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Husaberg FC470E Engine inside an Aprilia RS125

E

Expat2000

Joined Sep 2021
6 Posts | 5+
Norway
Hi all

Thought I'd introduce myself.

I'm Stuart. British but living in Norway, just north of Oslo.
Currently enjoying six month winter down time from bikes as temperatures and snow mean riding just isnt fun on my old bones. Rode and raced (supermono) in my youth then break of 25 years, now enjoying the bulding as much as the riding.

Joined here as picked up a Husaberg FC470E engine and associated bits for my winter project. Got it all from a guy who had an idea to build a cafe racer about 15 years ago but finally admitted it wasnt going to happen, came with a Honda CB350F frame and running gear and the price was right.

My plan is slightly different....
I have a 2000 Aprilia RS125 which I bought as a minor crash damaged project a couple of years back. Easy fix, mostly cosmetic and paint. Its a laugh to ride but needs to be a bit more mad :) So the 470 engine is going into the 125 frame. Both have right hand chain drive.

Some initial photos below, not in great rush to finish, maybe by summer this year. Too cold in the workshop for long days just now, was a tropical -5degC (23F) yesterday so got a few hours work in. -20C (-4F) isn't unusual.

Should be a giggle when its done, expecting about 135kg (300lbs) wet weight on the road.

Will keep you all posted and will inevitably have questions when its gets close to starting it up.

2000-aprilia-rs125.jpg

aprilia-rs125-frame.jpg

husaberg-aprilia-engines.jpg

husaberg-FC470E-frame.jpg

husaberg-FC470E.jpg
 
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Hi Stuart, after the forum conversion, I've been going through the backlogs of forum discussions, and your thread was stuck as pending in the moderation queue. Long time, but now approved...

How's it going with the Husaberg engine swap into the Aprilia?
 
zen said:
Hi Stuart, after the forum conversion, I've been going through the backlogs of forum discussions, and your thread was stuck as pending in the moderation queue. Long time, but now approved...

How's it going with the Husaberg engine swap into the Aprilia?
Click to expand...
Hi Zen

I thought I had done a thread, you may find another one with similar content from last week, just delete that one.

Anyway, not much progress since January until last week. Mainly due to lack of funds and motivation as out of work. Finally after 105 job applications I have a new start on 1st August so actualy had some free time and motivation.

So now: rear of engine in in, swingarm pivot sleeved to match 14mm swingarm pivot, spacers measured and made so chain run is good, engine sits 6.5mm to the right of centre (which I can live with). I did have to shave the swingarm slightly to clear the cases through full movement, less than a millemeter so wont be a problem. Front mount is coming along. Usual story for me, design on paper, build with cardboard, transfer to metal, tack in place. I will get it welded properly as I can stick stuff together but dont trust my ability with structural elements. It's probably over engineered but should give some bracing to the frame as well. The shapes are a bit rough, might tidy up before paint but it will all be hidden by the fairing anyway. Cutting 6mm and 10mm steel plate with an angle grinder and drilling it with a cordless hand drill takes time :)

20220715_192313_small.jpg20220715_142055_small.jpg20220715_163353_small.jpg20220718_151851_small.jpg20220718_153709_small.jpg20220718_165902_small.jpg20220724_122350_small.jpg
It is quite heavy but I dont think having more weight near the front will be a bad thing, might keep the front wheel down a bit. I can always revisit it later if I start chasing weight reduction.

Engine sits OK in the frame, the top of the carb is 20mm below the base of the tank so may need a right angle bend on the throttle cable.

Have started thinking about wiring, intake and exhaust. Cant decide on custom made airbox, huge cone air filter or an open stack. Advice is welcome. If I do go on the airbox route it will probably be fibreglass based on cardboard model :). If someone has the volume of the original airbox then that would be excellent.

Look like the aprilia radiator support will go back in nicely so probably run that radiator.

I think the exhaust will be the hardest part. If anyone has a good design regarding pipe lengths and/or dimensions I would really appreciate it. I have the original system but its got no chance of fitting as the frame is in the way. It looks very short to my eye as well. Prelimiary plan is: headers will go straight down and under the engine, join together into a larger diameter and then sweep left to an upswept cone. The swingarm has a banana shape on the left for the original expansion pipe. I have a non-standard muffler already as came with the engine (and it looks nice so will be getting used.)
20210907_164509_small.jpg

Realistic target is to get it mostly finished by end of the season before winter sets in and then technical inspection and on the road next Spring.

Spare time at the moment is being taken up teaching no. 4 son to ride his motorcycle as he decided to join us :)

Will keep you posted.

Stuart
 

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Expat2000 said:
Hi Zen

I thought I had done a thread, you may find another one with similar content from last week, just delete that one.

Anyway, not much progress since January until last week. Mainly due to lack of funds and motivation as out of work. Finally after 105 job applications I have a new start on 1st August so actualy had some free time and motivation.

