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BF8D - milky gear oil, seals to replace?

jaziniho

Member
Working on servicing the BF8D that came with my boat - same one I posted about remote steering.

After a fair battle with the drain bolts (impact driver and some heat got them off), I’ve managed to drain the gear oil from the lower unit.

It is very milky, so looks like water has got in. I’m aware that for some time before I acquired, the engine was left in ‘lowered’ position with prop etc in water, which can’t have helped.

I’m assuming a seal, or more than one seal has gone bad.

Looking at the diagrams here:
https://www.boats.net/catalog/honda...d1-sa-2001/water-pump-vertical-shaft-l-s-size

and here:
https://www.boats.net/catalog/honda...ge/8hp/bf8d1-sa-2001/gear-case-extension-case

I’m trying to work out what the different seals I might need to replace are.

It seems there’s a large o-ring seal that goes round where the water housing fits:
https://www.boats.net/product/honda/91351-ZW9-000?ref=15426df81c7b86ce29131a54714cd35d6c0b62ec

Plus seals around shaft (parts 25 and 26 in the water pump diagram).

Are there others I’ve missed? I think i saw some threads mentioning seals around the prop?
 
Well, this isn't as easy a question to answer as it may seem because there are so many places that water can enter.

Item 25 in the first link you posted is the mainshaft seal and item 26 is the shift shaft seal. Both of those CAN and do leak but neither one is real easy to replace. Also, seal 28 is the same seal you mention in the last link you posted. That seal is very reliable but would require replacement if the housing is removed to replace 25 and 26.

There's no seal in the extension case (second link you posted) that would allow water to enter the gear case. However, in that same link is depicted the gear case housing and the drain and fill plug seals (item 24 x2) are often the cause of a leak.

In the link I've provided below, item 20 is the prop shaft seal and item 21 is the seal for the prop shaft holder.

https://www.boats.net/catalog/honda...e/8hp/bf8d1-sa-2001/propeller-shaft-propeller

The prop shaft seal can be a real pain to replace on an outboard that has a lot of corrosion. It can take a lot of care to get one out "clean" without damaging the holder's shaft seal boss. If you damage that boss cavity the seal's shell will leak at that area.

I have had to just replace the entire prop shaft holder assembly (item 10) in many instances because of corrosion.

Replacing the holder assembly may also be necessary because the bearings suffer progressive damage if run too long in diluted or no gear oil.

To reliably seal up an outboard gear case, it is necessary to test the case and seals by applying a slight positive pressure and also a slight negative pressure (vacuum) with a vacuum hand pump attached to a fill plug screw adapter. This is the method used to identify which seals are actually leaking and to verify that the replacement seals have been properly installed.

Good luck.
 
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Thanks...

I remain fairly hopeful - I don't believe the engine has been run much in this state (or run much at all in last 2years), maybe briefly idling in the water to turn over. I think the water has most likely seeped in whilst the engine was left down, with leg in water whilst tied up on pontoon for some months.

Photo of oil being drained below... the vast majority was a very milk gold-ish colour.
gear-oil.jpg


I also don't think there are massive levels of corrosion - I will get some better photographs. The Anodes on lower leg are very worn... seems like (again hopefully) they may have been doing their job.

If I want to try and do a proper pressure test, would something fairly basic like this do the job?
I can't see me using it very often, so don't want to spend too much on the tool!

Braked bleeder test set, up to 13 PSI.
https://www.amazon.co.uk/DiscountSeller-Bleeder-Tester-Motorbike-Bleeding/dp/B07BYKYTS4/

Suspect we are getting close to the limits of my mechanical abilities here - but going to keep pressing on for now.
I'll read and look more on what it would take to do the seals, see if I can handle it.

Cheers,
Tom
 
Hi Tom,
That oil doesn't look very badly contaminated to me. I have seen MUCH worse. So, your hopes of not having a bunch of internal damage are probably correct. These gear sets are also fairly rugged and I've seen them take no maintenance and unbelievable abuse without failing.

As far as using that tool, yes, it will work fine IF it has a fitting that will seal to the gear case fill opening. I had to make the adapters I use out of fill screws drilled through the center because the Honda threads can be hard to match with commercially available tool adapter fittings. But maybe you'll get lucky.

WARNING though! That tool can also destroy the seals! 13 psi is way too much pressure to apply. Same goes for the vacuum test. You only want to create A BIT of positive pressure...around 2 to 3 psi...and have it not bleed off to check the seals. Any more pressure... or vacuum... will push out or pull in the seal "lips" and they will leak during your test. This could have you condemning perfectly good seals. Displacing the seal lips like that could also keep them from returning to their proper position on the shaft they sit on.

If you can master this delicate little task though you will be able to install your gear case with the confidence that it's leak free. I wouldn't trust ANYONE at ANY shop to do this on my outboard unless I could watch them do it. Too many quacks out there "repairing" outboards these days!

Good luck.
 
OK - so I got a little hand pump, but unfortunately I managed to order one that only does negative/vacuum pressure without realising.

I put a bit of vacuum on the upper gear oil port (using the adaptors that came with gear oil bottle pump kit to attach the hose).

The vacuum held really well - no noticeable drop off in pressure at all even after 10+ minutes or so.

However, I’m not sure whether just using negative pressure is really a valid test? Is it the positive pressure that matters more?

If I’ve got a good seal with negative pressure, is it likely enough for me to be confident I don’t have a serious leak?

Half hoping I can just put it down to maybe the drain screws just not having been done well in the past.

Cheers,
Tom
 
Thinking at this point probably best thing is get some fresh oil in, and just make sure to check it after first few times running the engine in the water?
 
Well, if it holds vacuum that well, it's not likely that it's going to ingest water. I'd fill it and run it keeping an eye on if it leaks or not. An oil sheen in the water after you've stopped for a few minutes is the tell tale sign of a leak. It will build pressure when you run it so I guess that will be your test.

Good luck.
 
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