Jul 282014

I had to modify the seat pan because the gas tank that was originally on my bike had big dents that are very hard to repair. I didn’t know about the damage, because someone filled the holes and repainted it. After removing the paint this was a big surprise. I bought a replacement gas tank on ebay. It had 1972 decals, but I was sure it is not a 1972 gas tank. When it was repainted I noticed the replacement tank is about 5 centimeters longer than my original tank!

Well, the replacement tank fits, but than there is no room for the seat. I relocated the seat 5 centimeters to the back and hopefully this will solve my problem. I will have the pan cleaned and powder coated and the seat will be recovered.

damaged-tank1 damaged-tank2 pan1 pan2 yellow-seat

 Posted by at 11:14
Jul 182014

Received back the freshly polished engine covers. I will also replace the single leading shoe front brake with the better double leading shoe. Hub is the same only brake shoes and brake plate needs to be replaced for that.


 Posted by at 09:24
Jun 032014

lenkschloss1-1 Lenkschloss2-1 Lenkschloss3-1

As I couldn’t find a correct steering lock for the Aermacchi I tried my luck with something that looked similar and made it fit with a lathe. Surprisingly it worked on the first attempt.


 Posted by at 10:58
Apr 182014

New seals for the carb today.

  • Dellorto PHB 32 Ad
    • Needle K7
      • middle positon
    • Throttle piston 40/1
    • main jet 115
    • main nozzle AB260
    • low speed jet 55
    • starting jet 70
    • float valve seat 250


 Posted by at 20:09
Feb 072014

Before you start:
There is no guarantee for the correctness of the information provided. That following steps describe the procedure for my 1970 GT-350. It’s a different procedure on other model years!
To my knowledge (again, without guarantee) this is valid for 1969 to 1972 Sprint 350cc street bikes and not for earlier bikes and not for the 1973-1974 electric start!
Please ailways use a few drops of oil to fit the parts together.

drivegears-arrange1Pic 1.

  • We start with an empty right side crankcase. Only the shifter pawl carrier (C) is already put in, as it must be inserted before the primary drive gear.
  • Pull out the connecting rod (A) to tdc (top dead center), this will move one of the three notches (B) on the flywheel shaft to 3 O’clock position.

drivegears-arrange2Pic 2.

  • Slide clutch drive gear (D) on shaft of flywheel. It will stop in the correct position because of the conus of the shaft. Don’t turn the shaft! The mark on the clutch drive gear (arrow) is of no meaning at this point.

drivegears-arrange3Pic 3.

  • Put the woodruf key (E) into notch of the shaft. It must be the notch at 3 O’clock positon while connecting rod is at tdc position!

drivegears-arrange4Pic 4.

  • Slide pinion gear (F) on shaft with woodruf key in position at 3 O’clock and make sure the mark on the pinion gear points to 3 O’clock also (arrow)! It sits correctly if the surface of the pinion gear touches the surface of the clutch drive gear.
  • Put the lock ring and nut on the shaft. One latch will be bend into the notch of the pinion gear the other around the flat side of the nut after the nut is tightend! (These steps are not pictured)
  • When tightening the nut you must make sure the shaft will not turn.

drivegears-arrange5Pic 5.

  • Next we  put the primary drive gear on the transmission shaft. On that picture you can see what parts must be fitted inside the gear. A thick spacer (G) that must have the correct thickness to arrange the primary gear in one line with the clutch drive gear (D).
  • Inside the gear are two roller bearings. On top of the bearings will fit another distant spacer.

drivegears-arrange6Pic 6.

  • Put the primary drive gear (J)  on transmission shaft and don’t forget the stuff explained in Pic 5. You will need probably 2-3 trys to make the two marks fit the one mark of the clutch drive gear. For that operation you may turn the flywheel shaft with the clutch drive gear.
  • The marks on the primary drive gear (J) and the clutch drive gear (D) however are not time critical. It’s just the way the teeth are fitted together by factory. That’s the reason for using gears always in matched sets! If you don’t, you will risk damage to gears.

drivegears-arrange7Pic 7.

