I don't think they're brand names. The companies that exist called AE or YE don't seem to be car engine manufacturers. AE supplies components, and this surely can't have anything to do with the Yorkshire Engineering Co., which makes or made railway engines. But it's not uncommon for car manufacturers to identify different types of engines with two-letter codes. Here's a document on Pontiac, for example:

"400 1968 WA,WB,WD,WE,XH,YC,YD,YE engine"
http://www.avrosystems.co.uk/realsteel/section5.pdf

Or there's this one, on the Volkswagen Golf, with three-letter engine codes — same idea:
"VW Golf Mk3 1.6,Passat 1.6 Distributor (Engine Codes-AEK,AFT)"
http://www.ebay.co.uk/itm/252090889666?clk_rvr_id=8996795139...

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Note added at 27 mins (2015-09-22 14:30:47 GMT)
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Of course the practical outcome will be the same: they can't be translated.

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Note added at 47 mins (2015-09-22 14:50:19 GMT)
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OK. The same goes for any kind of manufacturered vehicle or equipment with an engine, whether it's a car, a truck, a loader, a crane, or whatever. The engine will normally have a code.

If you know the manufacturer and the model of the equipment you could probably confirm that they are codes. But for translation purposes, as you say, it doesn't really matter; they will be left as they are.

I don't believe they are generic types of engine. AE can stand for application-engineered, but that's unlikely to be relevant here, and I don't think there's any such meaning for YE.