Category: Sven’s GT-350 (1970)

Together with a friend I attended the Oldtimer gathering 2022 in Langenzenn. It was suspended for the last two years because of Corona.

I had a very nice sunday ride on my GT-350. The bike was starting and running very nicely.

Just a short round with my GT-350.

The gas tank had to be repainted as gasoline went underneath the paint around the gas cap. As the decals got to be pulled of for this I decided to go with the 1970 this time instead of the 1971. I also replaced the rear shocks with higher quality Hagon shocks.

Just a little autumn ride out. Sadly a short circuit blewed out a fuse and the bike had to be transported back home on a motorcyce trailer.

I took my GT-350 to a small Oldtimer festival in Langenzenn, Germany. It was a nicy & sunny day. Perfect ride.

First test ride with the GT-350 on public roads since it’s restoration. In the background you can see the castle “Cadolzburg”.

I really have to take care of getting the bike street legal now. I rode 4 kilometers and there is still some trouble, but I will get it managed…

Required by law for this production year in Germany already. As in Italy turn signals were not required and the bike delivered without them I had to find a solution that does not insult the eyes and so I did use period correct italian CEV turn signals

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.

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.

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.

Paint code MG645.30 Standard Glasurit 90 CPS2

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.

Pic 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.

Pic 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.

Pic 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!

Pic 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.

Pic 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.

Pic 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.

Pic 7.

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

Pic 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

Pic 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).

Pic 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.

Everything within factory specs now and putting engine cases back together.

The new ballerings, the new rod and the overdone flywheel getting back together. Rudolf than trued the flywheel to 0,01 mm which is much better than factory Defaults.

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.

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.

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.

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.

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.

New tube and new tire, Heidenau K34 3.25-19

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.

Brand new rim and new stainless steel spokes

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.

Left to right: 98302, 16006, 6305. Tony Foale suggested to use C3 bearings for the flywheel (3305 and 6305) and so I will do.

I needed help from a machine shop to get the large doublerow bearing out of the right engine half.

I found a NOS tach. in perfect condition for a good price.
I also received back a first pile of parts that have been corund blasted in the meantime.  The wheel hubs will now be polished to shine as new again.

Oil seal 15x24x7. In a later right side cover (71) it is 15x32x7

Smaller bearing for Transmission in both sides of the case. 15x40x9 mm. One was marked x98302 KH SRO. The other was just marked Made in Italy and something I could not read like PVR AVP. Don’t know.

The wheels are totally disassembled. I will give them out for cleaning (sand blasting) and I will probably have the hubs polished. Cylinder head and barrel will also be sand blasted.
Yes, there is a X-90 cylinder head also on this picture. 😉

double row ball bearing for crank in right engine half: 3305 FAG O.B Germany. Size: 25x62x25,4mm

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.

The engine case is open now and it looks like I did no damage. *Happy*

I will discard the wheel rims and buy new ones as re-chroming them would be more expensive and Radaelli rims are still available today. Thanks to Moto Italia I also now own a engine split tool.

Almost ready for splitting the engine.

Now tool for my Aermacchi-tool-collection. 🙂

Before disassembling. Rear wheel bearings: SKF 6204-2RS1

I built myself a pinion gear puller that worked good. As you can see on the last picture the piston rings are totally baked into the piston.

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.

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

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.

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.

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.

There – the idea of the cafe racer is back in my mind…
No, not this time. I will restore it to factory defaults. 😉

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.

I took some pictures before disassembling as construction plan for a later assembling. 😉

I found this NOS original seat in perfect condition on ebay. This is the correct one for a 1970 model. On my bike a previous owner mounted a seat of a 1971-1972 model which looks more modern and also is not so heavy. The 1970 seat is old school style with metal springs.

I collected parts that need to be replaced or were missing on my GT-350. The chain guard is in bad shape and will be replaced by this usable one after painting. The old style fork covers have been missing on my bike. They are not necessary but they were mounted by factory in 1970. Those mufflers are perfect NOS parts which costed me some money. I know, most people replace them by a single exhaust as a one-in-two exhaust just makes the bike heavier, but I like it as factory original as possible.

The orange one is the correct fender for the 1970 model. Bought it on ebay USA and had it sent to Germany. That is why it has got the tail light as used on the SS-350 (export) models with HD vin. When restoring, I will use a European style tail light, which looks modern and sleek compared to the US version.

My first picture of the GT-350. I took it at a resting area at the “Autobahn” on my way home from the seller, who lives close to “Lake Constance”, which is a 2 hour car ride away from me. Well, the bike wasn’t too expensive, but it is in a worse condition as it may seem at first sight.
It has got an Italian VIN and still the Italian license plate, which means this bike wasn’t for export which makes it a GT-350 and not a SS-350. Differences are minor to a US-model. Odometer showed 17128 kilometers and the bike was in an overall bad condition.