Hi, this is my first topic on OSO.
Im from Sweden and drive an swedish built Arrow 830 (27 foot, similar to Magnum 27) with 770hp@5500rpm, 598 cui Dart engine.. ran 92 mph last year with approx 700 hp..

Now, my problem, the intake valve on 7th cylinder is really cracked..

No damage to the piston, almost no damage to the seat, no leakage on the gasket..
Any ideas??

This is common in the rear cylinders when you have exhaust manifold leaks and can also happen in other cylinders as well when you use a lesser quality valve. Check valve spring press and if nothing replace all the valves. I would replace valves springs retainers valve locks and lifters. Use quality components Ferrea, Manley sincerely Laz Mesa
Www.mesabalancing.com

Any chance the valve lash was to tight

I have seen similar damage caused by reversion or leaking headers.

Doesn't that usually happen on the exhaust valves

May also want to check the valve guide, the valve may have been hitting the seat crooked stressing the valve head on one side. You may even notice the seat is more worn on one side if this was the case. From the look of the top seat angle you have some flat areas that made me think this may be your problem, then again it might be the photo that is tricking my old eyes.

You are right, took for granted it was an exhaust valve. I would still not rule out water though.
How does the plugs look like?

Thanx for all answers!
I believe that everything in this build is good (angels, valve lash etc) because it was rebuilt just last year, but one never nows But i will ask the builder about these items.
One thing I´m going to do, is to test my CMI-headers..

The plugs look wet, but i believe all plugs can be affected by the fact that this intakevalve lets the mixture go back up to the intake, then distribute all the wrong mixture to "all" cylinders?
Sorry for my poor english

wow

that sucks but man were you lucky that didn't let go.

krille Joli

What you have is a radial fracture of the valve. This type of crack is initiated at the margin, working its way inward to termination. There are a number of causes including thermal,pressure, and excessively elevated contact stress.

Bob