/5 Engine in a /2

[fredheiler@aol.com]

Does anyone have specs for the spacers and slightly longer bolts needed at the transmission output flange when a /5 engine and trans are installed in a /2? My conversion bike is nearly complete, and I know these spacers are necessary.

As background, my very first bike was a 1967 R60/2, which I regret selling. My son Tim found it and badgered the owner for years to sell it to him. It finally happened, so he got five friends to help him winch it out of a basement on Long Island and load it on a rented trailer. He surprised me by giving it to me, and I was blown away. However, it was in bad shape -- rusty frame and missing cylinder and head.

Earlier, Tim had bought a nearly complete R75/5 basket case that turned out to have a bent frame, but a really good engine and trans, which I have rebuilt. I also stripped the /2 frame and got it powder-coated -- looks like new. My goal is to complete the restoration of the /2 bike, but with the /5 engine and trans. Since I'm 77, I'm hoping my son will like riding it enough to sell his Triumph T120 (he's already disillusioned with chain drive maintenance). He has grown to love /2 bikes, and says all they need is "a little more power."

 

[20774]

Welcome to the forum! Never been around conversions before. As for engine bolts, aren't you just going to use the /2 engine bolts? I'm assuming that the mounting holes on the /2 frame match the holes in the /5 engine. I guess the spacers will essentially be equal to the difference in width of the two engines were the mount bolts go through.

I can't think of where someone has documented this type of work, but I ran across this site with some general info about these types of transformations:

https://cybermotorcycle.com/archives/bynum/2convers.html

 

[fredheiler@aol.com]

Driveshaft Bolts

Sorry, I was too vague in my initial inquiry. I'm referring to the bolts that secure the driveshaft to the transmission output flange. Apparently, the /5 box is about 1/4 inch shorter than the /2, which means the sliding splines where the driveshaft engages the rear drive are not engaged enough.

I've read that a number of good conversion bikes (/5 engine and trans in a /2) use spacers and longer bolts on the trans output flange. I'm hoping to find specs for spacer thickness and corresponding bolt length.

 

[20774]

Fred -

The bolts used to hold the driveshaft to the transmission output shaft are the same for /2 and /5 bikes, so there aren't any longer ones that I know of. That website I linked too has a discussion about the swingarm and final drive and there's mention of spacers and other options. For some reason, when I look at that page in my browser, the images on the right side fall on top of the text. You can highlight the text, copy, and paste it into Word (as an example) and be able to read what they say.

 

[fredheiler@aol.com]

Driveshaft Spacers

Dear Kurt:

Thanks for keeping an eye on all this dialogue. Yes, I've seen references to these spacers on Bynum's site and other places, but no one mentions any details. I know stock /2 and /5 driveshaft bolts are the same, but longer ones are needed when a /5 engine and trans are installed in a /2 bike (as Bynum and others have done; a sweet conversion!)

I'm guessing it's something like "12 mm spacers, with correspondingly longer 8 x 1 mm driveshaft bolts." I'll let you know when and if I find something definitive.

Regards, Fred Heiler

 

[20774]

I don't know about the spacer, but seems there should be a way of backing into what it has to be. As for the bolts, wouldn't it be possible to find something that is the length you need at McMaster Carr? You know the thread pitch and diameter...you would just need them to be longer than the stock bolt by the depth of the spacer. You said that the transmissions are 1/4 inch different. Is that the size that the spacer needs to be?

 

[fredheiler@aol.com]

Driveshaft Spacers

Hi Kurt:

I think you're right, and if I don't hear from anyone with definitive specs, I plan to measure the exact length of the assembled /5 and /2 transmissions, and calculate the spacers and bolts accordingly.

According to Bynum and others, If this detail isn't addressed, the sliding spline at the back of the driveshaft where it engages the rear drive unit won't be engaged deep enough.

Thanks, Fred Heiler

 

[20774]

Could you maybe measure how much the /2 driveshaft moves rearward to get a sense of what the engaged threads are? My thinking is that with the driveshaft in its /2 position, how far back can you push the shaft before it "bottoms" out. That could be dimension that you could double check once you get some spacer length figured out. Ultimately, with the /5 setup installed, the /2 driveshaft should be in relatively the same position.

 

[fredheiler@aol.com]

Driveshaft Spacers for a Conversion Bike

I heard from Chris, a really good guy at Boxer Metal, which sells a custom driveshaft that works great. He said the spacers are 0.135 inches (about the thickness of two good flat washers), but he cautioned there is a 0.011-inch lip on the driveshaft that centers it on the trans output flange. He offered to provide spacers, which hopefully will also address the centering issue. Stay tuned.