Flathead Spark plug Thread Repair
 

I just picked up a set of aluminum cylinder heads for my flathead. One of the spark plug holes the threads are not in the best condition and the plus has a little wiggle. What is the best process or the best kit to use to repair this head?

Re: Flathead Spark plug Thread Repair
 

Heli coil
Lawrie

Re: Flathead Spark plug Thread Repair
 

Yes they do a good job


R

Re: Flathead Spark plug Thread Repair
 

For the repetitive use that a spark plug thread gets I like this style over the spring type inserts. I have had luck with them on chainsaws and motorcycles with alloy heads. Helicoils, although good, have historically backed out with me when I remove a plug.

Re: Flathead Spark plug Thread Repair
 

I prefer to use Time-Serts - they are a threaded sleeve and when properly installed, really do a nice job. They are available in different lengths and they supply the various tools to do the job. The "kits" are not cheap, but many automotive machine shops will have the kits and inserts.

https://time-sert.com/

Re: Flathead Spark plug Thread Repair
 

Helicoils are good if you can drill and install them with a mill or drill press to insure they are square with the plug washer seat on the head.

Timeserts have the washer seat integral with the insert so if they have to be drilled by hand as in field repair, the seat will still be square with the thread.

Re: Flathead Spark plug Thread Repair
 

I'd used these albeit on rare occasion as a tool maker. Installed properly, they are STRONG. A MUCH better alternative than a Heli-coil. Heli-coils were NEVER used.
Me? Working on an aluminum head? Well, I'd figure I have one opportunity to do this task correctly. There's no question that I'd spend the extra money and buy the time-sert.

Re: Flathead Spark plug Thread Repair
 

Time Serts for me, I have many sizes, more $ than helicoils but so much better.

Re: Flathead Spark plug Thread Repair
 

Since you've the heads off already it is a simple matter to use a time-sert, I used these for a Lawn-Boy jug with stripped plug threads and they work really slick. Aluminum accepts a tap like butter, it's so easy a cave man could do it. The result is very strong, and permanent.

Re: Flathead Spark plug Thread Repair
 

Something that is seldom noted but essential on race engines only is, a sparkplug thread insert of any kind will normally change the plug range one notch.

Re: Flathead Spark plug Thread Repair
 

Hotter?

Re: Flathead Spark plug Thread Repair
 

Are the Time Sert inserts closed at the bottom? Hard to tell from the picts.

Re: Flathead Spark plug Thread Repair
 

Yes Tim . . . they are completely closed off at the bottom, which totally seals off the combustion chamber - increasing gas mileage and reducing the need for any spark plugs at all!

Just kidding yah - couldn't help it! :D LOL Not sure what you're asking, but they are a threaded sleeve with a plug gasket sealing surface at the top. Is that what you mean?

Re: Flathead Spark plug Thread Repair
 

Haha. Good one, Dale. I was thinking of the smaller ones 3/8" for intake repair.

I guess going by pictures on the internet is not the best plan of attack, but they appeared to have a closed bottom which was confusing me as to their usage for the exact reasons you joked about.

Re: Flathead Spark plug Thread Repair
 

Pete, Why would that be?

Re: Flathead Spark plug Thread Repair
 

Colder. The heat dissipation has to go through another joint and stainless steel is a poor conductor of heat so it takes longer and the original plug runs hotter.

Re: Flathead Spark plug Thread Repair
 

Thanks Pete.

Re: Flathead Spark plug Thread Repair
 

This probably is a dumb question, but I will ask it anyway, did they ever make a adapter to change the plug size on the earlier heads that used the bigger plugs that were I think 7/8 maybe to the later size commonly used in the 59AB heads? Just curious.

Re: Flathead Spark plug Thread Repair
 

I had a set in a model A engine once. They may still be available from model A parts stores.