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Old 10-21-2017, 06:18 PM   #41
revkev6
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Default Re: Moving on from the cracked block to an undocumented rebuild

Did the piston clearance with my edelbrocks and old fell to gaskets that measured .075 and came up with .125 of clearance! Seems way high?
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Old 10-21-2017, 07:07 PM   #42
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Default Re: Moving on from the cracked block to an undocumented rebuild

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Did the piston clearance with my edelbrocks and old fell to gaskets that measured .075 and came up with .125 of clearance! Seems way high?
supposed to say Felpro gaskets...
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Old 10-21-2017, 08:03 PM   #43
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Default Re: Moving on from the cracked block to an undocumented rebuild

Way high. Sounds like the wrong pistons are in there.
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Old 10-22-2017, 01:40 AM   #44
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Default Re: Moving on from the cracked block to an undocumented rebuild

Some pistons are made with reduced compression height to keep original CR.
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Old 10-22-2017, 06:18 AM   #45
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Default Re: Moving on from the cracked block to an undocumented rebuild

Call Jerry at Schneider’s and have him grind you a cam for your car you will not be disappointed.


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Old 10-22-2017, 07:23 AM   #46
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Default Re: Moving on from the cracked block to an undocumented rebuild

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Some pistons are made with reduced compression height to keep original CR.
I don't know why that would even be a thought... this motor is stock... stock heads cam etc. Looks like it was decked. Each side has .010 marked on the deck so I'm guessing it wasnt much. Im going to play around and check my other motor to see how that one looks. I've also got a brand new set of edelbrocks on the shelf I can try. Given have so much room I will also try sans gasket for 100% accuracy
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Old 10-22-2017, 07:49 AM   #47
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Default Re: Moving on from the cracked block to an undocumented rebuild

Yes - check it without any gasket. Most gaskets will be about .052 compressed - use that in your math. I could see the block had been decked, so the clearance should be closer than stock. From the outside, looks like some nice work on the block - I think you'll have a nice engine when you're through.

You can have any flywheel redrilled for a different clutch - simple machine shop operation. I would definitely run a smaller diameter clutch - I prefer to run a 10" Long or 9" Long. You can have the clutch rebuilt at Ft. Wayne Clutch - and get the correct disk at the same time.

I would have the flywheel and clutch balanced as a pair - such that you know they are correctly matched . . . never a bad thing to do.

Valves: In many cases folks will use exhaust valves for all the valves on a flathead - they tend to be thicker in the heads (as they are exhaust valves). Given what you're doing - really won't hurt you any (this isn't a high RPM screamer).

Squish Height: This is one of the most important things you can do - so getting it at about .040 - .045 really makes a difference. If you're worried about the pistons potentially being wrong, just take a picture of one at TDC on any cylinder - and post it. Take a few shots - from the side so we can see what the dome looks like. My bet is that they are correct. Once you figure out what may need to be done with the piston clearance, also check the valves - to figure out if you need to add clearance for them (up at the TOP of the chambers). The valves are angled, so the place they'll be the closest or hit are the top edges. You'll want to have .060 or so clearance on them.

If you need additional clearance in the heads (after a milling operation), this can easily be done with a high speed die grinder and a 'flame shaped' aluminum cutting bit - will carve aluminum like nobody's business. Then clean/polish with small sandpaper rolls. Tape the deck surface off on the heads - to protect them if your grinder happens to "wander" every once in awhile! (It happens - so tape things up to protect them).
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Old 10-22-2017, 09:27 AM   #48
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Default Re: Moving on from the cracked block to an undocumented rebuild

Thanks Dale. Yesterday's measurements were in a rush. Never do it right when you don't have the time! I went out to the garage this morning and pulled everything apart and cleaned up both surfaces again. Without a gasket and everything clean I'm getting. .023 with the brand new edelbrocks and about .035 with the older heads. Also the older heads have about .100 less valve clearance at the top edge of the valve. I think I will make try to make these older heads work with this motor and save the others for a bigger lift cam. The pistons look exactly the same as my other 8ba so I don't think that's an issue. If I remember correctly 25 years ago at the age of 11 we measured around .070 of clearance on the old motor. Will be amusing to check it now and see if memory holds true! I'm going to take the heads and flywheel into work with me and see about getting it drilled to fit. Advantages of working at an aerospace machine shop.

