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Question here guys I ran a compression test on my 1982 GL 1100 Asplencade the other day as I was getting her ready for winter storage.

The bike has and still does run and idle great ,lots of power ect,however my readings for compression were

#1 cylinder=140, #2 135, #3 140, #4 135.

Idid the compression test with the engine at operating temp and throttle open

The readings are low according to the manual should I be concerned ,rebuild the engine.

What do you guys think?
 

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Hi Partsman 81. your compression is a lil low but it is also fairly equal. if you had valves that were not seating well, This could cause a drop in compression & I would repair that because your expence would be fairly low. If you were going after the rings as the culprit, Your now into alot of money & time. At that point I would just ride the bike & enjoy it.

Next best option it you like wrenching as a hobby, Find a used wing engine that is dirt cheap. Price all new bearings, rings, seals etc and pull it apart for a rebuild. You are able to take your time because your still riding your wing until you get your new engine built.

Wayne.
 

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if you want to find out if it is the rings or valve, do a wet/dry compression comparison test.

Looks like you already did the dry test, now do the wet test. Do the test as you stated only now add oil the cycliners, squirt oil throught the spark plug hole, attach your compression test and turn it if over, check numbers, if you'r number increase greatly, you rings are worn, if they don't increase greatly, you'r valves are worn and need to be relapped, seated. I don't remember the numbers for the break off point between rings and valves, have to look it up, but I think 25 lbs press increase or more is telling you your rings are worn, you better look that one up in the manual as far as the increase in lbs of pressure. I'll check back here sometime, if you can't find it, I will hunt it down. Or maybe someone else will chime in with the numbers.
 

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Problems with low compression to worry about-- (say 115- 120)

Burns oil and smokes

crankcase builds pressure and blows oil seals

cranks over fast and doesn't have any power when it starts

Exhaust may sputter at idle or backfire lightly(exhaust valves)

may belch or backfire thru carbs.(intake valves)

run rough and idle poorly with poor performance

If above symptoms are not evident, compresson readingsare Mox Nix. Run it and enjoy

:waving:Keno

Big problems, no compression on one side--No compression or real low on one cylinder.
 

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I really appreciate the replys, I ran a wet test compression did rise around 10-15psi in all cylinders, the bike has never backfired at anytime and like I said it idles and run good ,I did notice that #2 spark plug was a little oily and the other 3 were a brownish tan color.
It does use about 6-8 oz of oil every 1200 miles or so .
I purchased the bike in July of this year up untill then it had only been started once a month or so and not riden in 5 years . I have only put 5000km(3000miles) since I purchased but I have changed the timming belts,did the carbs ,spark plugs ect . I am worried about the compression being low .Again I thank you for yor replies
 

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Partsman, it's not really low enough to worry about. The bike is 25 years old, there will be a few parts that aren't exactly factory spec.

As long as it's running strong and even, I wouldn't worry about it until it becomes a problem.
 

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The test results say your rings are fine. Your valves may not be seating 100% great due to sitting. I would seafoam it, the fuel and the oil, run it for a while and take another test in a couple of thousand miles. Your valve steams may be a little gunked up. If it is running fine and your gas milage is decent, let it run for a while.

Edit, -- I just looked back at your orginal compression readings, that's not to bad. Again, I would let her run for a while.
 

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The compression readings vary a lot depending on the condition of your starter and battery. Since yours are within 5psi of each other they look pretty good to me. If the bike's not blowing smoke and runs as it should, fugettabotit! Better you should worry about something else.:cooldevil:
 

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Nice and even, it could always be your gauge that's off.
 

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partsman,

I started using only Shell 93 octain to help keep my Valves clean, and it works well after 3000 miles on it. Also, It seems to run better and gets better gas mileage.

Nightrider1

partsman 81 wrote:
Question here guys I ran a compression test on my 1982 GL 1100 Asplencade the other day as I was getting her ready for winter storage.

The bike has and still does run and idle great ,lots of power ect,however my readings for compression were

#1 cylinder=140, #2 135, #3 140, #4 135.

Idid the compression test with the engine at operating temp and throttle open

The readings are low according to the manual should I be concerned ,rebuild the engine.

What do you guys think?
 

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Odds are that the compression guage is pretty close. There are so many variables in checking compression that way that the most important reading is the differential between the cylinders. The actual pressure isn't that important unless it's extremely low. A low reading older engine will always show higher compression with a new starter. Obviously that doesn't mean the valves and piston rings got better, it just means that the engine is cranking over faster.

All cylinders leak pressure. The speed the pistons move in the cylinder have a very profound effect on compression readings. The air doesn't have as much time to leak down if the piston is traveling faster up the bore. Turn it slowly and more air has time to leak out. So battery condition, starter performance, temperature and the barometric pressure at the time of the test will effect the maximum psi developed.

The only way to measure compression accurately without having those things mentioned above effecting the reading is a differential pressure test also known as a leak down or blow down test. This is a check done by feeding a known volume of air at a given pressure into the cylinder and reading the pressure developed in the cylinder. If you did that on a number of similar engines you'd have a reference number for your bike to compare with.

The point of all this is that a direct compression test is only one indication of an engine's condition. It doesn't mean that much if all four cylinders are close together in pressure. Taken along with other indicators it can such as smoking, lack of power, etc. it can mean something significant.
 

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Couple of things...

As mentioned above, it could be at least in part a valve issue. I had the same problem with a V65 Magna- low compression because of gunked up valves.

I ran a can of BG44K through it and my compression went from 100-110 on all cylinders to 160-165.

BG is expensive ($20-25 a can) but it works better than any fuel additive I've ever seen or heard of. For a bike, put half a can in the tank when it's near empty, and fill it up. Run that tank out as far as you can without walking, put in a tank of "clean" gas, run that out, then put the other half of the 44K in and gas up. Run that out then re-check your compression. Might want to check your valve clearances too, if you haven't already.

In reguard to octane... I would recommend *against* running 93.... Any more, all grades of gas have the same additive package, so the only difference between 87 and 93 is how well it burns- higher octane=harder to burn (to decrease detonation). Unless you are running forced induction, NOS or 10+:1 compression, super unleaded can actually increase your engine's tendancy to build carbon deposits, and provides less heat per unit of fuel. It's a negligable difference in performance, but it's there, and spending more for less strikes me as conter-productive. The exception to this is if you have run 93 for a lot of miles... in which case there is probably enough carbon in there to cause detonation with 87.

The old rule of thumb we used when building import race cars was start with the highest octane you could get, and then go down a grade per tank until it pinged the first time.... then go up one grade and stick with that.

Merlyn
 
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