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Thread: 1950 chief 80 cub

  1. 1950 chief 80 cub

    G,day can someone tell me should an 80 cubic chief heads be trenched ?Rob

  2. #2

    Re: 1950 chief 80 cub

    3/16"............

  3. Re: 1950 chief 80 cub

    Ok cheers indiannut i am installing new pistons which are std in over height the old pistons are shorter from wrist pin and non trench heads? Trying to work out if the bottom end id 84 cubic are the 80 c and 84c rods the same length? Rob

  4. Re: 1950 chief 80 cub

    Hi,
    If you are going to have your cylinder heads cut for 80 inch stroke flywheels, the ideal situation is to install the cylinders with pistons (rings not necessary for this fitting procedure, but base gaskets are), and find out exactly how much each piston pops-up above the top of the cylinder. Do not be surprised if the pop-up distances are not the same. On some 80 engines the front piston pops-up higher, most likely due to lower front cylinder mating surfaces on the engine cases. Next decide what head gaskets you are going to run and measure how thick they are (this will not be perfectly precise, so don't worry about gasket compression). Once you know the pop-up distance for each piston above the top of the cylinder, take this number and subtract the thickness of the head gasket you are going to run. Now, take that number and add 0.040" for the ideal 'squish' zone directly above the piston area that is farthest from the valves. At this point you will have the amount of material that is to be removed from each cylinder head. The amount to be removed will be somewhere in the vicinity of 0.140" - with the number varying depending on your exact situation parts-wise. The 0.040" ideal squish zone has been determined by countless engine rebuilders as being the ideal for economy and power. The squish zone concept was pioneered by Harry Ricardo some 100 years ago and is the principle that all modern engines employ to some degree. The two attached photos are from the book “The High Speed Internal Combustion Engine” first published by Harry Ricardo in 1923.
    I am currently going through all of this with my 80 engine mainly because my generically cut heads were cut too deeply, and I have had to resort to recutting the heads’ gasket surfaces and also running super-thin head gaskets.
    Can you get by with simply cutting both heads 3/16” (0.1875”) as mentioned previously? Yes you can, and it would work, but you would be missing out on the maximum economy and power that the Ricardo ‘turbulent’ head design can give you.
    Pistons are a whole different issue. If there are questions; PM me and the issues can be discussed in greater detail.
    When it comes to the connecting rods; the 74 inch rods and the 80 inch rods were the same length, with the original 80 inch rods being beefier on the bottom. The 80 inch engine used 74 inch pistons that were cut on the bottom so that they don’t hit the baffles. When it comes to the larger engines, such as the 84, 88, and 92 inch engines, the rods might still be the same, but with different flywheels in order to get the longer stroke. Longer stokes mean shorter pistons (typically), and ultimately there has to be match of the flywheels, rods, pistons, and heads. Kiwi has some information on his site that might be helpful.
    One significant flaw with the original 80 inch engine design is that the pistons were not redesigned in order to lower the rings in the pistons. If Kiwi performance pistons are used in the 80 inch engine, special piston rings are available from Hastings that will better tolerate being high in the bore at Top Dead Center. The best Hastings ring is a high strength ductile iron ring with a molybdenum coating to help with scuffing and oil problems.

    The pre-modern side-valve engine era by Steven Bailey, on Flickr

    The modern side-valve engine era by Steven Bailey, on Flickr

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