Datsun Roadster Forum-311s.org

Your going to have problems with grit etc. Between the valve and seat. That setup has no narrowing of the seat
Which probably can't be done as not enough room to accomplish. You should have a machine shop test it where it's seating ...I guess back then it was it seated at the top with the taper difference

I'd talk to a performance engine builder before I decided. My bet is that with the high performance nature of you engine, a y weak spot will be a source of trouble.
I'd bet that you'll need to have it filled and new seats installed if you're goIng to feel confident if the repair.
Sorry man.
Dan

So today I took the head to a local machine shop that's been building race cars for years. After he took a look at it, the owner was not very concerned with the damage and didn't feel it compromised the head. He felt it would actually be better to just smooth out the sharp edges and call it good vs attempting to weld it up. Since I will be dropping compression down to 10.3 to 1, I don't expect a repeat of detonation or continued damage. I have since cleaned, inspected and lapped all the valves and they look perfect, so after I clean it up I'll put it back together, hopefully better than before.

Glad you got another opinion Greg. Now you'll be able to put it back together with confidence.
Then, you can get back to tuning.
Dan

The experimenter in me is tempted to fill the spot with yes, JB Weld. I saw a video the other day where they cut a fairly large gash all the way through an air cooled cylinder head (lawn mower) and filled it up with JB Weld, ran it for an extended time and it suffered no issues. Then they made a complete head out of the stuff, machined it and it too worked fine.
But I won't just in case it could pop out and jam a valve. A lawn mower is probably not under the same degree of stress...

Yep, resist the temptation to put JB Weld in a combustion chamber. A lawnmower engine is so very different from your application in terms of aluminum alloy, air cooled vs. water cooled, OHV vs. flat head, bridge area between the valves experiences drastically different conditions than a flathead on an air-cooled engine.
But the experimenter in me also would like to try it... on a test engine!
Pulling for you.

I thought I'd close out this posting...
After much investigation I determined I did not bend any valves and there were no mechanical issues. I did discover detonation damage that may have occurred several months ago, possibly on the dyno during the first pull (detonated badly). Fortunately, after consulting with experts the best option was to clean it up and run it as it was not expected to be an issue. There was a lot of build up on the backs of the valves that were likely causing the poor sealing I saw. I cleaned and lapped all the valves, reassembled and installed Dean's thicker head gasket to drop compression from 11.7 to 10.3 or so. The gasket worked great, torqued to 65lbft with ARP studs and ARP lube.

I added a crank scraper as a "while I'm in there" exercise that appears to have dropped engine temps significantly (see separate post if interested). I also found out that the Ford EDIS ignition system I use requires double platinum plugs due to the wasted spark design. With the EFI and the correct plugs, it idles like never before... smooth and even with a nice thud thud thud. I LOVE EFI... I can't even tell you. I've resumed tuning via Tuner Studio's auto-tune and analyzing data logs in Megalogviewer to fine tune the fuel table and work on enrichment (think accelerator pumps). I expect the dyno to show significantly more power, but the driveability is already worth the effort.

So, she's all back together and ready to roll. Hopefully this will be the last time I have the beast apart for a long long time! I will probably do a leak down and compression test just to see what's what now, but I expect it's great. Thanks to all for the input and expertise!

Hope all that hard work and experimentation pays off with a powerful smooth running engine.

Glad all went well and not as bad as you feared. Rolling again. Nice!