  • Next we put the roller bearing (L) for the camshaft into crankcase and also set the two tappet guides in (K).

drivegears-arrange8Pic 8.

  • A spacer will be used on camshaft to allign the camshaft gear exactly to the pinion gear.
  • I will not describe how to fit the camshaft gear to the camshaft as it can only be fitted in one direction

drivegears-arrange9Pic 9.

  • Put the camshaft with gear (N) into the roller bearing (Pic 7.) and arrange the two marks with the one mark on the pinion gear (F).

drivegears-arrange10Pic 10.

  • Screw the oil pump into case (4 screws) and make sure the O-Ring is still on the oil pump for a sealing to the crankcase. Put the gear on the oil pump shaft. It is not time critical and has no mark so it doesn’t matter how it will fit together with the pinion gear.
 Posted by at 22:13
Feb 022014

insertingplugs insertingplugs2
insertingcrankpin insertingcrankpin2

Pressing new plugs into the crankpin and than pressing the crankpin into the flywheel with copper paste. You need about 5 tons of pressure for this.

 Posted by at 12:42
Feb 022014

crankpin newrod

We polished the crankpin so the new bearings do not have to cut off material. The original bearings which consists of two parts rollers in each cage we replaced with “one-part only” bearings as you can see on a later picture.

 Posted by at 12:28
Jan 292014

Kurbelwelle-vorher lasergeschweisst
aufmassdrehen1 aufmassdrehen2

You can see some marks on the left shaft of the flywheel. I gave it to a laser welding specialist who added some material. Later we took the material off again on the lathe and the result is a very nice and smooth shaft within the tolerances of a new shaft.

 Posted by at 14:03
Jan 252014

rudolf1 rudolf2
rudolf3 rudolf4

Here you can see how we pressed the crankpin from the flywheel and the oil dirt we found inside the crankpin after drilling out the plug. This is a typical 4-Stroke-Aermacchi problem and the reason you really should change the oil once a year or every 1000 miles. Rudolf decided the rod is used up and that I will need a new one.

 Posted by at 18:49
Jan 232014


While waiting for the paint job to be completed I have reproduced the gas tank decals as vinyl stickers. These are the 1971 design as I will go with the 1971 US design in sparkling green.

 Posted by at 21:46
Dec 312013

8854 stem29

A lot of fresh grease and 50x new bearing balls (8854) for the NOS fork stem. The fork stem I got with the bike obviously got pressed together in the wrong way as the notch for the steering lock was on the wrong side.
The parts shown on the last picture like airfilter housing, kickstarer and some other stuff went out for rechroming that day.

 Posted by at 15:36
Nov 062013

cases-new-bearings done-front-hub

I have replaced every bearing in the engine case with new ones. The front wheel hub is also redone and waiting for new stainless steel spokes and a brand new 1.85×19 front rim. I have also replaced the bearings and the dust seals here. At the moment I am working front fork.

 Posted by at 22:03
Sep 302013

cheap kukko

I bought a cheap tool set to remove the ball bearings from the engine case (left picture). I totally regret it. It was a waste of money. The tool is from a much to soft metal and it bends while the bearing still sits tight. I now own a professional bearing puller that worked like a charm.

 Posted by at 19:25
Jul 082013

The inside of the engine looks not very good at all. Spark advance is broken and the primary gear is totally worn out. I am pretty sure more bad surprises will come, going deeper into the engine. I also noticed that the left engine cover has a 1971 production time stamp and the right side a 1968. I am pretty sure someone had the engine disassembled before me.

gt-clutch-side gt-clutch-side-2

 Posted by at 23:17
Jun 302013

The engine is the so called “ashtray head”. The cylinder and head are designed for the US market. It replaced the earlier, classic Aermacchi cylinder/head. Customers in Europe didn’t like that design much and so it was available in Europe just for a short time period from 1969 to 1970 before they changed back to the classic knucklehead with the 1971 models. In US they kept the ashtray design until the arrival of the 1973 model of the Harley-Davidson Sprint.

