Ever since the material quality of the TR tappets took a nose dive about four years ago, BFE and other firms have tried to develop a viable alternative. At first we all tried to strengthen the soft products from overseas by various hardening methods, which gave results much better than stock, but for some purposes not good enough. About a year ago we began to make our own tappets from homogenous grey cast iron, heat treated to Rockwell 61C. These have been very good, with no failures. However, we have found that in order to stay on top of the problem we really needed at least one more option to fall back on.
For the 6-cylinder cars we have been buying oversized hardenable iron tappets with the correct pushrod seat and grinding them down to the correct size. Not a very good solution cost-wise, but excellent for durability. They are Rockwell 61C all the way through and are very compatible with the cams. When it came to the 4-cylinder TR, though, no such happy solution existed. The 4-cylinder tappet is the largest in diameter of any regularly-serviced tappet and there was no substitute big enough. Now we think we have a solution. We have come up with a sleeve that will allow the use of a domestic tappet, one that has the correct pushrod seat inside.
For over a year we have been experimenting with these sleeves, using silicon bronze for the material. We have found that this material expands and contracts at different rates than the engine block itself. While we continue to work with silicon bronze, we have just now found a different material that has much more similar characteristics to the block and tappets and this looks like the best solution so far. We have incorporated a ‘shoulder’ on the sleeve, and in combination with the use of Loctite to retain it, it will not become loose.
So far with this system we have had no failures and no problems, but we will continue to work at perfecting this new solution to the point where tappet woes are ancient history. This sleeve system doesn’t come cheap, but the added expense is minor compared to repairing the damage caused by failed tappets!