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Hi All



I saw on David Silver spares in the UK, that they have a crankcase breather mod.



What was the reason for this modification to the existing breather setup.



Is it worth getting?



Cheers



Curt
 

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It's not a mod so much as a factory update. The earliest CXs had a breather from the back of each head to the airbox.

Around 80 or 81 they moved the breather to a "bottle" type assembly that screws into the timing inspection hole in the rear cover. As I'm not certain as to when the factory actually made these changes your bike could be either.

If you have an item like an alloy bottle below your right carb your bike is already the updated setup. If it is a plain cap with a 17mm bolt head it is the earlier setup.

The David Silvers kit comprises blanking caps for the head breathers, the bottle type breather and some hose.

The update was made because the earlier breather would pump oil into the airbox at sustained high speed.

The bottom line is that if you can get the bottle part from a bike wreckers, the blanking caps from the auto parts store you can probably come up with the same thing cheaper, - if you in fact need it.
 

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1980 Honda CX500 Shadow
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This modification was only required on the CDI models because the crankcase of the TAI models was vented through the top of the pulser cover.
 

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GL700Wing: I see that you have "1980 CX500 Shadow" in your signature. Was this a US-spesific model? Never heard of it over here.



Michael
 

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I think GL700 is an Australian and so is the "Shadow" name for the standard bike,from about 1980 onwards.



GL700 is also 100% correct.



Does anyone know if the 'shadow' designation is used in any other countries besides Australia? N.Z.?
 

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I can tell you that the "Mod" will also put oil in the air box at sustained high speed riding. My '83 GL650i came form the factory with the little alloy bottle. I ride mostly freeway at 80mph or so. Every 2K i need to wash may air filter in gasoline to degrease it and wipe out the airbox or the bike runs like crap. I've checked compression and I don't think my rings are bad.
 

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Try putting in a longer breather hose to the airbox. Loop it up as high as you can up under the tank with the most reasonably vertical climb you can manage and then back down to the airbox.



This will give the oil more time to condense out and drain back into the motor rather than being so inclined to make straight to the airbox.



If your bike is extreme it may not help much but is worth trying as it does cut down on the amount of oil pumped into the airbox.



My bike used to mark it's territory from the airbox breather drain and now doesn't lay down a drop.



Also, aside from normal breathing in these motors, wouldn't the rotor etc. throw a certain amount of oil directly at the breather outlet via centrifugal force? Especially at sustained higher RPM?
 

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Try putting in a longer breather hose to the airbox. Loop it up as high as you can up under the tank with the most reasonably vertical climb you can manage and then back down to the airbox.



This will give the oil more time to condense out and drain back into the motor rather than being so inclined to make straight to the airbox.



If your bike is extreme it may not help much but is worth trying as it does cut down on the amount of oil pumped into the airbox.



My bike used to mark it's territory from the airbox breather drain and now doesn't lay down a drop.



Also, aside from normal breathing in these motors, wouldn't the rotor etc. throw a certain amount of oil directly at the breather outlet via centrifugal force? Especially at sustained higher RPM?


My bike runs better if I have the plug in the bottom of the airbox drain hose. I just have to remember to empty it occasionally by removing the plug. Great tip on the longer higher breather hose, I am going to try that. Thanks!
 

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Curt, I'm currently in London England until May. Last week I went to a CX500 get together and noticed several bikes with the breather modification. One fellow (Tet?) told me it was done to reduce the "mayonnaise" in the air box. You get that slime when water, oil, and gas mix. To answer you original question, I don't think it's a critical modification. On CX500's for north America, you just periodically remove the plugs at the bottom of the hoses that come down from the air box. That drains out water and slime that would otherwise accumulate in the air box and eventually start plugging up the air filter.
 

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Hiya all,

I also looked into the cranckase breather mod, as i believe it is beneficial if you do a lot of high speed, highway mileage (which i do on my long jaunts with my 1979 CX500 Deluxe)

I found some good info here, but it is still on my "to do list"....


http://www.bunn.co.nz/



Dash, i think you are refering to "Tel" who is a very highly respected member of the Honda CX/GL UK mcc
( he drinks too much tea yer know...
)

Hope yer having a good time in the UK, wish i was there...


All The best........Keith.......
.......
 

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I believe that the Shadows are Australia specific. No other country got anything of that name. One similar name was the 400 wing which is the Japanese import model.
 

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... On CX500's for north America, you just periodically remove the plugs at the bottom of the hoses that come down from the air box. That drains out water and slime that would otherwise accumulate in the air box and eventually start plugging up the air filter.


