Timing at top dead center but gear pulleys don't match


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joseph548694
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1976 CB400F
1981 CB750K

Timing at top dead center but gear pulleys don't match

Post by joseph548694 »



Hi, '76 GL1000. I'm a new not terribly competent mechanic. I've changed oil and replaced an air filter or two, but that's really all my mechanical experience, so please bear with me here.

I went change my timing belts a few weeks ago, but discovered one of the tensioner bolts was rounded and I could not get it off (I was using the how-to on NGWClub-also going to post this there). Anyways, and this become relevant later, I am mostly sure that when I got the engine top dead center the timing marks on the gear pulleys lined up how they are supposed to, but I am not willing to say that with 100% certainty, I'm just know I did not take note if they weren't lined up.

Today I finally got around to trying to get that tensioner bolt off, but had no luck, just ended up rounding it off more. How to get that bolt off is however not my question. The belt looks almost new, so I was just going to leave it until I had to do something about it.

So I go on to my other tasks of replacing the thermostat, temp sender, and fan switch, and in the process got some coolant on the tensioner and belt. I know, I should have put the cover on, but I wasn't thinking. So, in order to thoroughly clean the coolant off, I (again, was thinking even less, and this one I knew better) I took off the tensioner on the left side, and immediately realized my boneheaded mistake. So in the process of trying to correct this, I zip tie the kick starter to the foot peg to allow for easier access to the generator bolt. I turn the engine but accidentally go past the T-1 mark, so I keep turning to get to it again. But then I can't turn any more. It is very solid and abrupt, I could turn it easily, and suddenly I couldn't. I then took out the spark-plugs, because I was thinking maybe it had to do something with compression (probably should have taken them out first), but still can't turn. So then I turn the opposite direction using the kick starter, and find T-1.

Now here's where I have a problem (aside from not being able to turn the wrench anymore). The engine is at top dead center, but the timing marks on the pulley gears are not lined up with case. Not even close (pics below).

Also, when I try to cycle the engine with the kick starter lever, the same thing that happened with the generator bolt happens.

I had just rode the bike the day prior.

Does anyone know what is wrong, and can I fix it? I'm pretty sure it's my fault and I hope it can be corrected.

Thank you all for any ideas you may have.

-Bob
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Rambozo
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Re: Timing at top dead center but gear pulleys don't match

Post by Rambozo »

What you need to do is turn the crankshaft either way until you are no longer at TDC. You currently have the valves hitting the pistons. 20 degrees or so should do the job. With the pistons no longer at TDC you will be able to turn the cams. once the cams are in position you can turn the crank to bring the marks back into alignment. Remember the cams turn at half crank speed, so one option is once you have it freed up, you can estimate the belt position, put the belt on and then rotate to align the marks and make any slight adjustments to the belts to line everything up. As long as you are turning the engine over carefully by hand (with the spark plugs out) you will feel when things get bound up and you would have to really work at it to bend the valves.
BTW coolant on the cam belts is no big deal. You could just hose it off, or even ignore it.
One other thing that helps is to put a mark on your crank pulley and case at TDC, so you can see everything together.
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dingdong
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Re: Timing at top dead center but gear pulleys don't match

Post by dingdong »

What he said. Except I recommend you get new belts before you continue. Pistons hitting the valves is what happens if your old belt breaks. "But the belts look new" is a mistake many have made with distasterous results.
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Re: Timing at top dead center but gear pulleys don't match

Post by joseph548694 »