Engine crankcase: L988

gt350-engine-off gt350-engine-off-2
gt350-engine-off-3 gt-cylinder-head

 Posted by at 22:29
Jun 162013
  • 06/16/2013: First oil change at 120 miles (193 Km) – out HD 20W50 – in Castrol 20W50
  • 06/19/2013: Re-Tightened nuts and bolts. Impressive how many became lose after that short period.
  • 06/30/2013: The plan was to attend an oldtimer get together and market in Ansbach (mototechnia) which is about 35 miles from my home. I made 2/3 of the way, when suddenly the engine cut off (odometer: 160 miles). Luckily that was very close to Aermacchi parts distributor Rudolf Jungjohann. The error was found quickly: The circuit breaker screw came loose and was damaged, so I had no spark at all. We put a replacement screw in adjusted the timing and the bike did run again. Sadly there was no time left to attend the get together anymore on this day, but I did make it home on the bike without trouble (180 miles)
  • 07/07/2013: Believe it or not – the kickstand broke into two parts just out of nothing. (odometer: 213 miles / 342 kilometers) Luckily this happened while in my own driveway and still sitting on the bike. Imagine what could have happened, while the bike resting on the kickstand!
  • 07/08/2013: As I can’t ride the bike at the moment because of the broken kickstand, I decided to disassemble the right engine cover again to replace the oil seal for the clutch hub. Reason: I am losing tiny amounts of oil through the dry clutch. This happens because of my own stupidity, I mounted the oil seal with the wrong side facing the oil. I realized that by looking at pictures I did during assembling the engine.
  • 07/08/2013: Replaced the tach drive because of a worn out oil seal. I had a NOS one at home already, because I expected that problem.



 Posted by at 23:06
Apr 282013

The GT once belonged to a fast rider. Those footpegs tell the whole story and it fits well into the picture together with the modifications made to this bike with a later and lighter seat, lighter tail light, missing fork dust-covers, cut-out clutch cover and other modifications – all with the goal of getting the bike as light as possible.
Because of the bad overall condition of the bike I assume the previous owner once lost interest in the bike and had it stored outside somewhere in a tiny Italian alley for decades.
Those footpegs will go directly into the trash bin. I have restored footpegs and reproduction rubbers in my inventory. The engine will get a good cleaning before disassembling and the airfilter will be replaced by a K&N replacement.

fast-rider lots-of-cleaning

 Posted by at 18:54
Apr 272013

It is done, the bike is very handy now and easily fits into a large rack. The hardest part was getting the fork out of the frame. Heat and pure force did the trick. The weldseams look like having been done by an apprentice in his first year. Never seen such bad weldseams on my other Aermacchis.

The tires, rims and spokes will be replaced later. Hubs will be polished and reused. The oil in the front fork – or better what is left – is just mud, but there is hope that the fork may be repairable. The shocks are totally broken and can’t be reused.

engine-off-gt4 einzelteile
engines gabel-old-style

 Posted by at 15:36
Apr 262013

Getting the engine out of the frame was easy because of the original Aermacchi “backbone” frame. Somehow the engine also felt much lighter than the 1974 engine, but as I do not know the weight differences this is just a feeling.

engine-off-gt1 engine-off-gt2

 Posted by at 19:25
Apr 212013

So, here we are. I have started disassembling the bike. I have got this small original Ala d’Oro gas tank and seat as decoration in my garage. I couldn’t resist the idea of building a café racer and so I tried how those parts might look. However, I will restore it back to original condition, but ONE DAY I might build a café racer!

