12A rebuild - fix for dowel pin leak "fix"?
 

Hello all,

Been daily-driving my FB for about two years now. It's always had a very slow leak coming from the front dowel pin. It began leaking coolant a couple months ago as well, so I decided to tear the engine down when I had an opportunity (and the cash) to do so. I found the cause of both leaks: the water pump had a missing bolt (with half of it sheered off inside one of the holes), and the dowel pin O ring was trashed. I also found that the "fix" for said leak was attempted. There's a hole drilled into the front rotor housing. Normally I think this could be fixed by just filling it with some JB weld, but the hole was drilled in such a way that it just barely scratched into the front iron, leaving a big rip through the face of the housing between the "mazda" lettering and the dowel pin O-ring hole where the housing and iron meet. I've tried filling it as best I could with JB weld and flattening the surface with a razer blade, but it's obvious by running my finger nail across the surface that it's not flat. I've been searching around for what to do with this and mostly I've seen lots of recommendations to NOT apply hylomar or any kind of gasket sealant around the dowel pins or to the O-rings, so I'm a bit at a loss as to what to do. Anyone have any brilliant ideas that don't involve replacing the entire housing?

Also, I've discovered that due to some serendipitous angles and lengths between bolt holes, in the absence of a flywheel brake, you can use the front engine mount bracket to hold the eccentric shaft while you remove the nuts holding the flywheel and pulleys onto the shaft. I searched for this as well but couldn't find anything so I thought I'd share. See picture.

Its gotta hold up to 100#s of oil pressure, that's a lot. But its a small hole. Also, before the tear down it wasn't terribly leaking right? Also, before the tear down it had RTV in it, not something strong like JB weld. However, in my experience JB weld isn't a 100% fix for oil and gas things.

Dunno, that's all my thoughts on it. :blush:


I gotta say if I was in your shoes I'd fill it and slap it back together. :D


Here is another thought. Bevel the hole so the larger portion is facing the inside. Then assemble the engine like normal (no JB weld or anything) With the engine assembled do the "quick fix" and fill it with RTV. With the hole larger on the inside it would be more difficult for the RTV to work itself out.

Another option could be to bevel the hole out in the same manner as before and fill it with JB weld.



Kick ass flywheel holder BTW. :icon_tup:

It's too bad your engine was damaged in an attempt to fix it by a stupid previous owner.

A few years ago, there was some joker who "fixed" his leaky dowel pin with this drilled hole method and promoted it on the forum. Your engine may have been one of his "fixes".

I have a front iron and a rotor housing where some stupid previous owner attempted to fix a leaky dowel pin by grinding the iron and aluminum down to fill the enlarged gap with JB weld which... wait for it... didn't work. It never does, but human nature is what it is. Now I have a damaged but still usable front iron and rotor housing in good shape other than the damaged area. I'll probably build a nice 74 ported 12A out of them and run it NA or under low boost. This area is prone to cracking on boosted FC and FD engines so you gotta be careful.

sorry for the housing woes - my original-12A 80 has a leak, which was minimized about 6 yrs ago with a stop-leak product. No a minor weep.
engine bracket/flywheel lock is _inspired_ backyard work!! nice.
Best of luck on the housing !

Stu Aull
80GS
Alaska

Can the small hole be TIG welded on the outside?

I would try jb weld or devcon.i woild overfill the hole slightly because it shrunks slightly when it dries. Once it dries sand it flat,and you should be good.i have never ran into this personally, but a friend of mine had this problem, and it worked for him.also great idea for the flywheel holder.

+1 on the Devcon, its not cheap, but it will work

Thanks god my apex seal broke before I did this "fix"

Finally getting my engine torn down after 4-5 years, a marriage and two kids... good to see 7aull, Jeff20B, KansasCityREPU, and j9fd3s are still around

This is what I attempted to do. Attached is the result after filing down. I have the tension bolts all torqued down without too much trouble. We'll see what happens when I get the engine back in the car and running.

also, I took a peek around the rest of the car and noticed that my exhaust pipe is beginning to resemble swiss cheese due to rust. The split air pipe fell off a while ago; I was planning on trying to get it welded back on, but at this point it seems like it might make more sense to replace the whole exhaust system. I've kept the car pretty close to stock but that racing beat exhaust is looking tempting, especially because I'm not exactly sure where to find the stock parts. Rock auto only sells cats and I think anything I find from a junk yard is going to be just as rusty as what I've got now.

(sorry for the potato-quality photo; my phone is almost as old as the car)

I remember reading the posts about drilling a hole to stop that leak. I opted to let it leak.
If I recall correctly the leak is due to the O-ring failure. You'll have a new O-ring in there so hope for the best.

Smart man.

alright, I've got everything hooked up; started it up today. No signs of leaking but I only ran it for a few minutes. It won't stay running unless I keep my foot on the gas, and the exhaust note seems louder than it was pre-rebuild. As I said, the exhaust has had holes in it for a while, but it sounds "different" than before. I am going to check out the vacuum and timing tomorrow.

New apex seals?

More compression?

You probably shook some more rust off of your pipes and now more sound can leak out!

Got it idling and coughed out all the smoke today. It was running well enough to take it around for a drive after turning the idle throttle screw a bit. Actually, it drives better than it did before, but the idle is still a little wonky, and it's still making that strange noise. It really sounds like an exhaust leak (like a lawnmower running with no muffler) but the manifold and the pipe leading to the cat is the only part that isn't rusted out, and the noise is definitely coming from the engine bay. Also, the noise doesn't happen while coasting or braking, but it does while accelerating and idling.

I didn't poke around the rats nest too much as it was getting dark out by the time I got back from driving it. The timing was nearly spot on. However, while I was checking the timing, I pulled on the throttle and the timing got "stuck" in advance (or something which would cause the timing to be advanced), and it idled around 1.2k rpm, with the strange noise also subsiding. I'm suspecting something vacuum related, but I have no idea how something like that could be so loud.

The good news is: no more dowel pin leak!