There is a lot of disparate info floating around out there about the puch Athena 45 reed cylinder, small reed, AJH, and the AJH clones ‘DMP/single exhaust’ vs. ‘1977/Dos house brand dual exhaust’. I’m trying to offer a countersunk head setup to make these work, but the information on these things is confusing and incomplete. I’d like to do a blog/wiki writeup on all these but I don’t have the kits handy and I only have some of the information, if anyone can help fact check me or add anything they know/remember it would be great to get all this knowledge in one place. I’d just start with a wiki entry but this seems to get more attention on the forum, so lets discuss and I’ll put it all together into an article.
The ‘real’ AJH/ athenas have been around a long time, mopedwarehouse and heeters and the shops supplying the moped scene back before 1977 used to sell them with the Amal carb in a kit. Quality was top notch, really nice fit and finish. Probably selling dead stock from the 90’s. Sometime around 2005 they went out of production or became unavailable and the only kit you could get from Athena was the ‘small reed’ 70cc kit. The old ones had this weird AJH marking cast into the fins:
Then at some point, maybe around 2008 or so, they came back on the market but they were noticeably lower quality. Packaging was different. This might have been because AJH was making the old ones and Athena bought them out? I don’t know. I would hazard a guess that they went from European manufacture to Taiwan.
The small reed athena’s have never been too popular AFAIK, I don’t know much about them. Perhaps this was a kit that Athena was making historically and when AJH went out of business they bought that tooling for the ‘big reed’ kit? For the time that the AJH was off the market, the small reeds were the only ‘athena reed kit’ being sold. These are using the same reed block as the 80cc athena sachs. The big reed athena uses MB5 reeds, but there are only 2 petals in the reed block so flow area may or may not actually be bigger than the 'athena' style reed.
Then we skip a few years to 2015 ish when the clones showed up on the market. I don’t exactly remember how or when they showed up but around the same time there was a DMP branded cylinder coming in a kit with reeds, intake, piston, cylinder and no gaskets, and a ‘1977 house brand’ split exhaust version of the kit. A good thread came out around this time <LINK> and a few sources international and domestic were providing similar versions of the same kit.
Both DMP and ‘House Brand’ (lets call them ‘Single exhaust clone’ and ‘split exhaust clone’ for clarity) are characterized by these really poorly formed ports, spacing issues, a ridiculously too big exhaust, poor finish, etc.
They appear to have very similar reeds, intake, piston to the genuine Athena. The Single port clone/DMP kit that I got has no bolts, studs, crappy circlips, no gaskets.
The porting on the ‘single port clone’ I have is 46.5 mm from bottom of exhaust to top of cylinder (aka, stroke) the transfers are a bit higher. Transfers are pretty ok size and shape but they have some gnarly casting boogers… the exhaust is a really crummy shape, way too tall with too much blow down, but with aux ex. Ports it could be made to work and a lot of clean up on the intake.
Anyhow, that’s where I’m at, I’m probably not going to run this cylinder, just picked it up to prototype a sunk head to make these workable. I’m going to return it and grab a split exhaust kit which I am going to build on to an A55 bottom end. I’ve cut a handful of heads for these for people over the years with really good results, but its been really tough to get something that works across the board. I’m looking forward to be able to put out a head that can take care of the port spacing issue and make this a really gnarly little budget blaster. Getting it for <$150 with the intake and reeds and everything is a pretty rippin deal if you can make it work.