User Tag List

Page 1 of 2 1 2 LastLast
Results 1 to 15 of 19
  1. #1
    Join Date
    Jul 2017
    Location
    upstate ny
    Posts
    47
    Thanks (Given)
    0
    Thanks (Received)
    0
    Likes (Given)
    3
    Likes (Received)
    7
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    head with too close of a shave..copper gasket fix?

    First post after 3 years lurking. So..I bought an ebay head for my 76 omc 9.9/15hp. Year 1989 with thermo on top to replace the poorly designed 76 head. After checking head space and looking over the head I see that someone got out of control and took off .040 or so. The piston hits the head.

    I am in internal discussions with myself about using a copper head gasket. I have made them in the past with success. But this one needs to be .080in or so.

    What does my minimum head space need to be for a cross flow motor? I am not looking for 200 psi or anything. Just want to use this head in my mota. The head hits the piston at the exhaust side of the diverter.

    Maybe 2 stock gaskets?

  2. #2
    Join Date
    Sep 2008
    Location
    Mass
    Posts
    450
    Thanks (Given)
    0
    Thanks (Received)
    16
    Likes (Given)
    1
    Likes (Received)
    39
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by rudderless View Post
    First post after 3 years lurking. So..I bought an ebay head for my 76 omc 9.9/15hp. Year 1989 with thermo on top to replace the poorly designed 76 head. After checking head space and looking over the head I see that someone got out of control and took off .040 or so. The piston hits the head.

    I am in internal discussions with myself about using a copper head gasket. I have made them in the past with success. But this one needs to be .080in or so.

    What does my minimum head space need to be for a cross flow motor? I am not looking for 200 psi or anything. Just want to use this head in my mota. The head hits the piston at the exhaust side of the diverter.

    Maybe 2 stock gaskets?
    I dont like thick copper gaskets. They tend to leak in my experience. Also two gaskets not a great idea. Can you just find another head? How expensive is a 15cc head? If 80 thousandths has been taken off the head compression will be way to high anyway.

  3. #3
    Join Date
    Apr 2012
    Location
    windham nh
    Posts
    3,182
    Thanks (Given)
    151
    Thanks (Received)
    117
    Likes (Given)
    951
    Likes (Received)
    755
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    OMC or the aftermarket may have made a lower comp.(thicker) gasket for these engines as they did for other motas when the quality of fuel went down. I would check with BRP as they might have some nos. Gary
    "12" Super Lite Tunnel (11') "88" 25 Yammy twin carb "BANANA SPLIT"
    "77" Hydrostream Viper "87" 140 Rude heavy modded w/15" mid, Bobs nose and lwp "DANGER ZONE"
    "72" Checkmate MX-13 "80" 75 Rude w/15"mid and Nitro Lu (to be restored)

    "Too much is never enough" Keith Richards " Dreams become reality via hard work and perseverance" G.A.Carbonneau

    "This coming from an old man that strapped two bananas together, hung a motor on it and calls it a boat" XstreamVking

  4. #4
    Join Date
    Apr 2012
    Location
    windham nh
    Posts
    3,182
    Thanks (Given)
    151
    Thanks (Received)
    117
    Likes (Given)
    951
    Likes (Received)
    755
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    BTW If you do make a copper gasket make sure you spray BOTH sides with Permatex Copper coat . We had good luck with the Copper coat on high comp. sled motas in the 70s. The only up side to gettin old!!!! Gary
    "12" Super Lite Tunnel (11') "88" 25 Yammy twin carb "BANANA SPLIT"
    "77" Hydrostream Viper "87" 140 Rude heavy modded w/15" mid, Bobs nose and lwp "DANGER ZONE"
    "72" Checkmate MX-13 "80" 75 Rude w/15"mid and Nitro Lu (to be restored)

    "Too much is never enough" Keith Richards " Dreams become reality via hard work and perseverance" G.A.Carbonneau

    "This coming from an old man that strapped two bananas together, hung a motor on it and calls it a boat" XstreamVking

  5. #5
    Join Date
    Jul 2017
    Location
    upstate ny
    Posts
    47
    Thanks (Given)
    0
    Thanks (Received)
    0
    Likes (Given)
    3
    Likes (Received)
    7
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by olboatman View Post
    BTW If you do make a copper gasket make sure you spray BOTH sides with Permatex Copper coat . We had good luck with the Copper coat on high comp. sled motas in the 70s. The only up side to gettin old!!!! Gary
    Yea..Hearth, Sacks, rotax..memories from the 60s and 70s...In fact I made copper gaskets for some of my sleds back then. I have over ported many piston port motors..a lot of spit from the carb..add no air box and my parents hated the gas smell from my sno suit.

