Navigator guide block and followers

The, club has new bushes for sale and followers I think, but the prob is the angle of the followers I think which soon wear oval?

Previously arthur_fish wrote:

Having stripped a couple of navigator engines the cam followers and guide blocks are all badly worn in the barrels , I have ground the tappet assemblies [20871]lightly until true [ they were more worn than the tappet bushes ] and still had good hard grinding sparks coming from them , I was going to make new tappet bushes in leaded bronze and wondered if anybody had done this and perhaps scrolled the oil return as a cam shaft bush instead of the two slotted oil returns down the side of the cast tappet bushes that look a poor design.

I played about with a couple of of the tappet assemblies when grinding thinking I would get under the hard surfacing but as mentioned I had good hard sparks well downbut did try to cherry red and case harden one as a test, guess what they are hollow! the push rod locating cup ricocheted off the workshop roof never to be seen again. [i was wearing safety gear].

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Hi.

The Cam Followers & bushes are the Achilles Heel of this engine design. The designer (Bert Hopwood) had originally wanted a one piece head & barrel design - hence the more upright valve angles. The cam follower would also have been the pushrod. To 'force' the cam follower to rotate, it was designed to sit offset on the cam. So far, so good.

Now the fun begins. At some stage it was decided that motorcyclists enjoyed de-coking their bikes on a weekend, 'lets make it easy for them' - detacheable cylinder heads were needed. The law of unintended consequences kicks in.... The cam followers are now very short, & separate (short) pushrods are now required. The cam followers run in short guides, and are still lifted off-centre. The result is that the cam follower stem wears into a barrel shape, which means it no longer sits flat on the cam, which means the (hard chrome) face also wears unevenly. As you found, the original cam followers are hollow inside (to reduce weight), with the pushrod locating cup pushed into the end.

The cam follower guides have a groove either side to allow oil to drain into the sump. As long as the grooves are East-West across the bike, all should be well - as the thrust faces are front & back. Cases were known where the factory assemblers did not know this & bashed them in any old how (Source: John Hudson) which inevitably meant some grooves ended up in the worst position possible.

I am interested to hear that you were able to grind the stems back. The original guides were made of (self lubricating) cast iron & wore out less quickly than did the followers. Its possible other materials can do the same job. I would be interested in how you get on with re-making them.

When I came to my first Navigator rebuild in 1976, the Main Dealer (Taylor Matterson) was still in business - but he had no cam followers in stock even then. The NOC spares scheme has since remade several batches - but they are expensive to manufacture, as a lot of the treatments (hard chroming, for example) are very strictly controlled.

Good Luck with the project. Andy S.