843cc engines

Discussion in 'Rear-Engine Fiats' started by Kent Baird, Jan 15, 2019.

  1. Kent Baird

    Kent Baird Italian car collector.

    Lakewood Colorado
    I have some 843cc and 817cc engines that I need to do a performance redo. Reverse CW rotation in my 600 and CCW in the 850 car. I have some of the parts. But I have some questions.

    Has anyone offset bored the 843 block to use the 67.2mm size 965 engine style pistons?

    The cheap Chinese connecting rod sets on eBay have the floating pin size of 18mm and 110mm length. Are pistons available for the 63.5 stroke.

    If you put a 903 crank in the 843 block and 843 rods. Do you have get custom pistons made or can you machine the stock piston tops off 2mm?

    I have a 70mm Giannini crankshaft and stock 843 rods. What can you use for pistons?

    Can the 850 3-bolt water pump fit and run CW in a 600 car?

    I had planned with John Edwards to install a special center cam bearing to use a 600 camshaft in the 850 block. Does anyone know of a machine shop doing that kind of stuff these days?

    Kent B.
  2. Frank L. Di Gioia

    Frank L. Di Gioia True Classic

    las vegas, nevada
    For what it's worth years ago I machined 903 pistons to fit a 74mm crankshaft in a 903 block using 843 rods and it worked. HOWEVER it had rather high compression when used with a PBS 8-port head. Something like 180 PSI on a compression test. Ate plugs till I found a motorcycle plug that held up. We're talking 20 miles before they shorted out. I just sold an 843 motor with a 903 crankshaft and 110mm rods but it did have special pistons. Last but not least I just got a set of the Chinese rods and they look fine (means nothing) but will probably drill a small end oiler and add lower oilers (holes) for the piston bottoms.
  3. Kent Baird

    Kent Baird Italian car collector.

    Lakewood Colorado
    Hi Frank,
    My block needs the bore up sized.
    So I was hoping to find some larger pistons to fit on the MaxSpeed 18mm pin rods.
    Changing to the larger crank is going to be custom pistons I guess.
    My 600 car is a lite weight street car. So if I can get around 65hp I would be happy.
    My plan was to use a hot 600 cam so I could use the simple mechanical fuel pump.
    Also I wanted to save $$ on not getting the gear drive set.
    I have a 127 cam but no fuel pump lobe.
    Thanks for your input.
  4. Frank L. Di Gioia

    Frank L. Di Gioia True Classic

    las vegas, nevada
    Hi Kent,
    As to the water pump question go to Ebay and punch in "post water pump fiat 850-850 special" and it has a Fiat water pump impeller for a good pic out of the housing. . It's NOT directional and IF it's the same as the 843-817 impellers it will go either way and work but maybe not quite as efficiently give the shape of the pump housing. I asked Clark at PBS once about the short pump they made with the Toyota impeller and he said about the same thing.
    As to the 843 block taking the 67.2 bore I don't know but do have an 843 block with some damage to it. A rod slapped the lower cylinder web on one side and took out a chunk. It's actually similar to what you need to do to a 903 block to run a 74mm crankshaft. That and an overzealous person overtightened the oil pressure sender threads and broke out a piece. Both faults shouldn't actually effect running but look bad. It's semi set up for reverse oiling as the center main is drilled to the oil gallery. If you pay freight I'll send it to you to "test bore" to see if 67.2 works. If it won't, trash it. If it does you owe me for whatever you think it's worth. I wish John Edwards was still with us, RIP.

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