warning regarding high compression heads

Discussion in 'Performance Mods' started by jaguar, Jun 3, 2016.

  1. jaguar

    jaguar Well-Known Member

    According to this paper http://www.bridgestonemotorcycle.com/documents/oilpremix6.pdf the maximum safe cylinder head temperature is 425 to 450 degrees farenheit.
    When I was testing my own high compression head with squish band the temperature got up to 425 degrees. That was with only 155psi cranking pressure. I think most of the high compression heads create more pressure than that. And I was using the Jaguar CDI which reduces head temperature a bit because the timing is less advanced that the stock ignition.
    If you have a high compression head you definitely need to monitor the head temp with a gauge. The one I used which worked good was from JNMotors at http://www.jnmotorsbikes.com/product_p/jnm1183.htm

  2. Frankfort MB's

    Frankfort MB's Well-Known Member

    Have you tried using different oils such as caster based? Oils make a lot of difference in temperature. Not trying to counter your research Jaguar since you have way more experience than I do but I've found out plenty of ways to blow a motor up. Thomas Edison said "I have not failed. I found 10,000 ways that won't work." I take that to heart;)
    Hello Moto! likes this.
  3. jaguar

    jaguar Well-Known Member

    info on castor oil from https://www.penriteoil.com.au/tech_pdfs/0The Rise & Fall of Castor Oil - NOV 2014.pdf

    On the positive side, it was reported that castor based oils ran cooler. It was an old adage that castor had the ability to leach heat away from hot metal. Technically, castor based products are more polar, having a greater attraction to metal, than mineral oils, and improved heat transfer from highly loaded areas. This polarity also improved oil film load carrying ability and these beneficial features could not be matched by the straight mineral oils then available.
    On the negative side there was a problem with excessive gum deposits resulting in almost continual oil changes, whilst also sharing the same problem encountered with
    mineral oils that being high viscosity at low temperatures and a very rapid drop of viscosity as temperatures increased. The problem of excessive gum deposits due largely to very poor oxidation stability was not an issue with radial aero engines, as in their case having a total loss oiling system the oil never had the opportunity of gumming up.
    Alexander Duckham, of Duckham Oils fame in 1912 carried out tests whereby he measured carbon deposits on pistons after 1000 miles using six different oils one
    of which was castor. The results showed quite definitely that castor oil produced the greatest amount of deposits and in his summing up states "that in my opinion castor oil can only be used in fixed cylinders with impunity for short distances and then with repeated cleaning between runs."
    As earlier mentioned, castor is highly polar, but the film strength or load carrying capacity is much lower than a mineral oil treated with ZDP.
    Modern motor oils, with their vastly improved viscosity and anti-wear characteristics, will extend engine life to a marked degree. Competition engines of the 1920's and 30's had to be rebuilt at least once a year. The current combination of better materials, improved lubricants, oil and air filtration makes such annual rebuilds a thing of the past.
    Mineral oils can be treated with dispersants and detergents, anti-rust agents, oxidation inhibitors, antifoam agents and corrosion inhibitors to improve internal engine cleanliness. None of these additives can damage components used in classic or vintage engines.
    To summarize, the castor based material gave the best lubrication in its day. However, it is now a dated and long since superseded technology.
    Its use, although traditional, should no longer be contemplated.
    The only thing that castor can do that a mineral oil can't is to make the right smell in the exhaust.
  4. HeadSmess

    HeadSmess Well-Known Member

    they say you could always tell a WWI pilot from the smell they emitted...

    breathing in atomized laxative for hours at a time...

    eau da le poo... :p
  5. butre

    butre Well-Known Member

    castor oil does a better job of blending with straight ethanol than mineral oil. worth noting if you're some place where the price difference of e85 is worth the reduced energy, or if you're distilling your own fuel.
  6. 45u

    45u Active Member

    Shoot and I worry about my motorcycle head temps running 280 degrees here in the deep south during the summer. I am able to read the head temperature sensor at all times for the EFI. Will have to check my motorbike head with my heat gun one day.

    This is the oil I use. It is synthetic with castor and will mixed with alcohol.

  7. butre

    butre Well-Known Member

    280 will hurt a liquid cooled motor, but not an air cooled one. if china girls had iron sleeved cylinders I wouldn't even worry about 500 degrees. head temp isn't all that important for air cooled motors, pay attention to the exhaust temp instead. as long as you don't exceed the melting point of aluminum for too long you're fine

    of course the different expansion rates of aluminum and iron play a critical role at that point too, and preignition is always a bad thing, but just use your head. if it's pinging, give it a second to cool. baby stuff.

    my head might hit 350 on a bad day. riding during the winter you can touch the head and come back with all your skin, but during a hot mississippi summer it gets pretty toasty.
    Last edited: Jun 7, 2016
  8. Frankfort MB's

    Frankfort MB's Well-Known Member

    I love these little things, 'your fine!!! Just don't let the engine melt!!' ;)
  9. mrbg

    mrbg Member

  10. 45u

    45u Active Member

    My motorcycle is air cooled not water cooled and has never seen much over 300 and that was in stop and go traffic. Now it does not get that high even in stop and go traffic cause it now has a fan on it for when the engine starts to get hot. No matter what others might say the temps folks talking about here are bad for any engine particularly when you get in the 400 range. Do not believe everything you read on the net or you are in real trouble. But like I say do it how you want on yours.