[h2pmr]

cannot remember if i posted about this on TOS.
many years ago i bought a set of Colin Jenson's tri flow cams, 3 out of the 4 bolted down perfectly, but one was a very tight fit, the cam cap would not fully tighten down.
as i tried to remove the cap a small section of the cam broke off, pictured.
i have tried it in another head and its the same so has just not been machined wide enough.
i could get a local machine shop to make it the correct width,.
but is scrap already?
cheers
Phil

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[smiffypr]

My guess would be: get it welded back up, re-ground, then retest the hardness of the nearest cam, and if necessary get it re heat treated. But I would be slightly concerned that the cam was too brittle, maybe get it fully re-hardened and tempered, but I don't know how it was supposed to have been made in the first place.

[worf]

I have been told by several reputable sources that all of Colin's cams don't really fit. They are a smidge too big. Those that used them had the heads (re)align-bored to fit. Those that didn't, ran the risk of not enough clearance with the bearing surface and caps.

As a rule, I will not modify an expensive piece of a 928 (e.g. body, head, harness) to fit an aftermarket part. So, I have two sets of the cams sitting on a shelf.

The cam in the OP can either be fixed or not. Take it to an old guy in a shed that has messed with cams for decades.

[maddog2020]

I had a similar problem with my Simard cams. Factory cam journals have very sharp break between the journal and thrust surface in the front or back of the heads. Factory cams have the same very sharp corner. Aftermarket cam makers are reluctant to make this sharp edge as it can create stress fractures and if you force it the cams will do exactly what you pictured. I had to machine a small bevel in the corner of the surface of the heads for this to work. I'd probably have the cams turned down if they are too tight before align boring the heads.

[h2pmr]

thanks Gents, i did think they were all on the snug fit side of tight in the heads.
and without modification to head / cams, and a hope it works thought in the back of my mind, i think i will put them back on the storage shelf i got them from and maybe put them on ebay in the future.
cheers
Phil