Sachs 505/1a performance
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Introduction
The Sachs 505/1A is the most common of the 505/504 series engine. It's distinguished by the tapered cylinder marked 40kph. A stock horse power rating of 1.8 puts it on par with most Puch E50 engines and thus deserves a second look as a potential platform for tuning. Though there are not many kits for these, there is some potential nonetheless for a little creativity to take the place of bolt on parts and a thick wallet. During the course of this article I will be referring to the 505/1A, though everything mentioned should apply to the 504/1A as well, but for the sake of clarity I shall only be using the 505 designation.
Regarding the B,C, and D Engines
These are the less common variants on this design, and will not be addressed in this article except for in the following:
505/1B If you have one of these heavily restricted engines you can replace the header pipe and carb to convert it to a 505/1A and then proceed to the following sections
505/1C some things apply to this engine it shares it's cylinder with the 505-1D. You can install the "A" cylinder on this as well but you would not want to, because it would be a downgrade.
505/1D This engine produces 2.7HP stock! It has a better jug, carb and a longer stroke than an "A". The C and D also have a flat intake mount which allows them to be flipped forward to easily fit a 15 Bing or SHA carb. The C/D jug can be swapped in place of the jug on your 50x/1A or B for easy performance gains. The mounting holes on the jug are slightly different but can easily be drilled out using a base gasket as a guide.
Fuel System
The stock setup of the 505/1A features a 14mm intake with a "Square" Bing 12mm carburetor. It's different from the Bing used on Puch as it has a shallow square float bowl secured by 2 screws -- much like a Dellorto -- as opposed to a round threaded bowl. The shallow bowl allows it to clear the engine case, and this carb is therefore not easily replaced. Unlike other engines, the intake cannot be flipped toward the front on this engine as the mounting flange is angled. It also uses jets unique to the "square" Bings. Square bings are also found on some late model Puch Korados. The D engines have a higher-performance 12mm carburetor which doesn't use a needle, and if available can make a good replacement for stock "A" carbs. The B uses a nearly worthless 10mm version.
Boring The Stock Carburetor
The square Bing can be bored out to 14mm, but to allow for some margin of error, I recommend 13.5mm. This carburetor body can be bored with ease as it can be quickly stripped and it will sit nice and flat on the bed of your drill press. It also does not have an idle circuit in the traditional sense, rather it has a notch cut out of the back of the slide allowing fuel to be drawn from the main jet. This means that you won't run the risk of closing off your idle jet, nor will you need to re-open it with picks. Unfortunately, there are few or no jets available for it (check handybikes for type 85 bing jets), so you must drill out your jet. Alternatively, you can use the jet holder from a round Bing and then use standard Bing jets, the end result is a robust and easily serviced 14mm carburetor. For detailed instructions on boring your Bing, see Over Boring Carburetors 101.
In conjunction with boring the stock carburetor it is also possible to convert your old square Bing carburetor jet into a jet holder. This enables you to use other manufacturers jets in your Bing carburetor, which means you are capable of serious tuning without replacing your carburetor. This has been successfully completed with a conversion to 5mm threaded Dellorto jets (used in SHA series).
Mounting a Dellorto SHA:
The Dellorto SHA is a very close fit, and with some simple modification to the intake it will not only fit on the engine, it will also still fit under the side covers. There are a couple different ways of doing this,but before you start check the fit of the carburetor as due to slight model differences and casting variations it may already fit. The first way requires no skill or really anything other than wrenches. You start by removing the two intake bolts and washers. Next you remove the intake and reinstall it with the two washers, both on the rearmost bolt between the intake and the intake port. This will angle your intake perfectly, allowing the carburetor to slip on easily, clearing the top of the engine. The last step is resolving the problem with this method; that's sealing the big gap left over. This could be filled with plumbers putty or a similar compound so long as it is both heat and gasoline resistant. Plumber's putty may be neither so read your labels well!
