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Discussion Starter · #1 ·
Hi guys.
I´m trying to find new pistons and rings for my 402, but what a jungle.
The car is a standard 1970 Chevelle SS 396, I did change the rings and hone the cylinders years ago but now I have constant blue smoke so I decided to overbore it ,030.
I have not opened the engine and mesured the cylinders yet but I cant imagine it to be more worn than that.
Could anyone guide me to what kind of pistons and rings I should by for this engine to get it right .
I think the standard comp.ratio is 10,25 and the bore/stroke is 4,0125/3,76 on this engine.
I don´t need any hard core racing stuff ,just a descent set for a street car.

Thanks Tommy
 

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Hi guys.
I´m trying to find new pistons and rings for my 402, but what a jungle.
The car is a standard 1970 Chevelle SS 396, I did change the rings and hone the cylinders years ago but now I have constant blue smoke so I decided to overbore it ,030.
I have not opened the engine and mesured the cylinders yet but I cant imagine it to be more worn than that.
Could anyone guide me to what kind of pistons and rings I should by for this engine to get it right .
I think the standard comp.ratio is 10,25 and the bore/stroke is 4,0125/3,76 on this engine.
I don´t need any hard core racing stuff ,just a descent set for a street car.

Thanks Tommy


Hopefully this page pops up for you.

https://www.summitracing.com/search...isplayPrice&SortOrder=Ascending&keyword=4.155


396 pistons are what your looking for 4.094" , your 402 is just a 396 bored .030 over for 4.125" and if you want another .030 over 402 is 4.155"

When you call or ask for pistons for a 402 bbc it's best just to refer to your engine as a 396 in your case .060" over (if you plan on .030 over bore). The books show more piston choices as a 396 either .030, .060. .090 over bores.

It can confuses some techs if you keep asking for 402 pistons, they tend to push you to custom pistons I have found in the past.

So if your wanting to go .030 over on your 402, your really asking for .060" over bore 396 pistons/ 4.155" bore.

Hopefully this helps
 

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Discussion Starter · #3 ·
Thanks Dennis.
Any recommendation on which brand to use? And rings?
Are my original heads open chambers ?

Tommy
 

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I would use (Sealed Power/Federal Mogul) Speed Pro forged pistons, which are superior to cast pistons. I just purchased a set for my .060 over 396/375 HP and opted for the original L2242 model, which produces in the neighborhood of 11.0:1 compression when mated to original equipment "840" rectangular port heads. Your engine, however, sounds like the 350 HP version, and would take the L2240 piston, which, when capped by the original closed chamber oval port heads, works out to 10.25:1 compression. Speed Pro recommends finish honing the block to a piston to bore clearance of no less than .003. I prefer a bit more clearance, and request my engines' cylinders be finished honed, when using this piston, to .004 diametral clearance.

I believe Summit charged me $394 for a set of L2242 pistons.

I bought Speed Pro file-fit Plasma Moly rings, which I finish gap to .018 on the top ring and .016 on the second ring. They cost somewhere in the $120 neighborhood.

Other guys may recommend different pistons, rings and clearances.
This is just my 2 cents.
 

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One more thing, Tommy. I for some reason assumed your engine was equipped with closed chamber heads, but I am not altogether certain that this is true. Check your casting numbers for me and I will check my "Chevrolet By The Numbers" booK for you. You must remove a valve cover to do this. If you are unfamiliar with with Chevrolet casting numbers, it would be a large, 7-digit number cast into the surface of the head.
 

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I used the Speed Pro 396 .060 over pistons in my 70 402 with 290 heads. Dome is a few CC's larger than the 402 piston. The 396 pistons were less expensive than the 402 pistons. I was worried about the tight clearance but after asking questions on Team Chevelle I went with the manufacturer recommended clearance.
 

