Cylinder Head “T” Washer Inserts.

The majority of original twin cam lotus cylinder heads are now more than fifty years old. With age, comes degradation and decay, but with the twin cam cylinder, it will most likely also suffer from head bolt recession – Caused by the numerous tensioning cycles (Pull downs-reassembly) of cylinder head bolts over the very long life of the twin cam cylinder head.

Some alloy cylinder heads can also become quite soft if they have been subjected to several “over heating” cycles, and with that, the aluminium will compress under the tension or torque of the head bolts and a noticeable bolt head depression will form under the cylinder head bolt as shown in the photo below.

Despite looking quite ugly, the bolt recession does not help in keeping the head bolt tensions correct, and if for some reason, a larger washer is placed under the head bolt, with out any remedial work, the problem will be made even worse.

There is really only one way to resurrect the head and correct the problem.

Special head savers or T washers as they are called are available, which can be inserted into the bolt hole. But before that can be done, some special milling or machining work is required. Of course the ideal time to carry out this work is during a cylinder head rebuild. Most people would be reluctant to pull an engine down just to do this job

With the twin cam head set up and squared off on the milling machine bed, its then time to zero in on one of the head bolts to begin the careful job of milling the first and smallest bore… for the shank of the T washer.

With this particular project there’s no DRO, and no CNC assistance, this machining job was achieved completely by careful old school, manual milling work.

After the milling work is completed, the tooling is changed and the indexable boring head is installed, and set up to bore the final (Top) recess for the T washer, When machining work is being done, careful measurements are required. The depths of the machining must match the shank width, length, and the width and depth of the T washer head.

The aim is to achieve a “light press fit” of the T washer into the cylinder head metal, DO NOT initiate a forced press fit, other wise the head could warp slightly due to the press fit pressure created along the top of the cylinder head from all ten T washer inserts.

The T washers can also be secured with the addition of Locktite 680.

After the machining preparation has been completed, the end result is a stepped bore that the T washer will securely locate into, and provide better support for the cylinder head bolts during and after the final cylinder head bolt torque has been applied during the reassembly stage, remember to apply the correct bolt thread lube for ARP studs or bolts, which ever is being employed.

The end result after the T washer has been installed and fixed into the cylinder head. There are ten bolts in total, and you’ll need to repeat the machining operation for each bolt hole. It can be painstaking work, so don’t be in a rush.

A two step counter bore tool, or end mill would make the job a whole lot easier and quicker.

And when the job is finally completed, there exists another twin cam cylinder head that will provide good service for several more decades.

Steel T washer inserts can be purchased from various suppliers. But if you have the right workshop equipment, IE, a good lathe and milling machine, plus the machinists operating skills, this job can be achieved by the DIY machinist mechanic.

But of course most will choose to send the head off to the “specialist shop” to have the work done at considerable expense.

So here’s the overview; The T washers in this instance were machined from high tensile steel, they were then heated and quenched in sump oil to increase the hardness, they are not brittle, just pretty damn tough to endure any continued pull down and re-assembly work.

The DIY cost would be zero for the time, (Your doing it for your own benefit) and material costs would be less than $20.00 at most for the alloy steel stock.

This is the kind of project that any engineer type enthusiast who has a long history of lathe and milling machine ownership would be quite able to carry out, if you fall into the category of having years of machining experience, then you’ll know all about fitting automotive parts and the tolerances required.

Many classic sports car owner enthusiasts simply don’t realize the vast array of work that can be carried out in the home workshop when equipped with a good lathe and mill and associated tooling. Yes, it is expensive gear to buy, but if one intends to spend half a life time working on classic cars, the time and money invested in good workshop equipment will repay the outlay ten fold or more, over time.

This has been the experience of the writer, who bought his first lathe as a seventeen year old, and of course the trade skills training was the result of attending one of those great Old Technical Schools in Australia, plus the night school trade classes, it was a sad day when they dismantled those great teaching institutions called Technical Schools, sadly they don’t exist any more.

Hope you enjoy the read and the learning, and might encourage you to have ago at doing some automotive engineering work your self, you don’t always have to run off to the guru to get things done.