Author Topic: Breather clearance  (Read 423 times)

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Offline MadMaxUK

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Breather clearance
« on: September 15, 2019, 12:04:36 PM »
I have a 89 Evo motor in for work and the breather bore is badly scored. The owner has supplied a + 0.030" breather but what sort of clearance do we need? First time doing this. Is an expandable reamer the way forward or steel sleeve the best solution? Thanks ...

Offline guppymech

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Re: Breather clearance
« Reply #1 on: September 15, 2019, 01:21:42 PM »
'84 FXE, '02 883R

Offline MadMaxUK

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Re: Breather clearance
« Reply #2 on: September 15, 2019, 01:35:08 PM »
Great link! Just 0.001" - thought it would have been more but we'll go with that then. That S & S American made quality reminds me that the pistons going in this build are S & S and made in Taiwan ... not joking  :wtf:

Offline Hillside Motorcycle

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Re: Breather clearance
« Reply #3 on: October 09, 2019, 04:13:54 AM »
I have a 89 Evo motor in for work and the breather bore is badly scored. The owner has supplied a + 0.030" breather but what sort of clearance do we need? First time doing this. Is an expandable reamer the way forward or steel sleeve the best solution? Thanks ...

Best way is in a vertical milling machine, is to indicate true C/L of the breather bore, and with a boring head, bore to establish the clearance dimension.
Otto Knowbetter's business rules;
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Offline BUGLET

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Re: Breather clearance
« Reply #4 on: October 09, 2019, 05:25:20 AM »
  Hillside, what clearance would you recommend.

Offline guppymech

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Re: Breather clearance
« Reply #5 on: October 09, 2019, 10:11:45 AM »
S&S makes a reed valve breather to replace the rotary breather if your bore is messed up.
https://www.sscycle.com/docs/default-source/instruction-sheets/51-1194_breatherreedvalve93-99bt_20110223.pdf?sfvrsn=4

Edit* I just noticed they say it's for head breathers only but I've read of guys using it on earlier engines.
« Last Edit: October 09, 2019, 10:28:48 AM by guppymech »
'84 FXE, '02 883R

Offline BUGLET

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Re: Breather clearance
« Reply #6 on: October 09, 2019, 01:23:10 PM »
   I used them in a couple of shovelheads just to try them out when they first came out with no problems. The bores were OK I just wanted to see if they would work.

Offline Flhfxd

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Re: Breather clearance
« Reply #7 on: October 09, 2019, 08:23:33 PM »
Had mine bored & replaced with S&S 30 over, when the lower end bearing disintegrated and turned everything inside to shyt. 94 EVO. Lifters too. No issues. Taiwan pistons ....on a (mostly) stock rebuild. Runs like a champ. Eats Twinkies any day.
"And the road goes on forever...... But I got one more silver dollar.....'

Offline Hillside Motorcycle

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Re: Breather clearance
« Reply #8 on: October 10, 2019, 03:56:39 AM »
  Hillside, what clearance would you recommend.

We usually set those at .002".
With a degree wheel, you can also set/re-size the breather port as per S&S instructions. :smile:
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