Tube Trainer
Neil Cocksedge is building a Triton using a 1953 Triumph Thunderbird bottom end and a late 650cc barrel and head. He has a selection of tappet guide blocks and pushrod tubes, but is unsure which combination of these to use. As these are a premier source of oil leaks, I decided to ask Arthur at Triumph specialist Rockerbox for his opinion.
Arthur says the best system is the 1970on type with two O-rings and a flat seal. The bottom of the pushrod tube is rolled to provide a housing for an orange O-ring – it’s softer than the black O-ring which is more heat resistant and fits the cylinder head end – don’t muddle them up.
Arthur lightly assembles the head to the barrel with a head gasket (but no seals) and measures the up-and-down movement of the pushrod tube. He then measures up the seals and looks for a 30% crush, so there’s enough squash on the seals for them to seal properly, but not so much that they squeeze out of place or split.
Problems arise when the cylinder head doesn’t match the tubes – heads that use O-ring seals have a deeper counterbore (or recess) – or if the head has been skimmed sometime, so you may need thicker or thinner seals. There are a couple of sizes available, although for skimmed heads a thicker gasket is also available. Arthur says you can deepen the counterbores in the head, but beware as they’re machined slightly off-vertical to match the angle of the tubes.
Finally, bear in mind that silicone is a lubricant and sealant can cause the seals to squeeze out. Personally, I stick one side of the seal down at a time, leaving the sealant to set overnight. Then it will stay put when you tighten the head down.