Jet boat 460 build

« **on:** February 25, 2018, 09:35:59 AM »

Can any one tell me if there is a difference in how a jetboat engine should be built as compared to a regular hp marine engine? Im looking into having my 460 rebuilt with a little more hp for my 77 glastron cv23. Thanks for any help. I would consider buying another hp motor already built if the price didn’t get too far outta wack. Looking for about 450 hp. Shipping would have to be a consideration as im in northern maine. Thanks JIM

« **Reply #1 on:** February 26, 2018, 03:11:56 PM »

Piston ring gaps need attention on a marine engine. KB Pistons has an easy to understand chart available with a net search.

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« **Reply #2 on:** February 27, 2018, 09:03:36 AM »

Bearing clearances have to be fattened up since jet boat motors have an open loop cooling system

« **Reply #3 on:** March 09, 2018, 03:03:57 PM »

What do you mean by the bearings need to be fattened up?

« **Reply #4 on:** March 09, 2018, 07:51:44 PM »

I believe he means since the oil won’t get as hot in a marine engine due to cold water constantly flowing through the engine the oil will stay a bit thicker, hence more space needed between bearings.

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« **Reply #5 on:** March 09, 2018, 09:22:29 PM »

However, a hate valve installed coming out of the pump will help regulate temp.

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« **Reply #6 on:** March 10, 2018, 05:34:29 AM »

Gate

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« **Reply #7 on:** March 10, 2018, 08:56:21 AM »

Bearing clearance/ piston to wall/valve clearance needs to be greater due to the block stays colder (doesn’t expand)due to cold water pickup but the pistons crank oil ect still gets to operational temperature and expansion will happen. If you run a standard automotive specs the engine will lock up probably on the first hard run.

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« **Reply #8 on:** March 10, 2018, 09:00:24 AM »

But to answer your question as long as it’s built for cold water pickup and not a closed cooling setup they are the same for a hp marine and jet boat especially in the under 500 hp range. Only consideration would be cam choice based on your hull and impeller. Howard cams are a great resource on which one to go with

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Jim64

Jet boat 460 build

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