1961 125 Sport disaster/ 160 compatibility

[john jupiter]

Hi Everyone,
I have a frame, engine, front end, and gas tank of a 1961 125 sport. The condition is so poor that I am hesitating on whether or not to restore it. I know parts are next to impossible to find. I am wondering from the experts what engine parts are interchangable on the 125S and the monza 160?

I took the engine apart using acetone/atf, heat and lots grunting...
The crank is siezed
the head has a dime sized chunk out of it
the piston has a matching chunk missing
The bottom end had sandy debris and some water in it..

The frame is twisted and the lugs are rusty... (Still has original number plate on headstock)

On the positive side
The cylinder is actually pretty decent and can be rebored.
The cases are nice with no cracked fins
The clutch and timing covers are in good shape.

I do not want to make a 160 engine.. I want to keep it a 125s, as it came from the factory or a 125s with some racing style mods if that is what is available. If anyone has any ideas, im all ears.

Thanks

[gtrench]

Any pics? Sounds interesting. My understanding is that the 125/160 share many of the same engine parts. I recently rebuilt a 125, and unless my parts were modified, a 160 head bolted onto the 125 barrel, but the 160 barrel is too big for the 125 bottom end. I can't comment on cranks and other bottom end internals since I haven't had them both at the same time to compare (but they look the same in diagrams). Covers (top and bottom end) are interchangeable. The frame and chassis on the 125 has more in common with the early 175/200's, than the 160s (125 Sport has early "triangle" tool boxes, longer swing arm, 31.5 alloy narrowcase forks, clip ons/smooth top clamp, ect). Early 125's had full size 180 front/160 rear grimeca hubs like the "big" bikes, and the later ones went with the smaller 160 Monza Jr hubs. Rims were 17's on all of them. The fenders are special to the 125 Sport (due to the 17 inch rims), and a bit smaller than 175 Sport/200 Elite fenders. Classicducati.com sells replicas. Headlight and taillight should be similar to other early 60's models (though I've seem some early models with unique headlights similar to early 175 Sports ie, lights down the middle, switches/key on each side).

Tom Bailey's book spells out some more details if I recall.

Here's some inspiration for you! The bottom bike is Ted Henry's beautiful 125 Sport "Rider" (1962 I think?) with the later small hubs and decal on tank, the middle is Mike Harper Smith's earlier 125 Sport (1959 I think?) with the big hubs and screw on badges. If you get too overwhelmed, you build a special!!! That's what I did, mine is the other bike (without tool boxes and such) . I'm going to build a "proper" 125 Sport soon, the first one was a warm up!

These bikes are beautiful and extremely valuable and worth any time and money put into them in my opinion.

Gabe Trench

[gtrench]

Thanks for posting a photo John. That looks like a project that was on ebay a few months ago. I agonized about it for a few minutes, and before I knew it the buy it now was hit by someone else. I think the auction was up for less than an hour.

It's definiitely a "project." My 125 Sport project started as just a motor....the rest was sourced all over the globe, so in some ways you've got a good start. Hopefully the frame is saveable, but even if it isn't, another frame could be made to work with some light fabricating/modifying. I look forward to hearing about your progress!
Good luck!
-Gabe

[Rick]

John,
I can offer some info on parts that the 125/160 engines have in common. My 125 engine came from a racer, and it has a 160 head- I'll attach a photo of the recess in the head that the cylinder liner collar mates with, 76mm. I'd like to know if your 125 head has the same pocket dimension, if so, the 160 head may have larger valves- mine has a 30mm exhaust and 27.5mm intake, or the guy just damaged the 125 head and stuck a 160 on in it's place. I've had a problem with other engines when fitting a liner with smaller diameter into a cylinder/head designed for a bigger piston- the squish band gets sort of 'shrouded'- if you measured your head I could draw it out and see how it looks on paper. I didn't get a cylinder, and making a liner thick enough to fit a 125 piston in a 160 cylinder, and then necking it down to fit the crankcase mouth looks like a mess- having a 125 cylinder will save you some grief.

160 head pocket.jpg

I think the 52mm stroke engines, 100/125/160, share lots of engine parts, and 160 engines aren't too valuable, so the engine may not be a big worry. The head bolt layout is the same between my 160 top end and the 125 crankcases- the 125 crankcase mouth is 62mm and the 160 liner OD is 67mm- I need to find a 125 cylinder...
It looks like your rear frame hoop is bent, but that's not critical and shouldn't be too hard to bend back- some 'U' shaped pads to spread out the force and a long pipe may be all you need. The relationship between the axis of the steering stem and the pivoting axle of the swingarm is important, but not likely to be knocked out of shape.
All in all, not too bad- if you're not in a hurry it wouldn't be too hard to restore it, plus you have a tank, even if it's paper thin.
Rick

[Paddy]

Shame you are so far away , i have some 125 parts on my website including a head and barrel etc.
www.ducatipaddy.com

[gtrench]

On the topic of heads, I was going through some parts and came across a pair of 160 and 125 heads. They appear to be identical in just about every way, except for the mating surface on the 125 head is noticeably bigger to accommodate the smaller bore cylinder (no surprise there). I haven't had a chance to take any measurements of the diff (haven't checked the valve sizes either).
The 125cc head is on the right.
I also uploaded a pick of a 125 crank....Anyone out there with a 160 crank they could compare?

[john jupiter]

Thanks for the information guy. I will try and get some measurments on the head this weekend.
Paddy, thanks for the link to your site. Too bad i was a hair late in emailing you. If anyone else has or knows of some parts that could help me pls PM me.

-john