many of us decided a while ago, there's nothing wrong with you basic engine and valves or gaskets. If the gage is jumping, it could be due to a momentary miss because of fuel or ignition issues.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Compression check try number two [message #255182 is a reply to message #255151] |
Sat, 12 July 2014 15:44 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Thanks again, my vac readings were reading better than the first time I tried it and had better steady readings with and without the vapor line installed at carb base. I blocked off the port and had pretty much 15/16 steady reeadings except the brake booster port which was jumpy 15-18. My tranny reading and pcv valve and such were 15 and steady. I think I need to focus on the carb. Thanks gentlemen for the insight.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Compression check try number two [message #255189 is a reply to message #255151] |
Sat, 12 July 2014 17:50 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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budworks521 wrote on Sat, 12 July 2014 08:15Gentlemen, the folks who helped me last week.... I tried the compression check again and have the following readings: 8-133, 6-135, 4-133, 2-132, 1-138, 3-132, 5-140, 7-133. It took awhile to get that high though. Certainly wasn't fast. Also, my vac gauge readings were 15-20 main port in front of carb jumpy readings (vac leak?), vacuum advance to distributor 0 at idle and steady eddy on dial as you increased the throttle. Got to a max of 20 and steady at a high rpm. Back port 13/14 (air cleaner port) and fairly steady. My timing is set at 13 degrees tdc at a slightly high idle. Any thoughts on jumpy vac readings and compression readings would be greatly appreciated.
Sounds like your engine is fine. I mention another cause that may be helpful to someone some time.
There is one other problem that can cause erratic vacuum. If the intake manifold is leaking at the valve ports at the head, it will cause vacuum to be twitchy especially if the leak is only at one or two ports. This happens because the air for the cylinder is being partially sucked out of the engine valley and not through the manifold. When the port that is leaking takes its turn in sucking in air and fuel, it only does a partial job as far as the manifold is concerned.
Because I had a number of issues with the intake manifold I developed a silly test that showed a big leak in a big hurry.
1. Remove the PCV tube and cap the carburetor tube it was on.
2. Remove the oil breather on the left side.
3. Make sure the oil fill cap is on tight
4. Make sure the dip stick is in place.
At this point an idling engine should be whiffing out a bit of blow-by from the breather hole. (If it is puffing like a steam engine you may have a hole in a piston or bad rings... Your engine will not likely do this because you have good compression.)
Take a piece of plastic shopping bag and stretch it over the breather hole... Hang on to it! If the bag tries to suck into the breather hole, you have a manifold leak. We had a 403 suddenly running poorly. This test almost sucked the bag out of our hands. When we pulled it apart, sure enough, the gasket was failing on a couple of cylinders. (Sucking air out of the valley can suck out lots of oil, as well.)
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: Compression check try number two [message #255206 is a reply to message #255151] |
Sat, 12 July 2014 23:20 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Wait a minute...didn't you say in the other post that you milled the heads? Intake manifold may not seat correctly on Olds big block if the heads were milled down too far...
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Compression check try number two [message #255241 is a reply to message #255151] |
Sun, 13 July 2014 15:44 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Senior Member |
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They only took off 6 thousandths. The number was low and the heads were barely damaged. The valves were seating pretty darn good on the heads as well. I'll try the testing again later in the week. Thanks for the info gentlemen. Dick Paterson has been guiding me along as well and giving great tips. What a great community of folks!
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Compression check try number two [message #255250 is a reply to message #255241] |
Sun, 13 July 2014 16:52 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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6 thousandths should not cause a sealing or alignment problem, and you already did the crankcase pressure test that George and I suggested, so did you look down the carb while it was idling and see any extra drips of fuel that would be causing that popping noise you heard? What about turning the idle mixture screws in to make sure each idle circuit is actually working?
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Compression check try number two [message #255308 is a reply to message #255151] |
Mon, 14 July 2014 06:06 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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My choke is not working properly and Dick said he would walk me through that later. I still need to readjust the idle screws and hope to do that later in the week. I am in no hurry for driving and using the coach this year. I decided not to take it for another test rive until I get it all squared away. I will look hard a a vac leak on the drivers side since the brake booster port is jumpy. All others were pretty darn steady at 15. Thanks for the help and I hope to test various ideas for vac leaks. Thanks for all the help gentlemen.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Compression check try number two [message #255428 is a reply to message #255151] |
Tue, 15 July 2014 06:17 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Senior Member |
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I still have the compression check tool and thought I would try the oil in the spark plug hole. One teaspoon per hole was given to me as a base right? If the compression goes up more than 10% the rings are supposedly bad right? So if I do a cylinder that measured 133 and it shoots up to 146 or so I would know. when the heads were off I pour oil in each cylinder to keep lubricated other a month or so and it never moved or changed much???? Anyway thanks guys!
