I have a head that I have done a lot of port work on. it is to the point where it is showing really good numbers on the flow bench.
In doing a final clean up, I opened up in to the water jacket in the bowl of one of the intake ports. This is a fully finished head, new bronze guides.

I found a machine shop that does furnace welding and they said they were 99% confident they could weld it, they said they also pressure check their weld repairs.
Part of the repair process included pounding out then reinstalling the new never ran bronze guides.

It took a month, but I finally got the head back. I had previously made up plates that I can bolt to a slant head and pressurize the water jacket to check for leakage into the ports,
and there it was, there is a spot of very small visual porosity in the weld and at that pore I can locate a leak.
Photos of the head with the plates installed for leak testing is below.

So I am taking the head back to the shop that did the welding next week and have them re furnace weld it to attempt to close off the porosity. My question is, how many times can the
bronze valve guides be re moved and reinstalled. Or should I be trashing the new never ran guides that were in and out once and starting over with new guides?

thanks

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

No sure of the process of furnace welding but if it is just one small spot, couldn't it just be preheated really well and stick welded with the proper rod?

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

My gut says I would not reuse the guides at all, but I don't have a good reference point for this. If the shop is really good and they remove them with minimal damage, then maybe fine. If you successfully get this fixed, I have a nicely ported head that needs fixing in this way (one spot on #6 exh port) and I would be interested to get their info.

Lou

_________________
Home of Slant6-powered fun machines since 1988

will do, be certain I will be asking them why I easily found a leak and they previously told me it passed their leak test.
It may be a few days before I get it back to that shop. I ordered on of those $18.00 iPhone borescopes, I want to look at the
back side of the port, where the porosity - leak is to see what that looks like.
being an apprentice welder, I don't know enough about that to recommend one way or the other, but I did look at a few internet articles, what I saw is that gray iron wants to be
fully heated across the complete part or it will crack.
I do know that from my foundry experience when blocks or heads were weld repaired, and those repairs were on non machined castings and they were always thoroughly heated in a furnace to a dull red
then gas welded.
There was limited welding done on cast iron exhaust and intake manifiolds, where they would preheat a localized area with a gas torch then gas weld or they would arc weld those
in non machined areas, but those were simpler castings. But generally, the foundry welding was not my area of expertise on how they made that work. I just know they did it.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

I wouldn't re-use any guide that was driven out of a head, and You will need to replace them all again if that head is heated up for spray-welding/brazing, they will loosen up in the head if left in, and fall out. Unless the guide quality is checked and verified, putting the guide back in can stray the valve center requiring a seat touch-up, so there is no advantage other than cost savings to try re-using them. It is very difficult to fix old cast that has been ground through, because sand & contaminant occlusion/inclusions are adjacent to the repair site on the water jacket side, sorry,....but the odds are it's as good as it's going to get w/o building a "cover" layer that will be proud (read intrusive) into Your port.
The best solution will probably be to leave the repair if it is structurally sound for service and use a chemical sealer after making sure the water jackets are clean and contaminant free.

I had two heads repaired in the way you describe, I never leak tested them like you did but neither of them ever leaked. I did have the inside of the heads coated with some sort of stuff (ceramic ?) I think Moroso sells something for this purpose. Welding cast iron is tricky and if everything else is all right and the hole is very small you might consider such a coating. On the other hand if it doesn't work it might further complicate any additional welding. I think I would use a new set of guides, pressing them in an out has got to be hard on them. It is good to know you are carrying on Mike's work!

_________________
If you didn't drive it there, it's not a street car.

So what exactly are we gaining by re using the "old" guides?

says in the initial post, these are new valve guides

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

To quote Clouseau,......"not anymore!!"..............If You try to leave them in they will shrink after the head is cooled due to the different expansion/contraction rates of the materials, and You can push a number of them out with Your fingers, and the port being repaired will have to have it's guide removed anyway. driving the guides out is going to deform them to some extent, and require the ID be checked/touched up, and again there is no guarantee bore center will be where it was when the valve job was done(if it was finished). So You're basically saving the cost of the guides only,...and may end up sinking the seats on a couple to re-establish concentricity..................