The second method will take a bit more time and is more desirable as the likelihood of sealant breaking loose and being sucked down the intake is much less. This involves making a spacer, for this I chose 1/4" Masonite (basically the cardboard stuff that goes on the back of your entertainment center). It's derived from paper pulp so it should compress and behave the same as a paper gasket. You start by tracing around the base of your intake and then cutting it out with a fine toothed hand saw (hack saw works, coping saw works even better). Once it is cut out and trimmed up nicely, get a stamp pad and push your CLEAN intake into it and then "stamp" the whole pattern onto the masonite. Start by cutting out the center whole by drilling in the middle of it then grinding the rest of the material off with a Dremel. Next use a C-clamp to fasten the spacer to the intake and a piece of scrap wood underneath making sure your holes are lined up. You will now use the bolt holes in the intake as drill guides so as to attain the proper angle, choose a close fitting drill bit and drill through the spacer and into the scrap wood. Once you've cleaned up all the little "fuzzies" and bits of peeling paper, your intake spacer will be finished! Now you need only mount up your intake with your new 1/4" thick gasket. This moves the carburetor up and will clear the engine case and should clear the frame. In some cases the spacer may require some tapering to achieve the desired angle. This can be done by sanding or any other appropriate grinding method. It is also worth noting that if you are using a 15mm or 16mm carb, you will need to further modify the intake. Simply grind down the diameter of the intake where the carb attaches until the plastic sleeve that came with the carb slides on with no resistance. At that point use a sealer, or glue of your preference to fix the sleeve to the intake creating a perfect sealing mount for your new carb. Having done this on my G3 I found that it still took some fiddling to get it to clear the frame, but it does. In the case of other frames the fit may require a thicker spacer to be made or may have no trouble at all. The only other modification required at this point is to drill a small hole in your side cover to run your throttle cable. For the C and D intakes, the mount is flat so they won't fit on an A jug. With the C/D the intake has a 14.5mm ID, and can easily be flipped forward to fit an SHA or similar carb, but may require cutting the top-right most cylinder fin.
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SHA 15 fits with little spacing required. A 3/16ths or so cork gasket works well. The SHA 16mm is too big to use without porting the intake as the inner diameter of the intake is only 15mm or so. Use a length of pop can for a shim between the carb and intake because the original plastic one is too thick. The pop can will need to coil around a creating a few layers to be thick enough. A rubber o ring from the autoparts store will seal the carb to the intake. Jetting should start mid 60s. Plan on getting a 7x5mm knarp to adjust the throttle cable on the throttle side. The carb side fits well enough on the stock cable. The idle screw can only be accessed with a 6mm wrench as it is really close to the frame. A lever choke may also be inacessible without bending the lever.
Cylinder Porting
The stock porting of the 1A cylinder is adequate in most ways. The transfers are good sized and the intake port is certainly large enough considering that the largest intake pipe for this engine is the 90 degree 14mm. The exhaust port though can be raised by 2mm. This is probably the most significant difference port wise between the "A" and "D" cylinders and is an easy adjustment to make. Just make sure to take your time. Doing this requires a fairly significant jetting change.
Compression
This is a stumbling block for this engine as Sachs uses a one-piece cylinder and head. To increase the meager 8:1 compression, one can leave out the base gasket. However, this will retard your port timing, so this if it is done it should be done in conjunction with porting. For any more increase to the compression ratio the cylinder base will require milling.
Also, the 505/1D engines use a slightly longer stroke crank, which increases both engine volume (47cc to 49cc) and compression (8:1 to almost 10:1). A D crank can be swapped into and Sach 504 and 505 cases. The longer stroke makes more of a difference in kitted bikes, where the increased bore of the cylinder combined with the increased stroke gives more of an engine volume boost.
Exhausts
If you can weld, you can put any exhaust on any bike. For those who can't, the options seem to be rather limited. The good news is that two piece exhausts for Tomos can be used with very little difficulty. Assuming you have the non-restricted exhaust, (26mm) you simply unbolt and remove the muffler from the header pipe, you then cut down your header pipe to the appropriate length (shorter = higher RPM or simply just match your 2 piece exhaust's header) and slide the expansion chamber on to the header. Of course its recommended that you measure diameter first so that you don't chop up your stock exhaust only to find the new pipe won't fit. From here the stock mounting bracket can be replaced with a hook or hoseclamp to support the back of your exhaust. A piece of 1/8 inch steel would be more than sufficient.
The Gianelli Circuit pipe has come back into availability recently, but suffers from a number of issues notably it's high price tag, low performance gains, and serious difficulty mounting it reliably. Ask anyone with one, they fall off ALL THE TIME.