Rambozo wrote: Wed May 12, 2021 10:23 pm What you need to do is turn the crankshaft either way until you are no longer at TDC. You currently have the valves hitting the pistons. 20 degrees or so should do the job. With the pistons no longer at TDC you will be able to turn the cams. once the cams are in position you can turn the crank to bring the marks back into alignment. Remember the cams turn at half crank speed, so one option is once you have it freed up, you can estimate the belt position, put the belt on and then rotate to align the marks and make any slight adjustments to the belts to line everything up. As long as you are turning the engine over carefully by hand (with the spark plugs out) you will feel when things get bound up and you would have to really work at it to bend the valves.
BTW coolant on the cam belts is no big deal. You could just hose it off, or even ignore it.
One other thing that helps is to put a mark on your crank pulley and case at TDC, so you can see everything together.
Thanks for the reply, I'm in a little over my head here. I understand why the left side cam pulley doesn't line up when at TDC (because took it off), but why isn't the right side cam pulley mark lining up? Is it because I am not TDC on cylinder 1, but on another cylinder? If that is the case, how can you tell which cylinder you are TDC?

So I need to back of TDC, remove the left hand belt, then bring it back to TDC, align the left hand cam pulley per the arrow, and put the belt back on.

Also, hypothetically speaking, how hard is it to bend your valves? Is it possible to bend them by hand?
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Re: Timing at top dead center but gear pulleys don't match

Post by Rambozo »

Since the cams rotate at half speed, you can have the marks out 180 degrees with the crank on TDC. Your photos don't look like that, but I don't want to guess where everything is from multiple photos. That is one reason I like to have a mark on the crank pulley so you can see all three at once, no confusion.
You would have to push pretty hard once it binds up to bend a valve, from either the crank or the cam bolts. However the electric starter or your foot on the kick starter could do it, no trouble. So as long as you are turning by hand, you are pretty safe. Just don't try to force anything. Take your time and make sure everything lines up. Once you have everything lined up, turn the engine over by hand for at least 4 revolutions, just to be sure. Make sure all the marks line up every other revolution. If anything is not as expected, stop and find out why.
One way to verify #1 TDC, is to stick a soda straw in through the spark plug hole while you turn the engine over. You will feel the piston as it nears the top.
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Re: Timing at top dead center but gear pulleys don't match

Post by GL1000dan »

With respect, but I think you should invest in a good workshop manual or, at the very least, a Haynes manual. Probably $10 on eBay.
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Re: Timing at top dead center but gear pulleys don't match

Post by JoBoy68 »

I agree with everything the other guys have said I just want to clarify one point. if your flywheel is at top dead center but the cam pulleys are off you are not on the compression stroke turn it around again to your top dead center mark and the pulleys should line up
I put neon green nail polish on my pully and case timing marks so I could see them better
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Re: Timing at top dead center but gear pulleys don't match

Post by boosted-gtr »

Looks to me like that engine has skipped time. That abrupt stop you’re talking about is the piston hitting the valves. Back the engine off them. If you don’t know when those belts were changed, change them. Beats shopping for an engine. Get a bolt remover set and get that tensioner bolt out. Replace with a new bolt. Both those cams should read UP pointing straight up with the engine at t-1. Looking at the engine install the right side belt first you slack the tensioner and rotate the engine slightly to set tension on the belt, then tighten tensioner. Left cam will need to be held In place with a wrench, while holding the belt and spinning the engine to set tension on that belt. It’s tricky. There are marks in the cam gear and the timing covers. Spin the engine a few times GENTLY and make sure everything lines up at t-1. Good luck. Hope this helped!
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Re: Timing at top dead center but gear pulleys don't match

Post by Swagonmaster »

And keep in mind that while the crank pulley will be lined up properly the cam pulleys may be a hair off of the mark. Since you can only be a whole tooth off and not just a smidge don't worry about that (unless it's a whole tooth off then worry and correct it). If you are 180 degrees out the marks won't even be close.
Try to learn from the mistakes of others..... you won't live long enough to make them all yourself!
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joseph548694
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Re: Timing at top dead center but gear pulleys don't match

Post by joseph548694 »

Hi, original poster here. I want to thank you all for your expertise and encouragement. It took a while and some hands on learning to translate your advice into reality, but I now have everything where it needs to be. Thanks!
JoBoy68
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Re: Timing at top dead center but gear pulleys don't match

Post by JoBoy68 »

Glad to hear it worked out for you


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