Deck Clearance - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 15 (permalink) Old Apr 8th, 01, 05:28 PM Thread Starter
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Aaaaarrrrggghhhhhh!!!! I bought zero deck pistons for my 400 SB rebuild. Now as I assemble the motor I find they are actually .040 in the hole! I measured this with a bridge and a dial indicator and double-checked it with a straightedge and feeler guages. Same answer both ways. This should totally trash my compression ratio and quench area plans.

I'm assuming that at this point (after all the machine work and balancing is done) that my only real option is to yank it apart and have the block decked? Any other thoughts?

(Of course, I realize this is a normal part of blueprinting an engine. I had just hoped that the pistons would be close enough that I could avoid going through the deck milling process.)


------------------
Scott
'69 400SB, Richmond 5-speed
www.geocities.com/sdenning1

[This message has been edited by RockyMtnRacer (edited 04-09-2001).]
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post #2 of 15 (permalink) Old Apr 9th, 01, 09:13 PM
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I have never heard of a zero deck piston myself. You are right...the only way to correct this is to dis-assemble the engine and get the block decked. Check all the cylinders though...it would be bad to deck the block based on one cylinders reading, if you know what I mean. I would think there is too much production tolerance to build a piston that is supposed to give a 0 deck height...both with the pistons themselves and the factory blocks.

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post #3 of 15 (permalink) Old Apr 10th, 01, 05:19 AM
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I am suprised who ever did your block didn't deck it for your pistons {did you tell them} You definately just can't put one piston and determine the deck height. It will scare you if you take a block and measure the height from the crank centerline it can be off a mile from one side to the other

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post #4 of 15 (permalink) Old Apr 10th, 01, 12:16 PM Thread Starter
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In the past I was always rebuilding generally stock motors and really never gave the deck height much thought. This time around I made the mistake of taking some advice from one of the tech guys at Crap-O-Motive. He convinced me that they had a "zero deck" piston which would work great with an original and unmilled block. This fit in nicely with the theories on quench areas and detonation and my compression ratio goal. Of course, when I called back to discuss it the other day, they claimed there was no such thing and I must have gotten bad info from some other shop. They also said I was basically an idiot and couldn't measure right.

I have learned my hard lessons with these guys. They sold me rebuilt rods that were poorly finished, had excessive bore taper, and were all twisted and/or bent slightly. Their rebuilt crank was evidently "polished" by some kid with sandpaper, and now I get the piston equivalent of chromed muffler bearings. I'm also rebuilding my motor due to their poor machine work. All my calls for a little assistance have been met with the general "you're a moron" response and no help whatsoever. I may learn slowly, but I do learn. BTW - if you want to know how I really feel about these guys just e-mail me.

I have already discussed this with my local and reputable machine shop. I'm installing all eight pistons (I had 4 in when I verified the deck height) and taking it in for exact measurements by their experienced staff. The deck milling will then be calculated and done by this shop. I will get this motor right and learn quite a lot along the way.

Of course, the support and assistance here on the site is outstanding as always and much appreciated.


------------------
Scott
'69 400SB, Richmond 5-speed
www.geocities.com/sdenning1
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post #5 of 15 (permalink) Old Apr 10th, 01, 02:15 PM
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I too have heard bad things about crap-o-motive and the one time I did call them asking about one of their stroker kits, I didn't like some of the attitude I got. The guy who answered my call was very condescending, making very rude, sarcastic, remarks when I asked about getting non-rebuilt rods. Something to the effect of "geez, all you damn people think that you must have forged rods." Maybe I didn't need them, but I was looking more for the piece of mind. Anyway, I haven't done business with them.
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post #6 of 15 (permalink) Old Apr 10th, 01, 03:30 PM
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Bill
 
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Scott,
Something does not add up here. Those pistons should really not be much more than .020 down in the hole. They are zero deck with 5.7 rods....if your block has a deck height of 9.005 inches, but that is pretty rare. Most production small blocks are in the 9.025 range, which means you should have had to cut about .025 off the decks to get zero deck. We have rarely had to cut .040 off a small block deck. I have to wonder if the crankshaft was ground with the stroke slightly off ?? You might want to check it, although it is hard to do without a long travel dial indicator. A slightly short stroke, combined with rods that had a lot cut off of them to resize the big ends, could add up enough to cause your problem. Did you check more than 1 cylinder to see if they are all the same ?
I hate to say this, but I am going to because I love to rub it in.. ..If you had purchased the parts from your machine shop instead of the "mail order" place, you would have known all this to begin with. It might have cost a bit more at first, but it would have been right. At least they could have measured everything and told you that you were going to have to deck the block. Just had to get in some friendly ribbing of the mail order guys.
Looks like your only choice at this point is to deck the block, which will mean intake alignment problems. You might want to mock it all up when you are done and have the intake surface of the cylinder heads machined to compensate. Otherwise you will have to mill the intake and then it will only be good for that motor
Let us know how you make out,

