Real world cylinder compression?

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luigipasto
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Real world cylinder compression?

#1

Post by luigipasto »

I've been reading up on expected cylinder compression for GL1000 and getting numbers between 140 and 170, with anything lower than 140 apparently requiring a rebuild. Has anyone checked the compression or a running GL1000? I'm not sure that a 45 year old engine, that hasn't been rebuilt, will ever get close to 140?? Thanks!
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Re: Real world cylinder compression?

#2

Post by desertrefugee »

My 78 has been happily chugging along between 130 and 140 for years now. Haven't seen any change in the time I have owned it. Runs fine.
Last edited by desertrefugee on Wed Nov 17, 2021 1:52 pm, edited 1 time in total.
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Re: Real world cylinder compression?

#3

Post by redglbx »

My 76 recorded an amazing 135psi from new with I believe 140psi being the highest number. Honda says it’s supposed to be around 171psi, the dealer as well as the area rep & I had a pretty intense discussion over my numbers when it was new. The area rep and the dealer mechanic & sales manager all claimed it would improve with miles and that consistant cyl-cyl was more important.

After about 35 years and milling the heads .040in and advancing the cams 4deg it finally was at 185-195psi. I have seen a number of 1000’s with 100psi or less cranking compression that just run sweet. They will run on anything at that CR, so unless it’s using a lot of oil or you’re trying to get more performance out of it, I just don’t think it’s all that important. My friend Ed’s 76 daily rider has low compression like that and it just motors down the road, a very sweet running bike, why mess with it.

Disclaimer: keep in mind this post is from someone who can never leave well-enough alone and regularly gets made fun of because of that !😜
Last edited by redglbx on Wed Nov 17, 2021 9:54 am, edited 2 times in total.
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Re: Real world cylinder compression?

#4

Post by Whiskerfish »

Have had a couple in the 90 area that improved with exercise and I have had many that ran very well in the 130-140 area. Have only seen a couple in the 160 plus area, in general those were low mileage and well maintained. One started off at 60 on one jug but I never got that one up over 90 and ended up scrapping it. So long as they are reasonable close to each other. If not work the low ones with a penetrate of your choosing and try to raise it. Leak down does help a lot determining if the issue is rings or valves. Exercise does wonders for them. So long as it is firing and you can manage a decent synch I would not condemn a low pressure engine until I had several hundred miles on it.
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Re: Real world cylinder compression?

#5

Post by Shadowjack »

If it starts without pushing, it's got enough compression to go on with. :lol:
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Re: Real world cylinder compression?

#6

Post by redglbx »

^^^^ this ! If it starts & runs ok, ride it and just enjoy it ! Whiskerfish’s point about being able to balance the carbs is an important one as well as adding miles. Syncing the carbs is affected by compression & valve lash. They must be good!

My other 76, an LTD sat as just a motor & frame on a shelf in a warehouse for 20+ years and the first year I completed it I found that as I added miles to it the valve clearances would close up causing it to not really run well, I suspect corrosion on the valves/seats that was beat off with use. But once it was stabilized it just ran very sweet highlighting how poorly my other 76 from new ran.

The ltd being a handbuilt blueprinted & balanced engine should run better and yet the last time I checked the compression I think it was around 160psi but I’m not 100% sure of that. But as time has gone on I have found so many things wrong on my 76 from new bike that I have corrected that it now runs about as nicely as the LTD but the LTD ridden back to back is smoother probably due to the blueprint & balance, probably not all that noticeable unless ridden back to back with a standard. They are special !
Red 1976 oe owner
1976 LTD restored
1980 CBX , in the que, to fix the ignorant heavy handed owner
1981 CBX
1977 CB750 K7
2014 FJR OE owner, sold
1980 GL1100
1984 GL1200 naked
1969 CL350, in the que
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Re: Real world cylinder compression?

#7

Post by ericheath »

GLTriker has an extensive post regarding compression, compression testing devices and their faults, and the result of using Mike Nixon’s suggestions of slightly increased valve clearances. He followed the advice and documented his findings.
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Re: Real world cylinder compression?

#8

Post by MikeNTexas »

I have a 75 and a 76. They have 120 to 130 on all cylinders and both run great.
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Re: Real world cylinder compression?

#9

Post by wannabridin »

Man, this is making me feel a LOT better about my numbers!! I thought all mine were low at 140-150 across all...
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Re: Real world cylinder compression?

#10

Post by luigipasto »

Thanks to all for responding. This is very helpful.
1975 GL1000, on the road but patiently awaiting restoration
1976 GL1000, in the middle of a frame-off restoration.
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Re: Real world cylinder compression?

#11

Post by redglbx »

Just an FYI, Honda says cranking compression with all the plugs out and the throttle held full open is supposed to be 171psi, seems to be a standard Honda number on all their bikes. I’ve only ever seen 1 stock bike (a 78) that was even close to that. I believe that the 78/79’s tend to have higher cranking compression but I believe the more mild cam timing of them contributes to that versus the more aggressive 75-77 cam timing.

