13084 W. 8th Avenue, Chico, California 95926
This article tells of the restoration of a Holt Model 60, #1838, manufactured in 1913. It was purchased by the Hahn Brothers for field and belt use on their farm in Arbuckle, California. The tractor never left the farm until the estate sale in 1980; then it was brought to Chico to be restored. As near as can be determined, the tractor was retired in 1924 and replaced by a new, full track Caterpillar 60.
The decision to buy the Holt tractor was made after a close examination of all parts that would be difficult to replace or rebuild. They were found to be in acceptable condition and usable after a thorough cleaning. Fortunately the tracks and drive mechanism were in new condition with many pieces having been replaced just prior to retirement. The overall appearance of the tractor was rather poor as there were no traces of paint anywhere; this was understandable since the tractor was parked outside for 46 years.
After moving the Holt to shops, a decision was reached to rebuild the engine completely before any further dismantling of the tractor.
A little research on the history of the engine revealed it was not until the latter part of 1913 that Holt absorbed the Aurora Engine Company which had been Holt's supplier until this merger. The engine in this tractor is an Aurora without the common markings found on all later Holt engines. Usually, Holt is cast in all four crankcase doors and the Caterpillar logo is cast on the exhaust manifold and a small brass tag on either end of crankcase with nomenclature. This engine has none of these.
The engine was partially dismantled in the frame to gain clearance for removal without disturbing the canopy. The engine was entirely torn down and found to be completely worn out. The crankshaft was turned .010 undersize on mains and rods after being straightened. The main bearings were found to be in good condition. Our machine shop could not handle the next step; so it was sent out to a truck engine shop. Some main bearing shims were removed and bearings installed in crankcase, torqued down, then line-bored. The block was boiled clean, power wire brushed inside and out, then painted inside with an electrical sealing paint.
The camshaft was found to be out of tolerance and was sent to a cam shop for grinding. The cam follower faces were grooved so they were ground flat and the stem turned .010 under. To compensate for this extra clearance, the worn lifter bores were brazed up and machined in a milling machine to get back to tolerance. The timing gears, unlike those in later Holt engines, are exposed with just a safety guard and are lubricated at the whim of the operator. All three gears were in acceptable condition.
The engine had a certain amount of water in the crankcase allowing condensation to rust all parts, the bottom of the cylinder barrels particularly. There was .050 to .060 taper requiring the individual cylinder barrels be resleeved as oversize pistons weren't available. The pistons, not being cam ground, were turned .030 undersize to make them concentric with the ring groove. Ring lands were enlarged from 3/8' to 7/16' in width to obtain a uniform size with a square corner for good ring seating. The bore is 7' in diameter. Sleeve material was purchased from a firm in Los Angeles with the dimensions allowing for the cylinder to be bored out for acceptance of the new sleeve. A small ridge was left at the top of the cylinder to stop any upward movement of the sleeve; the bottom end was secured with three nickel tack welds. After boring, the cylinder was heated and the sleeve frozen for an interference fit.
The connecting rod bearings were found to be beyond repair; so they were poured with 4X diesel babbitt and bored in a milling machine to obtain proper clearance.
The piston pins had some wear; so it was elected to grind them round. Grinding was necessary because the pins were chill-hardened and would not machine. Proper mill work was done to the connecting rod bushing to fit the pin.
It was necessary to obtain .030 undersize rings from a custom ring manufacturer. Vent holes were drilled in the oil ring grooves to drain oil ring lands. The valves were made with a steel stem and a cast iron head which was threaded to the stem. Most heads were loose on the stems; so it was decided to affix the head to stem with nickel welding. The stems were turned .010 undersize to remove worn areas. The valve faces were ground in a lathe to the proper angle. A special mandrel was fabricated for an engine shop to grind seats. All valves were lapped to check seat width and obtain a tight seal. The valve guides, which are replaceable, were removed from the heads and new ones fabricated from high density cast iron billet material. The oil pump shaft and top brass bushing were worn and so replaced. The oil pump unit was in good working order and was reinstalled after a boil out and glass beading.
