Home » Public Forums » GMCnet » [GMCnet] Opinions on Compression Check
| [GMCnet] Opinions on Compression Check [message #156959] |
Mon, 16 January 2012 15:29  |
Gary Berry
Messages: 1002
Registered: May 2005
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Hey All;
Just did a compression check on the 455 in the Stretch after
warming it up. Over the years the coach has been losing power and the
mileage is down to 6 mpg while towing. Will check other things out,
but this was the first thing to do. Here's the numbers...
First number is cylinder, second number is Without Oil, third number is with Oil
01 - 110, 120 02 - 120, 145
03 - 120, 130 04 - 130, 150
05 - 140, 150 06 - 140, 150
07 - 80, 120 08 - 110, 130
I got my ideas, but what do others think of these numbers??? Let me know...
--
Gary and Diana Berry
73 CL Stretch in Wa.
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| Re: [GMCnet] Opinions on Compression Check [message #156963 is a reply to message #156959] |
Mon, 16 January 2012 16:18  |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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| Gary Berry wrote on Mon, 16 January 2012 14:29 |
Hey All;
Just did a compression check on the 455 in the Stretch after
warming it up. Over the years the coach has been losing power and the
mileage is down to 6 mpg while towing. Will check other things out,
but this was the first thing to do. Here's the numbers...
First number is cylinder, second number is Without Oil, third number is with Oil
01 - 110, 120 02 - 120, 145
03 - 120, 130 04 - 130, 150
05 - 140, 150 06 - 140, 150
07 - 80, 120 08 - 110, 130
I got my ideas, but what do others think of these numbers??? Let me know...
--
Gary and Diana Berry
73 CL Stretch in Wa.
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If it wasn't for cylinder 7, it wouldn't be all that bad even though the variation between cylinder is more than some would like. The difference between oil and no oil on almost all of them shows the rings are getting worn. Looks like time for a rebuild to me.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Opinions on Compression Check [message #156964 is a reply to message #156959] |
Mon, 16 January 2012 16:24 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Gary Berry wrote on Mon, 16 January 2012 16:29 |
Hey All;
Just did a compression check on the 455 in the Stretch after
warming it up. Over the years the coach has been losing power and the mileage is down to 6 mpg while towing. Will check other things out, but this was the first thing to do. Here's the numbers...
First number is cylinder, second number is Without Oil, third number is with Oil
01 - 110, 120 02 - 120, 145
03 - 120, 130 04 - 130, 150
05 - 140, 150 06 - 140, 150
07 - 80, 120 08 - 110, 130
I got my ideas, but what do others think of these numbers??? Let me know...
Gary and Diana Berry
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Gary,
I am not fond of cranking compression because results are so easily skewed by technique and open to wide interpretation. But, if your technique was good and consistent and you have studied this at all and understand what you know then this will not be any surprise.
You got problems Man....
Cylinder 7 has a power cylinder issue (rings, piston or bore).
Several others show kind of high gain on oil for a warm engine. The oiled scatter is higher than I would like, but not outrageous for an engine of this type.
Unfortunately, the design of a GMC makes it very difficult to get a piston out. If it were in a more or less typical vehicle, I would say look into doing a ring job and get the valves done while the heads are off.
Lots of people that read this list have more experience with pulling engines than I do.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Opinions on Compression Check [message #156974 is a reply to message #156959] |
Mon, 16 January 2012 16:59 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Gary,
In a word:
Rebuild time!
Oops, that's two words!
Regards,
Rob M.
-----Original Message-----
From: Gary Berry
Hey All;
Just did a compression check on the 455 in the Stretch after
warming it up. Over the years the coach has been losing power and the
mileage is down to 6 mpg while towing. Will check other things out,
but this was the first thing to do. Here's the numbers...
First number is cylinder, second number is Without Oil, third number is with Oil
01 - 110, 120 02 - 120, 145
03 - 120, 130 04 - 130, 150
05 - 140, 150 06 - 140, 150
07 - 80, 120 08 - 110, 130
I got my ideas, but what do others think of these numbers??? Let me know...
