Chappers Reader
3/17/20 11:20 a.m.

This turned up locally on Facebook market place cheap. I'd never heard of Aermacchi or even knew that HD made 2 stroke bikes...

..but it looked fun for a father son project. 

The plan is to just get it running first, then clean it up and turn it into a little pit bike sized scrambler. 
Apparently it had a 125cc engine fitted, looking up the engine part number it looks to be from a TX125. But I took the head off and measured the bore and stoke and it actually measures 188cc. 


CJ GRM+ Memberand HalfDork
3/17/20 11:39 a.m.

Harley built 2-stroke bikes from 1947 through 1966.  The first ones were direct copies of the DKW RT125 that the US, England, and the USSR got as war reparations after WWII. 

Harley's version grew from 125cc, to 165cc, and then 175cc.

Ultimately, Harley couldn't complete with the Japanese and bought half of Aermacchi in Italy and threw the Harley badge on their bikes.

I actually have two of the 165cc examples in the shop - one is the first vehicle I ever owned.  I was 12.  Like below (not mine)

SaltyDog HalfDork
3/17/20 11:40 a.m.

Very cool little bike!

HD didn't actually build them, just rebadged and sold them through their dealers.

Aermacchi went belly up in the early 2000's, IIRC, so parts may be a bit challenging to source, but hopefully are common enough to cross reference.

Look forward to seeing this thing zooming around again.

Good Luck! 


914Driver GRM+ Memberand MegaDork
3/17/20 2:06 p.m.

The blue one above is a Hummer, I can't say if it is Italian or not.  Later they married up with Italy on 124 - 250 bikes.  Tis was pre-1976 when brake and shifter locations wer standardized to what you see today.  Blistering into a corner you may find yourself down shifting instead of braking.

Stock and not so stock photos below.  Nice bike Chappers, have fun!


maj75 HalfDork
3/17/20 4:27 p.m.

That bottom one has a 350 Sprint motor.  New a guy that had one back in the day.  

BoxheadTim GRM+ Memberand MegaDork
3/17/20 4:30 p.m.

In reply to 914Driver :

Both of those are Aermacchis - the bottom one is actually an older model.

stuart in mn
stuart in mn MegaDork
3/17/20 5:21 p.m.

I think it's a 1973 model, not 1970.  Those were pretty serious minibikes, when compared to a typical minibike with a Briggs and Stratton engine with a centrifugal clutch.  These days it probably has some collectible value, so I wouldn't make any big modifications to it.  This guy says he can provide tank decals for them:


This guy says on his website: " it’s not unusual to see clean, restored examples fetch around $5K or more"

Peabody here
Peabody here UltimaDork
3/17/20 5:26 p.m.

There were a few manufacturers building similar bikes in the day. I had a Garelli rebranded as a Bombardier before the Can-Am days.


I actually saw this run in a world championship round at Mosport in 76

Aermacch1 New Reader
4/6/20 8:07 a.m.

In reply to Chappers 

Interesting find. I saw that bike posted a while back. . A buddy of mine built one similar (x90 with Harley SX125 motor) He used larger wheels to stabilize the bike as well as some other modifications. Turned out pretty cool and is a beastly little thing. The engine is definitely from a 1973 TX 125. The H at the end of the vin stands for 1970, the number that follows is the year. H1=1971, H2=1972 etc. The 7A at the beginning of the vin is the model number and represents 125cc and the only 125cc they made in 73' was the TX125. The TX is considered the last of the Rapido family by some people.
There are a lot of misconceptions about these machines. They weren't re-badged as HD. Like it or not, they are Harley's. Harley owned,operated and designed them. The early models definitely have more of an Italian look. The blue 165 isn't an Italian made 2 stroke. The early 2strokes were made in the US from plans HD received after WW2 from the US government of the German made DKW. Thanks for saving it and have fun! And if you need parts. Hit me up. I've got a small shop that sells NOS/OEM Harley Aermacchi parts


Chappers Reader
4/6/20 11:21 p.m.

In reply to Aermacch1 :

Nice, Thanks for all the info!

We had a delve into the engine and found someone had been been there before us. the piston was damaged and an absence of rings. The flywheel bolt was loose and the woodruff key was sheared. 
We managed to find a TX125 piston and set of new rings for sale, got some top end  gaskets and I cleaned the carb. 





Chappers Reader
4/6/20 11:22 p.m.

Chappers Reader
4/6/20 11:23 p.m.

Chappers Reader
4/9/20 11:37 a.m.

