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Discussion Starter #1
I saw a site where a fellow had vented his crankcase off the timing pin hole with a 3/8 hose barb in place of the blanking plug. I looked for the site again but can not find it right now. My question is: What is the thread size in said hole and is a hose barb readily available. I ask because I measure it a 12 TPI and about a 3/8 hole. In checking my taps , I find 12TPI in 9/16 but not 3/8. Any insight would be of interest. Working on a 1970 T120R.
 

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Why aren't you using the existing breather system? Where is the timing pin hole, if you mean the hole in the back of the crancase for setting TDC then that is in line with the crank which throws a lot of oil. I unfortunately started a rebuild forgetting to fit the blanking plug and spent hours cleaning the back of the machine!!!!!!!!!!!
 

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What's wrong with just venting it out the back of the rear fender? There's absolutely no baffling of the venting coming out the timing plug hole.
 

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Discussion Starter #6
The thing is, on the later Triumph there is no timed breather disc for air control. You are just dumping a load of downstroke air into the primary with no provision for pressure equalization prior to upstroke. I believe this load of air is just being pulled back and forth from the primary. My tests with primary oil being sucked back into the engine in fairly lage quantities tends to confirm this. Consider the PVC system on an automobile. You have a one way valve (PCV) under negative pressure and you must have a fresh air inlet usually up on the valve cover for fresh air inlet to the crankcase. After reading about the Bunn set up, that is essentially what he is doing. He is flap valving both air inlet and outlet. Makes sense to me.
 

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Ok I think I am starting to finally understand John's pics but correct me if I'm wrong....
1)The timing plug hole is only for intake of fresh air through a one way valve when the crankcase is sucking on the piston upstroke. No exhaust there whatsoever.
2)The crankcase exhausts through the primary case/rear fender hose through a one way valve when there is crankcase pressure (piston downstroke).

questions: I believe pic#8 shows the exhaust vent pipe. Is the "T" fitting the exhaust valve and where does the small hose go?
-also where would the present rockerbox vent tube go on a 79 T140?
 

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Snakepit,
You've got the right idea.
The BBK has 3 suggested methods of crankcase breathing
1) Top to Bottom (in through the rockerbox and out through the primary case)
2) Bottom to Top (in through the timing pin hole and out through the rockerbox)
3) Bottom to Bottom (in through the timing pin hole and out through the primary case)
I only chose the Bottom to Bottom method because it was less obvious to people and IMHO looked like a neater way to do it. The OEM alloy air boxes are also a wonderful place to hide the air inlet pod.
The "T" fitting from the exhaust valve goes up to the breather hose at the front underside of the top tube (frame oil tank) see link below:

http://s184.photobucket.com/albums/x162/johnquinnell/Bunn Breather Kit/?action=edit&current=OIFLubesystem.jpg

Cheers
JQ
 

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Thanks John
I'm lost here abit...Does that hose coming off the exhaust valve going up to the oil tank vent "T" with the Rockerbox vent? Wouldn't that put crank case fumes into the rocker box/ oiltank?
 

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Hey that's a good question.
I've shown the designer of the BBK - Rex Bunn my layout and he didn't find anything wrong with it. When I turn the engine over by hand, you can definitely hear the air being sucked in through the timing pin hole as the pistons move up the cylinder and blow out through the primary case breather on their way down. It definitely has made some difference to my engine though. Annoying top end oil leaks have all gone and one peculiar change to the engine behaviour is that engine braking has reduced slightly but I can understand some of the reasons behind that with the way air can now flow through my crankcase.
JQ
 
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