Dowel O-Ring Replacement
 

My '85 12A leaks oil profusely from the one of dowel o-rings in the way that they do (right by the Mazda/12A marking). I've resolved all the other leaks but this one is still pretty bad, I can't really park in friends' driveways, my own garage floor looks like the exxon-valdez dropped by, and it's generally a mess. I would like to fix this, and unfortunately I know what it requires. I did try stop-leak last year, which didn't really do anything (was worth a shot). May have slowed it a little bit for a little while, but it still leaked out 2 quarts in 1400 miles on a weekend roadtrip last fall.

I've rebuilt engines before, but not a rotary. It runs so well so I'm hesitant to touch it, but the oil leaking has got to stop. Mid-summer my engine stand should free up (working on a 383 for one of my other cars), and I have two questions.

1) What are the odds I can get into the engine, replace all the soft seals, and have it back together and running strong and reliable as it is now?
2) What materials do I need? Does someone sell a kit with the appropriate gaskets and o-rings, etc? Is there a good book on the teardown/assembly process? Any special tools (other than an engine stand adapter)?

Thanks in advance!

1. pretty good, the 12A is just about the easiest engine in the world to build, its like the bottom end of a piston engine.

2. Mazda has a gasket set, its cheaper to buy the full set right now than just the O ring set. list price is like $120, so its not really worth buying aftermarket, which are usually just junk and not any cheaper.
2a. shop manuals are at Foxed.ca
2b. least expensive procedure is to pull the engine apart, measure everything any replace anything that is out of spec. it takes a long time to do this, but you're only replacing the stuff that is bad, and you end up with something a little better than just throwing a gasket set at it.

Thanks, good to hear it's not too difficult, just different!

Is the Mazda gasket set the one the Atkin's carries as N201-89-100B, or should I look elsewhere?

I have a print copy of the shop manual but it never occurred to me the whole engine overhaul procedure is in there :facepalm1: - doesn't look like anything too special is needed. I'll take my time and check everything out. Keeping all the seals and such sorted and in order sounds like the hardest part! Curious to see what I find, the car has 183k miles on it, no idea of the history of the engine (may not even be original) before I got it but it sure runs strong.

Atkins carries the Mazda set, its just expensive.

the rotary is nice, apart from the 54mm flywheel socket, you hardly need any tools at all inside the engine. a feeler gauge is the only real important one.

i've had about a dozen 12A cars, and the one i have now is the only one with the original engine in it, so its been my experience that at 180k its been swapped...

I suspect it's been rebuild or swapped at this point for sure, just not sure which.

Yeah that 54mm nut looks like it will be interesting. Might have to set some anchors in the floor for the engine stand to get the requisite ~450Nm when tightening it! Will have to do some head-scratching for that one; can probably impact it off. Maybe.

A pneumatic impact is the best if you have a good air source that can deliver 100 consistent PSI. Just remember to loosen the front e-shaft bolt first.

Shouldn't be a problem for a 5HP 60gal IR :) (nothing like overkill in the home shop!) - thanks for the tip on the front bolt. I'll have to re-read this thread in a few months when I'm gearing up to do the work.

The 54mm nut is easy. The front 19mm bolt can be very difficult sometimes.

Op,a suggestion. Every time the dreaded dowel leak post comes up,i've been meaning to relay this "fix". I don't know if anyone else here has done this or knows about it...This is for those cars/engines that are in good shape that you don't want to pull and teardown to rebuild to just stop the leak. I personally have only done one 12A engine like this,but it bought me almost 2 years and @20k miles without more than a film of oil at spot where oil was leaking.

I have done this more times than i can recall in a span of 12 years to Dodge Cummins 5.9L and 6.7L 24 valve diesel engines that had a pattern failure of a nasty timing cover gasket leak aggravated by oil slung from the big timing chain inside. Leaking a LOT of oil whenever engine running. Here's the deal,engine has to be hot,you must clean to get dry metal on engine pieces. 2+2 carb cleaner,steel brush,rinse with more 2+2 and blow dry the whole area around the leak spot=no oil present at all. On a Cummins this is an area about 5"in length.
The engine will cool some as you go thru cleaning process,and no matter how much oil was coming out of the dowel o ring,it won't come close to how dirty the engine is on a diesel leaking like this for sometime.

Once the engine is "clean" and still uncomfortably warm enough to hold your hand on, take a tube of crazy glue,regular not the gel stuff, and open just the end,some tubes have a pin in cap that pierces hole open,that size no larger. From about an inch in front of where the leak starts,the highest point on the engine where it is leaking,on the Cummins it's the top 3rd of timing cover, place the tip of crazy glue where it will bridge the gap between the 2 pieces and squeeze gently and let gravity flow it downwards til past the area it leaks by couple inches or so and stop and leave the engine to cool. You"re not trying to gob a lot of it on the engine,just enough to bridge the gap between the pieces a little longer than where it starts and stops. You may notice in the immediate area of leak,some of crazy glue will "disappear"into the gap between the pieces. Let the engine sit til cool to touch or overnight and start run/test drive/observe what is left of the leak if any.

When i worked on these trucks,this leak was an inspection fail as you'd imagine and i'd offer the customer the option to "reseal" the leak without teardown and associated costs with the knowledge it may only last a year or so(a few lasted 5+). A lot went for it to get another year or so out of the truck and keep it legal,a few traded trucks in to the same dealer where i worked a couple years after i had done this and they were only seeping and passed used car inspection,lol. I never actually told the customers what i did to fix it,even if they asked-they were good with it no longer leaking.

