Triumph GT6 MKIII
Nigel battled to make his Triumphs less incontinent!
Oil leaks have plagued the front of the 2.5-litre engine that I built for the GT6 a couple of years ago. Despite what I thought at the time was a careful build, it’s been disappointing to see the pristine new engine take on a grimy appearance as oil oozed out, spread and collected dirt.
The problem hasn’t been a single leak, but two. First there was the timing cover oil seal, which I reported last year had been cured by following Chris Witor’s advice to fit a good old fashioned leather seal in place of the usual rubber lip seal. Chris has found that, for no obvious reason, some Triumph sixes are ‘persistent leakers’ from this particular seal and the more forgiving leather seal cures the problem. So, it was with my engine; after three attempts with a conventional seal, the leather version has kept the oil inside the timing case very effectively.
Frustratingly, there’s still a leak from the front of the engine. It runs down the front of the sump and back along one side of the block and sump flange. With the timing case sorted, the two most likely culprits are the gasket behind the engine front plate or that old Triumph bugbear, the sealing block that bridges No.1 main bearing cap, abutting the front plate and sump. Both are potentially awkward jobs, but I fervently hoped it wasn’t the sealing block. The fine threads for the sump bolts often strip in Triumph’s original alloy sealing block, and I had invested in a stainless steel replacement, fitting it carefully during the engine build. Replacing this sealing block on a GT6 really requires engine removal to get good enough access to do the job properly; pulling the engine out again is not a prospect I would relish.
A hopeful endeavour
So, more in hope than expectation, I began replacing the front plate gasket. First the radiator has to come out, followed by removal of the fan and crank pulley. The pulley bolt on the crankshaft’s nose is always tight, but my battery impact wrench made short work of loosening it and the pulley slid off the shaft without a struggle. Next the water pump housing was removed to give access to the timing cover.
With the timing cover out of the way, I carefully aligned and marked the timing gears before removing the sprocket from the camshaft, along with the timing chain. Next comes the camshaft keeper plate then, at last, the front plate screws can be undone and the front plate lifted away from the block.
I had previously fitted the front plate gasket with conventional jointing paste on both sides, so
was surprised to find it came away almost whole, having expected the gasket goo to glue it firmly in place. The gasket seemed quite oily too. I took this to be a positive omen, that it may indeed be the source of the oil leak.
Right on time
I cleaned up the block and front plate ready for reassembly, but there was also another little job needing attention. Some of the timing cover screws are threaded directly into the front plate. Original front plates are made of steel, and the fine threads are strong enough to cope. Becoming a little obsessed with engine bay bling, I had fitted an alloy replacement plate when building this engine, and one of the timing cover screw threads had stripped, necessitating a steel insert thread repair. This is tricky, as the alloy plate is only 5mm thick and normal 5/16in UNF thread repair inserts are about 8mm deep.
I drilled and tapped the hole for the insert, which had to be carefully trimmed down to just under 5mm to fit within the thickness of the plate.
Thread repair successfully completed, I set about reassembling the engine. This time, the new gasket was coated on both sides with Reinzosil high temperature automotive silicone, which I’ve found very effective in sealing difficult joints before. It’s sufficiently viscous to stay in the joint while curing, and sets to a firm rubber-like consistency with excellent strength and adhesion to gaskets and clean metal. The front plate was lightly bolted in place, hopefully with enough pressure to achieve an even coating without squeezing the sealant out of the joint.
Next day, I fully tightened the front plate bolts then refitted the timing sprocket and chain without disturbing the camshaft’s position.
From there on, reassembly was straightforward. I refilled with coolant and fired up the engine to bleed air out of the cooling system, before checking for any obvious leaks and going out for a test drive.
Back home after a ten-mile run, there is absolutely no sign of oil leakage, and I’m hopeful this problem is now solved, without the ordeal of replacing the sump sealing block.
Stop press: I’ve just been for a spirited 20-mile run, and the front of the engine is still bone dry. practicalclassics@bauermedia.co.uk