Compression tester?


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shehawken
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Compression tester?

Postby shehawken » Mon Jan 23, 2012 7:51 am



Okay, I'm finally hoping to get into checking my compression on the GL1100 but, after asking both the father and the father-in-law, it turns out that none of us has a compression tester. Go figure. Anyhow, I'm looking for some opinions on what you would use. Are there certain pieces I need to have to make this work on a Honda or will a general tester work? I'm largely looking at single cylinder testers. Thanks.



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virgilmobile
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Re: Compression tester?

Postby virgilmobile » Mon Jan 23, 2012 8:21 am

I got mine at Advanced auto parts.Take a spark plug to be sure that the kit has the proper size adaptor.Compression is done with the kill switch "off" as in no spark and the throttle wide open.A viable engine should be above 135 psi with no more than 5 psi difference or so between any cylinders.A wide gap,say 15-20 psi will cause a poor idle and acceleration problem.

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thrasherg
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Re: Compression tester?

Postby thrasherg » Mon Jan 23, 2012 1:02 pm

And if you are not familiar with the correct practice, you hold the throttle wide open and crank it on the electric starter (wiith the pressure gauge screwed into the cylinder) until the gauge stops rising, that is then the correct pressure reading.. I prefer to remove all spark plugs when doing this as it strains the starter motor less and you need to check all cylinders. Many people fail to hold the throttle open, or don't crank it very long and that gives misreadings (low readings) and they then think they have problems that don't really exist..

Gary

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WingAdmin
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Re: Compression tester?

Postby WingAdmin » Mon Jan 23, 2012 1:05 pm

thrasherg wrote:And if you are not familiar with the correct practice, you hold the throttle wide open and crank it on the electric starter (wiith the pressure gauge screwed into the cylinder) until the gauge stops rising, that is then the correct pressure reading.. I prefer to remove all spark plugs when doing this as it strains the starter motor less and you need to check all cylinders. Many people fail to hold the throttle open, or don't crank it very long and that gives misreadings (low readings) and they then think they have problems that don't really exist..

Gary


I leave my battery tender plugged in while doing this, so that it has a chance to recharge the battery between tests on cylinders, to make sure the engine is spinning the same speed for all of the tests.

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RBGERSON
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Re: Compression tester?

Postby RBGERSON » Tue Jan 24, 2012 7:52 am

Ok a complete list:

hot engine
kill switch off
throttle held wide open
all plugs out..well all lose..so gas isn't sprayed out..see tip 6
charger on battery if you like
gas petcock off..I like to run carbs bowls dry too so no gas is being pumped into cylinders

cranks until needle stops moving up may take a few seconds no more than 5

you can make a connector for the Gl's by coring out an old spark plug and tapping out the top end to match a connector you have..use an o ring on the spark plug threads and the connector side. Gls' are 12mm and most kits don't have a 12mm connector.

140 to 150 is OK
150 to 160 is good
160 to 170 is great
over 170 = carbon issues on the pistons
under 140 time for rebuild..new rings or new valves/or lapping valves or both

The spread between cylinders should not be more than 5 lbs.

Note the bike will run nicely even at 130's all around but poor gas mileage.
HAD LOTS OF GOLDWING 75-83
NOW INTO 1500'S..RIDING A 1998 SE

FAIR WINDS,
RB

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RBGERSON
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Re: Compression tester?

Postby RBGERSON » Tue Jan 24, 2012 9:10 am

PS the manual says cold engine but I like to do it hot so I get a reading for when I am on the road. But not that much difference hot or cold.
HAD LOTS OF GOLDWING 75-83
NOW INTO 1500'S..RIDING A 1998 SE

FAIR WINDS,
RB

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Re: Compression tester?

Postby WingAdmin » Tue Jan 24, 2012 1:07 pm

Hot or cold is not as important as knowing that all of the cylinders are relatively close to one another in terms of compression.

If a cylinder is down in compression in comparison to the others, pour a teaspoon of oil into the cylinder through the spark plug hole and repeat the test. If the compression goes up, you have worn piston rings (the oil helps the piston rings seal). If not, then you've got a valve problem.

Keep in mind that people at higher altitudes (i.e. Denver) will experience lower compression numbers, simply because there is lower atmospheric pressure to begin with. Different altitudes need correction factors:

Code: Select all

 Alt  Factor
 500  0.987
1500  0.960
2500  0.933
3500  0.907
4500  0.880
5500  0.853
6500  0.826
7500  0.800
8500  0.773


Take your altitude, in MSL (feet above sea level). For instance, let's say where you live, it's 6500 feet MSL. Normal compression for a new GL1100 engine is 171 psi (cold). Multiply 171 by 0.826 (the correction factor for 6500 feet) and you get 141 psi, which is what normal compression for you will read.

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RBGERSON
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Re: Compression tester?

