How far out of the hole is too far?
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How far out of the hole is too far?

  1. #1
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    Default How far out of the hole is too far?

    Like the title suggests, just how far out of the hole is considered TOO FAR on a 454 Mark IV that will see marine use? The motor is being built to chug-a-lug-along and won't see much use past 5500rpm.

    Before I owned the boat the engine builder knocked the deck height down to 9.766" --- With the new 4.25" stroker crank, 6.385 rods, pistons, the piston will be approximately .014" out of the hole.

    Assuming there is sufficient clearance for the piston to the cylinder head, is .014" too far out of the hole for the sake of the piston and ring seal? And if .014" is too far, what's the best route to take to get it with a tolerable height? Custom piston? Shorter rod? Different block? I'd rather build this right the first time than put it all together and then next year have to dig back into it again because I cut one corner. But if .014" is AOK I'll run it and keep my fingers crossed.

    Jeff

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    Sit N' Spin Jetaholic's Avatar
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    Quote Originally Posted by AlohaJeff View Post
    Like the title suggests, just how far out of the hole is considered TOO FAR on a 454 Mark IV that will see marine use? The motor is being built to chug-a-lug-along and won't see much use past 5500rpm.

    Before I owned the boat the engine builder knocked the deck height down to 9.766" --- With the new 4.25" stroker crank, 6.385 rods, pistons, the piston will be approximately .014" out of the hole.

    Assuming there is sufficient clearance for the piston to the cylinder head, is .014" too far out of the hole for the sake of the piston and ring seal? And if .014" is too far, what's the best route to take to get it with a tolerable height? Custom piston? Shorter rod? Different block? I'd rather build this right the first time than put it all together and then next year have to dig back into it again because I cut one corner. But if .014" is AOK I'll run it and keep my fingers crossed.

    Jeff
    The compressed height of a stock head gasket is usually around .039", so that should give plenty of clearance.

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    steelcomp was here
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    .014 out of the hole with an .039 gasket, minus a few thou for rod growth only gives you about .022 quench. That's a little tight. You might want to find a gasket that'll give you about .045 compressed thickness. You don't want any less than .030 quench IMO. (Other's may say different) Rings shouldn't be a problem.
    If God is your co-pilot, change seats!
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    I run .002 out of the hole with a .039 gasket(.037" quench). The deck on the head and piston top both have 'shadows'(reverse mirror images) on them. That's where it runs best. Anytighter with a Steel Rod and piston rock on a V-8 and there's a good chance they'll impact, rather than just 'kiss' and leave a 'lipstick smudge'. JMO RR

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    If there flat tops have your engine guy put them in the lathe and face them off .015 or if its a dome he can jig them in the mill and cut around the dome,easy fix make sure the dome clears the chamber.

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    Quote Originally Posted by VAMI View Post
    If there flat tops have your engine guy put them in the lathe and face them off .015 or if its a dome he can jig them in the mill and cut around the dome,easy fix make sure the dome clears the chamber.
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    I'm not so worried about the clearance issues, that I think I can manage. My concern is the longevity of the piston and the ring seal. Normally I wouldn't care, but my cam guy said that if HE were building the motor for me he'd find a new block with a 9.800 deck height and build that. He's worried about piston stability and ring seal, which made ME worried about piston stability and ring seal.

    I was looking around online and .014" OOTH seems to be a lot more than what most guys are running. If it's not a big deal I won't worry about it and just build the motor with the correct gasket and check the clearances. I'm more in the foot or yard mentality, .014" just seems like a tiny amount. I had to put it into perspective... so I got my calipers and looked at .014" and it just seems inconsequential to me, as far as piston stability and ring seal are concerned. I understand the quench / squish / piston to head clearance idea (thank you Google). Which is why I ask if it's ok or not. I'm eager to get the boat back on the water and I have to keep telling myself don't take shortcuts, don't take shortcuts.

    Thanks guys!

    Jeff

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    " I had to put it into perspective... so I got my calipers and looked at .014" and it just seems inconsequential to me, as far as piston stability and ring seal are concerned."

    That would be my feeling also.
    Here is how I would approach this.
    If a flat top piston.....cut the top of the piston .014 so you have 0 deck. Use a .040 head gasket and forget about it.
    If a dome piston.....machine the flat of the piston .014. Install a rod and piston and the cylinder head with NO head gasket. Rotate the motor noting if the piston touches any part of the cylinder head. If it touches grind relief where it does.

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    Quote Originally Posted by Fiat48 View Post
    " I had to put it into perspective... so I got my calipers and looked at .014" and it just seems inconsequential to me, as far as piston stability and ring seal are concerned."

    That would be my feeling also.
    Here is how I would approach this.
    If a flat top piston.....cut the top of the piston .014 so you have 0 deck. Use a .040 head gasket and forget about it.
    If a dome piston.....machine the flat of the piston .014. Install a rod and piston and the cylinder head with NO head gasket. Rotate the motor noting if the piston touches any part of the cylinder head. If it touches grind relief where it does.
    Ditto that!!

    As far as the "out of the hole" effecting ring seal it won't (and could help), but if you end up cutting the tops of the pistons this will have only a positive effect on HP and ring seal as it is just getting the ring closer to the piston crown. With your build this "raising of the top ring" should have no adverse effect on durability.

  12. #10
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    The last few posts have been dead on. (If you have a machinist around that can and will do that for not too much expense, or if you have a mill.)
    If for some reason you do not have access, or no machinist, this engine sounds like just a normal deal. For a race type engine, I would make extra sure everything is perfect, but here, you could just throw a .052 crush head gasket and go. (Or close to there.) I have seen more than .014 with no problems at all. In fact one of the SBC race engine shops that I know well mandate that their super SBC's are .005 - .008 out of the hole, depending on which head. That is their standard. (Sure makes .014 sound a little better.)

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    I feel better about it now. Current plan is to have the pistons milled down. Not a race motor, just a boat motor that I don't want to mess with for a few seasons. Yeah, right.

    Jeff

  14. #12
    cfm
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    Why would you mill the pistons if you can get a headgasket that will give you proper clearance. .040"-.050" clearance will work fine for you so look for headgaskets that are somehwere at or between .054"-.064" thick.

    But if you can do the work yourself for free, then by means chop,chop.

    BTW: Have you measured it assembled ?

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    Distinguished Member David 519's Avatar
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    We had a similar situation on our last race motor. We used the Fel-Pro MLS gaskets. They were around .055" thick and gave us just over .030 quench. A bit expensive, but then I found out lots of people reuse them 2-3 times. If the pistons are flat tops and you have access to a lathe, it's super easy to machine off whatever results in 0 deck height. I've done it a few times on different combos. Working around a dome is a major PITA...
    Good luck.

  16. #14
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    Quote Originally Posted by cfm View Post
    Why would you mill the pistons if you can get a headgasket that will give you proper clearance. .040"-.050" clearance will work fine for you so look for headgaskets that are somehwere at or between .054"-.064" thick.

    But if you can do the work yourself for free, then by means chop,chop.

    BTW: Have you measured it assembled ?
    I haven't jumped in and said anything while I followed along, but I agree, use a .050" gasket rather than spend money cutting the pistons. You should be able to find that on the shelf without spending a ton of money. Cometix will build any thickness you want, but going to cost more.

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