Honda BF2 Cooling?

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BotleyBuoy

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I've picked up a cheap BF2 outboard and managed to get it to start but I'm puzzled by the cooling arrangement. The data plate does not indicate whether it is a 2A, 2B or 2D manual. The manual I've down loaded is for for a BF2A and this tells me to look for water flowing out of the "water check hole". My concern is that apart from an initial spurt no water comes out of the hole. However, looking at the construction of the engine, fins on the cylinder and head and design of the starter pulley, I'm wondering if this is an air cooled engine. Did Honda make the BF2 in air cooled and water cooled variants? If so how do I know which one I've got and whether or not I have a problem. The engine number is 1237325 (although the '1' could be a 'T' with a very small cross).
I don't want to risk running the engine until I know what's what so can anyone help here?

Many thanks.
 
AFAIK, they have both. The cylinder & head are air cooled but the exhaust is water cooled. However, the lack of water cooling does not appear to harm the engine. I've run mine for the last 15 years with no impeller and no ill effects.

For chapter and verse on these, you really need to get hold of Steve66 of this parish who knows everything.
 
BotleyBuoy said:
I've picked up a cheap BF2 outboard and managed to get it to start but I'm puzzled by the cooling arrangement. The data plate does not indicate whether it is a 2A, 2B or 2D manual. The manual I've down loaded is for for a BF2A and this tells me to look for water flowing out of the "water check hole". My concern is that apart from an initial spurt no water comes out of the hole. However, looking at the construction of the engine, fins on the cylinder and head and design of the starter pulley, I'm wondering if this is an air cooled engine. Did Honda make the BF2 in air cooled and water cooled variants? If so how do I know which one I've got and whether or not I have a problem. The engine number is 1237325 (although the '1' could be a 'T' with a very small cross).
I don't want to risk running the engine until I know what's what so can anyone help here?

Many thanks.
Click to expand...

Steve66, who is the forum Honda expert, will hopefuly be along shortly, if not PM him

aka Steve Evans of Evans Marine http://www.evansmarineservice.co.uk/

However ITYWF find that although the power head is water cooled early models ( BF2A) had a water pump to provide water cooling of the exhaust .
From your description it sounds as though yours is a BF2A but which my be in need of a new water pump impeller.

http://www.boats.net/parts/detail/honda/H-19211-ZV0-003.html

EDIT
Beaten by a few seconds by andrewbarker.
Sounds as though operation of the water pump is not all that important.
 
Last edited:
Thanks for the replies. I've spoken to the very helpful Steve and I think I know what to look for now.

By any chance does anyone have the vented piece which clips into the engine cover on this outboard? Beer tokens waiting if you have one to spare.

Thanks in advance.
 
If it's the same as mine (an old BF2) it was designed by Daft Designs of Japan Inc. The drive shaft which is exposed when removing the gear case has a female spline at the top of it which is larger than the diameter of the drive shaft. That means that the impeller won't come off that way, so instead it has to come off the bottom, which means removing the drive shaft, which means disassembling the gearbox. Item 14 (prop shaft bearing carrier) needs removing, along with the prop shaft (item 13). That then gives access to the C clip on the bottom of the drive shaft (item 25), the drive shaft pinion (item 11) comes off, and the drive shaft can be removed. Gasket (item 15) will need replacing. Why it was designed like that, instead of having a male spline at the top of the drive shaft so that the impeller will slide off as per every other engine, I cannot fathom.

Numbers refer to Steve's link.

Here's the diagram that shows the daft drive shaft (item 12)...

http://www.boats.net/parts/search/Honda/Outboard Engine/0/BF20F SA/EXTENSION CASE/parts.html

Just noticed that lots of the parts on boats.net for this engine are marked as no longer available since I last looked.
 
Last edited:
Steve - Back-flushing as you suggested last night didn't help much so there was no choice but to dismantle so sorry to bother you this morning but thanks again for your help. I hit it a bit harder and everything dropped off.

The problem was some roughness on the splines on the end of the drive shaft which was preventing the pinion from releasing. The back of the pinion is badly scored so I wonder if the thrust washer failed at some time in the past and has been replaced and perhaps that's when the splines were damaged?