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Discussion Starter · #7 ·
Thanx guys.
I will try to take one head off the engine to morrow, then I´ll come back with some cast numbers.
It´s for sure a L 34 engine, 350 horse
 

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Thanx guys.
I will try to take one head off the engine to morrow, then I´ll come back with some cast numbers.
It´s for sure a L 34 engine, 350 horse
Probably just a misquote but your not pulling a head, your pulling a valve cover. The casting number will be located in the rocker arm valley. I'm guessing 290's if the motor hasn't been pieced apart. Here's a link that would be helpful to you:
Head Casting By Year This is where you need to be:
 

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Discussion Starter · #9 ·
I am going to pull a head just to make sure the bore is original 4,125"
Now, the casting number is 3964290 on both heads, but what makes me wonder a bit is that one head seams to be made C 4 - 70 and the other one is C 5 -70.
But according to the body tag it is a Baltimore car made 04 70 ( April 04 A ) How can one head be made in May -70.
136670B171236 is the whole number of the car and the engine # is TO35CTX, I believe the trans is a M 21, Gears are 12 bolt 3;31.
Engine and trans is # matching
 

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I revised my post because I originally misread your post.

"C" is the month (March) the head was cast and 4 (or 5) is the date of the month. Your heads were cast one day apart. On many pairs of heads installed on engines at that time the dates were a week or more apart.

What is strange is that the engine was date stamped (assembled) the same day one of the heads were cast. According to the experts this has been confirmed to have happened on occasion. Example: Graveyard casts the second head at midnight, day shift machines and assembles that head at by 5PM and swing shift assembles and stamps the engine assembly at 11PM. Hard to grasp for an old machinist and production engineer like me, but apparently it did happen.
 

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I am going to pull a head just to make sure the bore is original 4,125"
Now, the casting number is 3964290 on both heads, but what makes me wonder a bit is that one head seams to be made C 4 - 70 and the other one is C 5 -70.
But according to the body tag it is a Baltimore car made 04 70 ( April 04 A ) How can one head be made in May -70.
136670B171236 is the whole number of the car and the engine # is TO35CTX, I believe the trans is a M 21, Gears are 12 bolt 3;31.
Engine and trans is # matching
That's a matching pair of heads cast up March, 1970. We work on these all the time for the 100% stock-appearing crowd!

Thanks, Gary in N.Y.

P.S. I PM'd you about the pistons, we have a bunch on the shelf! Single package with the pistons, Scat rods, Clevite brgs, and Mahle rings!

 

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Discussion Starter · #12 ·
Thank´s Ole, I did not know that.

Gary. I´m going on vacation to Florida in a couple of weeks and all the parts that I´m buying has to go down in my suite case, I have to think about the weight and I Don´t think I need new rods eather.
Thank´s anyway

Tommy
 

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Just trying to save you a headache later. My opinion is to take the block to the machine shop and verify the taper before buying your pistons and rings. You really can't be sure what size they need to bore it out to until it's mic'd
I had a used motor that I honed and installed rings into and ran it for a few years unail it started smoking. Ended up having to go 60 over. Jim
 
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Quite right, Jim Mac. The standard bore '69 L78 block I recently took to the shop for machining had been dry stored by its previous owner for 35 years. Somewhere along the line it must have seen some water as the number 7 and 8 cylinders both had enough pitting for the shop to take the bores out to .060.
 

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Discussion Starter · #15 ·
I get your point. If I only had the time to do it.
About the heads I found out that the comb. chambers should be 100,967 cc.
Is that closed chambers?
 

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My recollection is that the chamber size of '65-'69 oval port closed chamber heads were around 98 CC. I believe, however, that some castings were later opened up to un-shroud valves. They were still referred to as closed chamber, I believe. Your "290" heads were probably in that grouping.

Here is a good on-line source for cylinder head date:Chevy Big Block Cylinder Head Codes - Chevy Camaro

Another excellent source are the "Chevrolet by the Numbers" books.
 

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That's a matching pair of heads cast up March, 1970. We work on these all the time for the 100% stock-appearing crowd!

Thanks, Gary in N.Y.

P.S. I PM'd you about the pistons, we have a bunch on the shelf! Single package with the pistons, Scat rods, Clevite brgs, and Mahle rings!

PM sent.
 

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I get your point. If I only had the time to do it.
About the heads I found out that the comb. chambers should be 100,967 cc.
Is that closed chambers?
Yes, they are closed chambered heads. Your pistons should have anywhere from .100 to .200 dome that would put you anywhere from 9-1to 10-1 compression.
 

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Discussion Starter · #20 ·
The engine is at the machine shop now, I have to wait a day or two to see what they have to say.

Tommy
 
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