468 Clearances

[El Prosecutor]

I am looking at a boat built by a car guy, it has a newly rebuilt Mark IV 468 in it, four bolt main, Eagle connecting rods, Speed Pro hypereutectic pistons, 10:1 compression, lots of new parts. Sounds like the guy knows car motors really well. I don't know motors very well, but have read here that the clearances in a boat should be different than in a car.
On this motor the rod bearings are set at .0017 to .0020, and the mains are at .0024 to .0026. Is that good for a boat motor?

[Moneypitt]

Yeah, those clearances will work. BUT the most important difference is the cold water cooling effect and piston SKIRT TO WALL clearance. Usually the manufacturer will reccomend skirt to wall numbers for various applications, street, strip, MARINE..........If the "car" guy set it up like a street motor the pistons will tighten up in the bores.
Those pistons also REQUIRE an expanded TOP RING"end gap". Ask him what the end gap is, and if he doesn't know, or if it's the standard .004 per inch of bore, RUN. Those pistons are a "love em' or hate em'" kind of deal, depending on who you talk to, but that top ring gap deal is critical. I personally wouldn't use the Hypers in a BBC boat.........and they aren't any cheaper than forged, well maybe a little............Back to your question, the crank numbers will work........MP

[El Prosecutor]

Yeah, those clearances will work. BUT the most important difference is the cold water cooling effect and piston SKIRT TO WALL clearance. Usually the manufacturer will reccomend skirt to wall numbers for various applications, street, strip, MARINE..........If the "car" guy set it up like a street motor the pistons will tighten up in the bores.
Those pistons also REQUIRE an expanded TOP RING"end gap". Ask him what the end gap is, and if he doesn't know, or if it's the standard .004 per inch of bore, RUN. Those pistons are a "love em' or hate em'" kind of deal, depending on who you talk to, but that top ring gap deal is critical. I personally wouldn't use the Hypers in a BBC boat.........and they aren't any cheaper than forged, well maybe a little............Back to your question, the crank numbers will work........MP
What's the downside of the Hypers in a boat?

[MudPumper]

I ran those same pistons in a 485 Hp 468 for about 3 seasons, i've since sold the boat. Never had any problems with them but I've heard bad things about them. Heard they like to come apart sometimes. ????

[El Prosecutor]

Yeah, those clearances will work. BUT the most important difference is the cold water cooling effect and piston SKIRT TO WALL clearance. Usually the manufacturer will reccomend skirt to wall numbers for various applications, street, strip, MARINE..........If the "car" guy set it up like a street motor the pistons will tighten up in the bores.
Those pistons also REQUIRE an expanded TOP RING"end gap". Ask him what the end gap is, and if he doesn't know, or if it's the standard .004 per inch of bore, RUN. Those pistons are a "love em' or hate em'" kind of deal, depending on who you talk to, but that top ring gap deal is critical. ........MP
I asked about skirt to wall clearance and end gap, the answer I got was:
"2nd ring was .020 top ring is .018 -
Piston manufacturer wanted .0025 clearance however,
since it is in a boat and engine temp is always too low he
set it at .0035"
Is that a good answer??

[Moneypitt]

I asked about skirt to wall clearance and end gap, the answer I got was:
"2nd ring was .020 top ring is .018 -
Piston manufacturer wanted .0025 clearance however,
since it is in a boat and engine temp is always too low he
set it at .0035"
Is that a good answer??
Go to the hyper piston web site, and I think you'll find there is a problem, Forged, ballpark= .004 for each inch of bore. 4.310 X .004=.0172, so .018 is cool, BUT the Hypers want like .006 per inch, 4.310 X .006=.025.........Not cool. Don't take my info as fact, but go to the Keith Black web site and check for yourself. This is the reason the Hypers got a bad rep, the ring gap is critical to survival.................MP

[El Prosecutor]

Go to the hyper piston web site, and I think you'll find there is a problem, Forged, ballpark= .004 for each inch of bore. 4.310 X .004=.0172, so .018 is cool, BUT the Hypers want like .006 per inch, 4.310 X .006=.025.........Not cool. Don't take my info as fact, but go to the Keith Black web site and check for yourself. This is the reason the Hypers got a bad rep, the ring gap is critical to survival.................MP
MP Thanks for taking the time, good thoughts.
I am an ignoramous on motors, and you may have saved me a bunch of money. The last message I got from the seller sounded kind of offended that I was asking so many questions, but you got to know what your buying, and you can't know without asking. I will check out the KB site before offering up my $$$.