Btw... I'm eyeballing an eaton supercharger to mount on my old motor and use that as a mule to test a custom budget blower setup!
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Old 10-22-2017, 12:49 PM   #49
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Default Re: Moving on from the cracked block to an undocumented rebuild

So - given that you want about .040 to .045 clearance, then you'll need to mill the heads. A new head gasket should be about .052 compressed (buy your gaskets first - the manufacturer can tell you the compressed thickness) - then determine how much to mill to get the tighter clearance.

Also, check the dome radius on your pistons -- some have three different radius values (more similar to an elliptical arc), some are one consistent radius. I've seen quite a few cast pistons that do not have a consistent radius like a Ross forged piston, therefore the clearance to the Edelbrock dome will be inconsistent.

Every set of Edelbrock heads that I've had have a consistent radius. Due to this, last year I had to CNC rework a set of new Edelbrock chambers to work with a set of older Jahns cast pistons (4 ring versions) - to resolve the inconsistent clearance issue. I wanted a consistent squish over the pistons. I hope I'm making sense here?

The best way to tell is to clay and see if the clay thickness is uniform (which shows you that the chambers match the heads). Then determine how much to mill from the area where the clay is the thinnest.
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Old 10-22-2017, 03:44 PM   #50
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Default Re: Moving on from the cracked block to an undocumented rebuild

The gaskets are best copper units which claim .062? Anyone else have experience there?
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Old 10-22-2017, 07:35 PM   #51
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Default Re: Moving on from the cracked block to an undocumented rebuild

Then the piston is going to have to come up over the edge of the block surface to have any kind of compression. .062 - .050 = .012 So you would need for the edge of the piston to be .012 above the block surface at TDC to get good compression.
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Old 10-23-2017, 09:58 AM   #52
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Default Re: Moving on from the cracked block to an undocumented rebuild

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Then the piston is going to have to come up over the edge of the block surface to have any kind of compression. .062 - .050 = .012 So you would need for the edge of the piston to be .012 above the block surface at TDC to get good compression.
that is very true. the best I could do is chop the heads down so the dome comes tight. it would be better than nothing.

anyone have a lead on a thinner gasket?? thinnest possible flathead gasket.
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Old 10-23-2017, 10:24 AM   #53
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Default Re: Moving on from the cracked block to an undocumented rebuild

You can go solid copper or MLS...any thickness you want.
BUT the heads and block needs to be dead flat or they leak like a sieve.
Solid copper is a real pain to work with and the only time i would use one is with a real bad ass blower and oringing(another painful excersize on a flathead).
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Old 10-23-2017, 10:38 AM   #54
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Default Re: Moving on from the cracked block to an undocumented rebuild

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You can go solid copper or MLS...any thickness you want.
BUT the heads and block needs to be dead flat or they leak like a sieve.
Solid copper is a real pain to work with and the only time i would use one is with a real bad ass blower and oringing(another painful excersize on a flathead).
not looking to go that crazy. basically if I could get down to a thinner standard type gasket in the .030-.040 thousandths thick range I would be happy to just bolt on my newer heads and run em. put me at .050-.060 of clearance. which is high, but doable.

right now I have pretty consistent gap on the piston dome to cylinder head. once I shave the head that will go away.

A combination of thinner gasket and shaving a bit on the heads would be acceptable.
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Old 10-23-2017, 12:21 PM   #55
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Default Re: Moving on from the cracked block to an undocumented rebuild

did some google searches for gaskets and really was having a hard time finding much for compressed thickness on many of these gaskets.

I did see the cometic gaskets... from .018-.120 thick... holy cow! only for early motors and like $300 a set
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Old 10-24-2017, 02:02 PM   #56
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Default Re: Moving on from the cracked block to an undocumented rebuild

emailed cometic and they do have 8ba style gaskets that can be as thin as .027. that would get me into a range where I don't need to do any machine work to my heads. summit lists the thicker ones they stock at $128 EACH!

is it worth the price?? are these good gaskets?? would I be stupid to consider this?? i can get my heads cut for free and I have .062 thick copper gaskets to use... but that means that I will have to have like .040-.050 shaved off the heads and the pistons are still in the hole. thinner gaskets would be better for even dome.
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Old 10-24-2017, 09:25 PM   #57
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Default Re: Moving on from the cracked block to an undocumented rebuild

I'm using Cometic's on the full-race build in my 32 Cabriolet - the reason is that i wanted to try them out on a naturally aspirated setup and see how they worked.

