67 L79 Dipstick Tube Seal

[Tom E.]

[Joe L.]

Re: 67 L79 Dipstick Tube Seal

Original engine for this September 67 build 327/350 HP. When I went to install the dipstick a bushing on the end of the tube just fell apart. Old brittle plastic. The tube diameter is too small to fit without it and I am pretty sure it’s original to the car. I have looked at all the vendors and cannot find any reference to this part. See attached photo. Hopefully some one can provide some light. Thanks Tom

Tom------


The "sleeve" or "bushing" was not originally installed. I expect it's some sort of "field improvisation". Here's what I think likely occurred: the oil dipstick tube is a one-time-only sort of item. It is "swaged" into the block orifice and retained by the heavy interference fit thus achieved. Once it is removed, it cannot be re-installed with such a fit and, if installed, will be loose. So, if a dipstick tube which installs in the block is removed, it must be replaced with a new tube. In your case, someone probably came up with a means to allow the re-installation of a used tube by using this improvised device to re-establish a tight fit. There are other ways to do the same thing including "knurling" or deformation of the lower end of the tube. However, the proper way to do it is to install a new tube.

[Tom E.]

[Joe L.]

Re: 67 L79 Dipstick Tube Seal

Joe,
That makes perfect sense, explains why I couldn’t find any information on it. looks like I’m off to find me a new dipstick tube.

I started this restoration in may of 2019 and now that I’m retired I have quite a bit of free time to work on it. I have spent hundreds of hours reading threads on this forum gleaning valuable information and tips. There is a lot of bad information out there but I can always find the right answer here. Your knowledge of GM products and manufacturing is beyond remarkable and I thank you for taking to the time to share your wealth of knowledge to the rest of the world.
Tom

Tom------


The last available GM tube was GM #3865664 but it's discontinued. You might still be able to find some NOS examples of this tube but be aware that this tube was not actually 100% correct for your application. The original tube was GM #3876784. This tube was discontinued in July, 1974 and replaced by the 3865664. The latter was actually used in PRODUCTION for 1965-66 Chevrolet Series 10 pick-up trucks with small block but as far as Corvettes go, is SERVICE only. The difference between the 2 tubes? There is a slight difference in curvature but the primary difference is that the 3876784 has a reduced diameter for about 1-1/2" on the upper end. The 3865664 is a constant diameter for its entire length. Both tubes have the same developed length which is critical for dipstick accuracy so, functionally, both tubes are equivalent.

Reproductions of the 3876784 are available.

[Patrick B.]

[Joe L.]

Re: 67 L79 Dipstick Tube Seal

Joe—— Are 1970 350 dipstick tubes also not reusable?

Patrick------


Yes. Actually any L56-79 small block with a block mounted dipstick tube have the same problem with respect to dipstick tube re-usability. In most cases, if an attempt is made to re-use them there will be unsatisfactory results (e.g. tube pulls out when dipstick is pulled out, oil leak, etc.) .

1980+ small blocks went to a different design. The dipstick tube is still block-mounted but the tube is retained by an attached bracket and bolt. A light interference fit and sealer is used at the tube-to-block interface. These tubes can be re-used.

Big block tubes are oil pan mounted. These tubes are also retained by an attached bracket and have a rubber "o-ring" seal at the tube-to-pan tube interface and a light interference fit. These tubes can also be re-used.

[Joe L.]

Re: 67 L79 Dipstick Tube Seal

One other thing I should mention: installing new tubes can be a giant PIA. If a used tube is installed, it's easy; they slip right in. Unfortunately, they also slip right out and/or leak. A new tube has to be driven in "straight-and-true" with even pressure. If it's "cocked" in any way it will be ruined. Then, one has to obtain another new tube and start over again. In addition, one cannot use the collar to drive against with a screwdriver or similar tool. That will flatten the collar, cause the tube to be "cocked" and, ultimately, cause the tube to break off at the collar due to "flattening" of the collar.

Unfortunately, there is no currently available special tool I know of to install the tube. One has to make up one's own.

[Tom E.]

Re: 67 L79 Dipstick Tube Seal

One other thing I should mention: installing new tubes can be a giant PIA. If a used tube is installed, it's easy; they slip right in. Unfortunately, they also slip right out and/or leak. A new tube has to be driven in "straight-and-true" with even pressure. If it's "cocked" in any way it will be ruined. Then, one has to obtain another new tube and start over again. In addition, one cannot use the collar to drive against with a screwdriver or similar tool. That will flatten the collar, cause the tube to be "cocked" and, ultimately, cause the tube to break off at the collar due to "flattening" of the collar.

