Inside the Ape 50 engine.

Unfortunately, the images to this post were lost in a server crash.  i’m preserving the text in case it is of any help to anyone.

Hello World!

Just last week Hodgespeed acquired something not often seen in the United States. a 1998 Piaggio Ape 50.

This is the ‘smallframe’ Ape, and is even smaller than the main line of full size Apes. In some european countries, these qualify as a moped, and get much more lenient registration and driver licensing requirements.

It’s powered by a variation of the Vespa smallframe 50 engine.

See it back in there?

Because it is fundamentally a Vespa smallframe scooter engine, there’s tons of tuning parts available to fix the 23mph stock top speed. Yep. 23 mph top speed. takes four gears to get there, too. Piaggio did make a 125cc version of this vehicle starting in 1969, but stopped production in 1974 after only 1700 or so were made. The lenient laws regarding 50’s made the 50 the king in sales, but not in performance. The ape 50 has been in continuous production since 1969, till the current day.

When this project is done, this will become our shop truck; we hope to have it be the chase vehicle on rides and rallies in the Seattle area before Seattle Scooter Insanity this July. It should be able to haul a single scooter when we’re done with it.

Because this engine is not too common, yet familiar, I think there might be some interest in seeing what it’s like on the inside of these. So, I’ve documented the tear down for the rebuild on it.

Unfortunately, i didn’t document actually removing the engine from the frame. That was a real bear.  Suffice to say, if you have to remove an engine from an Ape 50, the thing is light enough to use milk crates as jack stands. You have to unbolt one of the A-arms from the frame and the shock and remove a circlip from underneath the boots on the differential to remove the half shafts.

Anyway, here it is, in all it’s glory. the Ape 50 engine.

This is the engine, propped up by a brass hammer on my work bench. if you’ve ever had or worked on a smallframe i’d imagine these angles look a bit familiar to you.

Here’s a shot looking from the side of the engine the rear wheel and rear shock would mount if it were a scooter. because this is an ape engine, this is actually the front; the cylinder faces to the rear on the Ape 50. On the Ape 50, the differential bolts to the engine case where the brake backplate bolts to the scooter version of the engine. that’s what that lump hanging off the back of the engine is. you can also see where the gear cables attach to the top of the engine, and where the reverse-selecting cable attaches to the differential.

Opposite the flywheel. for context, you can just see the starter poking out from behind the exhaust. just to the right of the exhaust is the differential.

Here’s the bottom.Note the stamped steel bolt-on cradle where you’d expect the swingarm to be. Also, the clutch cable on these is routed a bit differently than on the scooter. The cable stop is cast into the differential case just out of frame at 12:00 in this picture. Notice also- if this were a scooter engine this would be the bottom of the engine where the cables attached. However, on the Ape the offset linkage inside the case is omitted and the cables are attached to the top of the engine.

And here you can really see that stamped steel ‘swingarm’. Polini actually makes an aftermarket version of that  piece. I’m tempted to order one. You can also see the exaust. Becasue the engine faces the opposite direction in the ape as in the scooter, mounting a scooter pipe wold result in a forward facing tailpipe. In addition, one would need to come up with a bracket to mount the pipe to since there is no swingarn. neither is insurmountable; i expect to mount a hammerzombie pipe on this before i’m done.

And here you can see the differential with it’s cover removed. The big bit on the right hand side sticking up is the Planetary Gear System there are two freewheling planet gears inside there, and the sun gears are on the end of the axle half shafts.

The other two gears are doing something clever- first, the lower left hand gear. this is a single piece with thre gears on it. the lowest you cannot see in this picture, but it is always engaged with the ring gear on the planetary set. Above that, is a larger gear. and on the end, A helical Gear to drive the speedometer cable.

the upper left gear is freesliding on the splined shaft normally, as in this picture, it drives the ring gear from the shaft, propelling the Ape forward. now look at this picture-

In this shot, my grubby fingers are simulating what happens when you pul lthe lever in the cab to shift into reverse; the gear is lifted away from the ring gear, and drives that gear with the speedometer drive on the end. thus adding a reduction and driving the vehicle in reverse.

