PAIR Removal ( ST1100 ) *

[KoTAOW]

Submitted by Adam Frymoyer, STOC #949

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PAIR Removal

Over the years, there have been several very high mileage bikes in the ST1100 community that have had their PAIR valve diaphragms fail, causing a vacuum leak and drivability issues. When I say several have failed, I mean several. I know of only 3 guys that have had an actual failure of the PAIR valves themselves. A vast majority of the others have been from vacuum hoses getting dry rotted, cracking, disintegrating and causing loads of trouble. Some guys like them and leave them alone. Others don’t want a problem in the future and remove them as a preventative measure. A very few, have to leave them on and service them to meet local emission inspection regulations. I already had the carburetors out for overhaul and I don’t want to take them out again to fix a non-meaningful emission component. I also had coolant leaks at the elbows and the coolant hoses were mush. Another bonus to PAIR removal is a little lost weight and less complexity. With that said, mine are coming out.... And with good reason! You’ll see as you read on, that it was a great preventive step. I would have had problems in the future....

There are many articles in the ST Archive Of Wisdom (AOW) for body work removal, carb removal and different ways to block off the PAIR pipes. Have a look at them for guidance. There are many great idea’s. However, refer to your Honda service manual to properly work on your bike. Some of the pictures I posted are just for reference, to give you a general idea of where I’m at.

The first thing I do is take off most of the body work. I’ll need to also remove the fairing lowers and fairing centers to gain access to the chrome pipes.



The next thing I do, is to remove the carburetor’s and rubber heat shield. YUK... Full of mouse pooh and pee.






The PAIR system is now exposed.



The front mounted valve CANNOT be removed without cooling system being drained and the right coolant elbow removed. There is not enough clearance to get the right mounting bolt loose and out.



As you can see here, even with the right coolant hose removed, there still isn't enough clearance.



Now that the elbow is removed, the mounting bolt can now be taken out.



There’s no way that these elbow o-rings will re-seal. They MUST be replaced.






I then cut all of the hoses out with a pair of cutting pliers, un-bolt the valves and pull everything out. I then un-bolt the chrome tubes from the cylinder heads. The chrome pipes need to get bent, to work them around the cylinder heads and frame for removal.






Here is what it looks like with everything removed. I also take dabs of silicone and fill the thread holes. I don’t want water to sit down in there and possibly freeze during winter storage.









With everything removed, I noticed a brown fluid leaking onto the garage floor. What the heck... It’s coming out of the PAIR valves. I took them into the shop and took them apart before I throw them away.









With the covers removed, I find brown stinky slime in the housings. The rubber diaphragms are mush and starting to distort. I’m glad I took them out. As said earlier, I would have had problems in the future.






Now that the PAIR valves are out, I de-greased the valley of the engine. I also replaced all of the coolant elbow o-rings, water manifold o-ring and seal and coolant hoses going from the block to the thermostat housing. This is also a better look at the silicone down in the thread holes.



I can now remove all of the vacuum “T’s” and cap off both sides. I've also eliminated the auto vacuum fuel-cut valve.









I then scrape off all of the gasket material from the cylinder heads. As I said earlier, there are many different ways to block these ports off. I don’t want the pipes in there. Just my personal preference. I took a 1/8” NPT tap and thread the ports. I then take the extra plugs out of an air brake governor kit I've got kicking around and install them in the heads. Use your imagination and be creative to whatever you find the most attractive. I’m just a function over form guy...









During the carburetor overhaul, I’ve already replaced the rubber isolator / boots and ready to install the rubber heat shield. I first tape up the cut-outs in the shield with heat tape on both sides. These slots won’t be used anymore now that the PAIR valves are out. I don’t want any extra heat getting up to the carb float bowls. It gets really hot down in there! However, I still leave the little slot open to hook to the frame for mounting support.






Now that this is done, I can put the shield in. I strongly recommend replacing those carb boots. They get dry, brittle and leak as they age. If replacing, remember to face the raised tabs outwards as shown / circled.


That’s it for a PAIR removal. I can now re-install the carbs, accessories and body work.

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Thank You again for your contribution Adam Frymoyer, STOC #949