Its coming out for a complete teardown
 

It has been a really interesting journey but it isn’t budging and it needs to come out.

I have discovered the engine is a standard HP425 GenV Big Block from 1993 with Crane gold roller rockers, lifters and cam shaft. Forged Speedpro 14097021 pistons still on std bore. No scores and no lip at the top of the piston – although comp test got about 130psi ave couple of years back

First strange thing I noted was a build-up of rust on a cover below the intake manifold. No 2 cylinder seems to have had condensation on the bore and has created little mounds of rust which come off easily with a screwdriver but do not leave a pit on the cylinder wall. No 7 seems to have some salt corrosion on the crown not sure how that got in.

The nylon hammer test indicates that cylinders 2 and 7 are being held solid, all other will come out ok.

Penetrating fluids used;
Plus Gas
Auto trans fluid neat
Auto trans fluid with acetone
Mystery oil
ACF-50 corrosion

ACF-50 seems to eat the rust but it’s quite viscous and hasn’t really penetrated. None have freed it up but you can’t completely cover the piston with the V8 angles installed in the boat.

There is very light corosion on the cam, and the lifters are have a sliight greying of the surface. The centre lobes however have a little of the straw colour associated with a bit of heat - ie 290C - is that too much? Can it be polished out?

Intend to buy a 750kg engine stand – 4 wheel job to tear down and rebuild. Is that OK or do I need a more capacity?

Engine is I believe 650lbs heads on, 575lbs heads off, crank pistons etc. in. With a blower carbs, starter, alternator I guess an all up weight of 750lbs?
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You will be fine with the stand if your just using it for this project. I would have the short block hot tanked and start off fresh. Once you get some lube on the top and bottom of the piston it should free up enough to save the piston. Your machine shop would be able to advise on the cam, but you won't know until you take it apart. It looks like surface rust to me and if it will clean up good, use a really good assembly lube on reassembly. You need to determine where the water came from so you don't have any repeat problems. Exhaust is the most likely suspect, but it could be a valve guide.

Overall track record on re-using flat tappet non-roller cams is not very good. Definitely don't try to use the lifters again, unless you can keep them on their original lobes, and even that can be sketchy.

Engine teardown
 

All pistons out and OK apart from No2 position which required a metal drift and No7 which is corroded. No 2 piston pic below has corrosion on rings and over the crown. The GIL exhausts are good but there are no baffles fitted and I wonder if this is my true problem, i.e. water running down exhaust after a good run - what do the baffles do?. Piston at No 7 drifted out with nylon hammer and wooden drift.

I don’t think it needs a rebore – measures 4.25 max and generally ovality is 0.001ins. I have 3thou at top of No 2 bore locally where there is evidence of corrosion.

Broken two pullers and still can’t get the harmonic balancer off (even with a little heat) so off to the machine shop for that and cam bearings.

Bearings all look good but will be swapped out and thinking of putting back STD Speedpro forged pistons.Crank is very tidy.

New Crane followers, polish CAM, conrods OK, new Oil pump, gaskets, seals, headbolts?.

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Real busy at the moment so this will run to September. .

If you are going to buy new pistons then I would be inclined to go .030 overbore to ensure that you have a good, clean, round bore. Best to hone cylinders with a torque plate to simulate pulling forces of the head bolts, otherwise it will go slightly out of round when the heads are installed.

If spending this much time and money on it already, I would swap cam to a hydraulic roller for longevity.

I agree with budman on boreing..From what I saw in a couple cylinders in pics, I find it hard to believe those are honeable....Bore it .If you can't afford a roller ,at least buy a decent quality flat tappet cam and lifters and break in properly

Do I need a new cam to put in a roller rather than hydraulic lifters - was going to buy new Cranes

It needs to be a roller cam to use roller lifters.

I would put a new cam in it regardless of what lifters you go with. If it was a billet roller cam then I would say that you would probably be OK to just replace the lifters. However, flat tappet cams depend on the surface of the cam lobe to have a shape to it that keeps the lifter spinning in its bore for lubrication. Once this starts to break down and the lifter stops spinning, accelerated wear will take place and the lobe will wear flat in short order and send a bunch of ground up metal through your engine. The track record on using flat tappet cams over again, even with new lifters, is very poor.

raw water motor? I assume salt water use? junk the heads. they rot at the valve guides.