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Old 11-01-2013, 09:26 PM
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Ring gap?

My hot rod is a boat, 16' side winder jet, 351w
rebuilding a new motor, got a 1997. 351w from a lightning, roller ready, all tanked, machined, with a new crank, and pistons,
now the question,,,what ring gap??? i've done a lot of reserch on this, and gottin conflicting answers, from .040 to .014, i did the last engine at .014, that eat my cylinder walls, and killed the pistons, the motor is stock, stock and stock with a big cam, and a edelbrock manifold with a 600 carb,,,that i want to run at full rpm, all day,...even a 350 chev ring gap that we know works,,but i want the ring gap as close as posible with out binding,,,,
oh ya, its freash water cooled, at 4800rpm those rings are going to get hot
i have posts up on Iboats, and offshore, even mustang forums,,,boats are much differant then cars, even drag racing cars,,,maybe the same as circle track racers.....
any thoughts on this, would be great
what piston ring gap???

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Old 11-01-2013, 09:47 PM
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You might want to give a little more info. Like what type pistons...what engine temp do you plan to run ? What oil, weight, and what compression ratio. Lift on cam, and duration. It all plays a part.
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Old 11-01-2013, 11:07 PM
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pistons are stock
temp: there is no thermostat, it will be what it will be..? 160-180??
have not bought the cam yet, but was thinking a comp cam xe68h
duration 286
duration @.050 lift 224
valve lift o.51
rpm range 1600 - 5800
oil = 20-50w
compression stock
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Old 11-01-2013, 11:24 PM
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The rings you use depending on the manufacturers, have different formulas to figure their ring gap derived from extensive testing by the company's themselves because of differences in expansion rate, etc, etc, from company to company, take Hastings for example the stock low compression V8 I just did was .0045 inch per inch of bore, but the last tunnel rammed high compression V8 I did was .0055 inch per inch of bore! Call your ring manufacturer and tell them what your building and their tech people will tell you the formula to use for your application! I like Hastings and have been using them for over 40 years, and they have very good tech. people! remember Hastings ,Perfect Circle, Keith Black, Etc May all have different ring gaps for the same combination engine!!!

Or go online and ask for some strangers to suggest a ring gap for you < all well and good but not all on here are experts!!! But a simple Phone call to the manufacturers who are experts in their ring applications and Characteristics Is very easy!

My suggestion would be top .005 inch per inch of bore second by .004 Which is the gap I use on most normally aspirated mild engines with cast or molly Hastings rings. Marine or not.

Jester

Hey, no insult To my fellow members implied.

Jester

Last edited by painted jester; 11-01-2013 at 11:51 PM.
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Old 11-01-2013, 11:49 PM
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I forgot to mention that piston type and manufacturer makes a big difference too , They will have their specs and formulas with specific rings!!

Here is one manufacturers formula


http://www.hotrodders.com/forum/atta...1&d=1383371290

Jester
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Old 11-02-2013, 08:11 AM
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The type & brand of piston will determine the best gap.Some pistons such as certain KB pistons place the top ring higher on the piston creating more heat.Your tune is also a very important part of the equation.If not tuned properly,detonation will butt the rings no matter how much gap you use.I would call the piston maker & explain your usage & get their recommendation.Unless you are taking your own gas & know it's quality,play it safe.You never know for sure what your buying @ the dock.
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Old 11-02-2013, 10:07 AM
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Generally speaking, Keith Black/Silvolite pistons, marine applications, 0.008" gap per inch of bore.
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Old 11-02-2013, 03:21 PM
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This keeps bugging me...
temp: there is no thermostat, it will be what it will be..? 160-180??
rpm range 1600 - 5800
oil = 20-50w

at 4800rpm those rings are going to get hot...
ate my cylinder walls, and killed the pistons...

Three things important, car or boat... The engine running temp, the rpm's, and thickness of oil at that temp, and rpm's...
You might want to do a little checking of these things as well...
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Old 11-02-2013, 04:51 PM
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Most fresh water cooled boat motors that I have seen have a hard time getting to operating temp.
here in Michigan the water is usually COLD.

Be sure your cooling system is not restricted. Or your headgaskets are not on backwards, Fords are touchy about that,,

.020" should work with any plain stock cast piston. In a carbureted performance situation
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Old 11-02-2013, 06:57 PM
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Marine engine: Hot pistons but cold block , extended WOT running add .001" to .002" to the "stock" piston to wall clearance

Piston ring end gap .024 -.026. Get rid of the 600cfm carb it is too lean for marine.
Get a 750 marine version.
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Old 11-10-2013, 10:45 AM
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Our suggestions have run the gambit LOL !! Did you use one of our suggestions or picked your own? Is this thread dead?

Jester
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Old 11-10-2013, 05:23 PM
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I think i'll wait till i get the new rings, and call the manufacturer and see what they say,,, thanks for your input
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Old 11-10-2013, 05:33 PM
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Quote:
Originally Posted by stewd8 View Post
call the manufacturer and see what they say
Bingo!.......
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Old 11-10-2013, 07:19 PM
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Ah boats, got to love boat people.
Like already mentioned, depending on who's piston your running will determine your ring gap.
the Keith black hyper pistons require a huge ring gap. Figure .008 per inch of cylinder bore.
You can consult this link if you like. https://www.uempistons.com/installat...stallation.pdf
If you truly have a factory cast piston figure .0055 - .006 per inch of cylinder bore.
You state you want to run your rings as close to butting with out touching, your just asking for more trouble.
You could run a .050 ring gap and not see any performance loss in your boat.

When dealing with boat engines more is better. More skirt clearance, more ring gap and a bit more bearing clearance. And a lot more thinking about what you put your boat engine through.

If people drove there daily driver the way people drive there boats, there would be much more engine repair work for the mechanics.

Think about the day at the lake.
Unload your boat. Load up the family and coolers. Start it up, cruz out to the no wake zone, floor it and hold it down all the way to the far side of the lake. Engine is being cooled off of 70* lake water. Oil is thick as molasses, Cast iron block is cold pistons are cold, every thing is cold, except the flame at the top of the piston trying its best to beat the top ring and ring land out of your piston.
Try getting into your daily driver, back it out of the drive way, idle down the street a few blocks. Get on the highway and drive full throttle to work.
OK rants over.

Best of success with your boat.
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Old 11-10-2013, 07:46 PM
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As a boat owner myself, I highly suggest an oil pan with kickouts and baffles. The kickouts will add volume to help keep the temps in check(more volume to help keep oil temp lower) and the baffles help keep the engine from starving for oil in rough water. As I recall, my last inboard(350hp mercruser 454) was raw water cooled, but still had a thermostat. It had a belt driven sea water pump that fed the marine version of a standard water pump, along with running through an engine oil cooler and power steering cooler and the exhaust . Your ring gap really depends on your cooling system and the water temps you run in. You might want to go over to offshore only. There were a few other sites I used to visit but they slip my mind at the moment.
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