This picture shows the impeller and as you can see the vanes are not all curved in the same direction. I wonder if it has been replaced incorrectly in the past.

IMAG0072.jpg

In this picture you can see where the drive pin has broken through the side of the impeller when I pulled the gearbox assembly off the shaft.

IMAG0073.jpg

Perhaps this isn't an OEM part, or maybe I dismantled it incorrectly? Anyway I've cut out the broken plastic and the slot now runs the full width of the impeller making reassembly fairly simple.

Dressing and cleaning up the splines on the end of the shaft meant getting the pinion back on was also fairly simple. On test there is now a steady flow of water from the little hole at the top of the leg until revs increase at which point the flow stops. I'm guessing this could either be the knackered impeller or cavitation in the tub.

IMAG0062 - Copy.JPG

Bench testing :)

Steve, I'll be in touch on Monday for a new impeller, gearbox gasket and a couple of other bits.

Thanks to all and have a good weekend.
 
AngusMcDoon said:
If it's the same as mine (an old BF2) it was designed by Daft Designs of Japan Inc. The drive shaft which is exposed when removing the gear case has a female spline at the top of it which is larger than the diameter of the drive shaft. That means that the impeller won't come off that way, so instead it has to come off the bottom, which means removing the drive shaft, which means disassembling the gearbox. Item 14 (prop shaft bearing carrier) needs removing, along with the prop shaft (item 13). That then gives access to the C clip on the bottom of the drive shaft (item 25), the drive shaft pinion (item 11) comes off, and the drive shaft can be removed. Gasket (item 15) will need replacing. Why it was designed like that, instead of having a male spline at the top of the drive shaft so that the impeller will slide off as per every other engine, I cannot fathom.

Numbers refer to Steve's link.

Here's the diagram that shows the daft drive shaft (item 12)...

http://www.boats.net/parts/search/Honda/Outboard Engine/0/BF20F SA/EXTENSION CASE/parts.html

Just noticed that lots of the parts on boats.net for this engine are marked as no longer available since I last looked.
Click to expand...

Cheers Angus.
Yamaha and Mariner 2hp are the same. You dont have to remove the propshaft and it wouldnt come out until you remove the pinion gear and drain plugs. Fairly easy if you have done it once. Its a same parts are no longer in stock, they are lovely littke engines, but identical parts under different numbers / manufacturers are still available
 
Sorry chaps, one more question. In the picture of the impeller housing you can see what look like two small holes in the steel plate. One hole is blocked the other is partially blocked. Should these be open or are they just where the plastic moulding attaches to the metal plate?

IMAG0082 - Copy.jpg
 
Last edited:
BotleyBuoy said:
Steve - Back-flushing as you suggested last night didn't help much so there was no choice but to dismantle so sorry to bother you this morning but thanks again for your help. I hit it a bit harder and everything dropped off.

The problem was some roughness on the splines on the end of the drive shaft which was preventing the pinion from releasing. The back of the pinion is badly scored so I wonder if the thrust washer failed at some time in the past and has been replaced and perhaps that's when the splines were damaged?

This picture shows the impeller and as you can see the vanes are not all curved in the same direction. I wonder if it has been replaced incorrectly in the past.

View attachment 69636

In this picture you can see where the drive pin has broken through the side of the impeller when I pulled the gearbox assembly off the shaft.

View attachment 69637

Perhaps this isn't an OEM part, or maybe I dismantled it incorrectly? Anyway I've cut out the broken plastic and the slot now runs the full width of the impeller making reassembly fairly simple.

Dressing and cleaning up the splines on the end of the shaft meant getting the pinion back on was also fairly simple. On test there is now a steady flow of water from the little hole at the top of the leg until revs increase at which point the flow stops. I'm guessing this could either be the knackered impeller or cavitation in the tub.

View attachment 69638

Bench testing :)

Steve, I'll be in touch on Monday for a new impeller, gearbox gasket and a couple of other bits.

Thanks to all and have a good weekend.
Click to expand...

All photos are typical of what I would expect to see. The impeller has formed in that shape due to storage
 
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