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Thread: 74" head cracking

  1. #11
    Join Date
    Feb 2011


    I was recently on a Willy's Jeep forum. They were discussing old, barn type finds that had been sitting for many years.
    The discussion was based on what steps should be taken before trying to start the engine.
    One of the gentlemen mentioned that he used a product called "KREEN" in both the gas and oil to quickly remove
    old internal carbon build-up. Kreen is made by Kano Industries, the same company that makes Kroil.
    Wondering if anybody on this forum has used Kreen in their old motorcycles for this purpose?

  2. #12


    Howdy sir,

    Sorry for delayed response, new toy added to herd has been a distraction. Not to get into a discussion of pre-ignition/detonation - long topics - at a low 5.5/1 CR combustion stress will be limited to hotspots (glowing exhaust valves/carbon) and that rare, so you are unlikely to hear any rattling underway. Efficiency. If you were to remove a head and hit the piston with a soft mallet to mimic combustion in nearly all cases the most efficient range, ie, cylinder pressure generating torque, is between 15 to 18 degrees ATD to ensure maximum transfer of this energy into work. Too early, basically the rod is beating its big end against the crank pin like you hitting an anvil with a hammer rather than transferring the energy into rotation. Too late, piston farther down the bore resulting in more cylinder volume thus muting the violence of the expanding gases. Yes, in under square (stroke to bore) motors this less an issue as every millimeter of downward piston travel is not reducing cylinder pressure as much. Flat heads (and especially 38-42 Fours) have poor flame propogation, thatís why u see inconsistent carbon build up so thus the incentive to use your advance more often to ensure max burn leaving less residual deposits. Heat to a degree, ..pun intended, adds to efficiency, thus, on a cold motor with irregular fuel atomization and a cold cylinder enclosure you want less advance to ensure as much burn as possible.

    I run Cotton type floats lower than the old recommendation for the heavy copper variety as they control fuel more accurately. Jerry Greer use to joke that the carb and machine bounced down the road while heavy unresponsive copper floats stood still blubbering uncontrolled fuel out the top vent. The carb fuel feed (nozzle) has a sort of built in accelerator pump. Lowering bowl fuel level reduces surge on cracking the throttle with its attending richness. Modern fuel formulations make plug reads difficult. Especially as a low compression flathead, youíre going to have carbon build up within your exhaust and your plugs may look a bit darker everywhere but the center electrode. An offline poster asked about plugs. I use extended tip NGK BPE7 or 6ís. Later 80 inch heads have full depth plug inserts, early do not, thus, I turn off a third or so of the plug threads on my 346 to prevent binding on removal from entrapped carbon. I can only think Indian ran short J6ís to prevent oil fouling like JC Whitney once offered in their catalogues with plug extenders tubes. Unfortunately, the trade off here is lost efficiency with the plug enshrouded. Extended tips expose the entire electrode to the combustion chamber. But, it requires a little more finesse by the operator on a cold motor started on choke as you have partially un aerated fuel splashing around which can cause fouling. Again, prudent use of ignition retard will clear it momentarily.

  3. #13
    Join Date
    Feb 2011


    Does anyone know if this spark plug - "NGK BPE 7 extended tip spark plug" is still available. I have been unable to find any, including on the NGK website.
    Has the nomenclature number changed or been dis-continued?
    Thank you.

  4. #14


    The only cross reference I can find is BP 7 ES.


  5. #15


    I would agree with others, time to replace. Murphy's Law suggests that when it finally goes it will go in a big way and perhaps do more damage. You should be able to find a decent replacement.

  6. #16
    Join Date
    Jun 2001
    Central Illinois, USA


    Quote Originally Posted by PRG View Post
    ...I run Cotton type floats lower than the old recommendation for the heavy copper variety as they control fuel more accurately...
    Why lower, Peter?

    Brass must be set much lower for their mass, but mine are to be set to book spec.

    I went to a lot of trouble to calculate their proper volume for proper buoyancy to achieve the same fuel level in the bowl as OEM; Any arbitrary adjustments are at your own risk.

    PS: Buzzed Kanker published in his hard-copy rag that my floats should be set higher!

    I needed an attorney.
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    Last edited by T. Cotten; 09-23-2020 at 10:05 AM.
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