TOPIC:

Hi

Engine's out and on the bench, ready to split. In the meantime, I've got a few decisions to make following the pistons-and-rings blowout.

Do you think I can/should reuse this head (KZ440)? I've just given it a quick clean with some petrol and a toothbrush, to reveal the damage.

I would prefer to reuse it because it has some mild porting work, the valves are good and the cam bearing surfaces (the semicircular recesses) don't have much wear. 
I have been thinking that, given that the circular impression left by the head gasket shows that the damage (caused by flying bits of piston ring) is within (only just) the outer bounds of the cylinder head chamber, I could grind these out with a Dremel and make them roughly smooth. However, even if I do this, there will be little holes left over by sharp bits of piston ring (some bits were actually embedded in the head, and I plucked them out). 

Main concern: if I do this, hotspots within the combustion chamber may result. However, I don't have enough knowledge/experience to know whether I could live with these (i.e. would they be filled up with carbon deposits anyway and not be a concern?)

Option: use my spare cylinder head (it's actually the original cylinder head for this engine). Disadvantage: yes, it would work, but there is a horizontal scratch on one of the cam bearing surfaces, and the cam bearing surfaces don't really look semicircular any more. However, the valves in this spare head are also good and come with the head, wouldn't need grinding and lapping, etc.

Any tips/advice would be greatly appreciated. I've been thinking about pulling out the Dremel and also using some flux-core alu brazing rods to deal with the holes left by the bits of piston ring. Really would like to reuse this head, if possible.

 

As long as you stay inside the the gasket sealing ring and remove any sharp edges carefully I think you will be fine (it's the sharp edges that cause hot spots)

Ah, that's awesome! That will save me a lot of trouble, thanks.

Fill the holes after surfacing off and cleanup with a TIG welder   ( Low heat if only doing small area at one time  
 Then reclean and grind flat 
All fixed

Street Fighter LTD wrote:

Fill the holes after surfacing off and cleanup with a TIG welder   ( Low heat if only doing small area at one time  
 Then reclean and grind flat 
All fixed

Cheers, but I don't have the skills or the equipment to do that. I have taken evening courses in MIG, and am a hobbyist stick welder, but I have to be careful with going out of my depth as it isn't my field. There used to be machine shops where I live, but I have to send my barrels across the country to get them remachined. That said, I could look into getting the head professionally welded and machined, if that's best. 

As for what I could do at home, I could use flux-core brazing rods (they're sold as "aluminium alloy flux core welding rods") but I think they might not be wise, given that the melting temperature is given as 480C to 550C. They're really thin and easy to use but the issue is they're low temperature. If I could get away with simply removing just enough material to smooth out the specific nicks, that would be ideal.

 If I could get away with simply removing just enough material to smooth out the specific nicks, that would be ideal.



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Nebr_Rex wrote:

 If I could get away with simply removing just enough material to smooth out the specific nicks, that would be ideal
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What's your opinion?
Not the end of the world if I have to use the other head, although I'd rather not.

As mentioned, use some machinist dye, position the head gasket and scribe the inner circumference of it to the head. If damage and clean up can be done within that circle your good. You will loose some compression but I’d mill the head as a precaution and that will help restore most of the loss. 

DONT USE LOW TEMP BRAZING RODS!!! The combustion temperature would melt the end and ruin your day

Michi wrote:

Nebr_Rex wrote:

 If I could get away with simply removing just enough material to smooth out the specific nicks, that would be ideal
.

What's your opinion?
Not the end of the world if I have to use the other head, although I'd rather not.

Around the exhaust valve worries me the most.
A straight edge, a file, and you said you have a dremel?
Make sure the deck surface is flat.
With your dremel carefully clean up the contour around the exhaust valve.
If you want to touch up the rest of the chamber go ahead.
When using the dremel do not go all the way to the base metal, leave a lttle bit sticking up.
Then finnish it with some emory cloth/sand paper.
After that completely disassemble the head and clean it.
There is a memeber on here that did some machine work on a head and never cleaned it.
He reassembled the engine and proceeded to blow it up.


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Nebr_Rex wrote:

  wrote: There is a memeber on here that did some machine work on a head and never cleaned it.
He reassembled the engine and proceeded to blow it up.


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I just want it known that it wasn't even me.

No it wasn't, it happened some years ago..


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