Postby RBGERSON » Wed Jan 25, 2012 8:20 am

Good info on altitude didn't realize it could affect compression ratios that much..no wonder riding in the mountains take so much out of a bike..
HAD LOTS OF GOLDWING 75-83
NOW INTO 1500'S..RIDING A 1998 SE

FAIR WINDS,
RB

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littlebeaver
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Re: Compression tester?

Postby littlebeaver » Wed Jan 25, 2012 5:59 pm

This is the very best post I've seen yet on the subject, if you pull all the plugs it may be a good idea to cover them, so nothing can fall down in :shock: ...That could be a pain...Keeping the charger hooked up is a really brillant idea ... :D

dwight007fchr
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Re: Compression tester?

Postby dwight007fchr » Wed May 22, 2013 6:46 am

Glad I found this thread.

Last night I was trying to do the compression test on my 83 GL1100. Had all the plugs out, and first found that the kit did not have the right adapter size. Upon quick glance, it appeared to be the right one, but the thread size measurement was about 11.75 for the plug and 12.20 for the compression kit adapter. You could easily try to force it in and probably strip out the aluminum threads.

So I tried using the rubber cone-tipped compression kit adapter. I pushed pretty darn hard on it as I cranked, but was getting very poor (or no) readings on the scale. I figured I would have to go out and buy some adapters to make the kit work, and I happened into this discussion.

I had NO IDEA that I needed to hold the throttle open when doing the test. I guess that is so the engine can suck in enough air during the test?

I may go ahead and drain the carb bowls first to keep all that gas from mixing with the engine oil.

Good tip on the battery tender, and trying the oil in a cylinder if it shows low (so you can better determine what the issue is).

Will try it again (with throttle wide open).

dwight

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Re: Compression tester?

Postby WingAdmin » Mon May 27, 2013 12:23 am

dwight007fchr wrote:I had NO IDEA that I needed to hold the throttle open when doing the test. I guess that is so the engine can suck in enough air during the test?


An engine with no throttle will run at full power. The throttle controls the power output of the engine by restricting the air (and hence the metered fuel) the engine receives. When the throttle is closed, it is restricting the amount of air the engine is getting, resulting in a vacuum in the intake manifold. This means the pressure and volume of the air drawn into the cylinders (and subsequently compressed) will be less, so the measured compression will be less. Opening the throttle wide removes this restriction, and eliminates the problem.

dwight007fchr
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Re: Compression tester?

Postby dwight007fchr » Mon May 27, 2013 5:48 pm

RBGERSON wrote:Ok a complete list:

hot engine
kill switch off
throttle held wide open
all plugs out..well all lose..so gas isn't sprayed out..see tip 6
charger on battery if you like
gas petcock off..I like to run carbs bowls dry too so no gas is being pumped into cylinders

cranks until needle stops moving up may take a few seconds no more than 5

you can make a connector for the Gl's by coring out an old spark plug and tapping out the top end to match a connector you have..use an o ring on the spark plug threads and the connector side. Gls' are 12mm and most kits don't have a 12mm connector.

140 to 150 is OK
150 to 160 is good
160 to 170 is great
over 170 = carbon issues on the pistons
under 140 time for rebuild..new rings or new valves/or lapping valves or both

The spread between cylinders should not be more than 5 lbs.

Note the bike will run nicely even at 130's all around but poor gas mileage.


**********HUGE RELIEF!!!********I got the 12 mm compression tester adapter to thread into my 83 1100 Wing without any issues. My concern that the threads of 11.94 were too large was not an issue.....she threaded in by hand without any worries.

I got great compression....two cylinders at 170, and two at 165. The one cylinder that is burning a bit of oil upon start-up was fine at 165.

The engine was cold and had not been run in a week before I did this test. Would a warm engine result in lower or higher compression? (Just curious) Should I take the time to run the engine and redo this compression test, or should I just rest assured that I have decent compression?

My other question is the "leak down" time. The needle would stop on say 170, and then would move very slowly downwards after I stopped cranking. When getting to around 155, the needle would almost stop moving, but still was losing compression at an extremely slow rate. I assume this is good and means the valves are seating great.

Any other comments/info./reccomendations on this test?
Many thanks to all.
dwight

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Re: Compression tester?

Postby WingAdmin » Tue May 28, 2013 1:29 pm

Those numbers are excellent. You should be happy with them - go out and ride! :)

dwight007fchr
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Re: Compression tester?

Postby dwight007fchr » Tue May 28, 2013 4:51 pm

WingAdmin.........I still have to find out what is causing the "miss" while cruising. I have replaced the battery, tested and replaced one of the coils, tested the plug wires and all connections, checked compresssion, and am about to install a new set of plugs. (I was thinking that a hair-line crack in the porcelin of a plug could cause the spark to go thru the porcelan and ground right out to the plug metal side, and maybe that is happening on one cylinder). Who knows, maybe I dropped one on the concrete floor when I was working on the bike. If this does not work, it must be one of the carbs........or a spark stimulator, which you say you have never seen one go bad.

Am also going to pull the fuel filter and see if maybe it is getting clogged, and drain the tank and put fresh in.

dwight




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