Changing water pump in Honda BF100E

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Springcrik

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Apr 9, 2008
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My brother recently gave me what I thought was a Honda B100 that turned out to be a 1984 Honda BF100 version E. I got it running and tried it out as a kicker motor on my Lund Tyee Magnum 1950. Ran very well so I decided it would be worthwhile to get it in top shape. First thing after engine oil & gearlube change was to change the water pump impeller.

​I have been a diesel service technician and service manager for over 40 years and have access to a forklift at work. So made a mounting bracket for the little engine so I can raise & lower it to a comfortable working height:

​Next I removed the rectifier mounting bolt and gently twisted the rectifier out of the way. I packed the area beneath the shift linkage connecting pin with blue paper shop towels because that pin is difficult to reinstall and if you drop it, the pin will fall down in the tunnel for the shift linkage rod. The orange "marker" in the picture is a piece of weedeater string I pointed at the connecting pin.

​The lower unit was very easy to remove using a 10mm socket and a wobble joint for the 5 retaining bolts. I have read other posts on this forum about the housing & drive shaft sticking, but this housing came off easily. I only dropped it about a foot because I did not remove the threaded clevis connector at the upper end of the shift rod prior to dropping the lower unit.

​The water pump, plastic inlet housing, and the steel separator plate came off easily. Only tool needed was a 10mm socket and a scraper I used to gently remove the old gaskets that stuck to the plate.

​The Sierra 18-3279 kit came with the correct impeller, gaskets, & seals. The old impeller was in fair condition considering it's age.

​The water pump housing had very minor scoring and was reusable. Remarkable considering it's first life in a Zodiac rubber boat in Alaskan rivers. You might notice the prop; it didn't fare so well against Alaskan gravel bars.

Reassembly went very well other than dropping the shift linkage connecting pin twice. The paper towels did their job preventing it from falling down into the shift rod tunnel, which would mean you have to pull the lower unit back off. You have to carefully be sure the copper water tube slides back into the outlet of the water pump housing. Then gently raise everything and sorta jiggle it to get the driveshaft splines realigned with the crankshaft. It helped to rotate the engine clockwise (viewed from top) until the splines lined up.

​Final result of a 30-minute run in a test barrel was no overheating, strong pee stream, and water droplets spraying out the 2 small exhaust relief ports.

​Legendary. Honda. Quality. Amazing for a 1984 engine that has sat in storage since 1995.
 

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Tarinazo

Seaman
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Feb 18, 2019
Messages
55
I just got the same engine, don't know what version it is, but doing some research I can fairly state it's a 1984 B100L. I know it was used in salt water so I'm just hoping the previous owner took good care of ot.
In he meantime, I noted that the lower unit has two small holes a few inches above the "propelle bump" (tiller side), and was wondering if those where normal or caused by corrosion... judging by the first pic on your post, it seem to have those same holes, can you verify this? I don't want to start the engine this way.
 

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
I just got the same engine, don't know what version it is, but doing some research I can fairly state it's a 1984 B100L. I know it was used in salt water so I'm just hoping the previous owner took good care of ot.
In he meantime, I noted that the lower unit has two small holes a few inches above the "propelle bump" (tiller side), and was wondering if those where normal or caused by corrosion... judging by the first pic on your post, it seem to have those same holes, can you verify this? I don't want to start the engine this way.

Please start a new thread with your questions. These one is almost 2 years and was informational only.
 
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