A65 Spark Plug Bushings

MikeB · Post by **MikeB** » Tue Dec 19, 2006 18:17

I suppose this is a silly question, but why would a oversize spark plug bushing be needed? Is it just because the bushing got loose and wobbled around? It seems that once the bushing is 'set in place' it should stay there

(famous last words). I did note the Continental manual has several different oversizes of bushings but no (apparent) way to identify them that I could see

.

Sometimes the best way to solve these 'complex' problems is to pull the jug and send it to a shop like Bolduc where they deal with issues like this in a more frequent manner (my two cents worth).

Mike Berg

Ron Babos · Post by **Ron Babos** » Tue Dec 19, 2006 19:45

Mike: When new , I believe it's somewhat of a shrink fit so as to seal the threads for the combustion process. Loctite wasn't invented at that time. When you remove them they will chew, wear out some of the aluminum thread in the head, mainly from all the burnt carbon in the threads. With a slight oversize and heating the head along with chilling the bushing it's possible to somewhat duplicate this. I also think that in time the bushing yields somewhat or the threads in the head get compressed and the interference fit is almost none existant due to a somewhat differnt expansion cofficient of the two metals over time. What bears this out is if you had an interferance fit of say .002 on a thread, there would be no way to get that sucker out, but they will unsrew with minimal effort after you drill the pin out when replacement day comes.
Ron

gusc · Post by **gusc** » Tue Dec 19, 2006 21:44

Ron,

Again, thanks. After I put all your posts together on one page it reads like a primer on Bushing replacement! This will be my reference in the shop as I proceed on this job.

I won't get a chance to do this job until next year but will order two oversize bushings in the meantime. Do you have a good source to recommend?

If I screw this up I'll send the whole thing to you to repair for me!!

gusc · Post by **gusc** » Tue Dec 19, 2006 21:54

Ron,

I just had a horrible thought, what if this thing is already 0.009" over? I thought of this after reading your post about only being able to get that size bushing. If that is the case maybe I should send it to you since you already have the tap?

Do you use the actual pins from Cont or just plain 1/16" brass welding rod?

Also, what do you think about my idea of drilling and inserting the pin before removing the plug?

Ron Babos · Post by **Ron Babos** » Wed Dec 20, 2006 17:57

gusc: There is no way to get a .009 over in the head . I use the .009 over tap to freshen prior butchery. Won't help much if you're already there.The threads would have to be total scrap in the head for any chance of it happening. I'm sure it's been done, but it's mikey mouse in my book.

Since you have only one locking pin hole, I'd bet you are standard size. The pin is 1/8 brazing rod and the drilled hole must cut through the threads in the center of the bronze and aluminum. This way the pin locks equally in both.

It has to be done after removing the plug because it's under the washer of the plug. If you cleaned the bushing threads and head threads with lacquer thinner completely before the 680 loctite it will not back out when you take the plug out. Removable loctite is not all that powerfull but will help you with the intitial removals when you do the trial fits .

Mark the hole location where it needs to be and lightly center punch it. Start with a 3/32 drill with a drill stop. If you have number or letter drills for more exacting sizes go for it, or use a good 1/8 drill bit to finish. Watch out for the grabbing tendency of the drill bit.

The look on your face if you snap part of the drill in the whole off will be priceless

I use a slightly smaller drill than 1/8 and finish with a 1/8 reamer. Do not debur the hole on the face. Make the pin a about 1/32 longer than needed and square as possible on the end that will be at the face and taper the end slighly that goes in the bottom of the hole.

Once the loctite has been applied push the pin in . Use a sparkplug with a steel washer on it to press what's left sticking out flush with the bushing face. Oil the bushing face and steel washer so the squished out loctite won't make a mess and stick. If needed use fine sandpaper to clean up the surface. I usually glue a round disc of sandpaper that I cut out of a sheet to the end of a bar with a nice flat face on it.

A few twists is usually all it needs. If this is needed the top plug should be removed and air should be pumped in to blow abrasives away so they won't fall into the cylinder. An ordinary blow gun is fine.

