mystery black box

With most plastic off my 91, I now notice a black plastic assembly at the right rear of the motor which does not exist on my 99. Has a few hoses entering/exiting, one is a fairly large one that's connected to the bottom right rear of the engine (by the transmission linkage). Another hose on top of the box that heads who knows where and a smaller hose going toward the airbox perhaps? Anybody know what I'm looking at? Can't find it on schematics or the manual.

Is it one of these;

http://www.cmsnl.com/honda-st1100-1991-usa_model739/partslist/E++20.html

*likely this one
http://www.cmsnl.com/honda-st1100-1991-usa_model739/partslist/F++41.html

Crankcase ventilation. Only on the '91. Forward hose attaches to a fitting under the airbox.

Only the 1991s have an external crankcase breather box. The water pump is unique also.


John OoSTerhuis STOC 1058

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John OoSTerhuis said:

Only the 1991s have an external crankcase breather box. The water pump is unique also.

Click to expand...

So would either of these be trouble spots? Under which heading schematic would I find the breather box? I assume it was replaced with something else or was it redundant?
Thanks guys...

DeanR said:

So would either of these be trouble spots? Under which heading schematic would I find the breather box? I assume it was replaced with something else or was it redundant?
Thanks guys...

Click to expand...

The crankcase ventilation was redesigned. The only potential problem with the box is possibility of new hoses, which one could find aftermarket for probably less $$$.

I think the box is called a 'tank breather' found on the parts fiche under 'fuel tank'

+1 on what Ralph said. You shouldn't have any problem with the 91s' crankcase breather system. The water pump will have to be replaced if it starts leaking. Some folks replace their water pumps at the same time as the first timing belt R&R, at around 90K per the manual; but, most would wait until the second timing belt along with the tensioner and idle pulleys (me included). Here's a file of some research I did a while back to confirm the part differences:

~~~~~~~~~~~~~ Crankcase breather info-PNs.txt ~~~~~~~~~~~~~

1991 Honda ST1100 Crankcase Breather System:

[using the remote desktop fiches accessed through Service Honda:
http://www.servicehonda.com/test/index.htm
Aug '08]

--FUEL TANK fiche --
17551-MT3-000 / TANK, BREATHER [plus 3 hoses and their clips]
17358-MT3-000 / TUBE [air cleaner hose]
95002-02130 / CLIP, TUBE (B12.5) [air cleaner hose]
95002-41250-08 / CLIP, TUBE (D12.5) [air cleaner hose]
17359-MT3-000 / TUBE [gearshift linkage cover hose]
19505-KS6-700 / CLAMP, WATER HOSE [2 ea - gearshift linkage cover hose]
17357-MT3-000 / TUBE [transmission case hose]
90682-SB0-671 / CLAMP, CANISTER HOSE [ 2 ea - transmission case hose]

[92-02std&abs: Only the 91 has an external crankcase breather chamber. All other years/models have theirs internal to the crankcase and vent to the airbox via a port/nipple on the water pump housing]

-- SHIFT COVER fiche --
11350-MT3-000 / COVER, SHIFT
[92-02std&abs: 11350-MY3-000 / COVER, SHIFT]

-- REAR CASE fiche --
21110-MT3-000 / CASE, RR.
[92-02std&abs: 21110-MY3-000 / CASE, RR.]

-- WATER PUMP fiche --
19200-MT3-000 / WATER PUMP
[92-94std&abs: 19200-MY3-010 / WATER PUMP plus breather hose and clips]
[95-02std&abs: 19200-MAJ-G20 / WATER PUMP plus breather hose and clips]
[92-02std&abs: 11150-MY3-010 / HOSE, BREATHER]
[92-02std&abs: 90646-657-000 / CLIP (16MM)]
[92-02std&abs: 95002-02130 / CLIP, TUBE (B12.5)]

-- CRANKCASE fiche --
11000-MT3-000 / CRANKCASE SET
[92-94std&abs: 11000-MY3-010 / CRANKCASE SET (replaces 11000-MY3-000)]
[95std&abs: 11000-MY3-020 / CRANKCASE SET]
[96-02std&abs: 11000-MAJ-G20 / CRANKCASE SET]

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Apparently, you can no longer order the 91s' breather box or water pump. Just this week I learned that the 92-94 water pump is a suitable substitute.

Regards, John

Guess I missed it on the fuel tank fiche.

I am not an engine guy, but have done most other stuff on these bikes. Could I ask just what a crankcase breather does?

Thanks again guys for your experience and help..

DeanR said:

Guess I missed it on the fuel tank fiche.

I am not an engine guy, but have done most other stuff on these bikes. Could I ask just what a crankcase breather does?

Thanks again guys for your experience and help..

Click to expand...

Just found an explanation on Wikipedia, though obviously not regarding our engines.

Typically several jobs for the crank case breather, one is to accommodate the pressure changes in the crankcase caused by the moving pistons, it's not just he air above them they are moving around, the air trapped below in the crank case is whipped to a frenzy. If the crank case is not adequately vented you can have what engineers call pumping losses where real horsepower is lost due to restricted air movement in the crank case resisting piston movement. Older engines used to just vent to atmosphere but because the air in the crankcase also contains fuel mixture that has blown by the piston rings, doing such is a source of unburned HC emissions - not acceptable anymore. So the second job is to vent this blow-by gas and crankcase air into the intake system to burn any unburnt fuel and reduce HC emissions. Simple venting, such as just running a hose from the crankcase vent to the intake tract, can cause entrained oil mist to be sucked into the engine and burned, leading to an oil consumption problem. So the third job and the reason for the elaborate breather tanks, is to separate as much of this entrained oil as possible from the air and allow it to drain back to the crank case. This reduces oil consumption, emissions, and combustion chamber deposits.

Thanks for the explanation Jeff.

Thinking a bit more about this. Seems that this breather box may just an emissions related thing and could potentially be eliminated ala the PAIR system? Or is it necessary for proper engine functioning. (I suspect I know what John Oo will say).

Has nothing to do with the Secondary Air Supply System. The crankcase must be vented somehow.


John OoSTerhuis STOC 1058

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In the old days 60s and before car engines vented crankcase to the autmosphere. I had a '63 Falcon Ranchero and I knew it was time to change the oil when the blowby turned blue.

^^^ I had '64 Ranchero as a hand me down from my dad. It used to do the same thing! From the factory the PCV hose was attached to the air cleaner, but it tended to drench the air filter and cause running issues. I just ran a longer hose down under the car instead. It had a little 170CI straight six in it.


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