[Black Lab]

This is a wild guess from me.

Because you heard a loud bang, and then a sound like a loud Harley, my thoughts are that one of the new sparkplugs blew out. It is quite possible that they new sparkplugs were not tightened down enough.

There are FOUR sparkplugs to your bike; two per cylinder. It seems to me that one, or two of them blew out of their hole.

 

[greywolf]

That sounds like a pretty good guess to me.

 

[New_on_Strom]

Because you heard a loud bang, and then a sound like a loud Harley, my thoughts are that one of the new sparkplugs blew out.

What can be the consequences? Is it possible that the thread was stripped and it needs a major service? Or just the plug shook loose and it needs to be put back, tighten and I'm good to go?

Is it reasonable to expect the shop to fix it under warranty?

 

[greywolf]

If a plug came out, it is the shop's responsibility. The threads will have to be checked for damage. They could be fine but they might not be if the plug was the cause. Before getting into too much conjecture, the exact cause has to be determined.

 

[New_on_Strom]

Thank you for your word of wisdom to both of you!

 

[Heavy]

Sounds like you've got good advice so far.

Good luck with it New_on!

 

[DrPaul47]

Please keep us informed.

 

[New_on_Strom]

Please keep us informed.

I'll do. It will be shipped back to the garage tomorrow morning. So far they were very responsive. I hope it is a good sign.

 

[Firefly]

My brother had a fairly new spark plug on his Harley blow out at highway speed. Luckily it just blew the center out and all they had to do is unthread the threaded part. Even new plugs have defects apparently.

 

[New_on_Strom]

My brother had a fairly new spark plug on his Harley blow out at highway speed. Luckily it just blew the center out and all they had to do is unthread the threaded part. Even new plugs have defects apparently.

I hope I'm not in for anything more serious than that.

 

[New_on_Strom]

Update

Email from the shop:

It appears that the spark plug cap was overtightened. We will be replacing it. They are checking to see if we have one in stock. I'll let you know.
There will be no charge to you. I apologize for the inconvenience.

 

[gryphon51]

If the bike was run on one cylander for ANY length of time, make sure they replace the engine oil, it could be contaminated with unburnt Gasoline.... and they might not volunteer to eat that cost if they think they can slip it by you....

 

[greywolf]

The spark plug cap is pushed on. I'd want to know what really happened and how they will fix it. If they damaged the head, I'd want a written guarantee on the repairs for the life of the bike as they will likely use a heli-coil or time-sert to fix it. It could be they manhandled the spark plug and the insulator blew out. That would be a simple fix once they get the old plug casing out.

 

[New_on_Strom]

I'll ask them what has happened and how they have fixed it.

 

[New_on_Strom]

Briefly talked to the tech, he said the spark plug broke. They did change the oil. I hope for the best, the seem to be honest folks. Time will tell.

I'd like to thank to everybody for the valuable comments.