aluminum block, cam bearing retention question... for the engine builders

[XR7]

On the new BBM aluminum block, there are un-machined "bosses" in the valley, above and on both sides of the 3 center cam bearing bores. This was for retaining the cam bearings inside the cam bores. Has anyone used this feature? They are blank and un-drilled/tapped. I imagine that is what the thinking behind it was, drill & tap and a set screw of some kind. I would think it could be a benefit, but looks like a pain to try and do correctly. It would be hard to get the depth and location exactly right, to lock the bearing in... but still have clearance for the cam journal to install the cam!

Anyone tackled this, or do you just use green loctite on the bearings or what? I am a little gun-shy as the cam bores measure on the high side already, I do not want any issues with cam bearings moving around or fore/aft... and taking out the short block. I have heard of this happening, not on an FE or the BBM in particular, but on any aluminum block.

[Joe-JDC]

Usually the set screws are used with roller cam bearings in aluminum blocks.  Also, on some of the higher flowing cylinder heads, the guides are installed with less interference fit so the guides don't split the thinned port or grow too much with engine heat so as to seize a valve stem.  These guides are pinned with a very small set screw drilled into the guide and flush with the spring cup seat.  Joe-JDC

[CaptCobrajet]

I've done it in some Shelby and Pond aluminium blocks,  You need a keyhole tap,  I used a socket head screw, and turned a dowel titty into the end of it.  Drill the hole the size of the tit in the block and bearing after the bearing is installed,  then measure the depth and drill the hole bigger to tap the set screw thread, leaving the hole small at the bearing.   You can grind the dowel to fit without hitting the cam journal.  I put a 1/8 pipe plug in the valley to access the set screw.  I usually don't pin a drag engine........only street or road racers that will see heat soak.  If the housing bore is not on the low, or smaller, I would think about doing it to a drag race piece.  The block will definitely grow, just like the mains do, except worse at the cam bore location.

[blykins]

I've always just used green Loctite and haven't had any issues.  In all the years on the forums, I think I've only read one instance of a cam bearing walking in an aluminum FE block and it was installed without any fail-safes whatsoever. 

I think if I were going to do anything with pins, I would pin the cam bearing through the bearing into the block so that it can't spin or walk either one. 

Make sure that when you knock the cam bearings in that you check to make sure they clear the adjoining lifter bores.   The bearings are so wide that they can catch a lifter if not positioned correctly.

On Dart aluminum SBF blocks, there is a threaded boss directly above each cam bearing.  You then use a set screw and tighten the set screw down against the bearing after installation. 

[XR7]

Thanks for the information, it helps.

[DEANs427]

I had #4 cam brg walk all the way out of my pond block on first pass after dyno run, broke the cam.
prominent builder had prepped block for assembly but did not pin the cam brgs