Questions regarding breather connections and transmission case covers

misterguitar

misterguitar

1993 ST1100, 1982 GL500, 1977 GL1000, 1975 GL1000
Joined
Jun 12, 2019
Messages
39
Age
52
Location
Chapel Hill, North Carolina
I bought a 93 ST100 and have been trying to sort out the breather/emissions connections. So it would seem there are two versions of the transmission case on these bikes? One that has a hose connector in the main housing and one that is cast with no connector. And there is also a connector on the back plate of the transmission housing. I'm trying to sort out which bikes had which? I was told by the prior owner that the ABS and california bikes had both and the 48 states bikes had only the one on the backplate. Is this true? the one hose I have coming from the backplate has a bolt shove din it. Where did that connect originally? I would suspect it has to go to the intake somewhere! I have a factory manual and have tried to decipher the connections but it is not very clear and show NOTHING about the transmission case conenctions that I can see or find! Any help you can provide is appreciated! thanks!
 
The hose with the bolt in the end is probably the #3 cylinder intake manifold vacuum hose used for a carb sync. It is normally connected to the Auto Fuel Valve which has probably been removed.

I don’t know what you mean by “backplate.”

Edit: rereading, I guess you’re not talking about the carbs...

John
 
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Except for the 1991 USA ST1100s, all other years’ crankcase breather chambers were internal and vented out through the right front of the crankcase through the water pump housing with the hose running back and in between the cylinder banks to a nipple on the bottom right side of the air cleaner.

Pictures would make commenting easier.

John
 
Do you know the history of the engine? Rereading I’m thinking you may have parts of a USA 1991 engine that has the external crankcase breather chamber with the ports and vent hoses in/from the shift cover and trannie case. I’m scouring my archives for pictures. One of yours would help a lot....
 
I was told by the prior owner that the engine that was in it with 60k miles had some issues. he said he pulled an engine from a salvage yard up in Virginia that only had 3000 miles when it was wrecked. The engine had been stored inside. He did not indicate what year it was. He mentioned the replacement engine had some extra connections he had blocked off. He did give me the original engines transmission. He had blocked off both breather tubes and also removed the PAIR. He said he didn't keep the correct transmission case as he thought it would be better to keep the low mileage transmission on the replacement engine. And as such there would be a blocked off connection. The bike was a 48 state bike and never had an evap system on it. After studying the manuals I have decided I won't be putting that on (the evap canister and valves) as I had originally intended. But will put the PAIR back on and get the breather connected properly. I plan to replace the old alternator (still working) with the 40 AMP upgrade, also plan to take the headers, heat shields, and exhaust pipes to Jet Hot to have them ceramic coated for durability. I figure since I will already have the swing arm off and exhaust off its not that much more work to take the engine out and just swap the transmission casings to get the right connectors. Here are two pictures. One shows the hose I have on it now. This hose had a bolt stuck in the end. Bike was running with no breather at all! Second picture is of the transmission case I got with it. the engine on the bike has the upper hose connector cast into the case. And the nipple on the lower one on the rear transmission cover was removed. No idea if it was actually blocked off or not. As you can see the cover that was originally on the bike did not have that upper connector cast into the case.... Where does the breather hose usually go on these bikes? a nipple on the bottom of the air cleaner?
 

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Yes, these appear to be USA 1991 ST1100 crankcase breather parts, unique to that year. Mine has them. They are shown on the fuel tank microfiche (fiche link), the three hoses attach to the external crankcase breather chamber (item 18).

I described the breather system on all later years/models above. The bike can’t run for long without venting the crankcase air/pressure. If the folks that did the R&R on this bike correctly you should be able to find the hose leading from the water pump to the bottom of the air cleaner. If so, you’re fine as is, IOW just leave the plugged, unused hoses alone and GO RIDE!*

BeST, John
STOC 1058

* official motto of the ST1100/1300 Owners Club
 
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Here’s a picture of the external breather chamber on 1991s showing the hoses from the Shift Cover and Rear Case ports.

241322241322
 
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OK. I dug through my archives and found a few illustrative images. They didn’t load in the order I wanted but I’ll just add notes as they are.

This shows the 92-02’s internal crankcase breather chamber’s exit port in the case (#1 cylinder, lower left corner next to the frame gusset). USA 1991s don’t have this port. This was taken at Rob Parker’s techSTOC. 2010 IINM.
241323

This one from Jim Neagle’s wrenching gathering. Shows the vent nipple in the water pump just above the frame, with no hose attached as he was installing a 92-95 water pump on his 1991. ‘91s vent from the back of the engine/trannie to the external breather box. There is no port in the case (as show above) so the nipple on this water pump is a blind hole/unused. There are no NOS ‘91 water pumps but 92-95 pumps can be installed on 91s without any modification. On all other models/years the breather vent hose connects to this nipple and lead up and between the heads to the air cleaner.
241324

As shown here. Jim is holding the water pump and his middle finger is on the through port that routes 90° to the nipple (touching his trigger finger) for the hose. The hose is detached in this picture of course and is visible at the bottom of the shot touching the frame, and just above the spark plug that’s resting on the valve cover IINM.
241325

If you’ve got this crankcase vent system on your particular ST1100 you are good to go. Please report back. I’m very “invested” in your query now. TIA

John
 
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OK! This make s a LOT more sense now! So in theory then I could black off both of those breather connections coming from the transmission and it would just breath through the front breather vent then. But only if it is a 92 or later engine. If it is a 91 then I need to vent it form the back. So if I follow this correctly then I need to look at the front and see if I have a nipple coming off the water pump. if I do then it is a 92 or later engine. if not it is a 91 and I need to vent form the back. I'll take a look later tonight when I get home and snap a pic of what I have.
 
