An attempt to stop a GL1000 from smoking

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cfairweather
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Re: An attempt to stop a GL1000 from smoking

#106

Post by cfairweather »

When we were discussing the compression numbers, I forgot to mention that I live at an altitude of over 6000 feet. Recently, I read that compression tests will be lower, but I don't know just how much it affect the readings.
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gltriker
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Re: An attempt to stop a GL1000 from smoking

#107

Post by gltriker »

cfairweather wrote: Thu Jul 03, 2025 4:26 pm When we were discussing the compression numbers, I forgot to mention that I live at an altitude of over 6000 feet. Recently, I read that compression tests will be lower, but I don't know just how much it affect the readings.
That is a keen observation, Cedric!
Nixon had posted a photo of a compression gauge test result of a recently (May,2018) rebuilt high compression engine.
I think he took that reading at Prescott, AZ.( Google says elevation there is less than 6000 feet above sea level)
He stated whatever the reading was on the gauge face. it would be 200psi when the compression tester gauge reading is, "altitude corrected."

Is it reasonable to believe Honda's standard procedure for testing their motorcycle engine cranking cylinder compression pressure is presumed to be performed at sea level? ideal Barometric pressure? ideal Temperature range? etc, etcetera, et cetera

google informs me the elevation in my neck of the woods is a measly 381 ft above sea level. ;)
Last edited by gltriker on Fri Jul 04, 2025 9:10 am, edited 5 times in total.
Cliff ;) )

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'75 GL1000 home built trike; http://www.ngwclub.com/forum/viewtopic.php?f=30&t=39996
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Track T 2411
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Re: An attempt to stop a GL1000 from smoking

#108

Post by Track T 2411 »

Generally speaking, atmospheric pressure at sea level is 14.7 PSIA (absolute). At an altitude of 6000ft., it is 11.77 PSIA. My non-math brain figures this is about 80% of sea level pressure, so the compression numbers should be about 80% of 'ideal'... and this is all from my little noggin, lol!
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Re: An attempt to stop a GL1000 from smoking

#109

Post by Track T 2411 »

Simple explanation... 10:1 compression ratio times 14.7 PSI = 147 PSI. 10:1 X 11.77 would yield 117.7 PSI reading... plus variations due to temperature, high/ low pressure weather systems, etc, etc...
"I have no special talent. I am only passionately curious." - Albert Einstein

"He that is good with a hammer tends to think everything is a nail" - Abraham Maslow

"If you can't take the time to do it right the first time, how are you ever going to find the time to do it over?" -Unknown

Current Rides:
'Grumpy' - '81 Standard, now fully dressed.
'Layla' - '81 Standard w/dealer installed fairing and Hondaline bags.
'Scarlett' '76 'Survivor' nekkid as a j-bird!

Under Construction:
The 'Jalopy' '78-'79 Mash-up
'Quikie' '81 gl1100I back on the lift, project with the step-son!

In The Shed:
'81 gl1100I barn find aka "Josie, the farmer's daughter." (almost comatose build)
'77 gl1000, roller parts bike.
'82 gl1100I, 'Old Crusty' titled roller parts bike (free!)
'82 gl1100I, My first 'Wing, and an expensive lesson!
New2U Bike? Read Me.
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dontwantapickle
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Re: An attempt to stop a GL1000 from smoking

#110

Post by dontwantapickle »

From some guys that race on the salt flats...
These are pretty standard conversion ratios for compression numbers at different elevations compared to sea level:

4000' .8881 = 88.81%
5000' .8617 = 86.17%
6000' .8359 = 83.59%
7000' .8106 = 81.06%

Of course,
everything affects density altitude numbers. heat, humidity, etc. so I would consider these numbers as
a pretty close ballpark, but not gospel.
cfairweather
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Re: An attempt to stop a GL1000 from smoking

#111

Post by cfairweather »

So, my reading of approximately 140PSI on the freshly rebuilt GL1000 is adjusted to about 168 using a correction value of .836. Now, I have some concerns about my 750 with high compression pistons. It registered about 169PSI, so it is adjusted to about 202PSI which is pretty high. I have a stock camshaft in it, but it has not pinged or had any issues here in Cheyenne. If I rode it at to sea level, it might ping, I don't know.
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gltriker
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Re: An attempt to stop a GL1000 from smoking

#112

Post by gltriker »

cfairweather wrote: Thu Jul 03, 2025 8:47 pm So, my reading of approximately 140PSI on the freshly rebuilt GL1000 is adjusted to about 168 using a correction value of .836. Now, I have some concerns about my 750 with high compression pistons. It registered about 169PSI, so it is adjusted to about 202PSI which is pretty high. I have a stock camshaft in it, but it has not pinged or had any issues here in Cheyenne. If I rode it at to sea level, it might ping, I don't know.
Don't worry... be happy! :-D

read posts 28 and 30
viewtopic.php?t=63468&start=15
Cliff ;) )

Keep your eyes and ears open and you'll learn something new, everyday. tumb2

New users please visit our "Shop Talk" for common tips and help: <---jdvorchak
http://www.ngwclub.com/forum/page/ST
^^^^^^^click up here^^^^^ :oldies

RE: a thorough fuel tank cleaning
"And your carbs will thank you. They no longer live down stream from a sewage plant." -gregforesi tumb2
"Can't see the paint when your looking thru the handlebars..........." -Oldewing ;)
"I'd rather Ride than Shine" -RAT tumb2 Me Too!!

Cliff

'75 GL1000 home built trike; http://www.ngwclub.com/forum/viewtopic.php?f=30&t=39996
October,2017 BOTM :shock: https://nakedgoldwingsclub.com/forum/page/Welcome

previous rides:
1953 H-D Servi-car, naked, 1969-1978 (serial#53G1559 committed to memory!)
1980 CB900 Custom (triked) 1997-2003 .... R.I.P.
redglbx
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Re: An attempt to stop a GL1000 from smoking

#113

Post by redglbx »

Cedric, great job ! On the compression thing, I wouldn’t be to concerned about it, I think it will run fine w/o any detonation. When I redid my 76’s heads years ago where i milked .040in off of them as well as advancing the cam timing 4deg I had a cranking compression of 200-210psi, I initially ran premium fuel in it and then stepped down to mid grade and then ultimately 86 grade with no noticeable spark knock, I tried to make that happen by whacking the throttle open at very low rpm to lug the engine and see if it knocked,,, it didn’t .

But I’ll add that I learned years ago that when I built hot rod car engines that I would deburr things in the engine, pistons and heads. I radius edges and corners so there are no sharp edges for hot spots to form and cause preignition. So if you’re are worried about your 750 just run mid grade in it, being an aluminum engine helps with all this as well because it dissipates heat and hot spots better.

So anyway,, great job !
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cfairweather
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Re: An attempt to stop a GL1000 from smoking

#114

Post by cfairweather »

Steve and Cliff- Great information, so I will not worry about it. This engine is very strong for a CB750 and enjoyable to ride. All three of my CB750s run incredibly well, but you can tell a difference with the one with high compression pistons. It is the 1970 K0, which is my favorite. I don't need three of these, so I will probably sell one in the next year or so.
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