How Standard are Standards?
It was many years ago I asked a friend in India, “just how many standards are there in the making of Listeroid engines?” I had given the example of the ID at the top of the Tappet Guide. This was a surface I had made a tool to grab hold of, but soon I realized that India had no standard for this ID, and each machinist took the liberty to finish it as he wished, and my tool only fit a portion of the tappet guides made 🙁 Yes, I had assumed way too much.
The answer I received, ” for many things, individual shops do what they think best”.
Today I’d like to give another example, and this is CS Standard (Listeroid) Valve Guides. Steve Hutson in Australia recently wrote me an email about the Lister 6/1 engines in his country (real ones), They generally have one press in, and one screw in Valve Guide. Some where between 1958 and present, the Indians thought better, and made both sides ‘press fits’. This lowered the cost, and since it’s a world standard for valve guides today, it’s highly probable that no benefit was lost other than backwards compatibility with the older original engines and earlier copies they made.
I didn’t research to see what David found Dursley to have done, they may have dropped the screw in at some point as well?
But today, we might ask, just what does a standard clone valve guide look like? And if they are different why? How long should a guide be, and if it’s longer or shorter what is the advantage or disadvantage? I volunteer to give at least one answer. If the guide is so long the valve can not seat, then it’s too long. As for typical, I can tell you that most times the exhaust valve is fitted with the longer valve guide.
The picture I enclose is of guides removed from what I’ve come to think of as a standard Listeroid 6/1, they were removed from a head about 2003 vintage. The valve guides to the right are from Central Maine Diesel and look very much different from the parts they display on their ‘on line parts order page’. But it was standard parts I ordered.
The hex head on one guide make me curious, I’m still the student, as I know I haven’t yet seen it all, nor do I know why it is. My first thought is this guide is a universal part, and is finished according to need. If it’s a batch made for the screw in guides, it gets threads, if not, it’s built as a press in. If it need be shorter, it gets cut off?
Now.. you have my guess, what’s yours?