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PostPosted: February 27, 2018, 12:35 am 
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I've been stuck on the idea of building a locost with a Triumph Rocket 3 engine. I haven't found much mention of this engine here other than by 962porsche in a 2013 thread. 148 hp @ 5750 rpm and 163 ft lbs of torque @ 2500 rpm (roadster version) in an engine and trans that I'm guessing weighs about 250# seems like a great candidate. Similar to 962porsche, I would make a gearbox for the back of the engine to correct rotation and help center the driveshaft. By using gears from a quick change rear, I'm hoping to be able to change gear ratios. There shouldn't be a lubrication problem as the engine has a dry sump. I know the earlier versions of this engine had some geartrain weakness, but I think this was corrected in 2010-11. Carpenter Racing has gotten over 265 hp out of this engine, but the mods are not locost. These bikes are not common on the salvage sites but do show up now and then. Am I missing something here? Any input would be greatly appreciated.


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PostPosted: February 28, 2018, 1:21 am 
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Are you saying it uses the same rotation at the output as an FJR 1300?
If so I may have to look for one too.

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PostPosted: February 28, 2018, 2:07 am 
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It's about the same weight as a Ford Duratec with a T5 transmission and probably a little more delicate. The Duratec comes in several flavors. Hmm, now I'm remembering that bellhousings are an issue. It's something else to look at though. The Duratec is much lighter than the small engines that can make big power on Turbos.

If you want the Triumph though, go for it. Look carefully at the transmission and final drive ratios...

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PostPosted: March 2, 2018, 2:51 am 
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Although I've been lurking here for a 2-3 years, I haven't posted much. So as a relative newbie feel free to point out my mistakes.

RichardSIA wrote:
Are you saying it uses the same rotation at the output as an FJR 1300?
If so I may have to look for one too.


I think the FJR 1300 and the Rocket 3 both have the driveshaft on the left side which would mean they both rotate in the same (wrong) direction.

horizenjob wrote:
It's about the same weight as a Ford Duratec with a T5 transmission and probably a little more delicate. The Duratec comes in several flavors. Hmm, now I'm remembering that bellhousings are an issue. It's something else to look at though. The Duratec is much lighter than the small engines that can make big power on Turbos.

If you want the Triumph though, go for it. Look carefully at the transmission and final drive ratios...


I haven't been able to find the actual wt. of a Rocket 3 engine. If anyone has weighed one I'd love to know. What I have done is to research the wt. of 6 other large bike engines, and then divide that by the dry wt. of the bike. By averaging them I came up with .332 or engine weight being 33.2% of dry bike wt. This x 736# for the Rocket 3 Roadster = 244# plus about 10# for the reversing gear box = 254#. I'm sure this is just a ballpark figure. The Duratec I think comes in at about 275# ready to run with starter, flywheel, and pressure plate. To that you need to add a bell housing (15-20#) and T5 trans. (about 75#) = 370# total. The plus side to the Duratec is that my wife has an Ecoboost 2.0 version sitting in her 2013 Escape, but I know she would have my number as soon as she hit the start button.

The other advantages to the Rocket 3 with the homemade gearbox is that it not only reverses the rotation and helps center the driveshaft, but also allows me to change drive ratios and adjust the vertical position of the driveshaft by rotating the gearbox mounting position around the Rocket 3's output shaft. This may allow me to lower the engine and CG since I don't have a large bellhousing/flywheel to deal with. Also I may be able to go with a narrower driveshaft tunnel without a trans. hanging off the engine, which would allow more pedal room and seat width (or maybe a narrower and lighter frame).

Another advantage at my age is that it's a lot easer to part out a doner bike than a car.

I haven't even decided on a frame design yet so I'm probably getting way ahead of myself here. I do appreciate the deep knowledge base here and look forward to more input.


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PostPosted: March 2, 2018, 5:20 pm 
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The Duratec I think comes in at about 275# ready to run with starter, flywheel, and pressure plate. To that you need to add a bell housing (15-20#) and T5 trans. (about 75#) = 370# total. The plus side to the Duratec is that my wife has an Ecoboost 2.0 version sitting in her 2013 Escape, but I know she would have my number as soon as she hit the start button.


Maybe we're both right on the weight? I weighed one at a friend's dyno shop right after it came off the dyno, it was still dripping. The picture is in the engine weight thread somewhere. Maybe it was 225? It did have an aluminum flywheel. It was an engine from a Caterham dealer. We tried to be honest it has a pile of ignition parts and some stuff on top of the motor.

You should be able to get the motor from any old Escort or focus at a junk yard. Again, not pushing you here if you prefer working with the bike engine.

Another thing on bike engines is they can have more backlash in the drivetrain. Not an issue at all on a track but if you want to drive it on the street things like backlash and ratios will make a much bigger difference. On the bike engines the FJ might give you availability and parts sources.

I think we have made some progress on figuring out how to fix direction of rotation in differentials. I have also thought a jet ski motor with a VW or Audi transaxle might work. They are bike engines without transmission. We had a fellow trying to build a reverse box from motorcycle gears but it seemed to be turning into a lot of effort.

Can you run a Subaru diff upside down?

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PostPosted: April 11, 2018, 3:56 pm 
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Joined: September 3, 2012, 10:48 pm
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Location: Hamden CT.
i have done a few of them to date. i like the motors they do offer good HP and torque i did scale the weight of the motors but don't remember what they are off the top of my head. 180 i think is the weight????
to reverse the driveshaft is easy the 1st one i built i didn't build a box around it to lubricate the one to one counter rotating gears i used. they are still holding up good but are kind of loud ( gear noise)
the other ones i boxed in and fill the bottom of the box with grease up about 1/4 way up the gears. they make no noise at all.
i go to a miata rear diff with miata suspension and hubs. with the miata diffs they have different gear ratios so you can pick one you like for your needs.
the last one i did this past fall was swapped into a MG midget it was tight real tight to get into the car swapping out the suspension was not to easy either but i got it in and it worked out great.
when the customer gets more money he will be bring the car back for me to do the miata front suspension. he is also talking about me doing fender flares for bigger tires.
swaps i like to do are using suzuki GSXR motors goldwing motors and the rocket motors. the rocket motors are just torque monsters they will not rev like the sport bike motors but they just keep pulling and pulling to red line then you shift and they again just keep pulling. they come out of a 800 lb bike so going into a 1100 lb car you don't lose much in the way of power.


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PostPosted: April 11, 2018, 3:58 pm 
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The new Goldwing has a Dual Clutch transmission and fuel injection so it should be much better than the older models.

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PostPosted: April 12, 2018, 8:54 am 
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Joined: September 3, 2012, 10:48 pm
Posts: 329
Location: Hamden CT.
yes the newer goldwing motors i like .
i have a guy that keeps stopping in my shop talking to me about swapping a goldwing motor into his geo metro convertible.
it's just not going to fit! he really wants it med engine rear drive with a budget of 8K. he has the 1992 geo and a 2001 goldwing stolen recovery all the panels were stripped off the bike.
it's to wide to fit in the front and to long to fit in the middle of the car.


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