Piston to Wall Clearance For Marine App

I am looking at a 1974 Glastron Carlson with a 460/Berkley jet drive. The engine is toast - current owner says previous owner ran it without the engine cover on and it gulped some water and seized the engine and bent the rods. Not sure about this story but the price is real good and I can get a short block cheap too.

My question is: Does the piston to cylinder wall clearance need to be different in this application? It is set up with the water cooled manifolds and thru-transom exhaust. I presume the water temp is much lower than running a closed cooling system with a rad, is this true?

Thanks for the help!!

Bill

from what i know, extra clearance is required if you are not using an exchanger and are running lake water through the block. I think a closed loop system is the way to go and will save alot of cylinder wear.

Depands on the pistions Forged, Cast or Hyper?

Paul Kane, Randy or Lem are All into the Boat Builds, I think one of them should be along in a bit.

Thanks Randy!!

I've heard of guys ruining engines in jet/V drive boats because the pistons get stuck. This boat has a three year old crate engine so I guess this is likely what killed it, not the water splashing into the carb.

How much would the clearance need to be increased in a stock 460 bore?

Bill

rmcomprandy wrote:

billandlori wrote:Thanks Randy!!

I've heard of guys ruining engines in jet/V drive boats because the pistons get stuck. This boat has a three year old crate engine so I guess this is likely what killed it, not the water splashing into the carb.

How much would the clearance need to be increased in a stock 460 bore?

Bill

That depends upon that particular piston; (cast, forged, skirt design, material and believe or not compression distance)).
Two thou EXTRA will be safe in all applications yet a bit to much for a lot of combinations.

Good deal, Thanks Randy. I will know more details if I can get the deal done.

Bill

Randy, how do you maintain oil temp in an open loop system? I cant get enough even in a closed loop system and have zero experience in an open loop system

billandlori wrote:I am looking at a 1974 Glastron Carlson with a 460/Berkley jet drive. The engine is toast - current owner says previous owner ran it without the engine cover on and it gulped some water and seized the engine and bent the rods. Not sure about this story but the price is real good and I can get a short block cheap too.

My question is: Does the piston to cylinder wall clearance need to be different in this application? It is set up with the water cooled manifolds and thru-transom exhaust. I presume the water temp is much lower than running a closed cooling system with a rad, is this true?

Thanks for the help!!

Bill

If the rebuilt short block that you're considering for the swap has been built up with looser than OEM clearances (crank ground on the low side, etc), then you'll be fine. Because of the jet boat's sustained rpms, ditch the half-grooved passenger car main bearings and roll some fully-grooved main bearings into the freshened short block's saddles to get more oil to the rods; that's what Ford did with their Marine 460s when the production parts were gathered for the Marine 460 engines (rather than turning the crank differently, bores, etc). If you already know the clearances on the rod journals then 3/4-groove may do.

If you have thru-transom logs and snails, then they're supposed to be plumbed so as to pre-heat the lake water before sending it to the water pump holes in the block. In other words, you are not sending cold lake water straight to the block as with most jet boat engines with over-transom headers...those blocks get the cold lake water and you can not only measure but can also see the additional wear in the #1 and #5 cylinders (they get blasted with the lake cold water).

Paul

cooter wrote:Randy, how do you maintain oil temp in an open loop system? I cant get enough even in a closed loop system and have zero experience in an open loop system

That can be challenging in your location. A gate valve at the jet pump is often used to reduce water flow through the block and will bring up water temps; oil temps usually follow accordingly. But you might need a system a little more sophisiticated with your very cold lake temps.

Down here in California most jet boater (hot boats) oil temps range from 180*-220*, which is fine. The racers go much higher than that and many use oil coolers, usually the endurance race guys or roundy-round guys.

Paul

Thanks Paul, good info!!

This boat does have the thru transom exhaust. I will be buying a short block to replace the seized engine in the boat now. It was a new crate engine three years ago so the heads are good I'm told. I thought if I need to do any machining to the block I would like to know ahead of time - it will help in the negotiating lol!!!

I am getting pretty exited about getting a boat but I don't want that to cloud my better judgement!!

Bill

one thing i have found with water cooled headers is the exhaust valves can have rust from the water in the exhaust so make sure to check them out completely

rmcomprandy wrote:Water jacketed exhaust manifolds with snails are the best for maintaining consistent oil and water temps however, what they lack is power production so, what to use is a personal decision usually based upon how the boat is to be used.

Sounds good, this is just going to be a fun boat, not an all out drag boat.

Good tip on the exhaust valves too Cooter!!

So, this boat does have the water jacketed manifolds with snails. Should I get the bores opened up from the stock bore a bit? It would be stock cast pistons, if its going for a bore or hone, I might get it zero decked too. Likely should have a marine type cam too.....

Break
Out
Another
Thousand

ha ha ha

Bill

make sure the cam doesnt have to much duration as to much cam causes water reversion (the motor sucks in water at idle)

cooter wrote:make sure the cam doesnt have to much duration as to much cam causes water reversion (the motor sucks in water at idle)

Damn! That can't be good!!

Thanks!!
Bill