Atomic 4 Oil Seal Replacement

So, I had promised to post about the great "rear oil seal replacement job" on my Atomic 4. I finally feel like I've beaten this oil leak gremlin to be able to declare victory.

First a recap: oil was leaking from the rear of the engine, but only while running AND in gear. I visually eliminated the oil pan gasket and two other common sources of leaks, the valve cover and oil pressure regulator. Both of these areas were dry and there was no trickle back found on the cast iron mounting flange of the engine leading to the rear. Also the volume of oil leak was A LOT while in gear, so the obvious source was the seal on the output shaft.

Hopefully you have a large access panel in your cockpit to reach this area, because this would be a difficult if not impossible task to do otherwise without pulling the engine. Gaining access, you first unbolt the propeller shaft from the output coupling and slide the propeller shaft aft as far as it can go. I first marked across the flange/coupler with a sharpie because I wanted to reassemble with the exact same alignment, just in case. Sliding the shaft back was a little difficult because my cutlass bearing and packing were recently replaced so it was a little tight. I used a little grease on the shaft to help and a pry bar to help move things aft. Luckily, no leaks resulted as this was done in the water and what I thought was going to be a couple of hour job turned into several weeks! Who knew? Also remember to move the tiller fully to one side to allow enough room for the propeller to slide aft without hitting the rudder.

When fully aft, there was barely enough room to get a 1-1/8" socket and 1/2" breaker bar on the output shaft spindle nut. I threaded a couple of the bolts back into the output coupling and put a hefty screwdriver across them against the hull to keep the shaft from turning while I broke the spindle nut loose. Remember to bend down the retaining ear of the "lock washer" underneath before trying to remove this nut. This actually came off pretty easily. Remove the washer underneath.

Next the fun part, I used some slightly longer 3/8" fine thread bolts threaded through the coupler holes until they pushed on the flange casting underneath. Tightening each successively pushed the coupler off the shaft after a hour or two of tedious tightening with a box end wrench, because there wasn't room enough for a socket and ratchet (boo!). The bolts I had weren't quite long enough to push it all the way off, so at the last little bit I had to back them out and put a screwdriver or something underneath to be able to push a little more. Of course have a magnetic retrieval tool on hand to recover the wrench that you are going to inevitably drop into the bilge.

With the coupler removed, the seal is right there, exposed in the opening of the mounting flange. Logic would suggest that a simple pry with a screwdriver would pop it right out. Having a spare engine at home in the garage proved this point. The attached picture shows how I practiced this concept at home and sure enough, the seal popped right out without having to remove the flange (seal on the left) from the engine. For this reason, I did not order new gaskets for the flange because WHY remove it??? Well, as one should have known, the real engine in the boat, it seems like someone must have welded the seal in place and no amount of prying or knuckle banging was going to budge it. How could such a tiny seal hang on so tight? I had bought just the replacement seal that I had planned to just tap right in. The replacement seal is a National p/n 473227 available at auto parts stores. There may be other equivalent parts from other vendors being used. So I ended up having to remove the rear flange anyway to take home to a vise to pound/pry out the offending seal. The result is the seal shown on the right in the picture. It looks like it was removed with a stick of dynamite! The gasket you need is also shown (you need 2 of these).

Be sure to inspect your coupler for wear at the interface with the seal. The old seal, instead of being flexible, had aged to hard plastic and will have a tendency to wear a groove into the coupler. If the groove is noticeable then go ahead and replace the coupler. These are available at Moyer's for about the same price as buying his "repair sleeve". The delta is only about $4 so why buy the sleeve? Anyway, I decided mine was ok and I reused it.

Unfortunately, I now had to order 2 of these flange gaskets and that resulted in the 2-3 week down time (first place I ordered them didn't have them in stock and placed them on backorder). Buy them from Moyer's, they have these in stock. Lesson learned! If you can remove the seal without removing the flange then do that and you'll be way ahead. Also considering when you remove the flange it will immediately dump your oil so be prepared to catch this mess in a pan or something to keep it out of your bilge! Also, before removing the flange, I marked its alignment with the engine block with a sharpie so I wouldn't have to guess upon reassembly since the bolt pattern looked symmetrical.

Reassembly: Obviously clean all surfaces of old gasket material and apply the new gaskets. The rear flange actually comes apart in two pieces exposing a bearing in the inner plate. That's why you need 2 identical gaskets. I tapped the new seal in place with a hardwood block until seated flush with the opening and lightly greased the bearing just because I could.

Back at the boat now. Having been forewarned. I lightly wrapped some electrical tape across the exposed output shaft and key to cover sharp edges and protect from nicking the new seal when fumbling the flange assembly back on the engine (clean any old gasket material from engine too). The output shaft is loose and "floppy" when it is unsupported, so use one hand to hold it in position while guiding the flange assembly into position. After installation, remove your electrical tape.

Next, the fun part and lesson learned. Reinstalling the output coupling on the shaft. First use plenty of grease to make this as easy as possible. Grease both the shaft, the bearing inner race within the rear flange and both the inner and outer mating surfaces of the output coupling. Key to remember is that the coupler is both pressed onto the shaft on its inner surface as well as the bearing and oil seal on its outer surface, so grease both. I used the tapping method with a hammer to start the coupler on the shaft far enough to finally be able to thread the spindle nut and then by tightening the spindle nut until the coupler was fully seated against its stop.

So here's the trick: it will seem that progress is being made a little tap at a time while standing on your head and with barely enough room to swing a hammer when it just won't go any further and stops just short of being able to thread the spindle nut on. The secret is, remember the "floppy" output shaft? You have to support the shaft, slightly wiggling with one hand, to center the shaft in the assembly while you are tapping the coupler with the hammer using the other hand. With much aggressive "tapping" the coupler will slowly begin to move into place again. Once the threads are exposed and you can get your spindle nut on again, the rest is easy. Use something to keep the shaft from turning and use your 1-1/8" socket and breaker bar to firmly seat the coupler. Then remove the spindle nut and install the "lock" washer underneath. Reinstall the spindle nut and bend up an "ear" on the lock washer to hold in place. Reattach the propeller shaft using the alignment marks. Luckily, the shaft pulled forward by hand with a little twisting and pulling perhaps assisted by the grease I had earlier put on the shaft. The rest was without issue.

Remember to refill the oil. Of course, like I like to overtighten stuff, I also like to overfill things. Don't do that. During the trial run I had excess oil overflowing from the oil fill spout area. My fill spout is on the rear of the engine and is probably vulnerable to over-fill issues because of the tilt of the engine. That is another area to check when you have oil leak/spillage at the rear of the engine. However, with all that cleaned up, I can happily report that I have no more oil leaks! What a blessed day this is!

Clay Pass
#449 Seeing Deep

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Page last modified: Friday 03-Feb-2023