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Compression lose on a 1981 GL1100

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#1 ·
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Hi,

I'm in need of help on a 1981 GL1100. First let me say that I rebuilt this engine and put it back in the frame. I tried starting it and nothing. I did all the test, compression, fuel, electrical, and ignition. All of these were positive. So, by reading the service manual I figured it was out of time. I begain by lining up the T1 mark located at the top back of the engine block. Then checking the timing marks on each cam (left and right) and they line up perfect!

Every time I tried to start the engine I would try to start then backfire.

A machanic friend of my told me that I could be 180 degrees out of time. So I begain.

First, I lined up the T1 mark, then took the belt off the left cam. I then turn the crank clockwise until the T1 mark came up again; reconnected the left cam belt and tried to start the engine. Nothing but a lot of backfires. I did the same to the right side. and nothing.

After several tries at this the engine sounded different. Freewheel, no back pressure.

So I checked the compression and had none. I just don't know where to turn now.

I've continue try to put in time thinking I'll get compression once I have back in time.

I've been at it for 2 days and now It's time to ask for help.

thanks, teacher
 
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#2 ·
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teacher wrote:
Hi,

I'm in need of help on a 1981 GL1100. First let me say that I rebuilt this engine and put it back in the frame. I tried starting it and nothing. I did all the test, compression, fuel, electrical, and ignition. All of these were positive. So, by reading the service manual I figured it was out of time. I begain by lining up the T1 mark located at the top back of the engine block. Then checking the timing marks on each cam (left and right) and they line up perfect!

Every time I tried to start the engine I would try to start then backfire.

A machanic friend of my told me that I could be 180 degrees out of time. So I begain.

First, I lined up the T1 mark, then took the belt off the left cam. I then turn the crank clockwise until the T1 mark came up again; reconnected the left cam belt and tried to start the engine. Nothing but a lot of backfires. I did the same to the right side. and nothing.

After several tries at this the engine sounded different. Freewheel, no back pressure.

So I checked the compression and had none. I just don't know where to turn now.

I've continue try to put in time thinking I'll get compression once I have back in time.

I've been at it for 2 days and now It's time to ask for help.

thanks, teacher
Teacher, unfortunately it's possible you might have bent the valves by cranking it withthe cams timed incorrectly. You REALLY NEED TO ALWAYS turn the engine over a couple of revolutions BY HANDafter ANY cam belt replacement or movement. IF, you had or now have it (cams)mis-timed by 180° you probably didn't bent a valvebut any other place could be fatal for valve life.

PUT IT EXACTLY in cam timing as the the book calls for & re-try the compression check & hope that is all that is wrong withthe compression.



First, I lined up the T1 mark, then took the belt off the left cam. I then turn the crank clockwise until the T1 mark came up again; reconnected the left cam belt and tried to start the engine. Nothing but a lot of backfires. I did the same to the right side. and nothing.


That crankshaft was turned 360° so the pistons were right back where you started. The crankshaft only knows ONE position for TDC no matter how many times you turn it as long as the timing mark lines back up. BUT the CAMS can be off to the pistons if they aren't also moved to line up when the crank is lined up with it's timing mark.

With any luck you now just have BOTH cams off 180° & that probably didn't bend a valve as that is a normal place to end up. Both cams off 180° will give you 0 compression.

I guess if you suspect bent valves pull all 4 spark plugs, then remove the valve covers & make sure the valves are closed on one cylinder at at time, then blow compressed air into that cylinder through the plug hole& see if the air comes out either the intake or exhaust,, if so you bent a valve on that cylinder.



Twisty
 
#4 ·
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teacher wrote:
Thanks guys,

To do a proper check. Can you tell me where the #1,2,3, and 4 cylinders are as you face the the front of the bike?
Teacher, sitting on the seat the #1 is the front on the brake lever side,, #3 is the rear on the brake lever side,, #2 is the front on the shifter side,, #4 is the rear on the shifter side.

Twisty
 
#8 ·
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hey jack,

I sure could use some help on this one. I can usually figure things out but I really don't understand valves and lifters and pistons. But give me a carb and I can fix it.

Send me an email at: hcbrothers@netzero.com and hopefully we can put two heads together and get me back on the road. Thanks again Jack. Teacher
 
#9 ·
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hi vic,

With all the response at least I have a start. I'm going to try some things twisty said and others. I'm even checking on price of valves. At least I have some direction. Thanks for the inquire. Teacher
 
#11 ·
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Teacher, if you get a chance & have the means take an old spark plug &break out the center electrode, then weld or braze in an air hose fitting that will fit your air compressor hose. That (special plug) will be a big asset in pressurizing the cylinders tocheck for a "leakdown" condition due to bent valves or other problems. That lack of compression really has to be addressed before it will even have a chance of starting.

