Agree with the comments above. Some of the earlier Diesels from 'Medalist - Universal" were often termed Atomic diesels, mostly in conversation. I have not seen many spec sheets that show them as Atomic Diesels but have read literature referring to them as such. Most if not all of the Universal diesels are based on Kubota blocks and are very reliable in my experience.
I myself have replaced my Atomic 4 gas engine with a Universal M25 recently and am very happy. I get most of my parts from
TractorSmart.com or from a local Kubota dealer. All you need to do is find out which Kubota bolck your engine is based on and then find a Kubota part list for that engine. My M25 is based on a Kubota D-850 block.
I am pasting a excerpt from the "History of Universal engines". IT will also tell you which Kubota blocks these engines are based on.
If you ever have any difficulty finding a part for any Universal engine, feel free to PM me.
Hope it helps.
"The first Universal diesel was advertised in 1976. Designated the Model 5416, it was a 45 cu in, 16 hp, 2 cylinder, based on the Kubota Z-751 block and built from 1976 to 1982. Approximately 1,000 were sold. It was replaced by the Model M20, which was produced in 1982 and 1983. Approximately 230 were sold.
In 1977 the Model 5411 was introduced. It was a 31 cu in, 11 hp 2 cylinder raw water cooled diesel, based on the Kubota Z-500 block, and fitted with a Hurth transmission. The 5411 was built from 1977 to 1982. Approximately 2,900 were sold. It was replaced by the Model M15, which was produced in 1982 and 1983. Approximately 370 were sold.
The Model 5424, a 68 cu in, 24 hp, 3 cylinder, based on the Kubota D-1101 block, was built from 1977 to 1983. Approximately 1,050 were sold. It was replaced by the Model M-30, which was produced from 1983 to 1987. The Model M-30 was the same size, but later M-30 engines were based on the Kubota D-1102 block. It was built from 1983 to 1987. Approximately 400 were sold.
The Model 5421, a 52 cu in, 21 hp, 3 cylinder, based on the Kubota D-850 block, was built from 1978 to 1981. Approximately 1,000 were sold. It was replaced by the Model M25, which was produced from 1981 to 1986. Approximately 3,650 were sold. It in turn was replaced by the Model M-25XP, a 57 cu in, 23 hp, 3 cylinder, based on the Kubota D-950 block, built from 1986 to 1999. Approximately 3,100 were sold.
The Model 5432, a 91 cu in, 32 hp, 4 cylinder, based on the Kubota V-1501 block, was built from 1978 to 1982. It was also called the Atomic diesel. Approximately 650 were sold. It was replaced by the Model M40, which was produced from 1982 to 1998. The Model M-40 was also a 4 cylinder model, and the same size at 91 cu in and 32 hp but it was based on the Kubota V-1502 block. Approximately 360 were sold.
The Model 5444, a 115 cu in, 44 hp, 4 cylinder, based on the Kubota V-1902 block, was built from 1980 to 1982. Approximately 280 were sold. The Model 5444 was replaced by the Model M50, which was built from 1982 to 1997. Approximately 520 were sold."