Oh yes, those silencers look pretty good. Just a little cleaning of the “Frankfurter Töpfe” and I can right use them again. 😉 Luckily I bought NOS replacements years ago and stored them safely in my basement.

zerlegen-1 zerlegen-2
zerlegen-3 zerlegen-4
zerlegen-5 zerlegen-6

 Posted by at 16:17
Apr 192013

The first step for getting the bike road legal again. I bought the bike without any papers in 2006 and as it was imported in very bad shape from spain it never had any german papers. The officials tested it 2 hours for beeing safe, beeing within noise regulations and so on. I also had them investigating the bike if it is in original condition as it was sold by factory in 1974. a car or bike older than 30 year ins original and very good condition can be registrated as “oldtimer” in Germany which brings some benefits and safes taxes for example.


 Posted by at 13:00
Apr 142013

I did some pictures of the finished bike. I am very proud. It almost looks like brand new with very tiny cut backs. On one picture you can see my special bike trailer which can be lowered to ground and lifted with an air compressor for easy loading by one person only. I just had to modify it a bit as it is designed for bike bikes with wide wheel base like my HD FXDL. The trailer also has pneumatic shock absortion and I love it. If you don’t use the trailer it can be folded and easily stored in the garage!

fertig-1 fertig-2
VanVossen-short skala-fertig
schraeg tank-oben

 Posted by at 19:56
Apr 112013

Finally I received the missing original handlebar switch for light, horn and turn-signals. There is no one in the world who can be worse at soldering than me, but in the end it is mounted to the handlebar and it works good. Thanks to Carl from the US for helping me out!

cev169-SS cev169-dran

 Posted by at 10:38
Apr 022013

I made a km/h scale and sticked it on top of the speedometer to make it road legal in Germany. 🙂
The local locksmith also made me a copy of the key for the ignition switch, as I had only one ignition key.

Tacho km/h

 Posted by at 17:00
Mar 172013

With a NOS main wiring harness there is still a lot of rewiring to do, but so far everything works out great. The original starter relay was broken, but with help I was able to find a brand new one to replace the original Bosch.

rewiring.jpg starter-relay

 Posted by at 17:16
Sep 102011

Used original alloy trim stripes on the side of the seat. I had to trade them against something else and I bought new T-bolts to mount them. The seat turned out great, but overall it was an expensive fun to get it there.


 Posted by at 22:22
Feb 272011

On the left side you can see the piston that came with my replacement cylinder. It looks good on the first look, but if you look closer there is no doubt a butcher worked on it. Now I have a usable replacement cylinder but no piston for it.

pistons.jpg idiot.jpg piston-ring.jpg

 Posted by at 21:30
Feb 252011

The used replacement cylinder I bought on ebay. Got it back from bead blasting today. On the second picture you can see parts I am going to send out for polishing and chroming.

clean-cylinder1.jpg needs-work.jpg

 Posted by at 21:37
Feb 112011

Here you can see the freshly powder coated seat pan and the reproduction seat cover I bought. The seat cover is professional made but does not have the original pattern on top.


 Posted by at 21:57
Feb 102011

I have removed all parts from the right side engine cover so I can send it out for polishing. The cylinder head need cleaning as well. The oil seal for the clutch basket is a42x56x7 the ball bearing for the advance is a 6203 and the oil seal a uncommon size of 17x32x5.

oil-seal.jpg oil-seal-bearing.jpg oil-seal2.jpg send-out.jpg

 Posted by at 22:38
Feb 092011

High precision, fine german engineering for a special tool 😉 to open the inner clutch hub nut.
By the way as I have a 74 SS-350 this is the improved alloy clutch hub which was introduced on late 73 models. It can be identified by the higher number of toothes compared to the earlier steel hub. The late version also needs different clutch plates.

special-tool.jpg special-tool2.jpg outer-clutch-basket-out.jpg outer-clutch-basket-out2.jpg

 Posted by at 23:19