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Discussion Starter · #1 ·
I've tried searching and have found bits of info that are leading me in the right direction, but any guidance would be appreciated.

So I am thinking about picking up a mts 1200 motor that had the common crankshaft failure. If I can get it at the price I am set on, I would need a crank. All the other parts needed are in a pile somewhere, so my question is specifically about the crankshaft.

My idea right now is to go through the engine, work on the intake ports to fit 1198 throttle bodies, and throw in the crank from the streetfighter, using the mts connecting rods. This isnt ideal, id rather use a crank from an engine im not using, but the potential has me curious.

Would this work? From the parts diagams, it looks like the sf/848evo crank is much lighter, but I dont know the specifics of how this conversion would affect stroke.

I would prefer to keep the streetfighter engine intact so I can throw it into a 996 chassis for a fun track bike, so if anyone knows which cranks would fit, I would appreciate it.

I'm relatively certain 1098, 1198, diavel and mts cranks would fit, but I would prefer to work with what I have(748 crank maybe)

Thanks in advance!
 

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The MTS and all 1200cc engines have shorter rods than 848/1098 displacement engines, so the crank/rods/pistons are not interchangeable.

If you’re wanting to use the rods and pistons out of a 1200, you’ll need 122.5mm rods designed for a 1200. The 124mm rods from the 848/1098 won’t work.


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Discussion Starter · #3 ·
The plan was to swap rods from the broken crank to the streetfighter crank. I'm hoping the crank is still good, the only damage seems to be where it snapped at the flywheel assembly.

Would the mts1200 rods not fit on the 848 crank? I plan on finding this all out by taking things apart and doing a lot of test fitting, but any info would help.

that engine in a 350 lb streetfighter package with a dry clutch would be ideal for the street, at least until i source more aggressive cams.

the thought of throwing a 1040cc testa evo into a 996 and the 996 engine into a 748 also has be drooling.

Thanks for the response, I appreciate it!
 

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The main journals are the same diameter in both cranks, the rod journals are also the same diameter.

Why would you swap rods from the 1200 to the 848? Not sure what you’re trying to achieve. The 1200 short rods must go with 106mm (1200cc) pistons.


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The only upgrade I’m aware of for the 848 cases would be the 104mm pistons and cylinders from a 1098 on the 848 crank giving 1040cc.

If you’re trying to achieve something similar with the 106mm pistons, cylinders and rods, I don’t think they’ll fit. As far as I’m aware the stud spacing for the 1198/106mm bore cases are different.


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Discussion Starter · #6 ·
No sorry I wasn’t clear. I have a 1040 but it’s too much of a race engine for the street, compression is like 13:1, so I was thinking of putting the motor on the shelf until I get the time to drop a 996 frame onto it.

I was planning on transplanting the entire mts motor into the streetfighter, already have a lead on a 70mm exhaust, so the swap would be easy, with the caveat of needing a crank. I would either temporarily use the crank from the sf until I found a donor or use a 748 crank if it would fit, which I’m assuming it would not.

i try to avoid splitting cases if I can, but the sf1040 motor will need beefier main bearings at some point, so that’s where the idea to use the sf crank came in.

I think the multi1200 motor in a sf frame would be more pleasant and the 1040 beast of a motor with a well setup 996 chassis will be great at summit point.
 

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there's a 6.7mm difference in stroke, so if you fit the 848 crank you'll need to make up the 3.35mm difference with longer rods or pistons. the reduced capacity will also reduce the compression a bit too, being about 10% less.
 

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Discussion Starter · #8 ·
Yeah, having only cracked cases once, I wasn’t thinking the whole thing through correctly. My cloudy brain was thinking the rods determined stroke length and not the offset from the crank.

If I threw a hypermotard crank, adjusted the deck height and did the necessary throttle body work to suit, would there be any problems running at around 1250cc?
 

