To rebuild a 450 engine.

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To rebuild a 450 engine.

Postby Rossguzzi » Sat Jul 18, 2020 3:03 pm

Hi all,
I've been looking at this forum for a little while and it seems like there is some very knowledgeable people here. So.
Long story short, I now have my old 450 Scrambler back in my possession after 45 years. It was crashed just after I sold it and sat in pieces since.
I'm planning to bring it back to near as new condition as I can. It had 35000 kms on the clock before the crash. Motor turns over manually and gears all select.
I have had a quote for a motor rebuild of between 5 and 7000 Oz dollars. (7000 worst case scenario) I have never rebuilt a motor, but a friend has, but not a Ducati. He has done Guzzi`s, Triumph Jap bikes etc.
Question is, should I take it to a shop that has done them before or tackle it with my friend. He is confident, but I am a bit full of fear worrying how to get preload shims and things right. I only want to do this once.
Could he do it with a decent workshop manual sub contracting out specific jobs like head work or crank regrinds etc. How hard is assembly ?
Are workshop manuals available ?

Many thanks for now, and I'm sure in the future.

PS previous owned Ducati`s inc 450 Desmo, 750 Sport, 450 Scrambler, 48cc Cucciolo.
6 Ducati`s, 6 Guzzi`s, 2 Aprilia`s, 4 Morini`s, 2 Montessa`s and a bunch of other stuff

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Location: Stafford UK

Re: To rebuild a 450 engine.

Postby ranton_rambler » Sat Jul 18, 2020 4:20 pm

I did my 175 myself. The shimming should be fine, as long as you’re methodical and accept that it will take a few iterations to get it right. You obviously need some stuff - micrometer and dial gauge are pretty essential.

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Re: To rebuild a 450 engine.

Postby Jordan » Sat Jul 18, 2020 10:52 pm

I think the trickiest work is getting the gearbox shimmed well.
If the box has been completely dismantled with some new parts to be installed, it's not a quick simple job.
Also, suitably sized shims are needed.
That's not to downplay the work on the bevel gearset.
These require a level of skill, perhaps beyond even an average professional mechanic used to simpler engines.
Someone with experience with bevel Ducatis would be good to employ.

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Re: To rebuild a 450 engine.

Postby ducwiz » Sun Jul 19, 2020 9:49 am

If you never have rebuilt a motorcycle engine, it might get very difficult to work on your 450.

- the gearbox shimming is indeed a bit tricky for a newcomer, but shimming of crankshaft, bevel gears etc. are tricky as well
- you need a couple of special tools for disassembling an re-assembling (see figures in the user manual)
- a set of measuring tools like micrometers for inner and exterior diameters, calipers and a a depth gauge are mandatory
- many shims in different sizes and thicknesses must be at hand
- you need patience, endurance and good cautiousness; never force any task with a hammer or inappropriate tools

Starting point: gather all possible infomation about the bike. A selection of the most important publications.

- the Motoscrubs tech page (many links do not work anymore)

more specific:

- 450 SCR user manual
- Haynes Ducati singles
- Revue Moto Technique (french)'officina.pdf
- MkIII/SCR spares catalog

A very useful but extremely rare book:


But your biggest source for information and guidance is the concentrated knowledge and helpfulness of many fantastic people domiciled in this unique forum. So, if you also have been professionally trained in mechanical crafts, you might finally succeed. In doing it by yourself you will save a lot of money and learn a lot, but it will cost you many hours.
Btw, working on a Guzzi engine is quite an easy job, compared to rebuilding one of a Ducati single.

cheers and good luck Hans

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Location: Essex UK

Re: To rebuild a 450 engine.

Postby George » Sun Jul 19, 2020 11:46 am

Everything Hans said. I have restored six various Guzzi's. Half way through first Ducati Single. More complicated but can be done with lots of patience and help from this forum. Good luck
George Essex UK

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Location: northern ireland

Re: To rebuild a 450 engine.

Postby blethermaskite » Sun Jul 19, 2020 1:48 pm

So the important question is, has this engine ever been dismantled before? if yes I would be very cautious of starting into it yourself, if no....are you sure?.....because if it is still an as factory built unit (while bearing in mind the need for some special tools) the difficult issues of re shiming every individual shaft in the engine should not be required unless something inside has become excessively worn or damaged, at 35000 K if well maintained in the past it should be still pretty much ok (except maybe for the big end and main bearings). So if you are really careful as you dismantle it, and insure all the shim positions are noted and are kept in place with each assembly as you remove it then on reassembly you just put it all back exactly as you took it apart. These engines were pretty much hand built and are really easy to screw up by careless dismantling. If as you say it was yours until the new owner crashed it presumably you will know if the engine has been messed with or not in your time of ownership. If you do decide to go ahead on your own you will get plenty of help on this forum......just go slow and careful and ask lots of questions, and be aware it might get pretty expensive before you are finished.

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Re: To rebuild a 450 engine.

Postby Rossguzzi » Sun Jul 19, 2020 3:25 pm

I bought it second hand. I cannot be sure if the motor has been opened before or not. The klm reading is what is showing on the 1/2 smashed speedo. I can't be sure if it is original kms. I'm guessing it is.
My friend is adamant he could do it. Though I doubt he has some of the special tools except for some common pullers, micrometer,dial gauge etc.
I was resigned to get the shop to do it until over dinner he insisted he could. He thought the quote of 5-7 $K was over the top.
So what special tools would be needed ?
If you could break it down, what would the steps be ? Im guessing;

1) Should I vapour blast the outside first after taping up the side covers ? Or just disassemble and bead blast at step 5 ?
2 Disassemble.
3) measure things.
4) buy parts.
5) bead blast.
6) Clean, clean, clean.
7) Assemble, ok I need help now. Crank first ? Gearbox 2nd ?
8) Help.
9) Help.

Many thanks for all this info.
6 Ducati`s, 6 Guzzi`s, 2 Aprilia`s, 4 Morini`s, 2 Montessa`s and a bunch of other stuff

Bevel bob
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Location: Bromley Kent UK.

Re: To rebuild a 450 engine.

Postby Bevel bob » Sun Jul 19, 2020 5:19 pm

Only use the correct puller for the flywheel. The crank cannot be re-ground. At a minimum it needs to be pressed appart ,cleaned out and re-assembled with a high degree of accuracy. This is one job for an expert. The rest is do-able but a non Ducati mechanic needs to be prepared to take 2/3 times as long as he would spend on say a triumph twin. Seeing the speed that some pro car mechanics work,I would not let one near it.

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Re: To rebuild a 450 engine.

Postby Jordan » Sun Jul 19, 2020 10:37 pm

Do the gearbox first.
The cases will be closed and opened several times, for locating the 3 shafts and checking their clearances.
A really thorough shim job means shimming each gear pair as well.
I don't think there is documentation for this detail. I was shown by a Gowanloch-trained mechanic.
Crankshaft end clearance adjustment is comparatively easy.

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Location: Tasmania Australia

Re: To rebuild a 450 engine.

Postby graeme » Mon Jul 20, 2020 2:18 am

Where in Australia are you?


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