Big Bang on start attempt


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shehawken
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Motorcycle: 1981 GL1100

Big Bang on start attempt

Postby shehawken » Fri Sep 09, 2011 11:33 am



I've searched a little and not found anything like this yet so I thought I'd add my own question:

I have a 1981 GL1100 (basic model- only ever had the vetter fairing). I had the timing belts replaced within the last year and it's only been run about 6-8 times this year (our first child turned one yesterday- bad year for riding), the last of which was about 2 weeks ago. This morning, I went out to start it. I set the choke, turned on the gas and hit the starter button. It turned over 2 times and BANG, a sound like someone hit my engine with a hammer. Then the starter just clicked. I waited a few minutes and tried it again (I really wanted to ride it). turns over a few times and BANG! I quit and put the cover back over it.

It had been running rough (dragging one cylinder until it warmed up) since I washed it earlier this year and forgot to check the drain holes in with the spark plugs for spider webs first. Thoughts? Dragging the engine out doesn't thrill me as I'm living in an apartment with no indoor work space. Thanks in advance.



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thrasherg
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Re: Big Bang on start attempt

Postby thrasherg » Fri Sep 09, 2011 3:54 pm

I can't think of anything that would make a big bang, but would then let the engine turn over again after a few minutes!! After a big bang, the motor usually stops completely.. I was going to say sticking valves, if the bike hasn't been run in a long time, rust sometimes forms on the exhaust/inlet valves and prevents the valves from fully closing, so you get a bang when the piston hits it, but it's not usually very loud!! Hopefully someone can give a suggestion, but I would be looking at trying to run a compression check on the 4 cylinders to see if the problem is in the combustion chamber or inside the engine..

Gary

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Re: Big Bang on start attempt

Postby sperryunivac » Fri Sep 09, 2011 8:26 pm

Is it a bang like a misfire or do you think it is mechanical? My only thought at this point would be to remove the spark plugs and the alternator plug and use an offset box wrench to turn the engine over by hand for a few revolutions. You will feel a bit of resistance at the point where the cam opens the valves but if it gets really hard to turn it may be possible that the piston is meeting up with the valves. Perhaps there is water in the cylinder or your timing belts have jumped out of proper position in which case you need to remove the timing covers and check that the arrows are aligned as per the manual. So checking that the engine turns freely by hand would be my first priority and checking the belt timing second before hitting that almighty starter button.
From my experience after putting my engine back into the frame, I had checked all the above and when I hit the starter the engine gave a bang and it sounded like internal components hitting. I rechecked everything and then remember that I had replaced all the fuel lines and filter. So with the kill switch on, I cranked the engine over to fill the new fuel filter and prime the lines with fuel. Turned the kill switch to run and pressed the starter and varoom, I was riding. Also make sure that you have fresh gas in the tank.
I hope this helps

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riffraff
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Re: Big Bang on start attempt

Postby riffraff » Sun Sep 11, 2011 12:25 am

If it's a metalic bang I would check to see if the belts are on right. Are the tensioners tight? If it's a backfire bang, check the plug wires. Are they on the right plugs? (firing order) If you can't get a wrench on the alt bolt try putting it on the center stand, put it in gear and spin the rear tire to see if everything is free. It's all check, check, check , etc. You get the idea. Hopefully nothing is hitting, or bent.

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shehawken
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Re: Big Bang on start attempt

Postby shehawken » Tue Sep 13, 2011 7:52 am

been having trouble finding time to open things up (and the brakes on the car had to be done yesterday) but wanted to say I'm thankful for the directions. I figure to look at the timing first because the original tech did say "the belts were off two spots on the cogs, I reset them when I put it together with the new belts." Then, I'll look in on the cylinders. This is one of the times I wish I had more space to work than the parking lot of my apartment building.

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thrasherg
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Re: Big Bang on start attempt

Postby thrasherg » Tue Sep 13, 2011 9:49 am

In your first post, you stated the timing belts had been replaced in the last year and you had run it 6 or 8 times. If the timing was wrong, you would have had a very poor running bike on those 6 or 8 runs.. It would not suddenly change? I assume it ran okay on the 6 to 8 runs, which means it's unlikely to be the timing!!
If it is however and the mechanical noise is loud enough for you to hear, you need to run a compression test on all 4 cylinders as I suspect you will have bent some valves!!

Gary

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shehawken
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Re: Big Bang on start attempt

Postby shehawken » Wed Sep 21, 2011 8:02 pm

just an update: pulled one of the timing belt covers and it looks like the timing belts are okay (though I did notice the flat spot on the outside had been rubbing on the edge of one of the gears on the inside... looked like it had worn itself a pathway) and are not loose. With the radiator in place and the gasket on the cover, it took an hour and a half to get it apart and then put back together. I'm going to have to leave the rest of the searching until I find someplace to put it for the winter and can leave parts off it if I have to order something (which is not under our stairs in the parking lot). I'm not looking forward to it, but paying for something like this is not in the budget.

New wrinkle: When I hit the deer 6 years ago, I put the bike down on the side stand side. There was a nice flat streak ground into that side. What I didn't notice until I started thinking about having to crack open the engine casing was that I had mostly ground the head off of one of the cover securing bolts. Anyone have a good way to get out bolts which don't have a lot of places to grip them?

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Re: Big Bang on start attempt

Postby WingAdmin » Wed Sep 21, 2011 8:06 pm

shehawken wrote:New wrinkle: When I hit the deer 6 years ago, I put the bike down on the side stand side. There was a nice flat streak ground into that side. What I didn't notice until I started thinking about having to crack open the engine casing was that I had mostly ground the head off of one of the cover securing bolts. Anyone have a good way to get out bolts which don't have a lot of places to grip them?


I've used E-Z Outs successfully for that, and for bolts whose heads sheared off...but you have to be REALLY careful, both drilling the center of the bolt out (I use a left hand drill so as to not tighten it any further), apply lots of penetrating lubricant (I use PB Blaster), and be VERY gentle with the E-Z Out, because they are very brittle and very hard - and if they break, there's no drilling them out (unless you happen to have a diamond bit drill on hand!).




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