Doing It: Dunstall 810 Kit by Sandy Roca

Taken from the November 1972 issue of Cycle Magazine.

Page 1 | Page 2 | Page 3 | Page 4

pic 13
pic 14
pic 15
pic 16
pic 17
pic 18
pic 19
pic 20
pic 21

One of the most direct ways to soup-up a motorcycle engine without destroying its tractability is to enlarge its displacement with a bigger bore or stroke. Or, as they used to say until the smog rolled, "There's no substitute for cubic centimeters." While stretching the stoke of an engine can lead into an alley of problems, a bore increase is an easy and effective way of increasing horsepower.

There are a number of drop-on, bolt-in big bore kits available and the procedure for installing most of these kits is well known. A 810cc conversion for the Norton has recently been developed by the Paul Dunstall Organization in England and you can now buy it through Dunstall outlets on this side of the brine. It fits all 750cc Commando and Atlas engines. The installation is a fairly straight-forward wrench and screwdriver job, but there are a few curves in the operation we should warn you about, so read on.

Preliminaries: Tools
Don't be alarmed at the tools we've laid out; they are not all essential, but they do make the job easier. At the very least you should have the following (photo 1):

  • Feeler gauge
  • Norton tool kit
  • Small metal file, or thin flat stone
  • Small needle-nose pliers
  • Norton deep socket for head bolts
  • 5/16" BSF - 1/4" W box end wrench
  • 3/16" allen key
  • Small butane torch or something to heat old pistons for removal
In addition it's a very good idea to have the following, but you could probably scrimp by without them (2):

  • Norton Commando (or Atlas) Workshop Manual
  • Torque wrench & attachments
  • Small vice
  • Circlip pliers
  • Piston support (two one-inch strips of half-inch plywood will do just fine)
  • One good friend
Finally, optional niceties (3):
  • Piston pin press (not necessary if you heat the pistons well)
  • Ring compressors (nice if you don't have six hands)
  • Piston ring expander (for 5-thumb types)

Preliminaries: Parts
The Dunstall kit is pretty complete as shown (4), but we needed to buy a cylinder base gasket (5) that was not supplied (and should have been considering the near $290 retail cost). Omitting the gasket will cause a lot of oil leakage, so don't try it. If you are stranded on a Sunday without it, you can make your own (by taking an impression from the crankcase boss after removing the studs) but don't forget to punch out the oil hole (6). Frank Camillieri, Service Manager / Webmaster / Last Updated 24th February 2000