European models don't have these plugs. Wonder why? There is a sponge inside one of the pipes instead, to avoid sucking in dirt and bypassing the airfilter.
 

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1980 Honda CX500 Shadow
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Hi MGR1,



To the best of my knowledge the CX500s with the 'SHADOW' decal on the sidecover were only sold in Australia and New Zealand between 1980 and 1982 (our '78 and '79 models didn't have the 'SHADOW' decal on the sidecover).

I've found some more technical information on the breather modification:

Crankcase breather pipe modification – 1980 CX500

1. A modified crankcase breather system has been introduced on the 1980 CX500 and retro-fitted to the earlier models.

2. It was found that when the engine speed was increased above 7000 RPM, excess oil was being blown out of the breather tubes fixed to each cylinder head and accumulating in the air filter box. To rectify this, Honda introduced a new crankcase breather system, whereby the timing inspection plug doubles as an engine breather.

3. In the event of the modified assembly not being fitted. The following parts can be obtained from an authorized Honda dealer.
Cylinder head plug (2 off): 90547-415-305
Timing inspection breather plug: 12361-415-610
O-ring: 91302-001-000
Breather tube: 95005-12460-20

4. Dismantle the previous breather assembly. Use the two plugs contained in the kit to blank off the cylinder head nozzles and secure with the wire clips used to retain the previous pipes. Fit the new inspection plug to the timing hole and run the breather pipe from the top of the plug to the pipe joint at the base of the air filter box.
 
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To my knowledge none of the 500 bikes have this modification but all 650 bikes do, at least in the US.



My 650 bikes consume some oil whereas the 500 bikes do not. Compression is good, there are no signs of leaks, and there is no noticeable smoke at any time. Leakdown tests not been done yet but my plans are to do so in the near future. The air box does collect oil, and presumably much of this oil gets burned. A significant portion of my riding is also at high speed.



The GL500 (TI ignition) has a single breather tube from the ignition timing cover. It does not have the breather ports found on the heads of many (all?) CDI ignition 500's.



Although the GL500 does not have this modification, I'm not aware of of any issues with GL500 engines related to the breather.



Since the 650 has the same basic breather tube port setup on the ignition timing cover, why not remove the modification from the 650 and plumb it like the GL500? I'm just thinking aloud here but may try this.



Alternately, the extended tube routed almost vertical sounds like a very good idea.
 

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Thanks for the picture. Seems like this mod revolves around the inspection hole cap tube. Everything else is pretty simple. I wonder if there is a simple way to do this on the cheap. The current inspection tube could be used and then I'm thinking something like a metal tire valve stem but bigger.



Not that capping the heads off is a problems but what if you connected the heads with a tube. Seems like it would work.



I might have to look into doing this.

Anyone know the thread size of the cap?
 

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Interesting read on the Bunn Breather. Here is his website. I know this guy has been in the "breather business" for many years, and has done a lot of research. Read the docs, a lot of it makes good sense.



I have installed one of these exhaust breathers (but not the inlet breather) on my '55 AJS 500 twin, with good results. Blowout and oil consumption is less than with the original setup on this bike.



I will also install the Bunn exhaust breather on my '78 CX500. This is possible to achieve without doing any non-reversable mods, and results should be easy to notice. I'll let the forum know when I have done some mileage.



Michael
 

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A modification on my bikes to do list is a version of the Bunn breather wherin the motor breathes in through the head breather via a small breather filter and out through the timing inspection bottle type breather utilising one way valves yet to be sourced.



These bikes [particularly the early ones with the head breathers] seem to be a natural for the Bunn setup.
 

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One unintended positive effect of a Bunn Breather setup, with the small inlet valve installed in the rear cover, could be better ventilation and thus cooling of the stator...
 

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Back in the day, when the E.P.A. was just firing up (somewhere in the early 70's), there was such a valve that slipped into a rubber mounted "sleeve" through the valve covers called a "Positive Crankcase Ventilation" valve, known as the "PCV" valve. Tis a "one-way" check valve that connected from the valve covers via a hose that (I thinks) originally connected to something akin to a "restrictor plate" (only thicker) on which the carberotor sat. As the E.P.A. started "flexing" its "government-funded" muscles , this eventually was piped to some Gizmo called an "air pump"(belt driven). It was also around this time that american vehicles started losing the coventional "breaker point" ignition and went "photo-electric and beyond" (LOL), which was around the time that I decided that this government-funded agency had its sites set on me, to either go BACK to school and be retaught (NOT gonna happen), er get out!........But, I digress........
 
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