And the Winner is Trek

Continuing on with my previous search for the best motorized bicycle donor frames.
Who built one of the best / strongest / semi-affordable frames available for motorization?
Forget aluminum frames for now (unless one can snap up an REI Novara MTB cheap).

Its an early Trek hands down:
Value: I sold a gorgeous Trek 830 Chromoly frame MTB that was in superb condition before getting back into the MB world. At any rate - it went for $200 cash. Not bad $ for a two decade old used mountain bike.
Light & Strong:
Here are two of the best Trek road bike frames to look for in terms of ultimate strength, hi-quality components and superb construction. Check out how they were built: silver brazing - by hand.
Its no wonder these frames can still command high prices - look at the quality.

TX300 Trek bike cost $110 features Ishiwata chromoly tubing (1977-78 price).

TX700 Trek bike $195 with the best Reynolds 531 chromoly tubes – same years. 

http://www.vintage-trek.com/trek_history.htm

http://www.vintage-trek.com/TrekPriceLists.htm

Stronger than they look

Collectable Trek

Even stronger? Use a Trek 830-870 MTB frame.  Approx. 28 lbs. all up.

We're talking a darned-near indestructible bike.  

I owned a red 830 MTB than went thru hell and thrived on a PO's abuse.

Motor ready to the max

Ross is a great donor bike!

Next - The Ross Signature series:

Now this is a real sleeper of a frame. It has Ishiwata chromoly tubing and hi-quality components for cheap dollars. 

Hand-built & brazed in the USA (Allentown, PA).

Approx. 27 lbs. - I own this one.

Want a cheap MTB frame that's a real sleeper?  

Look at a men's Huffy Blades 18 speed MTB bike - it has a heliarc welded, tri-sectional heavy frame.

Heliarc welding on these frames is fantastic, with deep penetration and very clean work.

The Blades' cheaper parts may break but not it's killer BMX quality frame. 

Caution: the Huffy oem brakes won't hold up. Use a front disc brake & better levers.

Crank-set is very stout. Needs a Trek oem Shimano gear cluster & Tourney derailleur on the rear (not that expensive) to get far.

Another bonus - oem heavy-duty Wald 26 x 1.50 rims with high tensile spokes.

Why bother? When you're done you'll possess a very strong MB for few dollars ($45 avrg).

Frame like a WW2 tank + wide Wald wheels

Many of these strong framed bikes can be found on Craigslist - usually for fair prices.

 

 

HRM 1.4 hp Factor & Vibration

Hey this one's for all MB hp factoring naysayers out there.

The 1.40 hp per cubic inch factor for a modified drag-racing engine, (2-strokes qualify), is real.
Just ask the authority, Hot Rod Magazine.
My only mistake was not having the HRM quote handy when I posted in the MB forum.
I said the 1.40 factor for each successive modification would apply to any 2-stroke motor starting from it's manufacturer's base hp rating. OK so that's stretching it a bit.
Why? Because no-one knows the 66cc HT motor's actual base horsepower rating.
Example; some retailers are saying the PK-80 generates 2.75 hp bone stock.

Thus a stock (low rated) 48cc engine making 1.6 hp @ 5,000 rpm x 1.40 would equate to 5.88 horsepower. [4.2 cu. in. x 1.4 factor] ... if modified.
I was pretty durn'd close using the old desert racer "rough method" figuring on a scratch pad. My simple method compared to complex VE vs. rpm, etc. was declared invalid.
Damn! then why does the seat-of-the-pants 1.4 hp per cu. in. factoring method work, come rain or shine, and served us well, in planning engine mods, for decades?

Show me any stock stroke, ported, piped, up-carbed, China two stroke of "66cc" (47mm bore x 40mm stroke) and it will make a maximum of 8.5 horsepower (without engine coatings). Got a real printed dynamometer test reading for that motor - signed!?
If you possess such a motor then you need to apply to a GP motorcycle racing team right away.

Killer Hornets
The real practical limit for using any motorized bicycle engine's horsepower is vibration.
How much vibration can you stand while riding over 25 mph?
At 23-24 mph my 66cc balanced PK-80 buzzed the ole Cranbrook frame like a million hornets on steroids. Everything on the bike was vibrating - hard!
The other input is road-related vibration. With poorly maintained streets rough as a cobb, a motorized bike MB needs some suspension.
Wally world bikes like Huffy, Bike Path and Micargi can develop frame stress cracks from metal fatigue.
Note to self - get thee a better, more rugged, high tensile steel bike frame asap.
Like the Giant Stiletto, Schwinn Spoiler chopper bikes. Bring a fat check.
These fancy dudes (bikes) are pricey!

So where are really strong, affordable MB frames to be found? Read on.

I'll stick with the all steel Raleigh M-80 MTB frame from the late 1990s, built to similar dimensions and specs as a vintage cro-mo Trek 830.
Both work like the proverbial blacksmith's anvil.

My cro-moly Trek 830

Stout is the word.