  6. #6
    Join Date
    Feb 2004
    Location
    Palm City Fla
    Posts
    7,194
    Thanks (Given)
    0
    Thanks (Received)
    829
    Likes (Given)
    0
    Likes (Received)
    6489
    Mentioned
    13 Post(s)
    Tagged
    1 Thread(s)
    Any time you clip a head , be it a little or a lot , you need to re establish the quench area back out to the size of the bore . It's just part of the job .


  7. #7
    Join Date
    Apr 2012
    Location
    windham nh
    Posts
    3,182
    Thanks (Given)
    151
    Thanks (Received)
    117
    Likes (Given)
    951
    Likes (Received)
    755
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I see what your sayin Chaz....Some of the OMC crossflow heads I have cut are cast with the bore size into the head quite a distance. I cut a 15hp 13ci (like the one in question) 30 thou without decreasing bore size in the head. Help me out if I miss understand your point as I'm always learnin. Gary
    "12" Super Lite Tunnel (11') "88" 25 Yammy twin carb "BANANA SPLIT"
    "77" Hydrostream Viper "87" 140 Rude heavy modded w/15" mid, Bobs nose and lwp "DANGER ZONE"
    "72" Checkmate MX-13 "80" 75 Rude w/15"mid and Nitro Lu (to be restored)

    "Too much is never enough" Keith Richards " Dreams become reality via hard work and perseverance" G.A.Carbonneau

    "This coming from an old man that strapped two bananas together, hung a motor on it and calls it a boat" XstreamVking

  8. #8
    Join Date
    Jul 2017
    Location
    upstate ny
    Posts
    47
    Thanks (Given)
    0
    Thanks (Received)
    0
    Likes (Given)
    3
    Likes (Received)
    7
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Chaz View Post
    Any time you clip a head , be it a little or a lot , you need to re establish the quench area back out to the size of the bore . It's just part of the job .


    I ruined my dads belt sander back in 1976 or so shaving a couple of heads on a twin cyl motor on a snowmobile. Had the sander clamped upside down and the shavings got into the motor. Sparks started to come outa the motor so I stopped, cleaned the al shards and put it back in the case. A week later I heard a yell and was called down stairs by dad. Yea..you know what happened..

    A question..how close on a cross flow should I be? Like .040 or so..like on loopers maybe..just lookin to be safe..

  9. #9
    Join Date
    Feb 2004
    Location
    Palm City Fla
    Posts
    7,194
    Thanks (Given)
    0
    Thanks (Received)
    829
    Likes (Given)
    0
    Likes (Received)
    6489
    Mentioned
    13 Post(s)
    Tagged
    1 Thread(s)
    Quote Originally Posted by olboatman View Post
    Some of the OMC crossflow heads I have cut are cast with the bore size into the head quite a distance. I cut a 15hp 13ci (like the one in question) 30 thou without decreasing bore size in the head.
    rudderless :
    A question..how close on a cross flow should I be? Like .040 or so..like on loopers maybe..just lookin to be safe..
    My first thought was , how much piston to wall clearance does the motor have . Because the looser the bore the more the piston can rock along the thrust line as it approach's and descends from TDC, which is really where you look when trying to set one up with a tight quench area .

    But for normal every day production line assemblies , .035 - .045 seems to be what the factories shoot for .

    Gary , it really comes down to what you have as a total number . I don't know if those motors have a head gasket or not . But lets just say it does and use some hypothetical numbers ....
    Piston is shy of coming up to flush with the deck surface .030
    Gasket is .040
    And the head has a recess pocket .050 deep .
    For a total of .120
    And a compression gauge says it pumps 90 PSI

    You might just clip the head .050 never need to touch the quench taper .
    Have .070 clearance
    Pump 110 on the gauge

    Add decking the block .030
    Have .040 clearance
    Pump 130 on the gauge
    Run 91 octane ... big prop , haul butt ..
    All hypothetical ... but you get the idea ....

