Please explain the plastic breather thing.
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Ultimate HDF Member
Joined: Jun 2007
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From: Richmond, VA
Please explain the plastic breather thing.
OK, Virginia is getting dumped on with piles of snow, so my EV27 install is approaching. My local Indy mentioned as long as I'm in there I should replace the plastic breather valve with a metal one. I have never changed one before but thought they were all plastic. Still, being the Shovel guy I figured metal parts are always better than plastic, especially inside a motor. Please give me some opinions. I was probably gonna replace the plastic breather with a new one anyways, so should I just go ahead and do the metal one or are they plastic for a reason???
Please advise.
Please advise.
Last edited by bikerlaw; Dec 16, 2010 at 06:12 PM.
Seasoned HDF Member
Joined: Aug 2008
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From: Ohio
The plastic breathers are claimed to get distorted and not stay in a round shape, possibly wearing the bore. When I disassembled my engine a few years back it had the breather bore grooved up (plastic breather) but also had a bearing failure so I can't be sure the breather did the damage, installed a S&S reed valve due to damage of the bore, the reed valve worked as a repair. Check the roundness of the plastic breather and go from there but the S&S steel breather is a nice item and peace of mind.
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Ultimate HDF Member
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From: Richmond, VA
Well, thanks for confusing me further....LOL. Am I correct the plastic one dates all the way back to the Shovels? I was a little concerned about the metal one causing issues, and the plastic one failing, thats why I posted up. Seems we have have some differing answers, dang.
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Seasoned HDF Member
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From: Ohio
Bikerlaw, glad I could help with the confusion LOL! The plastic/nylon breather is a tough item and gets harder with heat, harder than the alum case. A perfect round breather in a round hole with oil and clearance won't wear but a distorted breather turns into a oil wiper and removes the cushion, friction-heat and gaulding starts when the oil cushion is removed. Plenty of plastic breathers still in the Evo's and fine, some have had the breather bores resleeved from plastic breather damage which requires some jingle/labor to repair.
Small block Chev's ran the nylon toothed upper timing gear and after time plus heat, the teeth came off and just using this as a referance to nylon tendancies in a engine, some lived the life of the engine, some didn't SO you can add this to the other decesions Evo owners face like which cam, which lifters, which carb, which comp. ratio, syn or dino oil, which ignition, beer or whisky while thinking about all this stuff.
I'll leave it at this, reputable engine builders are not going to leave that nylon breather in there after known failures have happened. Bud or Jack for you my friend?
Small block Chev's ran the nylon toothed upper timing gear and after time plus heat, the teeth came off and just using this as a referance to nylon tendancies in a engine, some lived the life of the engine, some didn't SO you can add this to the other decesions Evo owners face like which cam, which lifters, which carb, which comp. ratio, syn or dino oil, which ignition, beer or whisky while thinking about all this stuff.
I'll leave it at this, reputable engine builders are not going to leave that nylon breather in there after known failures have happened. Bud or Jack for you my friend?
Last edited by 1997bagger; Dec 17, 2010 at 10:45 AM.
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From: Cookson, Ok
The theory that was explained to me is that metal particles, even from normal wear, can embed themselves in the plastic and act like a sanding drum on the bore. With a metal breather, these fine particles will wash through the system and be picked up by the oil filter. Made sense to me so I go with steel. All bets are off if chunks run through it though.
Last edited by Lakerat; Dec 17, 2010 at 01:24 PM.
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Ultimate HDF Member
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From: Richmond, VA
Well, those arguments go in line with what my Indy said, and why he recommended getting a steel one. But this stuff is to be expected in my life. There is never any easy fix for anything. When you make a simple decision to replace the crappy cam bearing Harley so foolishly put in, all the sudden a 15 dollar cam bearing becomes a bearing, then a cam, then adjustable push rods, then lifters, then a breather.... and 15 bucks all the sudden becomes 20 or 30 times the initial cost. 
