vethead

I keep reading where people weld the seams fo their frames for strength. I may be a bit slow, but aren't the frames already welded on the seams? I am looking to strenghthen the frams as well, but this seems like it was done at the factory. Can someone give me a clue as to what they mean. If it works, I will do it myself.

MikeC

The frames are stitch welded.... kinda like 2" of weld 4" of no weld.... 2" of weld.... repeat, repeat.

this is for ease of assembly cost, and required rigidity. You seam weld it to make it more rigid and eliminate as much of the chassis flex as possible.

If you have the time and the equipment why not do it.... it can't hurt anything if done properly. I just did it to my frame that I am preparing to put under the 78.

vethead

Thanks for the info. I had thought they were welded 100%, didn't know they were stitch welded. I don't have the frame seperated yet, so I have never taken a real close look, just thought they were fully welded.

Twin_Turbo

later year frames are almost completely welded and they have better welding on the suspension mounts too, still thére's lots of room for improvement.

reidry

I'm going to seam weld my '69 however in speaking with a couple of welders and an GT racer, who has been doing it a couple of decades, the weld should not be full length in a single pass. There is something to the way the heat affects the local area that the weld should be done in 4" sections and allowed to cool before continuing. The older GT racer stated that they always left a few one inch gaps in their completely welded frames in case that one of the weld seam areas began to crack.

I'm no metallurgist so this could be horse puckey ... anyone got any knowledge in this area?

Ryan

Twin_Turbo

yeah, if you weld all the way through in one big bead your frame will warp because of the expansion and contraction of the frame, weld short sections and cool the surrounding sections with wet rags.

stpman

Too much heat from welding will twist metal bad. I've seen 3"x3"x3/8" angle bend 3/4" from welding a bead across the width.

Steve :steering:

macx

From an American Welding Society Certified Welding Inspector -

First, you never want to weld "across" a member, beam, whatever,
(perpendicular to direction of tension - as on the underside of a frame member). It greatly increases the likelihood of cracking along the weld.

Second, yes it is best to weld in short segments then allowing the metal
to cool. Similar to welding sheet metal which will warp in a heartbeat when
heated more than just very briefly, only not quite as pronounced. But you also don't want to weld when the metal is less than about 50 deg F.

Excessive heat input also changes the metallurgy somewhat - more or less
changes the molecular structure into larger crystals - making it more brittle
and therefore susceptible to cracking.

Also the idea of leaving some short gaps may not be a bad idea - if a crack
starts it would stop at the end of the weld.

Whatever, be very sure to completely clean any rust and paint well back from
the weld area - at least an inch. If you smell burned paint, stop and clean it
back to bright clean metal farther back from the weld.

Keep the welding heat as low as possible while still getting good fusion and penetration - also helps minimize embrittlement. GTAW ("tig") welding is the best if you know someone who is good at it, GMAW ("wire feed") can also be done at lower input temperatures and is strong when done properly.

Whoever does the welding should be able to do it without causing "undercut"
along the edges of the weld bead. Undercut is a small area right along the
weld that is melted during the welding but that is not totally filled in with weld metal. That small notch is a major stress riser and crack starter.

Good luck!

RHD '68 L89

I welded the frame on my '68- 4" of weld 1/2" gap, continue ad finitum.
I also powdercoated and foam filled it.
The foam is to damp down the frame movements and all the work really made a difference to the ride. I still have the F41 suspension but she rides so much sweeter now
:cheers:
James

stpman

macx

I know you shouldn't weld "across a member, beam etc" BUT when you weld an angle 90 degrees to a HSS member you HAVE to weld across one or the other or you would have tack welds at 4 corners. these were support brackets for electrical trays.

Steve

rob75383

I was interested in welding the seams fully, but I read some interesting posts about 2 years back where some people said that the rigidity had caused the frame to crack very badly during autocross racing.
Maybe they didn't have it welded correctly, but, to me, this is still an arguement with good points on both sides.

Skyhigh82

If you weld, leaving an inch gap between welds, the frame can you grind it down smooth and powder coat for a slick look?