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.
Ed
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.
Ed