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Vertical Cylinder Head Crack

Posted: Sun Apr 22, 2012 4:52 am
by animosity

Having found a cracked valve spring seat whilst changing my 860GT's valve oil seals, I figured my luck could only get better - it was not to be unfortunately. Upon cleaning the carbon buildup from the combustion chamber, I noticed a crack in the cylinder head starting at the exhaust seat outer edge and extending about 10mm outward ( not quite to the edge lip). From here, I believe I have three options: Ignore it and hope for the best; procure a new/used head; or have the crack welded up and re-machined.

Has anyone come across this before and can offer some ideas on the best way forward? While I'm not keen on forking out squillions of dollars for another head, I'm not keen on ignoring the problem either. Has anyone had any luck with repairing combustion/head cracks before??

Again, any and all help would be really appreciated.


Re: Vertical Cylinder Head Crack

Posted: Sun Apr 22, 2012 5:14 pm
by rwhc80

The crack is not entirely uncommon, but luckily can be reparied by an experienced welder. I remember looking at one of Brook Henry's Vee Two's 60 degree conversions a few years ago and the amount of fill welding carried out before re-machining was amazing !! I'm no welder, or metallurgist, but there are plenty of those converted heads still thrashing around race tracks today, so cant be a complete failure !!

I'm not suggesting a replacement sound head wouldn't be a better option, but if it were me, I'd have no hesitation in getting the repair done.


Re: Vertical Cylinder Head Crack

Posted: Tue Apr 24, 2012 7:27 am
by ducadini
I've seen several cracked heads, all vertical and all coming from 860's and Darmahs, with the crack running from the valveseat to the exhaust port.
Made me wonder if they just run hotter because of the tank (sits lower) and sidepanels.
One repair was to drill a small hole and shrink a small alu butt into it, preventing further cracking.
You could ignore it, the engine will just backfire more, while searching for replacements (check thoroughly before buying).