It's also possible now to find 2 part exhausts through treatland.tv and elsewhere with a 26 or 28mm sachs header that will clamp on the same as the standard stock exhaust. You can then buy clamp-on expansion chambers like those from Jamarcol for a 28mm header and clamp that on directly.
Peugeot and Vespa exhausts also use a similar design where the exhaust clamps onto a lip on the exhaust of the cylinder. Unfortunately because of the angle of the cylinder, most Peugeot exhausts extend too far out and on a Sachs will nearly hit the ground. Spring mounted SPX exhausts allow most maneuverability and clearance. The springs can be hooked to the cylinder itself by drilling holes in the bottom of the cylinder fins. Many people have had good results using the Peugeot SPX Alsil Quich pipes, which are inexpensive and fit snugly over the stock Sachs header lip, and require only the spring mount holes and a custom rear exhaust mount as described above.
Gearing
The gearing on the Sachs mopeds is fairly limited. The stock gearing is quite low, as is typical of stock mopeds, and gearing up can be a good way to get the best gains from your better performing engine. The front gear is always 11 tooth, and no smaller gears exist, however 12 and 13 tooth front sprockets are readily available. The 12 tooth can fit directly on and gives actually a quite significant change in gear ratios. Moving further up to the 13 tooth option requires grinding of the case in order for the chain and larger gear to fit. This is best done with the cases split in order to carefully watch the depth of the grinding and prevent going all the way through to the clutch cases. Approximately 3mm will need to be removed at the deepest point (right where the 2 case halves meet) and also some meat will need to be removed from the tab behind the sprocket.
As for the rear gears, most Sachs mopeds use the Italian "Z" style wheels and can interchange those sprockets. A few different rear sprockets are available but to get much smaller on the rear one must find either some Derbi sprockets or make some. Tomos rear sprockets can be made to work by elongating the bolt holes on the sprocket and may also require widening of the center hole, but give a very wide range of gearing to choose from.
Performance Cylinder Kits
This is getting into the realm where you shouldn't need to be reading about this in the wiki, however here's some info regarding kitting your Sachs.
Athena 50cc
This is a simple 38mm 50cc kit for your Sachs. It is piston port and comes with a 15mm intake and 28mm exhaust. It can also accept bolt-on exhausts and can fairly easily be made to fit Minarelli, Garelli and Puch exhausts, as well as the standard Sachs options using the included adapter. This is basically a better ported version of the Sachs D motor, and is arguably not worth the cost but does provide a simple upgrade or replacement for stock. Uses long reach plug.
Athena 70cc
This is a piston port 45mm 70cc kit by Athena. It also includes a 15mm intake which fits the 15mm round Bings and can also easily be adapted to the Dellorto SHA. Larger intakes are available from MLM to fit larger carbs. It is a rather mild kit but can easily approach 50mph. At this point some clutch issues may arrise but the 70cc kit is typically regarded as the biggest you can go without seriosusly modifying (or rapidly deteriorating) your clutches. See: Sachs clutch modifications. Uses long reach plug.
Athena 80cc Piston Port
48mm 80cc kit by athena. You'll need to buy a larger intake from MLM or elsewhere. Not a great option and a pointless bridge between the 70 piston port and the 80cc reed kits.
Athena 80cc Reed
This is the mother of Sachs kits. At 48mm it's the biggest sachs kit available and features the Athena reed intake. You will NEED to replace the metal reeds with carbon fiber, the metal ones notoriously fatigue and break causing catastrophic cylinder destruction. It can also accept bolt-on exhausts and can fairly easily be made to fit Minarelli, Garelli and Puch exhausts, as well as the standard Sachs options using the included adapter. Flanged intakes are included for the 15mm SHA and 19mm PHBG and can be made to fit other carbs by using rubber adapters. This kit will require clutch modification or at least periodic removal and re-buffing of the clutch pads.
Autisa 64cc
This is another piston port kit by Autisa. It uses the stock 14mm intake which fits the 15mm round Bings and can also easily be adapted to the Dellorto SHA. It is a fairly exciting kit for its size and well ported with speeds easily in the 40s. Looks externally like D, it's a very reliable kit; however the availability is extremely limited.