Harley engine gets attention
It’s taken a while, but Project Harley is making progress. After weighing up the pros and cons of either re-sleeving the damaged front cylinder and fitting new rings to the original pistons or buying new oversized pistons and reboring both cylinders, Harley-davidson technician Gavin Cupit suggested the rebore route.
Krazy Horse in Bury St Edmunds (01284 749645) supplied the S&S pistons plus base gaskets and their machine shop took care of the rebore.
All post-1984 Harley engines feature aluminium cylinders fitted with steel liners. On these models, when the cylinder head is torqued down, the cylinders distort slightly. This distortion must be mirrored during the cylinder machining processes. This is done with torque plates – steel plates with the cylinder sandwiched inbetween. All Harley-davidson Evolution Big Twin, Evolution Sportster and Twin Cam engine models must have their bores machined (and measured) between torque plates. If they’re bored without them, when the heads are torqued down the liners will go barrel shaped. Piston slap, poor compression and oil consumption will follow.
The big bore 93 S&S stroker kit (raises capacity from 1340cc to 1524cc) also requires some machining of the crankcases to allow for the increased throw on the crank. After careful inspection, Gavin suspects the performance upgrades were made to the FXR from new, giving the modifications a thumbs-up with no further work needed. With all the other parts inspected and bearings and gaskets ordered, it’s just a case of removing all the peeling chrome plate and corrosion from the cases and bolting it all back together.
Inside the machined crankcase, ready for... ... the S&S crank with increased throw Torque plates replicate the effects of engine torque