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Thread: Kent AH4 cam shaft

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    Kent AH4 cam shaft

    Good afternoon,

    I am able to source a Kent AH4 cam shaft to upgrade my BJ7 engine, but I am not able to determine whether or not valve pockets in the pistons are necessary for this cam shaft.
    Does anybody know this?

    Thanks in advance for your advice!

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    Yoda John Turney's Avatar
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    Re: Kent AH4 cam shaft

    Do you know the lift for that cam? That will determine if you need pockets. Are you using the stock rocker arms? If you change the arms to a different ratio, you may need pockets.
    John, BN4

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    Re: Kent AH4 cam shaft

    Walter74,

    Welcome to the forum.

    Sorry, but I don't know if the block needs to be pocketed.
    I found the specs on the web site for Kent Cams.
    11.57 mm valve lift.

    This cam is for an MGC motor.
    Good Luck.

    Doug Glesmann

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    Re: Kent AH4 cam shaft

    I have just put a Kent AH4 profiled cam into my rebuilt engine and I did include valve pockets for clearance.

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    Re: Kent AH4 cam shaft

    How does your engine run with this cam?

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    Re: Kent AH4 cam shaft

    The lift is 11.57 as Doug mentioned. I think that is too much for safe running without pockets

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    Re: Kent AH4 cam shaft

    Yes, 11.57 mm definitely requires pockets. I have a Denis Welch DWR 8 cam with 10.18 mm lift and pockets are required. The Denis Welch DWR 1 cam at 9.09 mm lift does not.
    John, BN4

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    Re: Kent AH4 cam shaft

    Too early to tell as it is still in restoration. I have run the engine, but only to bed things in.

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    Re: Kent AH4 cam shaft

    Is it difficult to determine the positioning and depth of the pockets?

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    Re: Kent AH4 cam shaft

    Engine builders use a type of clay--PlayDoh works, I hear--positioned on top of a piston. They rotate the engine through a compression stroke and measure the depth of the pocket left; if a valve hits the top of the piston I'm not sure what they do (maybe mill pockets until the valve clears?).

    Betcha Dougie knows.

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    Re: Kent AH4 cam shaft

    Quote Originally Posted by Walter74 View Post
    Is it difficult to determine the positioning and depth of the pockets?
    In the case of the Healey motor it's pretty straightforward because the valves are vertical and the only interference is with the exhaust valve over the deck (it would take a very radical situation to have piston to valve clearance issues - perhaps Dougie's motors are that radical?).

    Locating the pocket is simply a matter of blueing the deck, setting the head on with a loose exhaust valve (no spring/retainer) and manually spinning the valve against the deck to make a mark in the blueing on the deck. Typically adding an 1/8" or so to the diameter of the mark for 'safety'.

    Depth of pocket is determined by knowing the lift at the valve of the cam you want to use. Then measure the distance from the surface of the closed valve head to the head gasket surface + gasket thickness (stock type is typically .040) + whatever clearance your machinist suggests (typically around .040 for this situation). So, if the valve lift is .450 and your measurements add up to .400, then you need .050 deep pockets. You don't want the pockets any deeper than necessary because they enlarge the combustion chamber size therefore lowering the compression ratio.

    And playdoh is a nice confirmation before running the motor.

    Dave

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    Re: Kent AH4 cam shaft

    There’s no pocket in the pistons, there are pockets in the block. The intake valves go wider than the bore. The head gasket has pockets in it to avoid the valves. That will tell you the position of the pockets. You’ll need to assemble the head off the engine and apply 11.57 mm lift to the rocker arm and measure how much the valve extends past the face of the head. That will tell you how deep to go.
    John, BN4

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    Re: Kent AH4 cam shaft

    Here's DWM's cam profile doc (for comparison): https://www.bighealey.co.uk/pdfs/6-C...ng%20Chart.pdf

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    Re: Kent AH4 cam shaft

    Here is a visual for you on the pockets.
    engine pocket ported.jpg

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    Re: Kent AH4 cam shaft

    Radical yes, but no pockets needed in the piston, just a beautifully milled dome. With the combination of cam lift and roller rocker ratio, I'm at the max pocket depth.

    '57 Domed Race Pistons.jpg
    Roller Rockers - Beehive Springs.jpg
    Dougie
    '65 BJ8 3000 MKIII GN.29
    '57 100-SIX MM Vintage Racer GN.1 #414
    Team Healey PDX

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    Re: Kent AH4 cam shaft

    What are the black flare fittings for Dougie , an external oil cooler ? Also what are all the threaded plugs for by the freeze plugs .
    "If it aint broke ....dont fix it "
    " Thats not an oil leak ..........its a special automatic British rustproofing system "
    Best Healey in show ABCD Ottawa 2013
    Best Healey in Show Boot n Bonnett Kingston 2013

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    Re: Kent AH4 cam shaft

    Quote Originally Posted by Healey Nut View Post
    What are the black flare fittings for Dougie , an external oil cooler ? Also what are all the threaded plugs for by the freeze plugs .
    Race motors never see freezing temperatures, but simple plugs can fail under extereme (6-24 hour) race conditions. The threaded plugs stay in place and the large freeze plugs are epoxied sealed. The black flare fittings are part a special designed and engineered side oiler system which inputs the oil from the oil cooler directly to the crank & main bearings first before circulating throughout the entire motor. This is the key to extending the life of the custom billet crank....

    Billet Crank 1.jpg
    Billet Crank 2.jpg
    Dougie
    '65 BJ8 3000 MKIII GN.29
    '57 100-SIX MM Vintage Racer GN.1 #414
    Team Healey PDX

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    Re: Kent AH4 cam shaft

    That crank is a piece of art . Tks Dougie .
    "If it aint broke ....dont fix it "
    " Thats not an oil leak ..........its a special automatic British rustproofing system "
    Best Healey in show ABCD Ottawa 2013
    Best Healey in Show Boot n Bonnett Kingston 2013

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    Re: Kent AH4 cam shaft

    Wow, that is next level engine building. A bridge too far for my road car
    I will stick with some simple pockets in my block. Thanks for all the useful information. I already found a good machineshop to help me out

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