Atom Bomb Custom's Triumph Dirt Bike


It's easy to get wrapped up in the details while building a custom motorcycle and forget about the overall stance, complete package, etc. Likewise you can nail the stance and then cut corners on the little stuff and end up with a disappointing pile of compromise. Clay Rathburn doesn't have this problem and is known for his stunning, hand-built motorcycles. Their clean lines and lack trendy frills makes his bikes easy to pick out as Atom Bomb Customs. For this particular machine, Clay kicked classic choppers square in the nuts and made himself a semi-modern dirtbike from scratch and a little help from an old OIF Triumph. It looks so well proportioned and finished from every angle that you could almost think it's a factory dirt bike, though you'd be hard pressed to figure out the exact vintage.




Engine, year and make, model, modifications: 1974 Triumph Bonneville 750; front motor mount removed, various other mounts removed and altered, intake ports relocated 1.5” inboard, exhaust converted to flange mount, more or less stock rebuild with oversize valves and 650 exhaust cam. New Amal carbs, Pazon ignition. Exhaust is stainless, fabricated in house with Burns Stainless collector and muffler. Jeremy at LC Fabrications made the carb tops and ignition cover.




Frame: One off mild steel frame and swingarm built by me. The frame reuses about a 1/2” x 2” portion of the original 1974 Bonneville frame. About the same size as the VIN. Totally custom frame geometry to actually work like a dirt bike.




Tire/wheel size and style: Sun rims on Yamaha TT600 hub in front and lightened Triumph conical out back, 2.75”x21” and 4.00”x18” Pirelli MT43 tires. 




Fork: 43mm KYB, revalved and resprung by Racetech. Originally on a 1983 Yamaha TT600. Shocks are custom by Racetech.







Favorite thing about this bike: Who else would be stupid enough to build this? That’s my favorite thing about it. Really, just being able to get something like this from my head to reality was pretty cool.




Other mods, accessories, cool parts, etc: Hand built fuel tank, center mounted oil tank, and side panels by me; Nickel plated frame, swingarm, headlight and kickstand; Carbon coated fork tubes, hand formed air filter housing, super sweet gas tank vent hose.




On the road or off, this thing rides like a beast. It’s got torque that dirt bikes normally don’t, and it’s big, so it can be a handful to ride hard. I was honestly surprised by how well the damn thing works, the suspension is awesome for being a standard twin shock setup.


Since this was a personal project and such an involved build, I got a lot of help from a lot of folks. Mostly from my wife who put up with this thing being a near obsession for a good long while, but a bunch of industry folks stepped up to help as well:


Race Tech Suspension:

Burns Stainless:

DC Plastics:

Carbon Raptor:


Rebel Gears:

LC Fabrications:

And don't forget to check out the Atom Bomb Custom site for more of Clay's creations:

Photos by Tony Hall

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Commented on 8-13-2012 At 06:32 am

That is freakin' AWESOME!!!!

Nice work Clay. I likes me some dirt bikes too.

Commented on 8-13-2012 At 07:19 am

Effing perfect. Why build bikes everyone would buy? That's the factory's job. You got skills.

Commented on 8-13-2012 At 08:05 am

Once again, Clay doesn't just take it to the next level, he goes so much further than that. I'm already in awe of his next build.

Commented on 8-13-2012 At 08:07 am

Good lord that thing is clean! Beauty

Commented on 8-13-2012 At 08:10 am

Great job man! Looks like a lot of fun!!!

Commented on 8-13-2012 At 08:19 am

I'd also like to admit I'm like Salieri to Clay's Mozart. 100% jealous of his overshadowing talent. Just when I think I've built something I casn be proud of Clay shows up with another opus that seems to turn my work into total shit. Why Clay??? Why couldn't you at least let me get my bike into paint before crushing my dreams?

I'm going to end up being committed in a sanitarium suffering from dementia and babbling about the great Clay Rathburn as I'm spoon fed apple sauce.

Commented on 8-13-2012 At 08:24 am

I just watched "On Any Sunday" last night and this reminds me of a lot of those bikes. Way cool. Makes me want a dirt bike.

Commented on 8-13-2012 At 11:10 am

absolute beauty man! just add dirt!

Commented on 8-13-2012 At 11:28 am

very nice!!!! classic

Commented on 8-13-2012 At 02:19 pm

Not to sound to cliche but--- U FUKN KILLED IT!
and ----That thing is TITS man!

Commented on 8-13-2012 At 05:44 pm

very cool bike. well done!

Commented on 8-13-2012 At 06:06 pm

neato fo sho

Commented on 8-15-2012 At 06:09 am

That is crazy good.

Commented on 8-15-2012 At 07:03 am

nice job Clay, I watched this thing going together and I knew I was gonna like it.

Commented on 8-15-2012 At 08:47 am

Ah, the dished bolts.

Commented on 8-15-2012 At 04:50 pm

"The frame reuses about a 1/2” x 2” portion of the original 1974 Bonneville frame. About the same size as the VIN."

Great line, that

Commented on 8-15-2012 At 04:51 pm

And that's about as custom as custom gets!

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