I’ve seen and tested a lot of these and no matter imho a reading in the 130-140psi range is about normal. As I said above my 76 when new was exactly that and didn’t Get any higher until I milled .040in off the heads and advanced the cam timing to +4deg. So again IMHO, if it runs good and doesn’t use a lot of oil just ride it and enjoy ! My .02
Red 1976 oe owner
1976 LTD restored
1980 CBX , in the que, to fix the ignorant heavy handed owner
1981 CBX
1977 CB750 K7
2014 FJR OE owner, sold
1980 GL1100
1984 GL1200 naked
1969 CL350, in the que
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Re: Real world cylinder compression?

#12

Post by Rednaxs60 »

Rebuilt the engine for my '85 Limited Edition. New rings - honed cylinders, heads refurbished two years ago. 155 PSI all round. The Honda manual(s) mention a compression from 170 upwards to the 210 range as well. Compression ratio on these 1200 engines is approximately 9:1. These are low compression engines and anything around the 150 range can probably be considered factory good.
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Re: Real world cylinder compression?

#13

Post by gltriker »

Post#13
luigipasto wrote: Wed Nov 17, 2021 8:42 am I've been reading up on expected cylinder compression for GL1000 and getting numbers between 140 and 170, with anything lower than 140 apparently requiring a rebuild. Has anyone checked the compression or a running GL1000? I'm not sure that a 45 year old engine, that hasn't been rebuilt, will ever get close to 140?? Thanks!
Set each intake and exhaust valves' lash clearance at 0.006" per Mike Nixon's recommendation. Leave the gap set there, too.

For truest testing results, utilize a 12mm threads compression testing adaptor that screws directly into the spark plug hole.
20191213_204517_1637796073345_resized (1).jpg
20191213_204517_1637796073345_resized (1).jpg (24.92 KiB) Viewed 410 times


regarding a Best Practice set-up, 14mm threads-to-12mm threads compression testing reducers are not X recommended
20200112_113223_1637982760730_resized (2).jpg
20200112_113223_1637982760730_resized (2).jpg (56.5 KiB) Viewed 157 times




by removing its check valve, this cylinder compression testing adaptor converts to a cylinder leakdown testing adaptor, too. tumb2
Attachments
20191213_162838_resized.jpg
20191213_162838_resized.jpg (65.16 KiB) Viewed 418 times
Last edited by gltriker on Wed Apr 26, 2023 7:54 am, edited 11 times in total.
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previous rides:
1953 H-D Servi-car, naked, 1969-1978 (serial#53G1559 committed to memory!)
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redglbx
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Re: Real world cylinder compression?

#14

Post by redglbx »

Cliff, what was the reasoning for setting the valve lash to .006in vs the factory .004in ? That said since I had the valves close up on my ltd after it had sat for 20+ years (prolly rust on the seats & faces) , they closed up to zero clearance a couple of times over the first 500 or so miles before it stabilized and would maintain its set clearances. I did start setting the lash at .005-.006in and generally now set it at .005in which should give up a minute amount of performance.

So I’m just curious as to why this is recommended.
Red 1976 oe owner
1976 LTD restored
1980 CBX , in the que, to fix the ignorant heavy handed owner
1981 CBX
1977 CB750 K7
2014 FJR OE owner, sold
1980 GL1100
1984 GL1200 naked
1969 CL350, in the que
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gltriker
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Re: Real world cylinder compression?

#15

Post by gltriker »

redglbx wrote: Thu Nov 25, 2021 10:23 am Cliff, what was the reasoning for setting the valve lash to .006in vs the factory .004in ? That said since I had the valves close up on my ltd after it had sat for 20+ years (prolly rust on the seats & faces) , they closed up to zero clearance a couple of times over the first 500 or so miles before it stabilized and would maintain its set clearances. I did start setting the lash at .005-.006in and generally now set it at .005in which should give up a minute amount of performance.

So I’m just curious as to why this is recommended.
"Cam", ;)
the recommendation to, and reasoning why to increase the valve lash gap to 0.006" is found in the text of this Mike Nixon topic:

see paragraph #3-Spec cylinder compression
viewtopic.php?f=54&t=63468

Mike also posted more info in Guru's Corner; see the Topic: Wing tips #8 - Cylinder compression basics
viewtopic.php?f=54&t=65099
you will find I stuck my neck out here, but it's necessary sometimes to sacrifice your dignity to get answers. :(
No photos though of Best Practice test equipment-versus-the make do method of utilizing a 14mm-to-12mm reducer
c'est la vie

and YES, setting all valves' lash clearance just 0.002" larger on my 1975 trike's already well-running engine early 2018 was immediately noticeable during a 300+ miles ride , in all engine speeds throttle positions , increased 5th gear engine roll-on power and an additional 2mpg fuel mileage, too.
Last edited by gltriker on Sat Nov 27, 2021 1:19 pm, edited 2 times in total.
Cliff (74yrs ;) )

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.
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