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If by Hyper you mean 1078cc air cooled crank, those have 71mm stroke and I believe the pistons would come into contact with the rods if using the 1200 pistons. Pretty sure they’re not interchangeable


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Discussion Starter · #10 ·
Man, this is more complicated than I was anticipating. I was thinking about piston to valve clearance and adding base gaskets to accommodate the stroke.

So you just mean the angle would be off and the rod would contact the skirt?

I came across a post where someone used a 71.5 mm crank in a mts1200, but there wasn’t much info other than modifying the airbox to accommodate the 3-4mm of increased separation of the throttle bodies.
 

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Discussion Starter · #11 ·
Also, my apologies for not conducting the proper due diligence before posting, but I really appreciate the info.
 

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The primary gears are also slightly different between MTS and 1198 street fighter/SBK. Not impossible, but they are not identical.
 

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Man, this is more complicated than I was anticipating. I was thinking about piston to valve clearance and adding base gaskets to accommodate the stroke.

So you just mean the angle would be off and the rod would contact the skirt?

I came across a post where someone used a 71.5 mm crank in a mts1200, but there wasn’t much info other than modifying the airbox to accommodate the 3-4mm of increased separation of the throttle bodies.
I just meant I’m pretty sure the 4v piston attached to the 71.5mm stroke would contact the rod at the lowest point. But I can’t confirm as a I’ve not tried this combination myself.


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You should contact Mark at Duc Shop. He’s got the experience and could say for sure. Or call Ben Fox i. Colorado.


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Discussion Starter · #15 ·
Yeah checking in with mark would be a good idea. He helped me out with my 1040 and I feel bad shelving that for the time being. It’s just not a street motor and streetfighter aerodynamics at the track suck for a tall guy. I really enjoy wind protection when going fast.

Thanks for the direction, I have a lot of material built up for build threads so hopefully I’ll find a way to tear myself away from the research and wrenching long enough to post all the videos and pictures like @Buzzer and @fastgas are doing. That content is easily my favorite part of the forum so I’m gonna make an effort to thread a cohesive story into the imagery.
 

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Discussion Starter · #16 ·
The primary gears are also slightly different between MTS and 1198 street fighter/SBK. Not impossible, but they are not identical.
Yeah I was planning on reworking the gears. I’m running a hypermotard evo primary clutch/crank gear set on the streetfighters dry clutch, so I know there is some cross compatibility.

Everything on the left side would be pretty much fresh. I have a multi stator magnet, flywheel, and flywheel spacer in a box somewhere, so all that’s left is the starter clutch and intermediate gear.

All of my building has been top end work, which seems like a breeze compared to crank work, so I’m doing my best to learn as I go.

Thanks again!
 

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Discussion Starter · #18 ·
Yeah that’s where I saw the conversion! Thanks!

I’ll pm him if he doesn’t jump on this thread. Pretty sure I have a tapered gear from a wet clutch, so I’m thinking this will all work.

1260cc with a smooth midrange sounds like a dream in a streetfighter 848 chassis 🤤
 

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I am in the middle of a built for my 848EVO which threw a leg out of bed last year.
I am effectively building a new wet clutch 1198 motor using MTS crank, cases, cylinders and heads.
Pistal HC 1198 pistons and Carrillo rods. I am using my wet slipper clutch and other parts on the8 clutch and chain side but everything inside the center of the cased have been changed, or replaced.

If you do get an MTS crank just make sure you get everything that bolts onto it as the crankshaft/clutch gears do vary. Also the timing lay shaft was shorter which caught me out,

The crank is basically an 1198 crank but has plugs in the webs which i assume are for balancing as the MTS has different pistons to the 1198. It was a bit more complicated to balance, but doable.

I agree with those who have pointed out the6 ride length difference, i know guys have put 106mm cylinders on 848 motors with the standard crank, but i have no idea how they got away with the deck height issues due to rods being too short?

Anyway my motor is going to work out, but its complicated. There are lots of differences with the MTS parts which required modification. (should have sold it and upgraded.

I will probably do a post on it, when its running for anyone interested,
 
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