So don't laugh...if you have the dreaded dowel pin leak,try it. Better chance of success if "repair" performed before leak gets too bad. In case you were wondering,i have re"repaired" Cummins engines again as necessary to buy customer more time. Remember,i only did this once with fair success on one of my 1st gens,may well work for you. Just time and materials,you're out really nothing if it doesn't work. One more thing to try before a teardown or getting rid of car...

the crazy glue is an interesting idea, its worth a shot, but i wouldn't really expect it to work well for long.

i've had a few cars where there was a small mountain of silicon/jb weld/stuff (one had a bottle cap to anchor the JB weld?), and it may have helped, but didn't fix it.

This is a very interesting idea - thanks. Since I don't expect to get around to the potential tear-down until mid-summer I may have time to give this a shot; worst case it's a little more to clean when I get it apart, and I have acetone (and stronger) that would take care of super glue residue. I question how feasible it is to get the whole area clean, down into the o-ring itself, though. I tried the 'gold eagle' brand stop-leak last year on the same premise (worst case it's the same as it was) so maybe this spring I'll give this a shot. Thanks again!

You wouldn't think so,cleanliness,still hot engine are key to this working. If oil can get out,crazy glue can get in that same void. Sort of reminds me how solder will suck into the joint on a copper pipe you're sweating but not as dramatic.
I sold the GSL with the dowel pin o ring still"repaired" after 20k miles and it only had enough dampness for dirt to stick to what was there,no oil flowing downside of engine like before i did it. I made new owner aware of it and what i did to fix it and got the stinkeye. Sold him a diff chunk for the car about 6 months after he bought it and it was same as when i sold it. I asked him to open the hood to look at the engine,told him to keep an eye on it. I really think he thought i was pulling his leg and there never was a leak to start with,lol.

Lost touch with him after that but that leak fix lasted 2.5 years and 22k miles that i know of. With all the shaking/vibration and various leaks on the Cummins,you'd think that wouldn't stand up for more than a very short time. Could be a handful still running around even now,been about 5 years retired from that job

Awesome, I think I will give this a shot when the car comes out of storage in a couple weeks. I'll probably clean it a couple times to get as much existing goo out of the void beforehand as possible (so when the real deal comes up it's only fresh, hot oil to clean off). Honestly if this gets it to even just a weep, it would avoid a teardown which is cool. It's not a show car, I nearly daily it in the summer so a weep is okay; heck if it works fairly well for at least the year I'll just redo it next spring ;) - I'll definitely make a post detailing the outcome of that when the time comes.

You'll really have to do your best cleaning that junk out of there for this to work. I don't like stopleak products,they work a fair amount of time but that product goes where you don't want it to also-especially cooling system sealers.. Really best to do this as soon as the leak has made itself known,before you start trying additives to stop it Doesn't work,not out much but time,worst case scenario...you have to pull engine for teardown/repair.

For sure. I have plenty of cleaners and the ability to blast them into the opening at excessive pressure (and, you know, aerosols), long brushes, etc. I'll get it clean enough to eat off of, I hope.

I'd never put stop-leak in the cooling system, those are a great way to block stuff you don't want blocked up and generally make a mess. The oil system stuff I tried (I looked into it) basically is just meant to swell rubber (aka seals) a bit to stop or slow things getting past; it's probably all leaked out by now but at a minimum the car is due for an oil change so it'll be gone before I try your method.

And as we've said, worst case I'm out a little time, a $3 tube of glue, and am back where I am now.

If you go the re-build route, the best $30 you will spend is on the Mazdatrix Rebuild DVD video. Covers all the "gotcha" tricks the OE manual does NOT cover (or buries so deep you will miss). Its for the 13B but its 95% the same as the12A. Lifesaver on my Build...

Stu Aull
80GS
AZ

There is a thread somewhere that discusses the red neck solution to stopping this specific leak. Basically you drill a hole in the right spot and depth to gain access to the o-ring, tap the hole, fill it with RTV, then cap the hole with a screw. Of course, then you have an unnecessary hole in your rear plate that could become a future leak, but if that's the only issue with the motor and it has strong compression, it could be worth it save a rebuild.

I had read that thread from some time ago,when my GSL began to leak oil in that spot and was progressively getting worse,I decided to try what I had been doing on other vehicles. I always like to begin with the least intrusive practical method and go from there.
I knew if it didn’t work,I wasn’t going to drill into the iron. I would pull and reseal.
It wasn’t a convenient time for car to be down and nothing to lose by giving it a try.
It worked and for longer than I had the car you could not see the “repair” and on teardown,no more than a razor blade would be necessary to remove what I had done.

I'm with you, it's a backyard hack. For high mileage motors that will likely have rough plates when you pull apart the motor anyway, it's an option for some. I personally wouldn't do it unless I knew I had decent spares on hand for the rebuild.

I tried the red neck o-ring repair at the race track. It didn't work because my leak was actually a cracked rear iron. I ended up rebuilding the engine and was able to repair the holes I drilled in the rotor housing using some JB Weld Steel Stick epoxy. So the repair doesn't necessarily mean you have ruined something. That said, if you have the time, pull the engine and fix it right.

this, its not hard. in fact its really neat in there

Yeah I've read the "inject RTV" thing, I'd have to be seriously desperate before I drilled into the housing to try it. Looking forward to trying out the super glue trick in a couple weeks (hoping to have it out of storage soonish) though!

Also look up using baking soda with super glue. The idea is that the baking soda helps it cure much faster.

I feel like with this you'd want it to cure slow, so that it has time to run down into any openings, hence the liquid (not gel) and hot engine.

^^^^ This,it doesn't really cure slow initially but where you want it to be it takes longer to cure than what's on surface. I'm aware of use of baking soda with super glue but no personal experience with it.