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Compression check try number two [message #255438 is a reply to message #255428] |
Tue, 15 July 2014 09:26 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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I was the one that gave you the guideline for adding oil to check the rings. You would be looking for increases GREATER than 10-15% with the oil added. Since you have refined your technique for a compression check and shown us the readings, it is apparent that you do not have a problem with the rings that is causing any rough running or such. They are all pretty close together and I wouldn't worry about the rings unless one cylinder was markedly different. Wish I was there to help you, but part of the diagnosis would involve substituting parts and watching for a change in behavior.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Compression check try number two [message #255732 is a reply to message #255151] |
Thu, 17 July 2014 18:36 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Senior Member |
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Yea all the cylinders were very close and took about the same cycle wise to reach the highest point. Dick Paterson said it was fairly normal for that mileage of an engine. I still have carb concerns and slowing gaining on the concerns. Thanks for the input and I am sure I'll be asking the vets for hints and help. Thanks a bunch folks!
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Compression check try number two [message #255844 is a reply to message #255732] |
Fri, 18 July 2014 23:55 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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budworks521 wrote on Thu, 17 July 2014 17:36Yea all the cylinders were very close and took about the same cycle wise to reach the highest point. Dick Paterson said it was fairly normal for that mileage of an engine. I still have carb concerns and slowing gaining on the concerns. Thanks for the input and I am sure I'll be asking the vets for hints and help. Thanks a bunch folks!
No offense but isn't it time for you to get your GMC on the road? I think everyone here feels your compression is judt fine.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Compression check try number two [message #256032 is a reply to message #255844] |
Mon, 21 July 2014 16:06 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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I wish I could but I still have some popping noises in my carb that I cannot peg for a fix. My carb base gasket might be leaking a teeny bit? I am a lousy mechanic that needs to be methodical in my approach to repairs. Thanks everyone for the help.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Compression check try number two [message #256045 is a reply to message #256032] |
Mon, 21 July 2014 18:02 |
fred v
Messages: 999
Registered: April 2006
Location: pensacola, fl.
Karma: 0
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budworks521 wrote on Mon, 21 July 2014 16:06I wish I could but I still have some popping noises in my carb that I cannot peg for a fix. My carb base gasket might be leaking a teeny bit? I am a lousy mechanic that needs to be methodical in my approach to repairs. Thanks everyone for the help.
It is my understanding that popping while decelerating is caused by a lean mixture. I found that to be true on my Moto Guzzi engine.
Fred V
'77 Royale RB 455
P'cola, Fl
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| Re: Compression check try number two [message #256131 is a reply to message #255151] |
Tue, 22 July 2014 17:18 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Senior Member |
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The thing is once I spin the dial to a richer mixture my choke doesn't go a full 90 degrees once the engine is warmed up. However, today I started it up much easier and every time I throttled the engine a pop would follow until the carb warmed up and then not much popping thereafter. Punch the accelerator pump and pop, again and again until it idled fine and then not much popping. I am still trying to find any vacuum leaks and then I am jumping on the idle screws later. Thanks for the info.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Compression check try number two [message #256300 is a reply to message #255151] |
Wed, 23 July 2014 19:46 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Senior Member |
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I have a diagram of the carb and will look at the stuff you mentioned and see if it is operating correctly. Unfortunately I am greenhorn on these issues and need to study and understand what I am doing. I do believe that I know what you are talking about. My butterfly closes about 2/3 on a cold start and does open to 90 once hot. I have thought about those plugs as well but the previous owner had a printout from a GMC meet years ago about the carb rebuild process and I think he knew about the epoxy aspect of the plugs. He put in a new float and accelerator pump arrangement a few years ago. Hopefully I can get it figured out by the weekend. Thanks gentlemen.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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Check the little screw on the lifter cam for the secondary metering rods and make sure it is unloaded when the throttle is closed. If the screw is engaging the cam at all, the metering rods will be allowing fuel to pass at idle. Make sure the upper butterfly plates are all the way closed so the lifter cam is in the idle position. If the screw is still lifting the rods, put a tiny split lock washer under the screw to space it up and allow the rods to drop.