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  #16 (permalink)  
Old 05-12-2009, 01:36 PM
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Thanks for posting your question Manchild... I am in the process of building a 408 using a 400 block with the same casting as yours, but bored over .040"... I will be checking your progress; I also just posted a question about my build recently. Hopefully some of your answers will help me. Good luck!!!

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Old 05-13-2009, 02:02 PM
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Cobalt, thanks for the reply and suggestions. The rings themselves are Moly and as far as honing is concerned I'm not sure what you mean. The bore was increased by 0.030" and the resulting finish was 'cross hatched'. The concern I have is whether or not they'll break in... I've had the engine running in the past (not for long... maybe 20 miles or 2 hours) and they still show the cross hatching as if they just came from the machine shop.

The head gasket I'm looking at: SUM-111505

Brand: Summit
Product Line: Summit Copper Head Gaskets
Part Type: Head Gaskets
Bore (in): 4.155 in.
Bore (mm): 105.537mm
Gasket Material: Copper
Compressed Thickness (in): 0.062 in.
Lock Wire: No
Quantity: Sold as a pair.
Notes: These gaskets are not drilled for steam holes. Installation of these copper head gaskets requires O-rings.
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  #18 (permalink)  
Old 05-13-2009, 03:49 PM
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Quote:
That cam looks little big for your intended use, but it will run fine, just not have as much low end as I would prefer.
A 406 will swallow up that cam quite easily, and it will have plenty of TQ in the bottom. Might be a good thing to soften it up a tad so the tires don't wear away too fast. Even with a dish that bore/stroke and small chamber will yield some good compression, probably enough to worry about. A smaller cam will not help in this sense.

You will not want to use those copper gaskets unless you are going to o ring the block or receiver groove the heads or both. JMO

You should stil see the hone after 100k miles. That's where the oil stays until it's wiped down the cylinder. I think your hone is probably still good. Any glazed brown walls, or other maladies to indicate a problem - other than seeing the crosshatch pattern??

Last edited by Deez; 05-13-2009 at 03:55 PM.
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  #19 (permalink)  
Old 05-13-2009, 06:26 PM
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Quote:
Originally Posted by manchildau65
I've had the engine running in the past (not for long... maybe 20 miles or 2 hours) and they still show the cross hatching as if they just came from the machine shop.
If there was no problems with the rings from this first build, why did you replace them- or are they the same rings you had in the engine that was run for a couple hours?

What I'm getting at is those 2-hour-old rings would (or should) have been fine. If you changed them, "just because", I wouldn't have- but what's done is done.

I'm a proponent of honing a cylinder before using new rings, if the cylinder has been broken in to another set of rings.

At just 2 hours run-time, the cylinders might still have enough "tooth" to break in your new moly rings- those rings are made to run on a comparatively smooth cylinder finish. I don't think anyone can say with 100% certainty that they will or won't break in.

Quote:
The head gasket I'm looking at: SUM-111505
You do not want those gaskets.

Look into measuring how deep in the cylinder (at TDC) the pistons are. This measurement along with the gasket thickness wants to be as close to 0.040" (no less) as you can get, and still retain the CR needed.
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Old 05-14-2009, 11:26 AM
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Wow! Great information, Thank you.

To answer some questions:

1) The rings are the original Moly rings I installed during the first build (2hrs.) old. The reason the engine wasn't run longer was because I split the tranny in two the first time I had it out (SM465...) and it's sat ever since. I now have ambition again so I thought it would be a good idea to tear it down, drill the steam holes, and to try and improve my compression ratio.

2) Again, I'm not sure what honing means... the cylinders have the cross hatching (nothing a fingernail will pick up) does this mean the bores were honed? - there were no glazing marks present, just some carbon in the combustion area.

3) It looks like I'll need to keep looking for the right head gasket... Cobalt, when you say to measure the distance from the deck to the top of the piston, should I simply use a vernier and go to the highest point? and if so, I know there is visually a deck to top of piston gap so 0.040" seems to already be consumed... I think I'm confused
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Old 05-14-2009, 11:30 AM
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P.S. all I originally built the engine with was a Fel Pro gasket that came with the rebuild kit... Engine started hard (stock starter - 1000 CCA battery) but ran well with 93 octane, no pinging, however, I didn't push it hard, because I wanted to break it in properly (well except when I split the tranny housing...)
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  #22 (permalink)  
Old 05-14-2009, 11:55 AM
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Quote:
Originally Posted by manchildau65
1) The rings are the original Moly rings I installed during the first build (2hrs.) old.
GREAT!!! The rings will be fine as-is, and my earlier concerns are not valid- good deal!

Quote:
2) Again, I'm not sure what honing means... the cylinders have the cross hatching (nothing a fingernail will pick up) does this mean the bores were honed? - there were no glazing marks present, just some carbon in the combustion area.
If the engine showed no signs of excessive blow-by (smoke from the breathers, etc.) or tail-pipe oil smoke (blue, oil smelling smoke with an attendant high rate of oil used from the engine), the rings/bore is fine.