I can see them working very well in a mildly boosted situation - might save me from the huge expense of having CNC o-rings done on the heads and deck. So far, I've had no problems. I'm running the ones that have a compressed thickness of .051 - I setup my squish for this number (to be at .040). The reason is that IF I had a problem with Cometic, I could then just switch back to Best and not have any squish or clearance issues. This is something to think about.

One thing that is important is the surface finish of the block and heads - they specify a finer RA than many machine shops used to (or do today) on their decking and milling centers. I made sure I had my heads and decks done with this in mind - see the picture I've included of the block surface.

With that said, it may not be a problem - just something to think about and to talk to the application engineers at Cometic about. You might also ask them if you can use a gasket sealer material (maybe Hylomar) to aid in sealing the deck? Let them know that you'll be torquing the heads to 55 lbs.
Given the cost of these gaskets - you want to know what you're dealing with before you spring for the high price for each.

Here are a couple pictures of my block and deck - I think it will be detailed enough for you to appreciate the finish quality:

Vavles1 copy.jpg

4PistonsIn copy.jpg
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Old 10-24-2017, 09:35 PM   #58
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Default Re: Moving on from the cracked block to an undocumented rebuild

Here are some pictures of how I do 'claying' on the pistons and valves. In one picture you can see the Cometic gasket.

Notice on the clay for the valves that the only place it gets tight is at the TOP of the chamber - you can see the valve angle in how the thickness of the clay changes as you move toward the cylinder. This is why you shouldn't have heads just flycut - with the cutters parallel to the deck - just opens up the chamber where it isn't needed and lowers the compression. I do my chamber work with CNC machines - off of 3D CAD models that I "tweak" to fit the engine heads, valves and chambers I'm working with. This enables me to get exactly what I want - in a consistent fashion - engine after engine.

2015-07-17 17.59.50 copy.jpg

2015-07-17 18.15.18 copy.jpg

2015-07-17 18.15.37 copy.jpg

2015-07-17 18.15.44 copy.jpg
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Old 10-25-2017, 08:12 AM   #59
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Default Re: Moving on from the cracked block to an undocumented rebuild

great to know dale, and if I'm not mistaken you have pulled the heads off to inspect your coatings and re-used those gaskets correct??

given that the machine work will be free, I am going to wait to get my cam back from pete so that I can check my valve clearance with the required machine work. the new edelbrocks have machined clearance for the valves unlike the older as cast units that I was running. I did the clay as dots in 4 spots on the piston instead of a line. you measure thickness with calipers on the depth or a depth mic.?

my deck height seems to be out about .007-.010 from side to side which I would take into account when I cut the heads. my pistons are down in the deck a bit which is part of my problem. I'm going to try to measure what the diameter of the dome sould be if I cut the heads. currently they measure 3-5/16 which is bigger than required.

the new edelbrock heads are cut very nice and these are the heads I would use with the cometics as they just make it to about .049 and .055 with .027 gasket. My deck is a standard flycut and nothing as pretty as your jewel of a motor. I would think a sealer of some sort would be required.
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Old 10-25-2017, 09:11 AM   #60
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Default Re: Moving on from the cracked block to an undocumented rebuild

If it was mine, I would at least talk with Cometic about surface finish and their gaskets. I have no idea as to if their MLS gaskets are malleable enough to conform/flex into your deck surface and therefore they don't foresee a problem.

Take some high-quality close-up pictures of your deck and send them to a Cometic App Engineer - that way your conversation is at least about something you can both see. One would think that since they sell these gaskets with the big boys like 'Jegs', that there shouldn't be an issue - so this whole conversation might not even apply! LOL

It isn't a bad idea to "true up" the compression/squish height when you have your heads cut - might as well make sure it is the same on both sides.

Are your domes a consistent radius . . or multiple arcs with more of a "pointed" crown?
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