Engine mounting S4 vs 851 frame

jakepeewee

Hi fellow ducatisti,

I have searched through this site and some others as well, but can't find the information I am looking for. It will probably be up there, so sorry for bothering you with my question.

I am building an engine based on S4 crank cases which will be mounted in my 851SP3 frame. S4 cases have 12 mm engine bolts, the holes in the frame are for 10 mm bolts. And since I want to be able to put her back to original, I don't want the frame to be drilled.

I did look into helicoils but found that a 10 mm insert requires a 10.3 mm drill hole, so that won't work I guess.

Can anybody tell me how to modify the cases from 12 mm thread into 10 mm or where to find info on this?

TIA,
Jacco

nine16

The cases themselves aren't threaded. You would just use a reducing sleeve through the motor. not sure if anyone makes one, but you could have one machined out of aluminum pretty easily.

Speedmade

Jacco,
I found some tubing that was the correct ID and OD to use as a sleeve. Just cut to length and slip into the cases.
I will look it up tonight and get you the specifications.

Reed H

RWG

Hi jacco
Just a question please, Are you replacing an SP3 motor from an Sp3 frame/Bike, or do you mean a strada series 3 frame.

I ask because some might say sacralige to convert an icon like an SP3.

Or do you just have frame?
Cheers
Paul

dudlington

I am building an engine based on S4 crank cases which will be mounted in my 851SP3 frame. S4 cases have 12 mm engine bolts, the holes in the frame are for 10 mm bolts. And since I want to be able to put her back to original, I don't want the frame to be drilled.

Why don,t you just buy some 12mm tube with a wall thickness of 1mm and cut to length where you need the support for the engine. Loctite it in the engine casings before you fit your original bolts. This tube is standard so cheap and easy to buy on fleabay. Once it it all clamped up where can it go ?. If you are worried then insert a steel tube.

https://www.ebay.co.uk/itm/50cm-Aluminium-Round-Tube-Pipe-Outer-Hollow-Shaft-Outer-Dia-12mm/183828067768?hash=item2acd01b5b8:g:HWwAAOSwd9lc7Vat

jakepeewee

Thanks all for your swift replies, what a great community this is!

And boy, do I feel stupid 😁, totally forgot that these bolts go through the casings so no thread in the casings.

Jacco

jakepeewee

RWG wroteHi jacco Just a question please, Are you replacing an SP3 motor from an Sp3 frame/Bike, or do you mean a strada series 3 frame. I ask because some might say sacralige to convert an icon like an SP3. Or do you just have frame? Cheers Paul

Paul,
I do mean replacing my SP3 motor. That way I will always be able to bring her back to original spec. I like the idea to build a rev happy, more modern and powerful engine and keep my SP3 engine safely stored.

Regards,
Jacco

dudlington

Jacco

Yes this would be a smart thing to do.