--
Gary
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Opinions on Compression Check [message #156985 is a reply to message #156959] |
Mon, 16 January 2012 18:08 |
Dennis S
Messages: 3046
Registered: November 2005
Karma: 2
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Gary,
I always wonder what protocol was used when someone does a compression check. You mention a warm engine...
did you disconnect the gas, have all the plugs out, have the carb at WOT
What sequence did you do the checks and how long did it take from first to last?
As for cylinder 7 and 8 -- consider rechecking them -- especially before determining to pull the engine.
Another check I have done...
If you have a compression check tool that has a hose disconnect -- connect to an air hose, turn cylinder 7 to TDC and pressurize -- then lessen down the intake with a hose/stethescope for air passing the valves.
Dennis
| Gary Berry wrote on Mon, 16 January 2012 15:29 |
Hey All;
Just did a compression check on the 455 in the Stretch after
warming it up. Over the years the coach has been losing power and the
mileage is down to 6 mpg while towing. Will check other things out,
but this was the first thing to do. Here's the numbers...
First number is cylinder, second number is Without Oil, third number is with Oil
01 - 110, 120 02 - 120, 145
03 - 120, 130 04 - 130, 150
05 - 140, 150 06 - 140, 150
07 - 80, 120 08 - 110, 130
I got my ideas, but what do others think of these numbers??? Let me know...
--
Gary and Diana Berry
73 CL Stretch in Wa.
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Dennis S
73 Painted Desert 230
Memphis TN Metro
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| Re: [GMCnet] Opinions on Compression Check [message #156990 is a reply to message #156984] |
Mon, 16 January 2012 19:27 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Yeh Gary and with 150,000 on your 455 I would be concerned with the wear on the 7&8 rod bearings. A spun bearing = tow truck. It's a bit of work to R&R the motor but piece of mind is worth a lot.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Opinions on Compression Check [message #156998 is a reply to message #156991] |
Mon, 16 January 2012 21:03 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
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| Gary Berry wrote on Mon, 16 January 2012 17:55 |
Yep Roy, that's what I'm thinking. Still need to make a trip to CA
(and Death Valley (appropriate name maybe)) before an R&R can happen.
On Mon, Jan 16, 2012 at 5:27 PM, <roy@gmcnet.org> wrote:
> Yeh Gary and with 150,000 on your 455 I would be concerned with the wear on the 7&8 rod bearings. A spun bearing = tow truck. It's a bit of work to R&R the motor but piece of mind is worth a lot.
> --
> Roy Keen
--
Gary and Diana Berry
73 CL Stretch in Wa.
____
I thought about making_that death Valley ralley but I'm already in Blythe & Quartzite and don't want to backtrack. The Bluegrass concert and the Big Tent is this weekend__________________________________________
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Roy Keen
Minden,NV
76 X Glenbrook
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| WOT [message #157014 is a reply to message #156985] |
Tue, 17 January 2012 00:15 |
bukzin
Messages: 840
Registered: April 2004
Location: North California
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[quote title=Dennis S wrote on Mon, 16 January 2012 16:08]Gary,
I always wonder what protocol was used when someone does a compression check. You mention a warm engine...
did you disconnect the gas, have all the plugs out, have the carb at WOT
What sequence did you do the checks and how long did it take from first to last?
+++++++++++++++++++++++++++++++++++++++++++++++++++++
Dennis,
What is meant be 'WOT' ?
Thanks!
Bukzin
1977 Palm Beach
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| Re: [GMCnet] WOT [message #157016 is a reply to message #157014] |
Tue, 17 January 2012 00:53 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Wide open throttle.
Jim Hupy
Salem, OR
78 Royale 403
On Mon, Jan 16, 2012 at 10:15 PM, Richard <bukzin@gmail.com> wrote:
>
>
> [quote title=Dennis S wrote on Mon, 16 January 2012 16:08]Gary,
>
> I always wonder what protocol was used when someone does a compression
> check. You mention a warm engine...
