Sachs 505 c/d Debate

I asked some time ago if there was another square head sachs motor, on a 505, that was not wedged shaped , that was not a D head.

Confusion reigned.

Lots of strong opinions, and lots of people who felt strongly.

I dont even remember who, but someone said all square heads were D, and someone else said only a D was a 30 mph bike.

Someone else said there was no such thing as a 505/c

Im all confused.

This is the balboa.

It says 30mph on the column.

It is a 505

it says 505/1C on the case.

It has the big square non fluted head.

It pulls like a monster, its got the bigger manifold, and a big exhaust.

Now im really confused, cuase if there is not 2 dif square heads...what is this?

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Re: Sachs 505 c/d Debate

Re: Sachs 505 c/d Debate

Re: Sachs 505 c/d Debate

i know a C head exists, i dont know if it was square or tapered. I have that exact same balboa right now i'm working on, and mine has a D head in it, but i believe that was added after the fact because the guy i bought it from said 'the jug was just replaced, but we couldnt get it to run' and it had a puch ring jammed into it.

Re: Sachs 505 c/d Debate

how many times can I say that the square heads are all exactly same.

The 'D' reference has nothing to do with the cylinder, and everything to do with the bottom end and crankshaft.

Re: Sachs 505 c/d Debate

really? could you break it down for the record, something like

X cylinders came on X crankcases, which are marked 501/xx, they are (square, tapered)

so i'm assuming the D case was the one with the long connecting rod/ GI ring piston?

was the other case called an A case? how can you tell the cases apart?

I have a lot of questions because i'm working on three sachs bikes right now, and this connecting rod bullshit is really crazy.

BTW: I accept the word of brendan barrans on all matters sachs, as the gospel truth. for the record.

Re: Sachs 505 c/d Debate



I noticed this today from a link in the wiki, If you look at the specs you'll notice that the "D" has a 2mm longer stroke, thus the "A" having an 8:1 compression ratio and the "D" a 10:1

Re: Sachs 505 c/d Debate

Re: Sachs 505 c/d Debate

so the A engine gets either an A or a B cylinder (taperd fins)

the D engine gets a D cylinder (boxy)

the main difference is stroke length

am i correct?

are there different pistons?

what does C mean?

are the clutches/internal gears the same?

is the 'a' what is called a 25 mph cylinder

the 'b' called a 20 mph cylinder

and the

'd' the 30 mph cylinder? i've seen the stickers on the bikes, and wondered if thats what people are referring to.

what cylinders/pistons came with PI gaps and which ones had FG gaps?

if people answer all this shit i'll type it up and wiki it, this is the kinda stuff i take for granted knowing about puchs... other brands i have a lot to learn about.

Re: Sachs 505 c/d Debate

I believe you are correct about the speeds, it is stamped in KPH on the cylinder itself, I would assume that the square cylinder would be for the higher compression engines for cooling, The A/B engine are the same but the "A" came with a 12mm carb where as the "B" came with a 10mm These were both 47cc the D used one ring only and the increase of stroke brought it to 49cc. The "A"s I took apart had rings where the gap was fitted around a pin, is that PI? It would appear that the power in the "D" came mainly from a drastically increased compression ratio. This would generate more heat and possibly require the extra fins of the square cylinder. This source does list a 505-2C which would appear to be a 2 speed version of the 505-1A.

Re: Sachs 505 c/d Debate

the letters can't be the only thing, and D's aren't the only 30mph bikes, I recently sold a Westlake with a 1/A and it was marked on the left fork tube with a 30mph sticker, and it did a solid 30 stock

Re: Sachs 505 c/d Debate

The speed ratings might not take into account the rear sprocket on the bike, The 1A being 25 mph 30 is not inconceivable with just a little bit smaller rear sprocket.

Re: Sachs 505 c/d Debate

What is the point of putting a speed rating on a motor it that has nothing to do with the speed of the bike?

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yeah, thats the confusing part, because i've heard of 30 and 40 kph 'a' cylinders. help us brendan! enlighten and entertain!

Re: Sachs 505 c/d Debate

and most importantly, which sachs mopeds come with the d motor stock? Just balboas and eagles? what about G3s?

this is super informative.

Re: Sachs 505 c/d Debate

some suburbans have Ds.

Re: Sachs 505 c/d Debate

All D cylinders have two piston rings as does all the 504 & 505 line of engines, if you observed one with only one ring it must have been a substitute.

Other differences that I've noticed between the 47cc "A-D" engines are the main gear weights, see the "spoked" main gear on the right? Well that is from a 47cc 505A and it is substantially lighter, just by the feel of it in my palm would suggest 40-50grams lighter. The one on the left seems to be the standard for 505d's, probably built a little tougher to handle the extra 1HP the cylinder puts out.

My current plan is to outfit one of my other stock 505D bottom ends with this lightened main gear and observer performance changes. I've been through 16 Sachs engines so far I think I can dismantle the things with one eye now ahah.

I have some more pics to post so stay tuned. It would be really nice if someone could build a few pages in the mopedwiki i'm totally inept at it


Re: Sachs 505 c/d Debate

Here are Sachs pistons from A, B, D left to right. The C apparently I've only come across once it may be a tad rare anyways I don't have the piston with me. Notice the height difference of the pistons and the location of the piston pins. Also notice the height and width of the port windows from A piston to D piston, it's hard to tell on such a bad photograph but the D cylinder is slightly wider than the other two but substantially shorter.

More pics to come.


