Liner sinkage, block stretching.....

[Keith Clements]

This was copied from the topic thread on the oldjowetttalk.

https://jowett.org/oldjowetttalk/_disc3/00000062.htm

You can go there and read the rest of the thread. There is lots of other useful stuff there; so search the forum.

You might like to discuss ‘my theory’ that the blocks stretch so not allowing the correct pressure to be applied to the head gasket thus causing leaks and overheating.

I was at Spero’s mending his Jup yesterday and did my usual set up of the liners by bolting down without a gasket to 20ft/lb (no more or you will crack the block!) and then checking for 8thou all the way around. Usually even if the liners were set correctly originally they will sink or part of the block will stretch particularly around the bottom centre studs. I have even found over a week the gaps close; signalling a creaping crack or necking of the block or bolt. Note it is VERY important to torque in the correct sequence and in 5 lbft stages or the head will not go on square. Try it, feeler gauging at each stage around the whole of the edge of the head.

Most of the gaskets I see from people with heating problems have the gasket in the top outside corners of the combustion chambers blackened while the rest is clean alu or cooper. This is caused, I think, by incorrect liner pinch.

I stick the shims on the head face of the liner and check without gasket at 20lbft before finally taking the liners out to fit permanently.

The Jowett Service bulletins (75,90,113)and manual say 8-12 thou and 40lbft final torque. If you do go to these limits you need a really good block which really should have been strengthened with weld. Even metal gets fatigue and old age!

Note I have also reused gaskets for years since they are already compressed which helps when you do not have the luxury of being able to retorque after 200 and then 1000 miles. Note if the nuts turn when retorqueing you may have a necking of the cylinder head bolt or cracked block problem. Make a note of which nuts turn so you can look for problems when you take the head off!

Doug Rath asked how to get a reliable Jowett. The answer is good engineering patience. You have to look hard and check everything. You cannot just fit components to Jowetts.