Best Way to Remove Carbon Deposits?

[Tommy]

Hi, have a 1650 341 AQS. Prior owner rebuilt the motor, I got it running ok, then sounded like a blown head gasket. I pulled the head and it’s full of carbon. Also, there’s a small threaded hole in head near spark plug with a matching hole in the engine tin. What’s that all about?

thanks,

tom

 

[glippert]

Tommy - I presume you are referring to the bolt below the spark plug in your photo? (I circled it in red). That looks like a "previous owner modification" to me. Does it go all the way through to the combustion chamber? There should be a couple of threaded holes on the sides of the head that the side tins connect to, but not on top.

 

[Tommy]

Yes. That’s it. Goes totally through. I tapped out the hole and put in a grade 5 bolt, but stopped short of the other side

 

[Tommy]

Admittedly, first time I’ve pulled a head off, so forgive my ignorance, but why would there be a hole in the head?

 

[glippert]

I probably know less than you about this, but none of the three heads I've removed (1250, 1450, and 1650) have had a hole like that. But there are some really knowledgeable folks on this forum who will probably weigh in on it.

 

[mfrade]

I can think of no reason for that hole to be there. Some P.O. mod for some unknown reason. Plugging it with a bolt should work okay.

 

[Tommy]

Any ideas why it would run ok at idle, but tougher than heck at hi? It has a new carburetor

 

[dschwandt]

Carb needs tweaked some

 

[rfunk]

I can think of no reason for that hole to be there. Some P.O. mod for some unknown reason. Plugging it with a bolt should work okay.

Agree with comment and solution. Possibly PO had some damaged tin they wanted to add support to? Not very mechanical, to attach like that!! Maybe was "gearhead" engineer, wanted to measure cylinder pressure? (and didn't know there are "under the spark plug" units to do that). Maybe wanted to add water injection? (also better ways to do that)