So now: rear of engine in in, swingarm pivot sleeved to match 14mm swingarm pivot, spacers measured and made so chain run is good, engine sits 6.5mm to the right of centre (which I can live with). I did have to shave the swingarm slightly to clear the cases through full movement, less than a millemeter so wont be a problem. Front mount is coming along. Usual story for me, design on paper, build with cardboard, transfer to metal, tack in place. I will get it welded properly as I can stick stuff together but dont trust my ability with structural elements. It's probably over engineered but should give some bracing to the frame as well. The shapes are a bit rough, might tidy up before paint but it will all be hidden by the fairing anyway. Cutting 6mm and 10mm steel plate with an angle grinder and drilling it with a cordless hand drill takes time :)

View attachment 15961View attachment 15962View attachment 15963View attachment 15964View attachment 15965View attachment 15966View attachment 15967
It is quite heavy but I dont think having more weight near the front will be a bad thing, might keep the front wheel down a bit. I can always revisit it later if I start chasing weight reduction.

Engine sits OK in the frame, the top of the carb is 20mm below the base of the tank so may need a right angle bend on the throttle cable.

Have started thinking about wiring, intake and exhaust. Cant decide on custom made airbox, huge cone air filter or an open stack. Advice is welcome. If I do go on the airbox route it will probably be fibreglass based on cardboard model :). If someone has the volume of the original airbox then that would be excellent.

Look like the aprilia radiator support will go back in nicely so probably run that radiator.

I think the exhaust will be the hardest part. If anyone has a good design regarding pipe lengths and/or dimensions I would really appreciate it. I have the original system but its got no chance of fitting as the frame is in the way. It looks very short to my eye as well. Prelimiary plan is: headers will go straight down and under the engine, join together into a larger diameter and then sweep left to an upswept cone. The swingarm has a banana shape on the left for the original expansion pipe. I have a non-standard muffler already as came with the engine (and it looks nice so will be getting used.)
View attachment 15970

Realistic target is to get it mostly finished by end of the season before winter sets in and then technical inspection and on the road next Spring.

Spare time at the moment is being taken up teaching no. 4 son to ride his motorcycle as he decided to join us :)

Will keep you posted.

Stuart
Click to expand...
Great project! Should be HUGE fun on the road- love little bikes compared to the monsters around now.
Definitely run an aibox- makes big difference, much easier to jet. Theory in the day (I played with Supermonos with Yamaha motors) was 10 times engine capacity at least. Measure original headers with a piece of wire to get their length then try to replicate that- shorter only good for revs, longer better for spread of power, but you can't go much longer without stepping up diameter.
That frame should be more than strong enough for road speeds- they were quite similar to the RS250 frame.
 
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You haven't picked thee best engine there Stuart. So we'll have to hope it is a good one. If you don't have a carb yet, try and get a keihin FCR. Try and get it so you can get the left engine cover off as it will need to come off a few times at the start. There's a whole buch of work needed.

Cheers

Taffy
 
Taffy said:
You haven't picked thee best engine there Stuart. So we'll have to hope it is a good one. If you don't have a carb yet, try and get a keihin FCR. Try and get it so you can get the left engine cover off as it will need to come off a few times at the start. There's a whole buch of work needed.

Cheers

Taffy
Click to expand...
Hi Taffy

The engine wasnt my first choice but it was a combo of price and availability so went for it.
Engine came with a 40mm carb, not sure what it is as havent looked closely at it yet.
Can you elaborate on why the left engine cover will need to come off and what work will be needed?

Just to stress, the point of this build is just to make something fun (and fairly unusual over here), and most of the fun will be in the building. I'm not chasing ridiculous weight or horsepower goals as its not a race bike (those days are a long time past for me), just a fun Sunday afternoon toy and maybe the occaisional trackday for giggles.

Cheers
Stuart
 
well they can stick in gear, the starter gears slip and generally the water pump seals can need replacing so they aren't a leave-alone item.

Taffy
 
Taffy said:
well they can stick in gear, the starter gears slip and generally the water pump seals can need replacing so they aren't a leave-alone item.

Taffy
Click to expand...
Ok, useful information to know. Thanks

Was thinking about what you were saying and I think access to the left engine cover will be OK.
 
OK, back again, not much has happened in the last year, was out of work for a while (corona cutbacks), then a new job which has kept me busy and been tryng to recover financially, then winter (-20C in the workshop kills the enthusiam).
But work has continued slowly.
Engine mounts finished.
Exhaust mostly complete.
Radiator mount made
Wiring sort of planned
Now the plumbing....
I've done some digging on the net and in my service book and I'm struggling. Can anyone provide a schematic of the coolant flow for the engine and radiators?
2001-ish FE470
To my eye there are 3 coolant pipe points on the engine,
1) low down on the left is the water pump,
2) left side on the barrel
3) top of the rocker cover (although not sure if this is for coolant or a breather?)

The engine came with some pipes but not a complete set and no thermostat. I do have the Aprilia coolant pipes as well but the termostat was in the engine so its been sold off.
Ideally I'd have a diagram or photo of teh standard setup with pipes and direction flow labelled so I can then try to integrate with the radiator I have.

The aprilia rad doesnt have cap on the top but has a reservoir instead, not sure how thats going to work?

Hope someone can help, cheers.

Stuart
 

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