> did you disconnect the gas, have all the plugs out, have the carb at WOT
> What sequence did you do the checks and how long did it take from first to
> last?
>
> +++++++++++++++++++++++++++++++++++++++++++++++++++++
>
>
> Dennis,
>
> What is meant be 'WOT' ?
>
> Thanks!
> --
> Bukzin
> 1977 Palm Beach
> Chico California
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Opinions on Compression Check [message #157020 is a reply to message #156959] |
Tue, 17 January 2012 02:51 |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma: 4
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Gary:
You did not indicate if other problems lead you to do a compression test (diagnostic) or just a routine compression test. The info you give would not be considered a sign of death.
(Here Comes My Humble Opinion) Your engine is not new - That is for sure. 150K Miles is not necisarily a lot of miles if your GMC has been on the highway for most of it's life. Some will have a whole lot more. Many engines also run with the statistics you indicate for many miles without giving other problems. If there are no other problems, let it get worse. However: if you do any engine work, at all, You will be doing a complete job. (Heads, Block, Pistons, Crank, Pumps,) Very Expensive of course (who does it and what they do will create a very interesting discussion and range of costs) In my opinion, with only this information, you give it simply confirms that the engine is not perfect. It won't even mean that your engine is any less dependable than it was a few years ago. (New engines break down too)
However, they would indicate to me that if I was doing a tune up, the engine may have a slight rock to it at idle Once the engine starts speeding up you should not feel anything. You would very unlikley even feel or notice any loss of power. It would also explain a slightly oiled plug, which I might have to inspect more often.
here are some other things to consider before getting too excited.
1 - Are plugs fouling in short Order.
2 - Is there an objectional miss(dead cylinder)
A-under load B-idle
3 - Oil consumption quite High or extrodinary (Wet exhaust)
4 - Blow-by that cannot be handled by the PVC System
5 - Engine mechanical noise
6 - Noticable Power or performance loss
7 - Oil presuure that is too low (Oil pump can't keep up)
8 - What are you intentions
Good Luck
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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| Re: [GMCnet] Opinions on Compression Check [message #157075 is a reply to message #156959] |
Tue, 17 January 2012 14:07 |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma: 4
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Senior Member |
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Hi Gary:
I really did not read the entire thread well enough. Sorry. Once I read it again with my own response, I see that I was a little too quick to answer as I did. I see you did state power lose.
However: The biggest point I wanted to make is : Before you jump into a new engine, check the other things such as distributor operation and other tune items. Bad filters can also cause those things. Then do some more diagnostic items such as leak down and cylinder power balance tests.
All that being said, I do get concerned with timing chains at that milage. Probably better to plan for this major work for a convenient time in the future.
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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| Re: [GMCnet] Opinions on Compression Check [message #157108 is a reply to message #156959] |
Tue, 17 January 2012 18:22 |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma: 4
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Senior Member |
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"YIPPEEE" !!!!  a New Project !!!!!
I think you've done your "Due Diligence" You've convinced, (most importantly) yourself (and us) that the engine is Geriatric, and has pretty well come to the end of it's useful life and needs some major surgery to be youthful and dependable again.
You can now go to the "FCFO", otherwise known as "Family Chief Finacial Officer" and justify this next project. Don't we GMCers Have fun!!! The diesel will certainly make it challenging. If you do, Please Keep your GMC friends in the Loop, and document all that you can. I see that there are many that are salivating to observe your process.
It would be a shame to see you in an ALPHA - But I can imagine that needing 7'7" would mean that the GMC is too low for you.
I wish I was going to California. The last couple of days, it's -38C outside. I forgot to plug my car in and it won't start. Just waiting for the block heater to loosen things up.
All The Best!!
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
[Updated on: Wed, 18 January 2012 01:28] Report message to a moderator |
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