Christopher, you don’t have to remove a single piece of tupperware to see if there’s a vertical hose just under the front of the right side valve cover. It’s right there, clearly visible if you have an engine with the internal crankcase breather chamber. You could also confirm by following the hose that should be plugged into the nipple on the bottom right side of the air cleaner. It should lead forward and to the right and you’ll know it’s the crankcase breather hose. Please let me/us know what you find. I’m pretty well versed in this particular stuff so you’ve come to (one of) the right guy(s) if I do say so myself. :cool:

Edit: still curious about what folks have done with your ST... does your ST have the ugly, odd-shaped black breather box on the right side? If it’s not there and the two rear hoses are cut and capped, I’m led to believe that they knew what they were doing. Your report will confirm.

John
 
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Looks like I have 91. Going to buy a separator on ebay. Just need to figure out if they use molded hoses now. And hose routing.
 

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I’ll assume that your salvage engine came with its original water pump. And that you’ve never actually run the engine. With capped vent and drain hoses the crankcase pressure would blow the valve cover gaskets, or pop the plug/cap and spew oil saturated air all over.

I’ve seen the breather boxes for sale cheap. Might even be able to find one with its hoses but I’d think generic hose substitutes should work fine.

Please keep us posted. This is a first in all my years on the forums. And good luck!

John
 
Yes. I drove the bike home. about 25 miles. City and freeway. It performed horribly. The throttle would stick. Bike idle was all over the place. It would periodically sputter under full load. ONce I got it home I took all the tupperware off. I found the following problems.

  1. The breather issue.
  2. Carbs had sat up for years and needed cleaning one carb had the emulsion tube clogged shut with gunk and the slow jet was totaly plugged.
  3. The push cable was frayed up in the throttle pipe and was causing the throttle to stick.
  4. The fuel pump had been replaced. Non Honda pump. seems to work great BUT they used a non submersible fuel line inside the tank so the hose is all bubled and coming apart.
  5. Missing the insulator blanket over the engine below the carbs
  6. Both crash guard/protectors had the part where the fairings connected all bent up so the fairings could not attach properly. So they made a lot of racket in the wind. A couple of side panels were not mounted.

My carb packing kits just came last week. I have them apart and cleaned. Just need to put them back together. I'm still on the prowl for all the molded breather hoses. I might go up to the junkyard he said he pulled the engine from to see if the breather stuff is still on the bike. Ordered a genuine honda throttle cable had to wait for it to get here from germany. It just came yesterday. Ordering the insulator blanket today. I get my bonus at work in a few weeks. Going to buy all the stuff to do the alternator and get the heat shields and exhaust headers and pipes ceramic coated. My mufflers are still in great shape so will leave those be.
 
I also have the crash bars on order now. Just ordered those! lol. I broke a tab on the right side cover. hoping some ABS cement will fix that.
 
Wow, quite a project you’ve undertaken. Respect!

BeST of luck. Please share with us as things progress. Let us know if we can help in any way at all. Love these resurrection stories!

John
 
Yeah after looking around at parts sites, I'm starting to think it might be smarter in my part to just get a used 92 or later water pump and replace that to make it a 93 gain. lol That and swap the transmission case back to the one off the 93. The hoses are readily available for the 92 and later water pump/breather. And I woudl fair better if my water pump ever went out. I notice those are no longer made by honda. I always seem to buy the bikes that the parts are becoming obsolete for. lol I just need the st's to become as collectible and popular as the old cb750's. You can buy just about NAY part in reproduction for that bike!
 
N.B. - if you have a 1991 engine, slapping on a salvage 1992-1995 water pump (no NOS, BTW) won’t work. There is no internal crankcase breather chamber inside the 1991’s engine, nor is there a breather port on the engine case behind the water pump housing. Sorry...

The 1991’s crankcase vent system works fine. And the parts you need are available and cheap. Plus the 1991 engines are rock solid, IMHO.

John
 
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Well I lucked out! Just found a breather chamber with all three hoses on fleabay! Id been searching for one for days. They had a lot of 91 engines listed with the hoses I needed attached but nobody was selling the chamber and the three hoses. Also manged to score a 40 amp alternator. Have to wait till i have more caus to order the rest of the alternator bits I need and I should be ready to rock and roll!
 
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