Unfortunately, there is no currently available special tool I know of to install the tube. One has to make up one's own.

[Robert W.]

Re: 67 L79 Dipstick Tube Seal

I used this tool after messing up on my first attempt using a wrench and a hammer (bent up the shoulder as described). This pic is from "Classic Chevy." Ecklers has them listed as well. It worked pretty easily

[Tom E.]

Re: 67 L79 Dipstick Tube Seal

Thanks Robert, that’s a great design and one I can copy quite easily. I had another design in mind but this is much simpler.
Regards, Tom

[Jeffrey S.]

Re: 67 L79 Dipstick Tube Seal

Tom,
I had a similar issue with my 69 (small block) and wrote an article for the Mich Chapter "Vette Signal" magazine which is attached. This solution may or may not work for you- my engine was out of the car so I had easy access. Hope this helps.
Jeff

[Joe L.]

Re: 67 L79 Dipstick Tube Seal

Thanks Joe,
Appreciate the additional info. A guy has a new original tube on eBay for $125. A bit steep! Before I buy another I am going to try and swedge the old one out to give me a few thousands of interference and see if I can make up a tool to seat it. If not I’ll buy a reproduction, I’m doing everything I can to keep this car original but I have my limits. Thanks again for the info.
Tom

Tom------


The one being sold on eBay for $125 is not the original part that was discontinued in 1974. If it were, it MIGHT be worth the asking price. The part being sold is the GM #3865664 which is the replacement part number. This number appears on the package and the tube can also be identified by having the constant OD all the way to the top. The 3865664 was never used in PRODUCTION for ANY Corvette.

So, the one being sold for 125 bucks might be worth that much to someone doing a state-of-the-art restoration on a 1965-66 Chevrolet Series 10 truck (however many of those there are) but it's certainly not worth that much to a Corvette owner. A Corvette owner is better off with the $10 reproduction of the 3876784.

[Joe L.]

Re: 67 L79 Dipstick Tube Seal

Tom,
I had a similar issue with my 69 (small block) and wrote an article for the Mich Chapter "Vette Signal" magazine which is attached. This solution may or may not work for you- my engine was out of the car so I had easy access. Hope this helps.
Jeff

Jeff------


I don't know where you found the GM #3865664 tube in the AIM as you mention in the article. That tube was never used in PRODUCTION for any Corvette, 1969 or otherwise.

Also, the reason that the end of the tube that inserts into the block is of the larger OD than the orifice is to ensure a tight interference fit. The larger OD causes it to be "swaged" into the orifice. Some folks reduce the OD of the tube "to make it go in easier". This is not wise because it will also make the tube come out easier. One can put the tube in the freezer for several hours before installation, removing it just before installation.

[Joe L.]

Re: 67 L79 Dipstick Tube Seal

I used this tool after messing up on my first attempt using a wrench and a hammer (bent up the shoulder as described). This pic is from "Classic Chevy." Ecklers has them listed as well. It worked pretty easily

Robert------


Below is a tube installer that I fabricated many years ago. It works quite well. But, I like the one you purchased even better. I think I'll order one.

[Tom E.]

Re: 67 L79 Dipstick Tube Seal

Tom------


The one being sold on eBay for $125 is not the original part that was discontinued in 1974. If it were, it MIGHT be worth the asking price. The part being sold is the GM #3865664 which is the replacement part number. This number appears on the package and the tube can also be identified by having the constant OD all the way to the top. The 3865664 was never used in PRODUCTION for ANY Corvette.

So, the one being sold for 125 bucks might be worth that much to someone doing a state-of-the-art restoration on a 1965-66 Chevrolet Series 10 truck (however many of those there are) but it's certainly not worth that much to a Corvette owner. A Corvette owner is better off with the $10 reproduction of the 3876784.

Joe Robert,
Robert, Thanks for the great tip on the tool. I made one up from a piece of steel tubing and it worked Perfect. I use a tube expander to slightly enlarge the tube and then drove the tube into the block. Access was easy as the body is still off of the car for paint.

Joe, appreciate all the formation, I have saved it all to my iles. Your advice Along with Roberts tool not only saved me money but I was able to use the original part. Awesome day!
Thanks Tom