Quick FYI- "Honing" is an operation done after the cylinders are bored, it brings the final dimensions and finish of the cylinders to what's needed for the type of piston and rings being used- it's a standard machine shop operation and was surely done to your engine, so you need worry about it no more- it's all good!

Quote:
when you say to measure the distance from the deck to the top of the piston, should I simply use a vernier and go to the highest point? and if so, I know there is visually a deck to top of piston gap so 0.040" seems to already be consumed... I think I'm confused
What you need to measure, is the distance from the top of the block (where the head's bolted) down to the highest part of the piston, with the piston at TDC.

This can be done w/the depth function of a dial or veneer caliper but is more easily (and accurately) done w/a micrometer that bridges the bore. But it doesn't have to be accurate down to 0.0001", either.

Better than me struggling to describe the deal, here's a brief description along w/a calculator to figure what it is: HERE.

Quote:
I know there is visually a deck to top of piston gap so 0.040" seems to already be consumed.
This wouldn't be too surprising. Often the pistons are made "short" on purpose- this is to compensate for the decking of the block that's often done on re-manufactured engines, usually 0.020" is cut from the blocks, so the rebuilder-type pistons are made 0.020" short to match.

"Squench" should be close to 0.040" as is possible, but sometimes this figure isn't possible w/the parts that are on hand.

To significantly chance the deck height, you can use gasket thickness (you would prob. need one of the thinner ones that are available) and/or change pistons.

EDIT- there are at least three different thicknesses of 400 head gaskets, four if you count the OEM steel shim that's out of production by GM, IIRC.

There may well be other manufacturers who make shim gaskets, and other thicknesses of composite gaskets- you'll just need to research it is all.

I'd suggest checking w/all the manufacturers to see who has what you need. The gaskets I listed earlier were for a 4" bore.

Last edited by cobalt327; 05-14-2009 at 03:32 PM.
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  #23 (permalink)  
Old 05-14-2009, 03:04 PM
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Cobalt, the OP has a 400, none of those gaskets will work because they have a 4.100" or smaller bore and the .030" overbore 400 needs at least a 4.155" minimum gasket bore. Choices are a lot more limited for the 400, such as there is no steel shim type available.
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  #24 (permalink)  
Old 05-14-2009, 03:16 PM
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can always get one made... I found a local place to make me a few gaskets a while back when I was fooling around with a pontaic 151 (never do that again), actaully wasn't as expensive as I thought it would be. They did NOT specailize in auto products though, more of an industrial supplier, give them enough money and they can make anything for you.
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Old 05-14-2009, 03:33 PM
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Quote:
Originally Posted by ericnova72
OP has a 400
Thanks, I've edited my previous post.
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Old 06-04-2009, 06:50 AM
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Deck to Piston Clearance

OK, so I finally got my hands on a pair of depth mic's (.0001" resolution - overkill) and measured a couple different pistons on both banks of the engine and found the tightest/shortest to be 0.025". I'm assuming they are all close within a margin, the problem I was running into was determining when the piston was exactly at TDC.

So, as Cobalt had said earlier, I want the 'squench' to be around 0.040"... does that mean that I want a head gasket that adds only 0.015-0.020" compressed? Why is the magic number 0.040 for the squench?

Thanks again for all of the help, the project is actually starting to move forward again!
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  #27 (permalink)  
Old 06-04-2009, 07:17 AM
How fast is fast enough?
 
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its quench, and you can go a little tighter, but not by much, .035" is the general limit though some people go as tight as .025" (and get lucky IMO). The tighter the better untill you get to tight, then its disaterous. .040" is a good balance.
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  #28 (permalink)  
Old 06-04-2009, 07:21 AM
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Quote:
Originally Posted by manchildau65
I want the 'squench' to be around 0.040"... does that mean that I want a head gasket that adds only 0.015-0.020" compressed?
Ideally, yes.

Quote:
Why is the magic number 0.040 for the squench?
This provides enough of a safety factor to assure that the piston can't hit the head under any normal circumstances, yet allows the piston to approach near enough to the cylinder head's "quench pad" to cause a good amount of turbulence to the fuel/air mixture.

This turbulence is what provides additional (low) octane tolerance and helps to quell detonation, w/o needing to unduly retard the ignition.
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Old 06-04-2009, 03:30 PM
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Thank you all for the information! Now, the hard part I'm realizing (and probably shouldn't be) is finding a head gasket that has the 4.155" bore and compressed thickness of .020 - 0.030". I checked on Summit but only came up with copper gaskets. Do you guys have any other suggestions on where I can look?
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  #30 (permalink)  
Old 06-04-2009, 06:27 PM
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You won't find a 4.155" bore or find one that thin for a 400 in a conventional composition gasket. Fel-Pro sells 4.166", 4.190 and 4.200" bore x .039-.041 thick, Detroit Gasket(now ROL IIRC) sold a 4.190" that was my favorite(.039" thick), but don't know if it still exists, got my last pair NOS off of Ebay. Mr Gasket has a 4.150 x ??? if you want to go really tight on the bore size, not something I would risk though and I don't know if it has steam holes. I have punched them in before, though. Fel-pro also has a 4.165" MLS gasket, and there are probably more if you search. Maybe GM still sells a .028" thick for the 400.
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