Getting aluminum spark plug threads repaired

[38plymouth]

I need several (if not all maybe) spark plug threads repaired on my fenton head. When I got it I was so excited to put it on I never checked the plug threads and I stripped 1 before I ever started the engine. I didn't want to pull the head back off so I used one of those kits where you tap the hole and put in an insert. I ended up doing several like that and they worked for awhile. One finally blew out of the head so I put the original head back on for now. I called and went to several local machine shops and none of them say they can fix it. I see that there is a company that sells big-serts but the kit to DIY is pretty expensive. I was thinking someone could weld the holes shut and then drill and retap them. Does anyone know where I could get this fixed correctly? There must be a way to repair this head.

[claybill]

the reason for the stripped heads is probably that folks are still using the short plugs from the iron head. NO. !! you have to use the long reach plug to get the total use of all threads for strength you need.

doesnt help you now but good future info.

plug number ...i'll get it from garage.

bill

[38plymouth]

the reason for the stripped heads is probably that folks are still using the short plugs from the iron head. NO. !! you have to use the long reach plug to get the total use of all threads for strength you need.

doesnt help you now but good future info.

plug number ...i'll get it from garage.

bill

I got the right plugs for the head and put them in to check them before I put the head on. I din't torque them though until the head was installed. I think they stripped because they were worn out a little. The guy that gave it to me had it on a race car for years.

[Big_John]

Where are you located?

Try Drakes Engines in Rochester or possibly Syracuse Crank and Machine in Syracuse.

[Plymouthy Adams]

while is is necessary to get the correct thread length to secure the plug..in an aluminum had you do not want to extend any threads bewlow the insert/threaded hole..this will allow carbonbuild up and the aluminum does not have the strength to "clean" the carbon and thus it galls the thread...caution number two..do not remove and install plugs in an aluminum head when hot..I do not think this an be said to often..I have repaired a good many heads from just those two related problems..I further do not know if the threads depth is consistent on the aluminum heads..I recommend a test of the brand plug you use and to make a note of each plug and if necessary adjust the depth with plug indexing washers..

[Flatie46]

I wouldn't think it'd be hard to fix. I've welded some aluminum in the past. It's cast alum I'm sure and cast is usually kinda trashy and will spatter a bit here and there. Where you weld these holes this area will probably be softer than the rest of the head and you may want to go ahead and put a helicoil in it. That way when the plug threads in it'll be steel on steel instead of the steel plug threads on the soft alum of the filler rod that welded the hole. Helicoils often get a bad rep but if done right they're pretty strong.

[48mirage]

http://www.timesert.com/html/sparkplug.html

[Rusty O'Toole]

If the head is too worn to take a Helicoil or insert you can tap it with a pipe tap and screw in a piece of 1/2" pipe, preferrably brass but iron will do. Then drill, tap, and put a regular insert in the pipe.

[Don Coatney]

You may be able to drill a larger hole and use a larger spark plug. BUT do the homework first to see if a larger sized plug is available in the heat range for your engine. Might be wise to invest in a set of spark plug metric taps. I bought this set several years ago and I believe I got them from McMaster-Carr.

[38plymouth]

I already repaired several holes using a helicoil type insert, the inserts eventually stripped out (one blew out while the engine was running). I either need to have the larger bigsert's installed or I think the holes need to be welded shut and then drilled and retapped. I can't find a shop that uses bigsert's and they don't want to buy the tools to do them, they are expensive. I'll try calling drakes and Syracuse machine, I live halfway between the two.

[Plymouthy Adams]

I cannot in any manner see the worth of this aluminum head at the expense of the time and effort to keep it in a state of repair..so many folks who have these have written for advice on this and that, having problems like stipped thread for thermostat housing, stipped plugs hole, porus casting that cause compression gases to enter the cooling chamber...and in one case 3 month I think getting the newly head serviced by the seller..you rarely will hear of a stock head with said issues...and the head itself can be shaved..and the later head design is great imporved..I think I would look to the later model for any performance enchancements..cool looking fins is only good for static ohs and ahs..

