70 L-46 dipstick tube?

[Mike F.]

My 70 L-46 dipstick tube is incorrect, it has a consistent one size diameter. I'm told it should have a slight flair near the top end.

Any suggestions on where to find the correct one, part #, etc.?


TIA,
Mike

[Jeffrey S.]

Re: 70 L-46 dipstick tube?

Mike,
I think you will find that there are other differences between an original and what is available today from any source. I went through this when trying to find one for my small block. Attached is an article I wrote for the Michigan Chapter's "Vette Signal" on the subject. As explained in the article, I found that the closest part I could find was from Paragon and it still needed work to get it to fit. I know that the part from an L-46 is different that the base engine but I thought it might be helpful to see a picture of an original out of the engine and see the differences.
Jeff

[Edward J.]

Re: 70 L-46 dipstick tube?

Mike I seem to remember Joe L. posting a GM part # on the SBC dip stick tube that is still available. Correct ??? I can tell you my 72 tube does have a flare at the top.

[Joe L.]

Re: 70 L-46 dipstick tube?

Mike I seem to remember Joe L. posting a GM part # on the SBC dip stick tube that is still available. Correct ??? I can tell you my 72 tube does have a flare at the top.

Edward-----


The tube is GM #3865664 and it is still available from GM. However, even though this is an old, 1965-era part number, it's not the original tube used for 1965-74 Corvette small blocks. That tube was GM #3876784. It was discontinued in July, 1974 and replaced by the 3865664. The 3876784 has a swaged down (i.e. reduced diameter, not flared). The 3865664 is the same diameter for it's whole length.

By the way, the 3865664 was originally used in PRODUCTION for 65-66 series 10, 20, 30 series light trucks with small block.

[Joe L.]

Re: 70 L-46 dipstick tube?

Mike,
I think you will find that there are other differences between an original and what is available today from any source. I went through this when trying to find one for my small block. Attached is an article I wrote for the Michigan Chapter's "Vette Signal" on the subject. As explained in the article, I found that the closest part I could find was from Paragon and it still needed work to get it to fit. I know that the part from an L-46 is different that the base engine but I thought it might be helpful to see a picture of an original out of the engine and see the differences.
Jeff

Jeff------


First of all, the base engine and L-46 dipstick tubes were the same.

Now a few comments on your article:

The original tube used for 1965-74 Corvette small block applications was the 3876784, not the 3865664 which is the current SERVICE part. As you noted, the most obvious difference between these two tubes is the reduced diameter of the upper section of the tube for the 3876784. The 3865664 is the same OD for its entire length. I fully expect that this is the primary thing that judges look for.

The reason that the OD of the portion of the tube that inserts into the block is larger for the reproduction and the GM SERVICE tube than the OD of the original is that the original tube was swaged as it was inserted into the block. In other words, the tube was very slightly reduced in diameter as it was driven into the block orifice and the interference fit was established. This is the reason that these tubes cannot be re-used after they are removed. A re-used tube already reduced in diameter during its first installation will not establish a satisfactory interference fit upon a second installation. By your reducing the OD of the reproduction tube, you "accomplished" the same thing (although you did make installation easier). You will probably find that your tube will loosen and come out sometime in the future. The slightly larger OD of the GM and reproduction tube CAN be driven into the block IF a proper tool is used.

As far as the curvature difference goes between the 3 tubes shown, the 3865664 (the GM SERVICE tube for the last 40 years) and the 3876784 (the original tube) do have a slightly different curvature. As far as the difference between the original tube and the Paragon reproduction, understand that the original tube may very well have been slightly "re-curved" over the years. There's really no reason to expect that the original tube is exactly the same curvature as when it was originally installed.

As far as alignment of the tube goes, you will note that there is a cast-in "cradle" on the exhaust manifold. The tube is supposed to align with this "cradle". However, even as originally installed, the tube did not actually fit into the cradle (i.e. it was not snug up against the exhaust manifold)

[Jeffrey S.]

Re: 70 L-46 dipstick tube?

Joe,
Thanks for the comments. I purchased the currently available GM part which is pictured in the article. I could not even get the tube started in the opening. I suppose that if I had the special tool used at the assembly plant I could have done so. Even after reducing the OD, the tube had to be driven in and that was difficult. We will see if this loosens up but I can't see how it will given that it was so tight driving in. The other frustrating part of this was that the dip stick would not go fully into the tube, even outside the engine. The ID at the top is significantly smaller than the original as was the reproduction part. After re-sizing the upper ID, the dipstick went in all the way, very snugly.
Jeff