This shot shows that gear inside it’s shifting fork in the other side of the differential case. This gear is dormally held in the forward position by a spring outside the case.

And here we find what i find the cleverest bit in the engine. there is a sleeve cast into the differential case that holds a needle bearing and seal that is exactly the same outside diameter as the normal smallframe rear hub bearing. this keeps the differential oil and gearbox oil separate.

And here’s what that mates up to on the other side. the end of the axle is this club-like splined shaft that that sliding gear in the differential slides on. notice the five large studs here instead of the two the smallframe scotoer engine normally has.

And surprise- a P-style stator. even more interesting, it is actually wired and color coded the same as an american market 70’s P200 stator. the crankshaft is one of those 20/20 mm types. not the ETS / P-style 24mm i had been expecting. This is one of a few things where developments on the scooter side of things did not make it back over to the Ape side of the family.

And here we get into the clutch cover area. notice that this clutch has six springs in it, not one large one. this late PK style clutch is kind of like the ‘cosa’ clutch of the smallframe.

Here you can see how low this thing is geared. look how tiny that crank gear is! More on gearing later, however.

and the clutch cover. it’s gear driven, not lever driven. and the button isn’t brass, either. on this engine, believe it or not the pressure plate has a ball bearing in it.  Curriously, the oil passages that feed oil into the center of the clutch and the backplate do not exist in this case or the clutch cover. perhaps Piaggio thought the ball berating didn’t need as much lubrication as the brass bit they used on earlier engines did.

Here’s a side by side of a early 2000’s LML smallframe case for comparison. notice how much rounder the Ape case on the left is at the bottom. since the shifter cables attach to the top of the engine rahter than the bottom like on a smallframe. also notice that the holes the stamped steel swingarm thingamajig are in exactly the same place as the cast swingarm is attached to.

look at all the meat on that 50 jug! anyone got a 75th oversize piston? In all seriousness, you can see from this the potential to increase the displacement. in addition, the 50 has a shorter stroke than the 90/100/125 small frames. so longer stroke plus cylinder kit would give a massive improvement on this engine.

Wee tiny piston!

Here is another interesting thing; when i saw the manifold had three studs, I immediately thought it was like a 3-stud PK manifold  (on the left) . Not so! the spacing is different. upon closer inspection i realized Piaggio had just added a third stud to the earlier 2-stud smallframe pattern. look at this picture:

See? a stock 90 manifold fits, leaving one stud out in the cold, unused.

and here’s the christmas tree. notice, there are no notches for a kickstart ratchet. early ape’s had a hand-start that used the scooter kickstart mechanism. Sadly, that feature has been dropped from this model.

And here you can see the strange axle that also serves as the input shaft for the differential. And while we’re on the gears; looking at this gearbox, something didn’t look normal to me so i started counting ratios. this has a very wide ratio gearbox, with very high 4th gear and very low 1st gear. at first, this confused the heck out of me, until i realized what they had done. On smallframe scooters, the three speed top and bottom gears are roughly equivalent to the top and bottom gears of the 4- speed with 2nd  on the 3-speed splitting the 2-3 gap on the 4. However, on this gearbox, 1-3 are roughly equivalent to 1-3 on the 3-speed scooter gearbox, but with one higher gear added.

Here you get a shot of the inside of the case. Very small frame-like.


And here’s a side-by side of the clutch side case. there are definitely differences; the Ape lacks the reinforcing webs the scooter motor has  the swing arm, as the Ape engine is not loadbearing.  The ape also has a few reinforcing ribs added, most notably on the edge next to the bearing the clutch basket primary rides on.

Well, that’s it. my tour of the inside of an Ape 50 engine. Keep watching here, as once business picks up enough for us to spend the money we’ll be building a real screamer of an engine out of this.

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