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NHT valves, spring packs, pushrods, cams with rotating breather

Discussion in 'Other Norton Motorcycles' started by dynodave, Feb 21, 2019.

  1. dynodave

    dynodave

    Joined:
    May 28, 2003
    I need to buy some parts for a variety of engines and heads I'm working on. Running all over the internet and as usual there is a lot of confusing information caused by inconsistent cross referencing of STOCK NHT parts applications.
    While not 100% complete, below is the quick and dirty so far...It does not include all the part #'s. 1960 may be a change point on valves and springs, I have not researched yet. 500CC only uses short tip valves due to short barrels and only one length of short push rod series. There are however skinny steel and fatter SS aluminum pushrods.

    There are three 1.3" diameter valves:
    intake V26 short tip- Iron + early aluminum pre SS twins w/small bolt pattern
    exhaust V27 short tip- pre Commando twins up to 125871
    exhaust V264 long tip- Commando, 750 & late 650 & Mercury post 125871

    There are two 1.4" diameter valves:
    intake NM 17221 short tip- later aluminum small bolt pattern 88 99 650 includes SS semi down draft-
    intake NM 25499 long tip- Last 650SS & Mercury-post 125871


    There are two 1.5" diameter valves:
    intake NM24330 short tip- 750 up to 125871
    intake NM25501 long tip- post 125871 750 & 850 Commando

    Valve springs:
    There are early spring sets 06-7174 , for which I can see no need other than for early mellow cams. The mass differences for all the valves listed above do not seem to warrant stiffer springs.
    However, the 22729 SS cam is quite a bit hotter than the 3 earlier cams and would seem to be the primary reason for using the stiffer spring set 06-7070.
    Similar heads could have different springs depending on cam application.

    Any insights?
     
    Last edited: Feb 24, 2019
  2. dynodave

    dynodave

    Joined:
    May 28, 2003
    Push rods:
    It is interesting that very late (post 125871) 650SS and Mercury(650) warranted a longer 650 valve set including the new long tip 1.4" intake 25499 and also used the long tip 1.3" commando exhaust. Now they can use the short commando push rods. This is all in the name of better valve/rocker "geometry".
    It is interesting because it opens the possibility to "upgrade" all earlier 600 and 650 assuming they...

    1. had a specific head with the 1.4 intake. (some 600 have 1.3"intake)-(yet to be verified)
    2. had adequate clearance in the barrel to accept the "shorter" fatter aluminum pushrods.
    3. 500's with shorter barrels are not readily candidates for this upgrade unless custom shorter push rods are fabricated AND barrel tunnel clearance is assured, such as later SS clearanced barrels.
     
  3. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
    RE ; " 500's with shorter barrels are not readily candidates for this upgrade unless custom shorter push rods are fabricated AND barrel tunnel clearance is assured, such as later SS clearanced barrels."

    You have 500 iron heads which have smaller valves, then the later SS alloy heads which are about the same as the 650ss except they have a smaller dia spigot.
     
  4. dynodave

    dynodave

    Joined:
    May 28, 2003
    Not sure what you referring to?
    See my web page for reference and give me the norton head PN I show, or the new correct PN if my page is lacking.
    http://atlanticgreen.com/nhth.htm
    I own and have measured 500-600-650 engines and own all the heads on my web pages except the no spigot Norton PN 25358 and small bolt pattern 06-0380(commando core).
    All small bolt pattern heads will bolt on any small bolt pattern barrel 500, 600. 650 and if it has a "spigot"... it is 72mm. I have not yet seen a small spigot barrel that is not 72.2mm Outside Diameter. Original valve size does not matter.
    Obviously a late "no spigot head" will not bolt on to "spigot barrels".
     
  5. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
  6. dynodave

    dynodave

    Joined:
    May 28, 2003
    I believe your assertion is incorrect. I have never measured other than 72.2mm spigot OD with the corresponding head counter bore on any small bolt pattern head..
    also:
    The S650/136 is a down draught head from a 1961 Manxman, 62+ 88SS and 650SS until the spigot removal.
     
  7. dynodave

    dynodave

    Joined:
    May 28, 2003
    pix of 3 types of rotary cam breather-
    edit:
    found that drive tab centers are in line with cam TDC
    From middle of breather slot CCW to drive tab center read:
    1. red 90deg 2. orange 60deg 3. black 48 deg
    [​IMG]
     
    Last edited: Feb 24, 2019

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