The MotoBi 250 Vintage Road Racer

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Aermacchi 250 CRTT

The MotoBi 250 Vintage Road

Date: Sun, 25 May 1997

VintRR Oh no! Another vintage race project


My is Michael, and I’m a projectaholic.

at Craig’s shop the last two I did a deal with his friend to buy his MotoBi (also known as horizontal-cylinder 250cc four stuff (at only $400 how I go wrong?). This is a fairly chassis with presumably engine and 2 additional engines. It that all the bikes are 4 speed models.

In the spares is a new race kit (with RR lettering stamped the exhaust port on the underside of the that looks to have bigger ports than the head. There is also a new with S designation, but we don’t if that stands for Sport, or Standard (maybe spatzle? probably not since it is an Italian

Craig and I spent about 40 looking at the parts and scheming on to change. The crankshaft is not a real looking item. It has the same as an XR200 Honda single is about the same width), and the on the Honda crank are enough that they could be down and modified to work in the

This would also a bigger crank pin.

The ring piston isn’t impressive either, but it is the same as an XL250, and they are both top pistons so that is solved The Honda piston uses a 1mm wrist pin, but since the height is a little lower would probably be taken of by ordering a slightly longer rod to the appropriate length/ID dimensions. in the combustion chamber will add without needing a dome on the

Megacycle is supposed to have a for the factory race kit cam, so contact them for timing on that to see what cam I’ve or if the race kit cam will be at all suitable. looked through some and found some 5.5mm titanium valve blanks in sizes, and I’m sure R/D Spring will either a suitable valve spring set or can up with one once I send a head. This time I worry about trying to up with replacements for the OEM parts as I did for the — whatever retainers got on the shelf are what will be

Craig said the intake didn’t look too bad, but the is one of the wretched flat ports the Italians seemed to love to put in engines. I see a bit of TIG welding in the exhuast future.

Ivar very took some time me some MotoBi information. He me that the factory bikes had with the side thrust the helical primary gears as do Ducatis — Nova a straight cut primary set for the Ducs) so is going to have to be addressed.

The is the other sticking point. All of the I got appear to be 4 speed boxes, strikes me as less than for a 250 race bike. 5 speed were also sold in the but Ivar tells me that all the racers used 4 speed

The standard 5 speed has a wider spread than a Ducati 5 (and we won’t even how it compares to an Aermacchi race and the top gears aren’t very together.

The immediate conclusion was to another transmission to install I know of another Italian 250 bike that is running a 6 speed). But wait — the uses an English-style transmission a mainshaft/layshaft setup (power in and goes out from the mainshaft), not a Italian/Japanese indirect crossover box where the power comes in on the shaft and leaves via the countershaft. The 4 cases are fairly narrow as well.

Hmmmm, this is to require more thought.

been emailing with a in Australia who has some of the 5 speed but even there new gears have to be made, though might be less trouble in the run than finding a different to swap into the engine. again, most of the tracks here don’t have first gear corners, so if I build a dry clutch that tolerate a lot of slipping on the start a ratio 4 speed might be

I don’t know yet if Zanzani or made straight-cut gear or different transmission ratios, but find out. I now have a good address for Werner who developed a lot of the factory racers and his own 500 twin based on the MotoBi so I’ll drop him a line and see if he any helpful information.

I’ll a new chassis for it. Ivar told me Zanzani made a space for sale for the bikes, and I see no problem a replica of that or a LinTo The lower rear motor appears to be usefully wide, but the top are only 30mm wide and 60-70mm apart.

Hmmmm, maybe a bit more TIG will be called for here.

The has a pretty narrow chain with about 10-15mm to a 3.00×18 Avon tire, so it may to be slightly offset in the frame to a 90 or 100 section tire.

I think a set of late model external-damper GP pattern leading link are likely, or maybe some type LL forks, whichever to be more appropriate for the link that I decide upon.

you know it (well, maybe next year) I may have a replica of the MotoBi racer everyone wished they riding in 1965.

As you might any bits of MotoBi lore, or engine components are desired you know where to find me. I I need to see if the Benelli club to MotoBi — or maybe have to start a MotoBi myself (in my copious spare — right).