Ron

gusc · Post by **gusc** » Sat Dec 23, 2006 18:19

Ron,

Thanks, more good stuff to add to my "Bushings 101" page.

If I snap off the drill bit it should make a good strong pin!

Merry Xmas

gusc · Post by **gusc** » Mon Nov 19, 2007 21:25

Ron,

Through all your great instructions I forgot to ask about the correct length of the 1/8" brass lock pin? I finally got the prop off and am about to tackle this job.

I remember one of your comments about drilling the pin hole too far so I want to avoid that problem! I'm ready with my drill stop just in case!

I don't know if I mentioned it before but I now have two bottom bushings out. When I removed the left front bottom plug that bushing came out also, I knew it as soon as I started unscrewing the plug-a really sickening feeling.

Neither of these bushings have ever been pinned.

gusc · Post by **gusc** » Wed Jun 25, 2008 19:35

If you look at these posting dates you will notice that I am a real procrastinator!

I finally got one bushing installed but haven't removed the 18mm installing bolt yet-it is now warming up.

The first time I tried installing it I used only one bolt lock nut and it didn't hold. I then quickly inserted a spark plug with copper gasket torqued to about 25lb-ft and screwed the bushing out with the plug. I figure I was pretty lucky that time. My goose would have been cooked if the loctite had hardened but the bushing was probably still pretty cold from being in the freezer overnight.

It was lucky that one of the two that came out was a perfect fit into the other cyl. I haven't checked the other one yet but logic tells me it will be too loose.

I have two other new bushings waiting to be tried but one is standard size so probably won't fit.

I also pinned all the other bushings since non of them were pinned. They all had an embossed mark which tells me that someone tried to swage them, probably the cyl overhauler. Well, I'm here to tell you it didn't work.

I used 3/32" brass pins because that happened to be what I had on hand. I figure if they don't work I can always go to 1/8".

One cyl has no bushing, this surprises me?

Anyway, thanks for all the forum help from all you guys, I may be back in the air before the summer is over. It is too hot tom fly now anyway.

gusc · Post by **gusc** » Thu Jun 26, 2008 20:49

Luckily the new 0.003+ oversize bushingsecond fits the second cyl perfectly. I is now in the freezer to be installed tomorrow.

So far I only broke two drill bits!! They both broke on the tip so were not too hard to remove. I decided the break happens when the bit goes through the small gap under the bushing flange and first hits the cyl and bushing threads. Anyway, I'll be a bit more careful with the remaining two bushing pins.

I've had good luck smoothing the pin heads with a very small cold chisel, makes a very smooth finish.

gusc · Post by **gusc** » Tue Jul 01, 2008 19:29

The job is finished.

The last bushing went in a bit harder than the others. It seemed to catch a bit every 180* but went in ok.

I used 27200 Red Permatex Hi-Temp(450*F) thread locker for threads up to 1.5" for both bushings and pins. It was all I could find and I decided the high-temp part was a plus. The label says it takes 500*-600*F heat to break the lock so that should do the job even without pins! Most thread lockers seem to be rated for 300*F.

In total I installed two bottom bushings and six pins. I suppose top bushings never come out because they are too easy to reach! It was not the most fun I ever had but I figure I won't ever have to do it again with these cyls.

On the other hand, the education was worth a bunch. I even learned how to remove a taper shaft prop hub.

One of my local AIs didn't know what I was talking about and he has worked on quite a few A65s. Without you guys this could have meant removing cyls and sending them away. No shops in this area. Thanks again.

Post by **joea** » Wed Jul 02, 2008 10:41

Gus,

Glad it worked out fine for you.

This forum is really a good help for things like this, sharing ideas and making life easier for everyone.

Joe

gusc · Post by **gusc** » Thu Jul 03, 2008 17:24

Joe,

I agree. I was a bit surprised when a local AI who has probably OH a bunch of engines, includint A65s, didn't know about the bushings. He isn't the one I normally use but have used him in the past. I'm curious to see if my usual AI knows about them?

There sure isn't any info about bushings in the A65 Maint & OH Manual!

Looking back in the engine log I just discovered that these same two bushings were replaced at Annual in '05? Hopefully my job will hold them since pins were obviously not used then.