Got the piston pin C clips in and top end back together. 
so took the engine outside and cleaned it up and the rolling frame. 


it feels like it's got decent compression (not measured yet until the rings seat) 

I need to find the right size woodruff key for the flywheel. 

Chappers Reader
4/14/20 11:28 a.m.


I bought a Harbor Freight woodruff key set and filed the 3mm wide x 5mm tall one down to 3x3.2mm and the flywheel was a great fit.

I cleaned the points and gapped to spec and grounded the coil to the engine but couldn't get a spark. 

I ended up checking the resistances across all the components and they looked good. It was pointed out to me that on wiring diagram the condenser is grounded not to the stator plate but through a green wire that should go to the tail light and then to ground. Strange, so if you have a tail light bulb go out, you can't get your bike started.

With that grounded to the engine, we got a nice healthy spark.

Put the engine in the frame, the fuel tank still needs cleaning out as its till got some old fuel residue/rust in there. So i just made a funnel fed fuel system.

Anyway a few kicks later and we had this..

A little smokey, thinking its the 2 stroke oil I used to assemble the top end. 

This is after it had run for a bit.

It has a fast idle, and seems to bog and foul the plug quite quickly. 

I'm planning to do a bottom end leak-down test to assess the condition of the crank seals.


44Dwarf UberDork
4/18/20 9:09 a.m.

Theres a place called Sonny's in Lowell mass.  He's not cheap but he's got the goods.  You may find some stuff at Tom's NOS parts 

Tom's Nos


Chappers Reader
4/21/20 7:19 a.m.

In reply to 44Dwarf :

Thanks! I will take a look. 

I managed to get hold of both NOS crank seals off Ebay. 

A friend of mine lent me his bottom end leak down tester. Immediately the stator side had a huge leak

the original seal was almost backed all the way out. Also the intake was missing a gasket. 

new seal in and a bit of RTV on the intake and it now holds 10 psi.

Chappers Reader
4/21/20 7:32 a.m.

I used this evaporust before on a KE100 fuel tank and it worked very well.

so I'm giving it a go on this fuel tank too.


it's already leaking out the bottom of the tank, and I can now see evidence of a previous fiberglass repair. 
So I'll be stripping that patch off to asses the damage underneath. 
The tanks are a bit pricey so I'm inclined to repair rather than replace. 

I also got some new "pitbike" cables, throttle mechanism and levers to replace the broken/missing original items. I'll hang on to them in case. 


Also noticed the seat that came with the bike is nowhere near the right one, the front brackets kinda lined up and the back was wedged into place. It was horrible to sit on anyway.

so I've ordered a new X90 seat cover and I'll make my own seat pan. 

Chappers Reader
4/24/20 10:39 a.m.

While I'm still waiting on brake cables I thought I'd fill the transmission with the rather thick 75w-140 gear oil and see if I can have a little ride around the yard. 

Now I was getting clutch actuation, but no clutch disengagement. 
with the clutch lever pulled in while running and shifting to first it would stall. 
so I tried running with the bike in neutral and then jumping on the bike, shifting to first and I could ride it!.... For all of 30 feet until it bogged and died. 

my wife took a short video, and she said it was like a smoke screen behind me! 

so even though the bottom end is air tight at 10psi, the fact that it isn't at 5psi means that clutch side crank seal was definitely toast.


Chappers Reader
4/24/20 10:48 a.m.

I decided to split the cases last night to get at that oil seal and to also look at the why the clutch won't disengage.


well the clutch problem is now obvious. 
pretty sure these shouldn't come out in one block

Chappers Reader
4/24/20 11:06 a.m.

The plates pried apart relatively easily, I think the surface corrosion will clean up. 

just need to pull the pinion gear off the crank and press the crank out of the case then I can press out the bearings and and replace the seal.


the rest of the transmission looks pretty good, no surface corrosion on the gears etc  

44Dwarf UberDork
4/24/20 7:24 p.m.

Plate glass with a DA 300grit stick on sand paper.  add some dawn an water and scuff the steel plates then wash in Acetone or brake cleaner.  Very lightly scuff the fibers don't take off the fiber just the dried lube then soak in light oil.

If you need seals buy modern new ones NOS will be old and dry.  Most seals have the sizes on them. go to Harwal seals for new ones.


Caswell sealer in the tank after the evap-o-rust (Great choice!) and a heated drying.  

As a side note if your coil wire is epoxied in to the coil and needs replacement left over Caswell can be used to fix in in

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