Spark plug hole crack in housing
 

cant make my mind to use this housing or not. the crack is 6mm long and your can catch your finger nail on it. I would hate to trash this housing as i just had it refurbished. The crack was not that noticeable at all before the housing was resurfaced :(


The housing was going to be used for a high hp 20 psi build but I don't think I'm gonna chance it.

Any opinions would be great.



http://i48.tinypic.com/34tbdr6.jpg

I wouldn't do it, but I am not 100% sure on this hopefully someone else will have a better answer

ive seen some tuners use something like a countersink bit and grind the crack out. its definately less than ideal.. but ive seen it done

I wouldn't trust it as it will cost you more money in the long run if it fails and you have to rebuild the engine again

I see these types of cracking often in 93+ engines, rx8s, and high power 2nd gens turbos.

It will not fail catastrophically or damage any other parts. However it will cause apex seal wear (unless you correct the crack) and it will reduce compression and longevity of the engine. Eventually it will reduce compression so much that you cannot reliably start and idle, and that is the mode of "failure" for this type of defect.

With less severe cracking I usually give the customer the option to reuse the cracked housing after I doctor it up a bit, or if it is in budget they can replace the housings. I put a 1-2mm bevel around the sides of the leading plug hole and I lightly sand down the crack itself about 1mm all the way around it. In doing so I hope to

1) keep the crack from growing further

and

2) keep the crack from swelling open at high temperatures and expanding into the path of the apex seal which causes seal wear and compression loss

These cracks cause significant compression loss if left alone. If you look at housings with cracking that have been in a running engine, there is always a "carbon stripe" extending from the cracks. The reason for this is that they swell open when hot, into the apex seal's path of travel. The seal hits the cracks like a car hitting a speed bump, and the seal is pushed off of the rotor housing surface. So compressed air from the trailing rotor face blows out from under the seal and you've lost some compression every single time the seal passes over the crack. The "carbon stripe" exists because the seal isn't in contact with the housing at that place and so carbon builds up since the seal isn't cleaning it off with each swipe.

The cracking on this particular housing you've shown here is very severe and I would not consider using it. You could make a running engine out of it however I would do significant grinding and doctoring to the cracks and the plug hole area if you want to try and use it.