Does anyone know if it's possible to weld up and re-tap a spark plug hole in one of these heads? Or if the cost for doing it would be less than the cost of another head? (anyone want to get rid of an aluminum 300 head?) Jim
So are the results. It may be possible that these days someone makes a thread repair that works properly but my experience so far has been that the threads tend to come out with the plug. I don't consider that a very good repair. Jim
I put your question to my mechanic today. He said without hesitating that yes it can and is done. Cost he estimated at 40.00. Bill has been neck deep in automotive engines since at least as far back as 1955. I had a somewhat similar question on my 215 block. An outer row head bolt boss was cracked. I didnt know if it could be rewelded, or how many hundreds of dollars it was going to cost. Ended up being easily done for the welding shop's minimum fee of $30. While they were at it they put a bead across some deep corrosion pits at the water jacket on the end, which will be taken down with decking.
When I went to big valves in my 300 heads, I welded the spark plug holes up, and added material in the chamber for a smaller diameter and longer length spark plug from a motorcycle. I used 10mm thread spark plugs. Doing this gave me a longer spark plug, and I actually repositioned the plug hole downward a bit more distance from the ledge in the head for the valve seat inserts. Lots of work, but the results have been great. In my opinion, a Heli-Coil or other spark plug thread repair isn't the way to go on a Buick aluminum head, removes too much metal from the head. I also went to 1/2 inch ARP studs for the heads. I would be very careful on welding a long distance on the head gasket deck, as welding changes the condition of the metal, and softens it in one place, hardens it in another. Regards, Milton
Thanks Mike, that's what I was hoping to hear. On those outer head bolts, current common practice is to just snug them down lightly or not even use them at all, since they tend to cock the head. Jim
Every threaded hole in my alum. heads are helicoiled. the ones for the spark plug holes are solid not a wrapped coil. you will need the shorter inserts. the tool for them is stepped and lines up in the original hole and cuts the hole in the head bigger,then once the insert is in the other tool stakes it in. then you can use a REGULAR TAPPER SEAT SPARK PLUG LIKE AN R44TS, i have used them in a head with out the thread inserts also, just lightly chamfered the top tread. 44FFS plugs are getting hard to find, HOPE THIS HELPS YOU.
I never Heli-Coil a thread in aluminum, I stud the hole, not bolt it. If I strip a hole out, I either go a larger thread, or weld/drill/tap. Heli-Coil just takes too much aluminum away, weakening the part and hole. Just my experiences from years of working on aluminum parts.
Thanks. I didn't mean to say helicoils are bad. I think they're a big advantage just about everywhere but in a spark plug hole. A solid insert that has a real thread on the outside and is mechanically secured so it cannot turn after being installed, even if the plug is hard to remove should be just fine but I'd want them in all eight holes rather than just one since they might affect the temp range of the plug. How they're secured would be important too, since removal torque could strip out the staking device. Installing the insert and then swaging it into place might work, but then again, heat cycles could cause it to loosen just a little, allowing it to turn which could lead to failure. I think the welded repair is going to be the best long term solution. Jim
I agree with you, Jim, about the threaded "slug" vs Heli-Coils. Also, about the welding as opposed to other methods, especially in aluminum Buick 215 and 300 head spark plug holes. The Heli-Coils are just too unstable for me. Also, it is essential to use a good anti-sieze on the spark plug threads when they are threaded into aluminum. Regards, Milton
