Reliant Scimitar SE6A
Nigel gets unleaded cylinder heads, and sees how it’s done
This is a story of how little classic car jobs can escalate and get completely out of hand, a tale of ‘mission creep’ on a grand scale. It starts with my Reliant Scimitar GTE, which had been running pretty well, clocking up the miles without fuss, albeit developing one or two small niggles along the way.
There was a leak developing from the connection between the right-hand exhaust manifold and the downpipe, and I’d noticed the frequency of oil top-ups had gradually increased. Neither were major problems, but the time had come to attend to the exhaust leak. Rather than smothering the leaking joint with exhaust paste, the Scimitar deserved a proper job, which meant removing the downpipe and remaking the joint.
Accessing the connection from beneath the front wing, it was obvious the nuts and studs fixing downpipe and manifold together were so thoroughly corroded that there was no hope of separating them. No problem, I thought – I’ll snap the studs, then remove the manifold and get the broken stud ends drilled out and Helicoiled. Snapping the studs was easy. As it turned out, snapping the bolts holding the manifold to the cylinder head was also rather easy. In my defence, it appears the exhaust manifolds had been untouched since the engine left Dagenham in 1977!
Clearly the cylinder head would need to be removed to deal with the broken bolts.
This created a dilemma… should I simply remove the affected head, fix the broken bolts then put it back together? Or should I remove both heads then have them properly refurbished. I chose the latter approach, it’s more than earned its place as a keeper in my little classic collection.
Doing it properly
Decision made, life in the garage began to run more smoothly. We’ve all heard horror stories of cylinder heads that were stuck fast to the block and needed to be separated with crowbars and engine hoists. Fortunately this isn’t one of those stories. After removing the carb and inlet manifold, the head bolts yielded to a socket on the end of my longest breaker bar. I squirted
‘The Scimitar has earned its place as a keeper’
generous doses of penetrating oil down the bolt holes and called it a day. Next morning, both heads lifted straight off without a struggle.
I chose Ivor Searle in Soham for the machining work. I delivered the heads and asked Trevor and Dan who run the classic engine department to fully overhaul them to standard specification, with the addition of hardened steel valve seats for unleaded fuel. Whether it’s a full engine remanufacture or merely cylinder heads, the process starts with stripdown and thorough chemical cleaning. Ivor Searle also extracted the broken studs and bolts, installing Helicoils where the original threads couldn’t be saved.
I’ve always taken the view that it’s not really worthwhile stripping an engine for an unleaded conversion, but if heads need to be removed for other work, it makes sense to fit hardened valve seats at the same time. This approach has certainly worked for my Triumphs, and the Scimitar’s Ford ‘Essex’ engine hasn’t shown any signs of serious valve seat recession either.
Giulio Vines was entrusted with the work on my Scimitar’s heads. Some of the machining processes can appear quite brutal, but it’s all carried out with great precision, with far more time being spent setting up and checking than on actually cutting metal. The process for the Scimitar’s heads is similar to converting any classic cast iron cylinder head. While the Scimitar’s heads were away at Ivor Searle, I had a little spare time. Dangerous thoughts began to form. With the heads off, should I consider getting the pistons out and replace the rings? With the sump off it wouldn’t be too difficult… and all the crankshaft bearings can be replaced without removing the engine. My little exhaust leak fix had morphed into a full engine overhaul! I don’t regret being thorough, though, as the fully freshened-up engine should be good for many more miles.