The MotoBi transmission ratios to some of the competition.

Articles to date:

MotoBi 175 Catria — Cycle World

Benelli Sprite 200cc — Cycle World

Benelli Sprite 250cc — Cycle World

Benelli Barracuda 250cc scrambler — Cycle Road Test Annual (tested in 1967)

Benelli Barracuda 250cc (with race kit) Cycle World 09/68

Barracuda 250cc street race kit) — 08/67

Benelli Barracuda street (with race — Cycle 04/68

Sprite 125cc street race kit) — 07/68

Benelli 250 Super — Motorcyclist 01/73

out the MotoBi pictures on the graphics

Update: 05/26/97

I just the head off of the fairly completely spare engine. It looks I may have two 250 engines, as this one has out to be a 125!

First performance/reliability The 125 had star-type lock washers the head nuts. Lock under head nuts; wonders never cease. MotoBi, bad.

They’ll get and hardened and ground flat substituted.

And now for some MotoBi courtesy of Ray Crenshaw on the Thumper

I wrote: Upon further one of my spare 250 engines that with the bike has proven to be a I’ll have to think of entertaining to do with the smaller to keep myself amused.


Ultra-Cool power-source for race starter-rollers?

Couple to a LUCAS generator so it’s not the weak in the chain? (sorry. )

World’s 1.2 HP weedeater?

Grill trackside on the pipe (if it holds together it’s hot)?

Money asset-on-hand power for lucrative Roto-Rooter franchise business?

windshield wiper motor for race van?

Bring out new of chic Italian-powered hedge equipment?

Mondo-cool hood ornament for F-150 race truck?

troublesome electric motor really cool portable with megaphone?

Aermacchi 250 CRTT

New line of drones for Air Force?

Budget to humble those annoying on NSR’s in the 125 GP class?(get weight

Graft to Titanium Spondon exploit Doohan-slaying handling-over-power in 500 GP

Use it’s bothersome existence to hush-hush money from new Benelli owner?

Utilize in to single-handedly squelch XR-750 of AMA dirt track series?

for yet another BEARS Sounds-of-the-

Weld 1-millimeter … to crank-end, no more laborious spoke-threading?

Test bed engine for new 38 Octane Super-premium?

For tax purposes to local college Physics Catastrophic Metallurgical Failures

…new Italian/American collaborative racer?

If you can’t get Muzzy I guess World Superbike is although Kocinski will be available by mid-season.


Yes Ray, I think that is enough!

21 November 1997

I weighed a complete 250 4 speed (engine, kick and gear 22mm Dell’Orto carb attached air filter), and the weight is 66 (+/- .5 pounds).

The engine for my + 125GP =? project will be 73 pounds, and I’m expecting bike (with special Dymag wheels, disc etc) to weigh in at about 185 The 250 Benelli road racer, the 5 speed engine weighs the same as the 4 speeder (and it be lighter as it won’t have the start stuff or flywheel/magneto), and that the wheels should be a bit should still be comfortably 200 pounds dry.

This is about 40 pounds than a standard framed 250 narrow-case racer. If both have 30 bhp at the rear wheel the will have a 1.3 pound/hp over the Ducati, or the equivalent of 36 bhp. I like t!

Phil was good enough to send me torque specifications for different from his owners manual on the 200 CC 4 4 stud engine


Cyl head = 22 24 ft. Lb.

Flywheel Magneto nut = 55 — 60 ft. lb.

sprocket nut = 65 ft. lb.

Primary shaft hub lock nut = 45 — 50 ft. lb.

Cam gear = 45 50 ft lb.

Pinion gear = 40-45 ft. lb.

adds: From personal Take extreme caution removing the pinion drive from the main crankshaft. Use a tool. It is on VERY TIGHT and be taken off with the proper

The crank shaft WILL if a conventional gear puller is Believe me. It will happen!!

are some interesting measurements various sports/racing MotoBi supplied by Peter Oort:

Aermacchi 250 CRTT
Aermacchi 250 CRTT


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