Before engine work was commenced, a glass beader was purchased. Every engine part, with the exception of the crankshaft and crankcase, was glass beaded and all pieces separately primed with Rustoleum Primer. The rocker arm bores and shafts were worn; so again, the rocker bores were brazed up and turned to standard and fitted to new rocker shafts. Push rods were in good order. The water distribution tube, which was fastened to each head and was the conduit for the hot water to return to the top of the radiator, was broken at one time and was repaired on the farm. The tube was cast brass so some concern was given to concealing the repair as the tube was polished. It was decided to braze up the broken area and have the piece brass plated to assure a uniform color.
The engine was equipped with a 1?' Schebler carburetor. The float bowl was brass and had a good many hammer marks, evidently to unseat a stuck needle valve. Many hours were spent removing these dents and yet obtain a round, smooth appearance. The throttle valve shaft and housing were worn very badly. These were repaired by bushing housing and silver soldering the ends of the shaft, then turning for proper fit. The cork float received three coats of shellac. The compensating air valve leather disc had, of course, deteriorated, so a new one was machined from a piece of 3/16' leather. After all pieces were polished, the unit was assembled and lacquered.
The tractor engine was equipped with a KW magneto, model HK. The mag was completely disassembled and evaluated and found to be in poor condition. A new coil was purchased from Standard Magneto in Chicago. All bearings were replaced and magnets recharged. All brass pieces were polished and lacquered with the steel pieces painted with a black wrinkle finish. This particular mag used a high tension terminal that was 90° to the cap and made of a phenolic material, with the tang and wire connector being of copper. Usable terminal could not be located, so new ones were machined to an exact duplicate of old. High tension wire with the correct tracer colors was purchased from an auto restoration firm in Los Angeles.
The shaft to drive the magneto, together with drive gear at one end and Oldham coupler at the other, were supported in two split babbitt bearings. The babbitt was missing in one bearing and badly worn in the other, plus the shaft was wasted. New shaft and bearings were in order here.
Checking the external governor, which was integral with the camshaft, revealed a broken spring which was housed in the hollow end of the cam. Also, all pivot linkage on the fly balls and throttle linkage was broken or badly worn. All were bushed back to standard and fitted with new pins. The brass sight gauge, which was fastened to the left rear corner of the crankcase, had a glass plate on either side to show four streams of oil to crankcase. It was polished and lacquered as were the priming cups.
The compression release cocks were in bad shape, mostly from being hammered on, and they required a good deal of die grinder work and polishing to achieve a good appearance. In the interest of keeping the engine clean, a copper manifold was fabricated and plumbed to each compression cock with a short piece of hose with the manifold routed to the ground. After going to some trouble to keep the engine oil leak free, it was decided to machine the compression cock stem to accommodate a 1/16' cross section of ring on each side of the release hole to seal this device so no oil leaked at starting or when running. This was Fred Heidrick's idea, and it works perfectly. This is the last model year for engines without starting bar holes in the flywheel with exception of all wartime Holts.
A heavy stand was made at this time to support the motor as it was in the tractor in order to facilitate assembly and to run in and dyno test.
After the engine was assembled, it was noticed that the three clutch bosses cast in the flywheel were badly worn. These were built up with nickel rod and hand ground to original dimensions.
With cooling water furnished and a gravity gas system, the engine was started on the second pull. With compression cocks open and properly primed, the engine generally starts with the second pull.
The engine was run at moderate speeds for several hours to seat the rings and to determine if there would be any problems. A shaft was machined to hook a dynamometer to the crankshaft. The engine turning 500 RPM was too slow to get a stall horsepower from the dyno, but 125 HP for 15 minutes was observed. The engine was run for several hours at varied speeds and was deemed to be satisfactory. The engine received a coat of Rustoleum Forest Green paint, the original factory color.
A total of 317 hours was expended on this engine restoration project; of this 141 hours was machine shop time.