Twisty
 
#13 ·
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hey twisty,

If I line up the T1 mark on the crank.... then, line up the Right and Left cam on their mark.....then, take the belt off the, say, right cam.....then turn the crank until the T1 mark lines up again....then put the belt back on the right cam will the right cam and crank be in time or maybe 180 out of time?

teacher
 
#14 ·
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CAUTION: If you turn the the cam or crank more than a few teeth you stand a good chance of damaging valves. If I were in your position at this time I would seriously consider removing the rocker arms to prevent bending any valves, then get the cams and crank lined up and timedcorrectly, then reinstall the valve gear.

Vic
 
#17 ·
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teacher wrote:
hey twisty,

If I line up the T1 mark on the crank.... then, line up the Right and Left cam on their mark.....then, take the belt off the, say, right cam.....then turn the crank until the T1 mark lines up again....then put the belt back on the right cam will the right cam and crank be in time or maybe 180 out of time?

teacher
Teacher, once the T1 mark is lined up turning the crank again gains you nothing. That crank (& pistons) are ALWAYS in the same place at T1 regardless of how many times you turn it. Now once the cam belts are hooked up the crank to cam position can change if the crank is turned with only one belt hooked up. Basically BOTH cams should be timed to their marks with the crank at TDC.

Be careful when turning the crank or cams with the belts removed,, do all turning by hand & if resistance is felt turn the cam(s) a little until you don't hit resistance. The cams can be lined up without pulling the rockers but you must be careful not to force the crank or cams past any resistance. If you (can) turn the crank to TDC (#1) then back it up about 1/4 turn that will allow the valves to clear the pistons as you rotate the cams.


Twisty
 
#18 ·
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Teacher, all it takes is for the piston to contact the valve slightly and you will then lose compression and will need to replace bent valves to get the compression back up.

If you know exactly where the valves are in relation to the pistons and money is no object to you go ahead and spin the crank until the pistons touch the valves, but, from what I've read so far in the posts it sounds like you may be uncertain about the cam to crank timing. Removing the rockers will give you great lattitude to experiment and get it right without risking anything except the time to remove the valve covers and valve gear.

Vic
 
#19 ·
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Goldwinger1984 wrote:
Teacher, all it takes is for the piston to contact the valve slightly and you will then lose compression and will need to replace bent valves to get the compression back up.

If you know exactly where the valves are in relation to the pistons and money is no object to you go ahead and spin the crank until the pistons touch the valves, but, from what I've read so far in the posts it sounds like you may be uncertain about the cam to crank timing. Removing the rockers will give you great lattitude to experiment and get it right without risking anything except the time to remove the valve covers and valve gear.

Vic
Teacher, if you do pull those rockers that would be an ideal time to pressurize the cylinders with compressed air to check for valve leakage as ALL valves will be closed. If valve leakage is present no need to go farther on cam timing as it will have to come apart anyhow.

Twisty
 
#20 ·
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Twisty has been very thorough and probably covered it all here, it does look like you bent some valve. The giveaway is when you took a belt off and turned the engine completley until the T1 mark came up. You shouldn't have been able to do that without one of the pistons locking up against a valve. I'd say some valves were already bent by that atage.
 
#21 ·
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dear all,

thank for all the help. With so much great advise I'm not sure where to start. If the #1 cylinder is at TDC whats open, in or ex? and Is in on top or bottom. I know all this questions seem very dumb, but I've never done a valve job before. I attempted to take it to the Honda dealership in Texas City, Tx. but they won't take it because its to old a bike (1981). So I'm reading alot. But is it true that when the crank travels 360 the cams will only travel 180. I'm thinking 180 for in and 180 for ex. Is this correct?

But went I start I will not force anything! I have the plugs out as twisty suggested and I can see what the pistons are doing but I can't see what the valves are doing
 
#22 ·
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teacher wrote:
dear all,

thank for all the help. With so much great advise I'm not sure where to start. If the #1 cylinder is at TDC whats open, in or ex? and Is in on top or bottom. I know all this questions seem very dumb, but I've never done a valve job before. I attempted to take it to the Honda dealership in Texas City, Tx. but they won't take it because its to old a bike (1981). So I'm reading alot. But is it true that when the crank travels 360 the cams will only travel 180. I'm thinking 180 for in and 180 for ex. Is this correct?

But went I start I will not force anything! I have the plugs out as twisty suggested and I can see what the pistons are doing but I can't see what the valves are doing
Teacher, #1 TDC (at firing) is both valves closed (they need to be to have compression for ignition)..

Just look at the carbs & exhaust for valve position-- carbs on top = intake on top,, ex pipes on bottom = ex valve on bottom.
But is it true that when the crank travels 360 the cams will only travel 180. I'm thinking 180 for in and 180 for ex. Is this correct?
For this look at the cam pulleys vs the crank pulley size-- the crank turns twice for each revolution of the cam so with 360° travel of crank the cam(s) only travel 180°.

