Yamaha IT frames, chromoly or mild steel?

[GT43]

Hi fellars,

I know that Suzuki PE frames are mild steel, so I am thinking the Yam IT chassis' are also mild steel ?

I was thinking of using my spare IT490 roller as a pre85 vmxer, but might not worry about it if being mild steel, as chromoly is more rigid and 30% lighter.

Anyone know if IT 's are chromoly steel ?

[Zakk]

a mate and i were discussing this very subject today, i've read in a few publications that the 1981 IT 'H' and later frames were chromoly but i think they're steel. i have 6 IT 'H & J' frames in my shed and they all have seamed tubing, chromoly is cold drawn and seamless.

[GT43]

Thanks Zakk.

Tomorrow Ille check for seems on the K frame.
Although it might be hard as it has a bit of surface rust on it. And I guess that might be a telling sign in itself - (mild steel) being rusty.

Just checked the weight diff between YZ490K and IT490K, and at 23kg, that leans more likely to mild steel, apart from the lights, blinkers, speedo etc.

Pretty crummy that Yamaha and Suzuki used Mild steel in their enduro bikes, and Kawasaki used chromoly in their twin shock KLX250's from the same era!!

[Nathan S]

I wouldn't worry about it, either way. A lot of the "chromoly" from back in the day was virtually indistinguishable from the mild steel - the only obvious difference was in the sales brochures...

The YZ-Es were supposedly the first of the chromoly YZ frames. Comparing a YZ125E frame to a YZ125D frame, and it's damn hard to spot the difference. The later frame has same/damn near identical material dimensions, weight (as you'd expect given the same dimensions), doesn't seem to be any more corrosion resistant, is no harder to drill... The only reason I have to believe that there's a difference in materials, is that I've seen more cracked E frames than D ones... :?

[Zakk]

easiest way to check is have a look inside the main downtube or main under tank tube with the hollow ends and see if there's a seam, if there's a seam then its not chromoly. although that doesn't mean its plain mild steel, it could still be a hi-tensile of some discription.

[GT43]

Its definitely mild steel Zakk.
Can easily see and feel the seem.

I have a YZ250K, and a J roller, and both also have seems !!
Then I checked my old 1981 KLX250 wreck, which has no seams.

So it looks as though early 80's Yamaha's skimped on frame material.
A bit piss poor one would think, when you look at bicycles having chromoly tubing.
I bet Broc Glover had chromoly in his works bike back then.

Agreed Nathan S, brochures are not reliable.

[mustanggrahame]

Not all chromoly is seamless. I believe IT's went to cro-mo for the F models in 1979.
Cheers, Grahame

[GT43]

Thanks Grahame.

Perhaps I'll sit on this IT frame idea for a little while longer, and if a YZ engine comes along at the right price, -  then go from there.


Cheers.

[cloggy]

 I used to be steeped in mountain biking lore. Some cromoly is flat sheet and then rolled and welded instead of being made out of a billet,  a lot of the taiwanese  stuff was made that way.

[mustanggrahame]

Reynolds chromoly tubing was seamless. There were different grades available as well. The reason it is lighter than mild steel is that it is much stronger so in a frame it can be a much thinner gauge and still have the strength required.
If we accept that YZ went cro-mo in 77 and IT in 79, what are the dates for the other Japanese manufacturers bikes?
Cheers, Grahame

[Davey Crocket]

PE's where chro-moly.

[HL500]

I've just been on the IT Forum and read a few old  magazine articles.  According to them the later IT and PE bikes were all chrome moly.

[topari]

According to my handbook, my 1979 IT400F is chro-moly.

[GT43]

Ok thanks guys, this makes me feel better and motivated for a project.

Cheers.

[OverTheHill]

Got me worried now as scrapped an IT250K frame a while back that was just 'Rotten', by memory in the front downtube & rails under engine etc. Could see the holes right through in parts. Worrying bit now is, long after that event i've ended up with a YZ465H in an IT250K roller & is great to ride but must go & inspect this one closely for rust. Have a YZ490K also so suppose same applies. Also have a PE250 twinshock frame with an Xr200 type motor in but cut the frame rails out underneath to get it to fit how i wanted it, always intended to weld something under there to tie it all together stronger but that was 20 years ago--still going, but am worried now--stop doing big jumps!!.