SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: bluenun on May 30, 2007, 12:19:11 PM
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I have been reading thru some posts and I see some people talking about clearances in some people's engine's being way to tight? I assume it is bore clearances? Why do some people say a jetboat is different and what shold they be?
Thanks
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The cylinder's get way hotter in a jet boat engine requiring "looser" clearances to avoid seized pistons. You can't run a "fresh" car engine in a jet boat for very long, a semi-tired car engine is a better choice. As far as specific clearances, I dunno...
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Hmm so my 454 just had a fresh .060 I do have a set of used .060 manley pistons I guess it would be better to use those instead of a new "tight" setup??
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Hmm so my 454 just had a fresh .060 I do have a set of used .060 manley pistons I guess it would be better to use those instead of a new "tight" setup??
Well the optinum set-up would be to have it all checked out by a shop that knows what jet boat engines require. I know I've read and have talked with jet boat mechanics that say it will never last if it was built like a car engine would be built. Cylinder temps are way too high for car clearences.
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as rod had mentioned the cyl get hot but actually its the pistons that get hot and swell, the block does'nt expand due to the open cooling sys that we use so as a rule of thumb 1-3 thous on the bore. bearings are'nt as picky i go with 1 thou for every inch of journal so if you have 3 inch mains that would be 3 thou clearance, these are just general guidlines you or your engine builder will have to make your own descions based on what you want. hope this helps
ralph
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Ok got it. Thanks for the info. So anti friction coatings are a good thing on a jet boat piston then. Plus I run Royal Purple oil which is the slickest stuff on the market and I think I am gonna install an oil cooler as well.