Twisty
 
#23 ·
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hey vic, old gold, and twisty,

got the carb connection off and the plug pulled at #1 and The #1 cylinder is at TDC but the intake is 1/8" open. Cause of my compression problem? But why? Whats the best case and whats the worse case? Is this a bent valve or something simple like airing up the front tire? teacher
 
#24 ·
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teacher wrote:
dear all,

thank for all the help. With so much great advise I'm not sure where to start. If the #1 cylinder is at TDC whats open, in or ex? and Is in on top or bottom. I know all this questions seem very dumb, but I've never done a valve job before. I attempted to take it to the Honda dealership in Texas City, Tx. but they won't take it because its to old a bike (1981). So I'm reading alot. But is it true that when the crank travels 360 the cams will only travel 180. I'm thinking 180 for in and 180 for ex. Is this correct?

But went I start I will not force anything! I have the plugs out as twisty suggested and I can see what the pistons are doing but I can't see what the valves are doing
If the valve covers were off you would be able to see if the valves are open or closed. As Twisty stated the intake valves are on top and the exhaust valves are on the bottom. When the lobe on the camshaft raises the rocker armthe valve spring compresses which means the valve is open. When the piston is at the top of its travel and both valvesare closed this is TDC. When I work on valve timing I use a degree wheel on the crank and a dial indicator on the camshaft, but, you don't really need a setup like this.You can use a drinking straw to feel where the piston is at TDC, just place the straw in the spark plug hole and slowly rotate the crankshaft. TDC is the pointwhere the piston is closest to the cylinder head andthe straw no longer moves in or out when you rock the crankshaft back and forth a few degrees. At this point you should have clearance between the rocker arm and the camshaft. You can feel it by shaking the rocker arms with yourfingers. If you find that there is no rocker to cam clearance at TDC the timing is definately off or you have set your valves incorrectly which raises another question, what did you set your valves at? This would be the clearance between the rocker and the cam or valveand measured with a feeler gauge. If all your valves are set too tight you will not havemuch compression and it can backfire trhough the exhaust or intake.

If any of the valves are extremely bent there may be a lot of valve to rocker arm clearance because the valves cannot close due tothe valvesinability to return to its seat.

To do a leak down test you need both valves closed and the easiest and safest way for you to do this at this point in time is to remove the rocker arms.

Don't be afraid to speak up and ask questionswhenyou don't understand something we suggest to you. After all, we are not here to impress you with how much we know, we're here to help you get your bike running again. Each one of us GURUS have our own unique ways of doing things to arrive at the same endand if we make an error it's quickly caught out here. Just follow thedirections that are easiest for you to understand and keep posting your results, eventually you will get the problems sorted out.

Vic
 
#25 ·
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hey vic,

thanks! now i'm closer to understanding it. When #1 is at TDC the intake valve is 1/8" open. The #2 at TDC the intake is about 3/8" open and only moves when i turn the crank about 1/8" more open but never seats. I haven't gotten to #3 or #4 yet. I kinda wanted to hear what ya'll had to say. I can't determine visual it what the exhaust is doing. I just know I have a problem with intake #1 and 2. And if ya'll think they are bent then there is no point in checking the exhaust of all or the intake of 3 &4. I would need to take the rocker arm off, remove the cam, then the head the each valve and check with a straight edge, right? I wish it could be just a minor adjustment, but with me seeing the #2 valve basicly not moving, I'm think bent valves. Plus #1 valve never seating. When I had the engine apart I DID NOT mess with the valves or their settings. All of this started with a knocking in the block after I got the bike running. Come to find out it was the starter chain hitting the inside of the engine case. New chain, new bearing, problem solved. yea right!

teacher
 
#26 ·
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teacher wrote:
hey vic,

thanks! now i'm closer to understanding it. When #1 is at TDC the intake valve is 1/8" open. The #2 at TDC the intake is about 3/8" open and only moves when i turn the crank about 1/8" more open but never seats. I haven't gotten to #3 or #4 yet. I kinda wanted to hear what ya'll had to say. I can't determine visual it what the exhaust is doing. I just know I have a problem with intake #1 and 2. And if ya'll think they are bent then there is no point in checking the exhaust of all or the intake of 3 &4. I would need to take the rocker arm off, remove the cam, then the head the each valve and check with a straight edge, right? I wish it could be just a minor adjustment, but with me seeing the #2 valve basicly not moving, I'm think bent valves. Plus #1 valve never seating. When I had the engine apart I DID NOT mess with the valves or their settings. All of this started with a knocking in the block after I got the bike running. Come to find out it was the starter chain hitting the inside of the engine case. New chain, new bearing, problem solved. yea right!

teacher
Teacher, I'm getting in here late so this might be too late to help. MAKE SURE you have #1 at TDC COMPRESSION & not TDC exhaust. The intake valve probably opens slightly before TDC at the end of the exhaust stroke. Try turning the crank one more revolution as it sounds like you are at TDC#1 exhaust & not TDC compression.

Twisty
 
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