------------------
Bill Koustenis
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[This message has been edited by BillK (edited 04-10-2001).]
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post #7 of 15 (permalink) Old Apr 10th, 01, 03:55 PM Thread Starter
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Bill -

I understand what you're saying about the measurements. I checked the first 4 pistons at the front (1,3,2,4)with both the dial indicator and a straightedge with a feeler guage. Same answer both ways all around. If I'm reading it wrong at least I'm consistent!

I'm taking everything back to the machine shop to get it carefully checked. The shop owner asked the same question you did and is suspicious of my measurements. I'll let you know what I find in a few days.

As you can tell from my comments before, I'm in agreement with you on buying parts from the machine shop. Live and learn I guess!

------------------
Scott
'69 400SB, Richmond 5-speed
www.geocities.com/sdenning1
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post #8 of 15 (permalink) Old Apr 10th, 01, 08:37 PM
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I am curious to know what kind of pistons you have...the last engine I built I used cast flat top replacement pistons from federal-mogul (trw, whatever you want to call them)...they ended up .040 in the hole also. I was told by the machine shop that the pistons were built this way to lower compression on older, originally flat top equiped engines to lower their compression to be more compatible with pump gas. I ended up with only 8.4-1 compression with my 76cc 882 heads...and 9.4-1 with the 64cc vortec heads I added later. I suspect that the quench thing may be over-rated...I can run 87 octane without detonation even with 3.08 gears and 4500 pounds of truck to haul around. Or maybe the vortec heads are just that good! I hope it all works out for you.

------------------
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post #9 of 15 (permalink) Old Apr 11th, 01, 04:05 AM Thread Starter
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Travis - the pistons are Silvolite H3424 hyperuetectic flat tops.
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post #10 of 15 (permalink) Old Apr 12th, 01, 11:13 AM Thread Starter
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Bill -

I've been thinking about the rebuilt rods comment. How much is typically trimmed each time rods are resized? I know mine have been done at least twice and most likely more than that. At what point do you normally decide the toss the rod?
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post #11 of 15 (permalink) Old Apr 12th, 01, 12:46 PM
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BillK,

You mention about having to mill either the intake or head to compensate for a decked block/head.

If you mill the intake surface on the head does this mean that the heads are married to the block as well?

Also, if it was decided to mill the intake manifold instead of the head what is the best way to determine the correct amount to mill off?

Thanks.

Carl


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post #12 of 15 (permalink) Old Apr 17th, 01, 03:32 PM Thread Starter
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Update - the shop measured everything and confirmed my measurements - .040 in the hole and all 8 pistons very close to that. They are going to deck the block today so the highest piston is at zero deck height. Yes - I may have to machine the intake a hair but I'd rather do that than touch my new AFR heads. I'm not sure how to measure that yet but if I have to I'll just cart the motor back to the shop and let them measure it so there's no mistakes.

I have no idea why there is that much clearance. The shop said the crank is right and he can't really measure the rods without pulling them out of the pistons. However, he said while it doesn't happen all the time, it's not unusual to have .040 deck clearance. Maybe the pistons are off a touch? Maybe the rods have been rebuilt a bunch? I really don't know - but decking the block should get me where I want to be.

------------------
Scott
'69 400SB, Richmond 5-speed
www.geocities.com/sdenning1

[This message has been edited by RockyMtnRacer (edited 04-17-2001).]
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post #13 of 15 (permalink) Old Apr 17th, 01, 07:07 PM
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rocky,

just huck your head's and intake to him. he can then take off what he need's to so the manifold will seat right. save's you a trip trying to huck a all most complete motor to him.

all he need's to do is test fit evey thing and he will know if and or what need's to be changed and how much.
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post #14 of 15 (permalink) Old Apr 19th, 01, 04:51 PM
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Rocky,

Just be aware when you put in your distributor. You might need to shim it to get proper gear alignment with a decked block. You don't want to chew up that cam gear. Rods that have been rebuilt several times will affect your piston to deck, but I wouldn't think .020.

Lonnie

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post #15 of 15 (permalink) Old Apr 19th, 01, 06:22 PM Thread Starter
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Lonnie - good thought on the distributor - thanks!

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Scott
'69 400SB, Richmond 5-speed
www.geocities.com/sdenning1
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