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Classic, Vintage & Veteran For Coventry and Meriden Models. Anything pre-Hinckley goes.

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Old 12-05-2012, 03:32 PM   #1 (permalink)
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chain case breather pipe

I have a question about the chaincase breather tube on my T140v. Last year I modified the pipe to hold a small air filter stopping just under the battery carrier. ( see old post here bottom of page)
It seemed to work ok and I thought it looked better than the pipe running along the rear mudguard. Soon after I started to get leaks around the cylinder base gasket and pushrod tubes. The leaks got worse with the higher revs. So I changed the setup to a short hose discharging down by my external oil filter. Still leaks way too much but the leaks seem to be less.
The question is did I restrict the breather enough to cause gasket failure ?
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Old 12-05-2012, 04:23 PM   #2 (permalink)
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dave, that hose still seems to have a kink in it which can still cause some back pressure internally.i would make it as straight as you can.it might be that at some point you restricted venting enough to find the weak spots in you engine gaskets which may never seal 100 percent again
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Old 12-05-2012, 04:28 PM   #3 (permalink)
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Are the cyl. Base nuts or any of the head fasteners loose?

That hose does look too small. I think the standard setup would work better.
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Old 12-05-2012, 06:31 PM   #4 (permalink)
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Quote:
Originally Posted by tintop48 View Post
dave, that hose still seems to have a kink in it which can still cause some back pressure internally.i would make it as straight as you can.it might be that at some point you restricted venting enough to find the weak spots in you engine gaskets which may never seal 100 percent again
I bet your right about the weak spots. I am renewing gaskets from the base up now.

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Originally Posted by Triton Thrasher View Post
Are the cyl. Base nuts or any of the head fasteners loose?
That hose does look too small. I think the standard setup would work better.
That was the first thing I checked when the leaking started. I'd to get it sorted out as I don't want to use the standard setup.
I wonder could a restricted breather really cause the leaks.
I have had the cylinders and head off twice before and never had a leak anywhere - until I changed the breather pipe.
thanks !
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Old 12-06-2012, 01:39 PM   #5 (permalink)
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filtered primary breather

I've run a K&N filter on my 72 TR6 for many years. I will clog and cause oil leaks if not cleaned frequently. I soak it in diesel fuel and blow it dry with my air compressor. I like to see daylight through the media. Bob
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Old 12-06-2012, 08:34 PM   #6 (permalink)
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Think how much pressure is generated in the cylinder by the upstroke. The crankcase has a lot more volume, but those pistons moving down still compress air and create pressure. I've never measured it, but I'll bet it is somewhere around 10psi or higher.

When you put that filter on the end, you created more back pressure without a doubt. Plus, anytime a tubing run takes a bend, it creates restriction to flow and that creates back pressure. Add length to a tubing run and that too add additional back pressure.

I agree that the set-up you show looks restrictive to me. I would come off the primary vent pipe with something that allows you to vent into the biggest tube you can find, if you want to run a straight vent. Better yet, if you put a PCV valve as was discussed here a year or two ago, you will create zero to possibly negative pressure in the crankcase and that does two things. First, it will suck instead of blow so leaks that currently exist due to pressure should stop. Sucking is good in this instance. And, with a vacuum in the crankcase, you'll reduce pumping losses so you'll gain a little HP.

Search here for crankcase vents and PCV valves I'm sure you'll find info. I think Gatornapper put one on his bike.

regards,
Rob
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