repairing sparkplug threads
 

Hi All,
Just acquired a set of crusty old Weiand heads for an 8BA. At first I thought I had a couple of busted off spark plugs that someone could not get out. I did the acetone/ATF soak and they came out fine. But, it was then I noticed that those two were the larger thread, 7/8" socket old sized plugs that someone had used to put in as I guess they ruined the later smaller threads. So, now I am pondering the best way to fix this mess. Should I drill all of the other holes out for the bigger old style plugs? Or, I just found where there are adapters that can be screwed in to use later plugs.

Kinda related, but not. Even though the heads are for an 8BA, the ears for the oil filter can are not on and not even cast originally. There is no need for any deep reaching plugs like we usually read about on here for Offy heads. The area for the plugs is only about 5/8". Did they make 8BA heads specifically for racing applications where one might not be interested in bolting on the oil filter? Thanks in advance.

Re: repairing sparkplug threads
 

Most likely made in '49, as '49 8BA did not have threaded bosses for oil filter.
Oil filter was bolted on using head bolts..

Re: repairing sparkplug threads
 

I think I'd use the bushings you mentioned on the two "modified" cylinders and then use 14mm plugs all the way around. There's a much better variety of heat ranges in the 14mm size, should you need them

Re: repairing sparkplug threads
 

I haven't seen any spark plug repair bushings specific to flatheads but I remember the ones we used on the Continental aircraft engines. They thread into the plug boss and are pinned with a single pin inserted in a drilled hole after torque set. I just don't remember what the outer thread was. Where there is a will, there is a way. Some might weld them up & remachine but that can mess with the heat treat of the head some and may cause cracking later. If there was a bushing sized at 18MM thread on the outer diameter, you would be back in business pretty quick as long as a 14MM plug would fit the bushing.

Re: repairing sparkplug threads
 

What is the od thread of the bushings you removed?

R

Re: repairing sparkplug threads
 

Here is the least expensive on I could find.
http://ipatools.com/products/index.php/ipa-7885.html
Aircraft Spruce has them too but they want a fortune.

Lock & Stitch has solid inserts for repair but they don't say what the outer OD thread is. They are the type that would be pinned in place.

Re: repairing sparkplug threads
 

Thanks, Rotor. Here's some I found, http://www.reamproducts.com/data/catalog.html. It looks like these things are used by the antique tractor crowd to update to newer plugs. When I said "7/8 inch" plugs, I was referring to the size socket required to remove them. Are the old plugs 18MM?

Re: repairing sparkplug threads
 

K-D Tools P/N 2125 is a kit that includes a combination reamer/tap and 4 different length inserts to repair your stripped out spark plug holes. PermaPlug P/N 2214N is a set of 2 each 1/2" long inserts and Plews P/N 72-249 is a set of 2 inserts 3/4" long. All of the repair inserts are 14mm have a shoulder made onto them so that once inserted and thread locking is used, they will not back out when you remove the plugs at a later date. Any automotive supplier will be able to get these or an alternative manufacturer equivalent. If you prefer the 18mm plugs, I know that they are also available, just don't have any on hand and therefore do not know the P/Ns.

If you are at all handy, these parts are very easy to use successfully, jsut be sure to kept the reamer/tap perpendicular to the thread. An alternative to investing in these tools (not too expensive) would be to take them to any automotive machine shop and the cost should not be too high.

Re: repairing sparkplug threads
 

If the outer thread diameter measures near .704" then they are 18mm. My old Harley 45 uses the big 1-inch hex 18MM plugs NGK-6 if I remember correctly. My old Model A uses 7/8-18 straight thread Champion #3 plugs but they have larger hex than a 7/8" on the old plugs.

That link you posted has a good cross section of automotive sizes. Aircraft plugs use 5/8-24 & 3/4-20 thread and they are all 7/8" hex but they are all shielded types. I just assumed the 7/8 hex was an 18mm thread but I've been wrong on more than one occasion.

Re: repairing sparkplug threads
 

Heli-Coil makes kits (these kits use inserts instead of coils), but I've only seen them for 14mm threads.