OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Kirby H4-4A engine rebuild

I own a mid-70s Scott Bonnar cylinder mower (Type 45) fitted with a Kirby H4-4A engine. When I got the mower the engine wasn't running, and hadn't run for some years, but would turn over. The previous owner did say that it was a bit smoky when it did run. The rest of the mower wasn't in bad nick, so I decided to undertake a restoration, including an engine rebuild.

The first issues I encountered were identifying the engine and then sourcing parts. To cut a long story short I discovered that the engine was based on a Lauson (US) model. Lauson were a manufacturer of small engines who were bought out by Tecumseh (US) who then licensed Kirby (Aus) for local manufacture and parts distribution in Australia. Kirby has long since folded but parts are still available in the US.

Basically these engines are quite robust and well built but had a reputation for being a bit finicky and, when running, a bit agricultural. Over the years, most owners with mowers fitted with these engines replaced them with either Briggs & Stratton engines or more modern Japanese equivalents (eg: Honda G100). Being something of a masochist, I decided to try to resuscitate this motor.

This is what I found -

Kirby 4H-4A = Lauson (Tecumseh) H30(A)
Bore 2 5/16" (58.74mm) x stroke 1 13/16" (46.46mm) giving a displacement of 7.61cin (125cc).
Horsepower 3.00
4 cycle L-head (side valve) vertical, single cylinder.
Air cooled
Cylinder is die cast aluminium alloy with a shrunk in steel liner
Piston is heat treated aluminium
Con rod is aluminium alloy
Piston rings are 1 x compression, 1 x scraper and 1 x oil control ring
Crankshaft is heat treated cast iron
Top bearing alloy, lower bearing ball race.
Cylinder head is aluminium alloy
Magneto ignition

So far, fairly standard.

After lots of research, I ordered parts from MFG Supply (http://www.mfgsupply.com/) in Wisconsin, US and Outdoor Distributors (http://outdoordistributors.com/index.html) in Alabama US. Both were very helpful, priced well and delivered overseas at reasonable cost. Locally available parts were the oil seals, roller bearing and new muffler.

I've attached a couple of photos of the parts.



Oil seals, bearing, carby gaskets, crankcase gasket and rings.



Coil and plug lead, valves, points, needle valve and main jet and head gaskets.

I will continue the story with more photos soon,
Chris