Valve size question...
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Thread: Valve size question...

  1. #1
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    Valve size question...

    I am going to replace my stock 1.9 valves with the larger valves of the 2.0 cylinder head size... The catalog says the valves for the 2.0 head are 42 mm and 37mm.....I already own a new set of 39mm intake valves for a 1.9 head.. Could I use the new intake 39mm valves as exhaust valves...that way I would only have to buy the 42mm valves for the conversion ??

    That would mean that my exhaust valves would be 2mm larger than normal 2.0 exhausts...will this work ? or might the exhaust valves made differently material ? I know the exhausts run at much greater temperature... it's just that I already have the valves... How about the closeness of the edge of the valves...maybe too close together ?

    Joel

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  3. #2
    Über Genius First opel 1981's Avatar
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    Quote Originally Posted by jrapose View Post
    I am going to replace my stock 1.9 valves with the larger valves of the 2.0 cylinder head size... The catalog says the valves for the 2.0 head are 42 mm and 37mm.....I already own a new set of 39mm intake valves for a 1.9 head.. Could I use the new intake 39mm valves as exhaust valves...that way I would only have to buy the 42mm valves for the conversion ??

    That would mean that my exhaust valves would be 2mm larger than normal 2.0 exhausts...will this work ? or might the exhaust valves made differently material ? I know the exhausts run at much greater temperature... it's just that I already have the valves... How about the closeness of the edge of the valves...maybe too close together ?

    Joel
    Exhaust valves take a higher heat load than intake valves. I'd advise to not use intake valves as exhaust valves.
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  4. #3
    OpelGT.com Übermoderator kwilford's Avatar
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    Quote Originally Posted by jrapose View Post
    Could I use the new intake 39mm valves as exhaust valves...
    No. Intake valves will not survive the heat that exhaust valves endure.

    You might also consider installing hardened exhaust valve seats to match the new valves (and 37 mm is usually big enough).

    The 42 mm intake valve is only 1.65". That is better than the stock 1.574" (40 mm) intake valve, but not a significant upgrade, given the cost and work. Most of the serious CIH engine guys here suggest intake valves should be at least 1.75", preferably 1.85", with appropriate unshrouding of the combustion chamber to be done. That might be more easily achieved using cut-down Chevy 11/32 stem valves and matching valve guides, unless you can source larger Opel intake valves.

    JM2CW
    Keith Wilford
    Finishing up a bare-metal, nut & bolt rotisserie restoration of my '71 Opel GT; next up is my 28,000 mile Garage Find GT, stored since 1975, which needs a LOT of love...

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  6. #4
    1000 Post Club Viny Charb's Avatar
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    When I rebuilt my 1.9 engine to 2 L spec i used the larger 2.2/2.4L 45mm intake valves with the 2L 36mm exhaust valves.
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