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07-15-2012, 11:38 AM #1
Cobra Engineering Chain Tensioner Pivot Installation Fixture
As many of you may already know the stock chain tensioner pivots tend to be one of many tender points on aluminum ModMotor blocks. The iron blocks use a hardened steel 8mm dowel that is pressed into a boss on the block. To my knowledge I have never heard of an iron block tensioner pivot failing in service. The same is not true for the aluminum block equivalents.
When a chain tensioner pivot fails in one of our engines it allows the chain to jump or more teeth. If you tend to be among the less fortunate your primary chain will find a way to completely escape the exhaust or crank drive gears. Either way the cams stop turning before the crank does and the valves, guides and potentially other expensive parts (along with your wallet) become the victims.
Michael (rtusnake) went through this experience and decided to fix the problem. He built a replacement tensioner pivot that actually was as strong as and probably stronger than the iron block tensioners. Here is a picture of Michael's tensioner and a stock aluminum block tensioner:
Michael's is the one on steroids. He has upgraded from the breakage prone 6mm OEM anchoring thread to a more robust 8mm anchoring thread, increased the dowel pin diameter to 9mm with a built in a thicker, larger diameter and more robust anchoring foot for the pivot. Michael's tensioner pivots have been used by a number of the guys on ModFords to correct the problems of the weaker, failure prone OEM pivots.
The challenge to using these has always been installing the new pivots in the block. To do it correctly it has been necessary to use a vertical mill to drill and tap the anchoring holes normal to the face of the block. If you had a mill or had access to one you were good to go. If you didn't you had to find a shop that was willing to do some custom work to get the new pivots installed correctly.
Not anymore! JamesHell at Cobra Engineering has come up with a fixture that allows the proper installation without the use of a vertical mill. James fixture is similar to a production drilling and tapping fixture that allows accurate hole placement and holes and threads to be placed normal to the work surface - like we need for our application. Best of all you can do it with a hand drill and a hand tap!
James built the fixture off Ford prints but did not have an aluminum block handy to test the hole location accuracy. I offered to help. Over last weekend I set the fixture up on a new aluminum block and tested the locating, attaching and drilling hole placements. All were not surprisingly, right on the money.
Here are some pictures of the fixture as it arrives and on a block for drilling and tapping. This is what it will look like on your door step:
When you open the package James has plastic wrapped the fixture, drill bushings, drill and tap into a single package that looks like this:
When you remove it and install it on the front of the block for installing Michael's tensioner pivots it looks like this:
There are two drill bushings on the fixture. One is for the 8mm tap drill you will use to drill out the stock bosses. One is for keeping the tap straight and square to the block face as you retap the newly drilled bosses to accept Michael's upgraded tensioner pivot dowels. The bushings allow you to keep the hole straight and square with the front face of the block and also tapped straight and square with the front face of the block - without the need to use a vertical mill.
The bushings rotate about thirty degrees allowing you to unlock and interchange them. The entire fixture locates off the timing cover dowels on the front of the block and is held in place by two or three (if you choose to use all) 8mm timing cover bolts. The one additional item I might recommend is a drill stop from Home Depot to prevent drilling the hole too deep. The installation is a breeze and is easily done in about 15 minutes. Be sure to use some lubricant during the drilling and tapping process. The drill bushings fit the drill and the tap quite closely.
This is a great reliability modification conceived by one of our own members, Michael, and enabled for all of us by James at Cobra Engineering. I can not recommend it highly enough. You can contact both Michael (rtusnake) and James by PM to get yours. BTW Jim (showme cobra) snapped up the very first one as soon as I had finished testing it.
This is good stuff designed and manufactured by our own guys right here at ModFords. If you use any of Ford's aluminum blocks this mod can save you thousands of dollars in broken parts.
Last edited by eschaider; 08-27-2016 at 10:34 AM. Reason: Fixed broken Pic links
07-15-2012, 12:13 PM #2
- Join Date
- Aug 2004
- Pasadena, CA
That fixture is nice enough almost to the point where one might be reluctant to take it off calling it a "Timing Chain Guide Post Reinforcement Plate".
07-15-2012, 12:32 PM #3
Very nice. If you upgrade the tensioner dowels and plan on installing them yourself, this is a must have. I tried free-handing it and ended up taking the block to the machine shop to helicoil the dowel boss because I didn't get it straight.
I'd like to extend a thank you to Michael and James for giving us an option to beef things up.
07-15-2012, 12:44 PM #4
this is great. i already have the upgraded dowels from rtusnake, but ive been hesitant to drill and tap the hole myself for this very reason. id rather do it myself than take it to a machine shop and risk something happening to my block by an inexperienced mill operator. now i can take my time and make sure its perfectly done. id like a price for one
07-15-2012, 12:45 PM #5
I agree Tony and forgot to add that to my initial post. Both these guys ar very talented and bring something to the table here at ModFords that simply can not be obtained anywhere else except from them. Thanks for the effort to create these tools and parts and thanks for sharing guys.
07-15-2012, 01:48 PM #6
07-15-2012, 02:43 PM #7
thanks james and ed for this, this came at just the right time!!
07-15-2012, 07:09 PM #8
These will be $90 plus shipping. That will include the plate, both bushings, drill and tap.
Measure the existing hole depth. We decided not to give a specific dimension being that this would be used on many different blocks and we are not certain on the differences. DO NOT drill the new hole deeper than the existing hole.
Yes using oil on the drill is recommended.
Then blow the hole out clean. Chips will mess with the tap.
Swap bushings. Use heavy oil or even grease on the tap. Work it in about 3 threads at a time. Back it out and clean between. Of course use judgement. If you feel heavy resistance stop, back it out and start again. Patience is your friend here.
Move on to the other hole
Now the bad news. We have a bad noise in the machine. This weekend we pulled the motor and transmision (just as much fun as doing it in a car). We are not sure but I bet we will be changing some bearings.
In theory it should be back together in a week or two. So I can't make anything till then. If you are serious please still PM me. That way I can have materials here and ready to go.
Thanks everyone, but Ed gets the credit for coming up with the idea. I just made it.
07-15-2012, 07:49 PM #9
Amazing. When I refresh my BB motor, I will be getting a set of these.
Great work guys.
07-15-2012, 08:04 PM #10
Very nice work to all involved.
07-15-2012, 09:33 PM #11
What is the price of the studs?
07-15-2012, 09:48 PM #12
07-15-2012, 09:49 PM #13
I'm going to go ahead and order this fixture now.
Just in case it gets decided that it's too much bother.
And whom do I order the new improved studs from? I should order two engine blocks worth for the same reason.
07-15-2012, 10:08 PM #14
07-15-2012, 10:35 PM #15
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