[stan's52]

This can be repaired by using thread inserts. I would use the type that has a shoulder to tighten against the head. This work needs to be done on a mill to keep everything straight. Unless you have a friend with a mill it may be rather expensive. I don't think welding the hole will work well. The older VW's had a problem with the plug holes also, I had one repaired with a insert. Stan

[38plymouth]

I cannot in any manner see the worth of this aluminum head at the expense of the time and effort to keep it in a state of repair..so many folks who have these have written for advice on this and that, having problems like stipped thread for thermostat housing, stipped plugs hole, porus casting that cause compression gases to enter the cooling chamber...and in one case 3 month I think getting the newly head serviced by the seller..you rarely will hear of a stock head with said issues...and the head itself can be shaved..and the later head design is great imporved..I think I would look to the later model for any performance enchancements..cool looking fins is only good for static ohs and ahs..

I have a couple of reasons for wanting to put this head back on. First is that it is a rare, original fenton head that was given to me for free from an older gentleman I met at a cruise. When he saw our car he said that he raced a mopar flathead back in the 40's and he still had the head hanging in his garage after all these years. He said that when he saw our car he knew that he wanted to give the head to us to put on the car. I agreed to meet him at his house and not only did he give me the head, he told me a bunch of stories about his racing days back in the 40's. He wanted to see the head used again and he was thrilled when I said I would be honored to have it and put it on the car. I want to keep my word to him and put it back on.

I also love the way the head looks and maybe it gave me a little power, maybe not, I don't really care. Stripping the plug threads was my fault and is the only problem I have had with it. When it's fixed correctly I'm putting this little piece of history back on the car for good.

I spoke with Drakes and Syracuse crank and they both say that they would have to see it to know if they can fix it. Now I have to find time to get to one or the other. It's an hour no matter which way I go.

[greg g]

If you just gotta have the finned head, try these guys. They have a very extensive set up. I have had some work done there and they are reasonable and have a fairly quick turn around time.

http://www.blossautomotivemachine.com/

[T120]

For those wanting a little bling under the hood,I rather like 1941Rick's idea of using the original cast iron head,flat washers and 3/4" flat bar.

[Flatie46]

I already repaired several holes using a helicoil type insert, the inserts eventually stripped out (one blew out while the engine was running). I either need to have the larger bigsert's installed or I think the holes need to be welded shut and then drilled and retapped. I can't find a shop that uses bigsert's and they don't want to buy the tools to do them, they are expensive. I'll try calling drakes and Syracuse machine, I live halfway between the two.

I've fixed a few motorcycle engine cases, toyota timing covers, dirtbike wheels that were all cast aluminum. The piece itself has a certain hardness when it is cast. When you weld up a plug hole, your filling it all in with filler rod. This area will be softer, when you drill it and retap it. The threads probably wont tollerate the torque spec required. That's why I say after you get it welded up, redrilled and tapped you may want to helicoil it. OR Drill it much bigger and weld a plug of anthor piece of alum in it. It can be saved, just may be more $$ than you want to spend. Trust me, in my job I save crap that ought to have been thrown out many years ago.

[Rusty O'Toole]

Once again. You can repair an aluminum head when the spark plug hole is too far gone to install a helicoil or insert. What you do is drill and tap with a pipe tap and screw in a piece of brass or iron pipe. Then drill and tap for a threaded insert or helicoil. I was taught this by an old motorcycle mechanic who did this repair on an aluminum Indian motorcycle head for me. So it is genuine old fashioned and it works.

If it seems too crude to you, go ahead and machine a threaded insert out of aluminum and use that instead. If you use a tapered pipe thread you can screw the insert in tight and it will stay tight with no Loctite or other substance. This is better and easier than welding.