Re: Sachs 505 c/d Debate

Here are pictures of a D cylinder and A cylinder. They are compared:

D cylinder has a wider and slightly taller intake window than does the A cylinder

D cylinder has a wider and slightly taller exhaust port

transfer port shape are virtually identical BUT the A cylinder has the transfer ports entering the cylinder at about 4-5mm farther into the cylinder compared to the D cylinder

base depth is reduced on the D cylinder by about 0.75-0.90 mm (accounting for compression difference??)

the piston windows are shaped differently and the D windows are wider by 4.5mm

their bottom ends have identical cranks but the rods do appear to have varying lengths


Re: Sachs 505 c/d Debate



Re: Sachs 505 c/d Debate

I took the number of rings from a spec sheet but that's not to say it didn't change when the single ring wasn't holding up. The "D" piston is rather surprising seeing as how it is a higher compression engine. I wonder if there is much difference internally between the two cylinders? My first theory was when looking at the data the "D" had a 2mm longer stroke and that the main difference was a 1mm offset on the crank as pushing the piston 1mm farther into the cylinder could result in the dramatic compression ratio change.

Re: Sachs 505 c/d Debate

Ahh, alright you answered some of that while I was still typing. (yeah, I'm that slow). Could it be that the rods are the same but there is just a 1mm difference in the crank offset?

Re: Sachs 505 c/d Debate

No the rods are not the same they is a few millimetres difference, it would be a terrible idea for someone to think they could swap an A cylinder to a D bottom end not just because of the different stroke and piston size but the size and timing of the ports. A single millimetre difference could throw an otherwise harmoniously running engine of balance and the transfer ports entering the cylinder on the D engine are several degress advanced compared to the A cylinder. It used to seem so simple at first just swapping this with that etc. etc. but those Germans put much more effort into restricting and making these engines incompatible with each other than we realized. The parts that really seem consistent are the internals such as the cluch, crank and gear. I'm very anxious to get started on that rebuild i'm planning: swapping the 505D main gear for the lighter 505A main gear, I expect torque and throttle response to go up and up but then again the sacrificed top end with less rotating mass...(sigh).

Re: Sachs 505 c/d Debate

My main concern in all of this is I'm looking at buying a 70kit for it and it would seem that this stroke difference will matter, perhaps there is a spacer to use with the "D" engine to make that up? I have an "A" so it probably doesn't matter that much for me as they are much more common and the kit is likely designed with the "A" in mind.

Re: Sachs 505 c/d Debate

The A is only common in North America, in Europe the D is standard and since all the manufacturers are based over there it's more likely that their kits are meant for the D cylinder. Remember that Europe has very liberal regulations on power+speed for their small vehicles, tried selling to America and found out they had to restrict everything. Thus the 20mph to 30mph models.

I don't forsee any problems in buying a kit it should slap right on since you are changing the cylinder _and_ the piston. Your timing, however, will most definitely need to be readjusted. My timing is retarded by 1mm on the stator plate markings and everything worked out fine, but then again I upgraded a 505D engine. Let us know what happens and don't forget to post it up.

Re: Sachs 505 c/d Debate

Jafar, Thanks so much for this super informative post. I'll boil it down and put it in the wiki.

There are two rings, i was referring to the pin being behind the gap or offset to the side of the gap. The cylinder i just pulled apart had two 'GI' style rings, meaning the pin was behind the gap, other cylinders i've seen with one of each, and some with two 'FG' with the pin offset in the gap. I'm curious as to which pistons were in which cylinder.

We built an 80cc athena over the summer here in milwaukee, and didnt know that about the connecting rod lengths. It runs like shit, barely does 40 mph. I think the jugs are pretty close, but the A is a bit shorter than the D, or perhaps they are the same and it is just the rod/stroke length. Either way, i'm very much interested in sachs engine geometries after that fiasco. I'm pretty sure the Athena kits are designed for D engines, because it certainly doesn't run well on a A engine. They do have oblong holes though so it can go on either.

Re: Sachs 505 c/d Debate

I'll have to order one. I forget that the de-tuned models are typically for the U.S. market. Those poor Honda PA50-Is


Re: Sachs 505 c/d Debate

An 80cc cylinder only runs you 40mph?! Damn that's lousy, I'm hitting 40mph pretty easily with only 65cc's and some worn out piston rings. think your issue is likely compression loss, or rather the loss of otherwise available compression. Shave the cylinder deck in 0.25mm increments with a straight file and leaving your timing at stock, test the engine with a fresh gasket after each 0.25mm shave. To play it save don't shave off more than 1.5mm, if you start pinging you can always add more gaskets to make up for it. I Is your kit piston ported or reedvalve? Must have been very expensive.

Re: Sachs 505 c/d Debate

This is using an 80cc athena reedvalve kit. they run about 280 bucks, its not mine, one of the other guys in the gang. We built the engine and put it on a columbia commuter, quite possibly the shoddiest moped frame ever made. Its a good thing it only went 40 because the bike felt like it was coming apart at 30, and was actually. We decided to scrap the whole engine, put the kit on a D engine one of the other guys in our crew has, and part the bike out since the frame cant handle the 50+ mph that kit is capable of.

So one more question, then i'm done buggin' ya. Is there any difference between clutches from the a/d engines? I have a feeling we'll be needing that one out of the A engine after the D engine blows it's own clutch up.

Re: Sachs 505 c/d Debate

No difference in clutches whatsoever. I like to sand down my clutch pads every few hundred miles with #600 grit sandpaper so they continue to grab well but not so much that it wears down quickly. Honestly, if you expect any kind of long-term reliability out of the Sachs clutch don't go any higher than 65cc's. Also, now that I know about the main gear differences in strength and weight I would be tempted to leave all A-C bottom ends in stock displacement, perhaps matching the transfers and getting a larger carburetor, switching the gears to no higher than 11/40th because anything lower than that without a bigbore kit destroys all hopes of low end response. Cruising between 38mph-44mph is just fine with me I've got the Balboa frame and it's quite sturdy with the exception of the engine's freaky wobble at high rpms

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