    For someone who want's to really do one up like this , there are plenty of programs out there that if you feed it good info it will give you real world numbers to shoot for . Lots easier than when I started out , we had to do everything with old fashioned math using pen and paper ...

  10. Thanks olboatman thanked for this post
    Likes olboatman liked this post
  11. #10
    Join Date
    Mar 2004
    Location
    Brooklyn Park, MN
    Posts
    2,493
    Thanks (Given)
    29
    Thanks (Received)
    190
    Likes (Given)
    944
    Likes (Received)
    965
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I always assumed you check your squish clearance on a crossflow at the corner of the cylinder and head on both the exhaust and intake side. Is that correct and where the piston is hitting the head in this situation? Or is the Deflector on the top of the piston hitting the head as well?
    1973 Viper - sold
    1978 Viking - sold
    1995 XB02

  12. #11
    Join Date
    Jun 2007
    Location
    Singapore/Melbourne/Italy
    Posts
    9,097
    Thanks (Given)
    1008
    Thanks (Received)
    354
    Likes (Given)
    4297
    Likes (Received)
    1951
    Mentioned
    7 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Chaz View Post
    Any time you clip a head , be it a little or a lot , you need to re establish the quench area back out to the size of the bore . It's just part of the job .

    Is this head going on something with custom domes, looks like a huge angle on that?

  13. #12
    Join Date
    Jul 2017
    Location
    upstate ny
    Posts
    47
    Thanks (Given)
    0
    Thanks (Received)
    0
    Likes (Given)
    3
    Likes (Received)
    7
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by rjdubiel View Post
    I always assumed you check your squish clearance on a crossflow at the corner of the cylinder and head on both the exhaust and intake side. Is that correct and where the piston is hitting the head in this situation? Or is the Deflector on the top of the piston hitting the head as well?
    Upon further inspection..its hitting at the deflector corners. The old head is back on for the rest of the summer so I can't do any real measuring until winter but it looks like .040 is missing.

  14. #13
    Join Date
    Feb 2004
    Location
    Palm City Fla
    Posts
    7,194
    Thanks (Given)
    0
    Thanks (Received)
    829
    Likes (Given)
    0
    Likes (Received)
    6489
    Mentioned
    13 Post(s)
    Tagged
    1 Thread(s)
    Quote Originally Posted by powerabout View Post
    Is this head going on something with custom domes, looks like a huge angle on that?
    Power ,
    That is a 300x head that had a little rash ...

    Tell me , what is the stock angle .. ?

    And what you super keen eyeball inclinometer tells you this one is ...

  15. #14
    Join Date
    Jun 2007
    Location
    Singapore/Melbourne/Italy
    Posts
    9,097
    Thanks (Given)
    1008
    Thanks (Received)
    354
    Likes (Given)
    4297
    Likes (Received)
    1951
    Mentioned
    7 Post(s)
    Tagged
    0 Thread(s)
    12.5degrees, lol

  16. #15
    Join Date
    Feb 2004
    Location
    Palm City Fla
    Posts
    7,194
    Thanks (Given)
    0
    Thanks (Received)
    829
    Likes (Given)
    0
    Likes (Received)
    6489
    Mentioned
    13 Post(s)
    Tagged
    1 Thread(s)
    Quote Originally Posted by powerabout View Post
    12.5degrees, lol
    Survey says :


Page 1 of 2 1 2 LastLast

Similar Threads

  1. head gasket and cylinder head
    By drtyTshrt in forum Technical Discussion
    Replies: 1
    Last Post: 03-26-2017, 08:47 PM
  2. OMC looper 60hp - Mild head Shave - Help
    By scott lambert in forum Technical Discussion
    Replies: 4
    Last Post: 10-23-2012, 03:40 AM
  3. Metal/copper head gaskets 3L omc
    By mmassm in forum Technical Discussion
    Replies: 6
    Last Post: 06-19-2007, 07:56 AM
  4. Copper head gasket
    By berg969 in forum Technical Discussion
    Replies: 1
    Last Post: 10-22-2003, 09:32 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •