Yamaha F300XCA Lower Seal Spins

[James Sterling]

Last December, I took my F300XCA in for regular PM (oil and lower unit fluid changes, all filters, water pump) to my local mechanic. When I received the boat back, I put it in the water and there was no water circulation. The culprit was a wear plate. After this repair, I took it back to the water and after returning home, the lower unit dropped some emulsified fluid. The mechanic determined it was the upper seals. Replaced those and the lower (prop shaft) seals, successfully pressure tested and back to the water. I took 3 trips out with no issues. However, after sitting in my insulated shop for 5 days, the lower unit once again dropped emulsified fluid. Back to the mechanic. He is somewhat stupefied at this juncture. He called yesterday to say that he noticed while replacing the lower seals again, the second one did not have to be tapped in. It just slid into place. He turned the prop shaft and saw that the seal would turn with the shaft - obviously not making sufficient contact with the casing. These are all genuine Yamaha parts. I've had no trouble of this sort with this engine. Anybody ever had a similar issue? Any resolution? Thanks in advance.

[99yam40]

I would think it is time to measure those seals and the bores they seat into, to see what is out of spec

[boscoe99]

What answer(s) do you want?

https://www.thehulltruth.com/boating...eal-spins.html

[boscoe99]

I would think it is time to measure those seals and the bores they seat into, to see what is out of spec

Could be a bore at the end of its outer limit and a seal at the end of its inner limit. The perfect storm.

Don't think that I have ever seen ID and OD specifications for the seal and the bearing carrier. Hmmm.

[99yam40]

Could be a bore at the end of its outer limit and a seal at the end of its inner limit. The perfect storm.

Don't think that I have ever seen ID and OD specifications for the seal and the bearing carrier. Hmmm.

maybe I am wrong,
but if one seal slides in tight as it should but the second one is a loose fit in the same bore,
something is going wrong.
measuring the seals and bores would be my go to.
even if you have to measure some other motors bore and multiple seals of the same part number

[boscoe99]

Without specs, what is as tight as it should be?

Certainly easy enough to measure the OD of the seals to see how they compare. Also to measure the ID of the carrier to see to what extent it exceeds the OD of the smaller seal.

[boscoe99]

Maybe some sort of locking sealant is needed.

[pstephens46]

There are similar seals for other uses. I know some have been used in lower units. There may be slightly different sizes that would work. May take a bit of searching and experimenting. Is it possible the seal locked up on shaft to the point of rotating and wearing a spot in the carrier? I would check for just a worn ring spot in that area.