30 Year Old Frame Strength?

[chuck]

I have a 72 125 six days. My questions is regarding the strength of the frame after 30 plus years. Visually the fame looks in good shape. I had to repair a crack on one of the front motor mounts. I will be racing this bike in AHRMA intermediate classes. Is there any need to beef up the welds for this type of use?

Thanks for your help.

Chuck

[Chakka]

I too am curious about frame strength. I have a 72' that I am working on and the area of the frame backbone where the side plates weld to it is all pitted due to corrosion. I won't be racing it but still don't want to ride a bike that may break way out in the woods.

Chakka

[desmond197]

In one of the old POG newsletters there was an article on frame gusseting for racing. This is the way to go. Pentons are very strong compaired to some other marques. I have seen a lot of Bultaco Pursangs snap in 1/2 and a few riders get hurt. The Aussies are using replica frames in thier vintage bikes,mostly CZ's and Bultacos. The time may be coming for replica frames as tracks are a lot rougher than they were 30 to 40 years ago. And the riders a little heavyer.

[tomale]

Do you really think that the tracks are all that rougher? no doubt alot of us are alot heavier now than we were back then, especially true it you are try to ride a 125 now...I have not really riden that many vintage tracks as of late but post vintage tracks at times are rougher now than they were back then. I have not seen anyone break a frame but I have seen bent fork tubes and last year I let a guy ride my MC5 250 and it came home with a bent swingarm and four broken spokes....[8D]

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
75' GS400 (project bike)
72'sixday (project bike)

[desmond197]

I have seen two Pursangs that have broken where the tank meets the seat and the lower frame rails. I have seen some CZ's where this has happened. One of the Pursang guys had a severly fractured leg. the bike spit in tow after a jump. I was just in the shop this morning looking at a couple of my bikes and found a big crack in my 1976 192 Pursang frame and a couple in my Greeves MX1. Luckly both these bikes are used for riding around the back yard. Time to do some welding. Check you bikes.

[Auto5guy]

If the POG newsletter article on frame gusseting could be scanned and posted in the files section or on the POG yahoo group I think many of us would find it useful.  

As far as the tracks we race vintage on today being rougher than what these bikes were originally raced on I have to disagree.   If you are trying to ride vintage on a modern track then yes there is no comparison but AHRMA and most vintage groups do not race Sportsman or Premier/Classic bikes on anything resembling a modern track.

I just recently picked of a DVD of On Any Sunday.  The movie was made before 1970 and the motocross tracks shown are ROUGH!!  I remember thinking if the whoop section were put on an AHRMA vintage track there would be a full-blown revolt.  

I think part of what is going on is that due to simply being older most vintage racers feel more "roughed up" after a race than they remember feeling back in the day..

Matthew


WARNING: The Surgeon General has determined that castor smoke can be hazardous to your health.  It is highly addictive and causes delusions of grandeur.

[Big Mac]

The other factor is the fat-ass lard factor of the vintage-racing equation (this coming from a guy with "Big" in his nickname). I believe prime racing weight for riders on these bikes in the day was maybe 150-160 lbs, with the big guys maybe closing in on 200 lbs? I'm flogging my 250-lb girth on a '73 250 HS, so frame strength gets to be more of an issue on even tracks toned-down from the rugged tracks of the day.

However...I think if the 30-yr old frame has no cracks, fractured welds or problems, they are not becoming brittle just due to age and should be sound. I added the two triangle gussets and welded additional beads in areas as recommended in the Kent Knudsen race-prep POG article a couple years back on my Harescrambler, and so far so good. I rode the Penton in an event at what essentially was a modern track in Alderdale WA last May, with several fairly big flat landings off jumps and a double that I was too C-S to attempt, and I hammered things hard enough that the upper shock mount bolt on one side bent upward about 20-30 degrees and pulled through the shock eye---but the frame and swingarm survived w/o a hitch. (knocking on wood now)

I replaced the upper shock bolts with hardened steel and added oversize washers to ensure no self-dismantling of shocks in mid-flight. I think you skinny young guys not only get all the chicks, but you have little to worry about in the frame-breaking department.

The frame gusset info should be on the site here somewhere, or I have a hard copy I can fax if anyone needs.  Fairly-Big Mac

[Chakka]

All this talk has got me thinking maybe I should do some welding. I ask the experts for your opinions. Take a look at the attached photos of my Berkshire Frame and the pitted areas. Since I will only be trail riding I wasn't too concerned but who knows:

Chakka

http://photobucket.com/albums/b60/chakka141/?action=view¤t=72100cc4.jpg

http://photobucket.com/albums/b60/chakka141/?action=view¤t=72100cc3.jpg

[Mick Milakovic]

HI All,
I added the Knudsen frame welding on my 250 HS also.  I remember the article saying that Kevin Brown rode his bike so hard that cracking may occur, and I know that I don't ride like Kevin does, I just wanted to make the bike was as safe as possible.  Seems to me the paticular article was from issue #15-17?