Guess it's possible so, But he would have to be stupid to get it that tight. But I'm still not sure it could be done with out something on the plug breaking first.

 

+1 I'd think that the plug would break or the thread would strip before the head would crack.

Where's the crack?

 

Usually, you just strip the threads, and need to put in a " helicoil" for the correct side plug.

 

I think what you have pictured is a timesert, at least thats what it looks like, much better than a helicoil. Althought wont do much for a crack. I've never heard of a spark plug cracking a head. Usually a crack develops between valve seats.

 

between exhaust port and plug

 

what i am trying to figure out...is if it is possible the dealership did this when it was serviced 2 weeks before engine problems

 

actually yes that is were the crack is between valve seat and plug hole....is this a result of over tightened plug or what would cause this

 

I meant between valve seats, one to another, not to the spark plug hole. I would think anything is possible, probably more so with plugs that have an beveled sealing edge, but most bike engines use plugs with a crush washer for sealing. It would be a hard one to justifiy thats for sure. You're going into "youre word against his" battle.

 

Any chance that you live where it's cold and had water and/or Water Wetter coolant? Having asked that, I'd really expect other things to fail first.

 

I reckon it's possible, not exactly likely?!?...hang on - i've seen some freakin stupid things come out of dealerships.
If the Dealer over tightened the plugs AND then the motor got hot, then the extra tension from metal expansion around the plug thread could definately transfer to a weak point in the head.
Have seen a similar thing in Alloy cars heads where the head mounting bolts were over tensioned.
Heat does strange things to metal....
Si

 

Also possible that he dropped his wrench into the plug well. If it impacted the top of the plug just right, it could crack the head.

--Wag--

 

Did you really struggle to get the plug out?

If no, then it ain't likely to be the cause.

Whale

 

I don't know if there are any material or mechanical engineers here but they might care to chime in on this. The spark plug has a M10x1x19 thread. This indicates that almost all of the clamping load is carried by the threads closest to the mounting flange and that the others are generally just along for the ride. This means that the tightened plug provides very little stress to the end where the compustion chamber and valve seats are. In order to stress that end you'd have to tighten the plug so much that the upper threads would start to yeild. With this thread size and length (probably 17 or 18 engaged threads) that would be quite a lot.

 

I don't know if there are any material or mechanical engineers here but they might care to chime in on this. The spark plug has a M10x1x19 thread. This indicates that almost all of the clamping load is carried by the threads closest to the mounting flange and that the others are generally just along for the ride. This means that the tightened plug provides very little stress to the end where the compustion chamber and valve seats are. In order to stress that end you'd have to tighten the plug so much that the upper threads would start to yeild. With this thread size and length (19 engaged threads) that would be quite a lot.

It is possible to do this by over tightening the plug, but unlikely.

With new plugs, the crush washer takes the stress, one really has to be nuts to tighten beyond that and still over-torque the plugs.

Did they perhaps remove and re-install the old plugs?

 

What if it were cross-threaded?

--Wag--

 

I've not heard of it happening on any vehicle, car or motorcycle ever. Not that it couldn't, I think it is very unlikely. Usually threads will strip with too much force, but nothing will get cracked.

 

Since the crack runs between valve seats, it is unlikely caused by the plug. Here's a possibility - it could be a weak knitline from the casting process that finally failed. Had a similar thing happen to the front fuel bowl of a Holley 4 barrel on our ski boat. Failed after 15 years, the gas leaked right through the casting due to excessive porosity of the casting that finally formed a crack. Pretty weird, but it happens. If the flow of the aluminum in the head wasn't as it should be, it could be a manufacturing defect. Extremely rare, but possible.

 

no they are new plugs NGK with crush washers