1998 kenworth w900 cracked frame rail :'(

If your going to bolt it you better pony up the money for the flange frame phos oil bolts they aren’t cheap about 12.00 each for a 5/8 x 2.5” bolt then another 3.00 each for the flange nut there’s a reason why the manufacture use”s them…just saying. Again I”am only voicing my option but buying a section of frame and cutting it to make it fit inside the existing frame is not going to be beneficial to strengthening the broken frame. There’s terminologies used for that . Which is not permitted for me to use on this site your just putting a band aid on a gash. But again it’s just my option and hey what do I know I”am just a stupid truck driver

 

When you weld the actual crack v both sides if possible. Weld from whichever side is hardest to access with a grinde first….Can’t imagine that wouldn’t be the inside but…. After you have welded one pass grind the groove deeper from the other side so there is very little or no metal that wasn’t melted together by the first weld. Then weld the groove you just ground on. This will produce a full penetration weld that will pass a ut. At this point go back with a needle scaler and chip the slag/peen the weld. This is important because peening helps reduce stresses and root cracking. Probably not all that important as a truck frame is relatively flexible but still good procedure. Then when weld probably 2 passes per side depending on your groove and chip slag/peen. Ideally you have welded enough to fill the groove with no undercut and also have the flange welded fully all the way to the edge. make absolutely sure there’s no weld crater at the edge. The very edge of the flange is quite important because any little nick is going to create a stress riser and increase the chance of recracking. I personally would take the grinder and grind about a 1/16 off of the edge of the flange tapering out around an inch on each side of the crack then gently round the corners. I also usually grind the weld bead down pretty close to the surface about 1/2 inch in front the edge.
Maybe this picture helps…it’s not really showing what I want very well but better than nothing. As far as my comment about not welding all the way to the edge on the flange that is to eliminate the chance of undercut or weld crater making a stress riser in a bad place. All the concern about the edge is because the very outside of the shape takes the highest stress.
this is what I would make the welded reinforcement look like

 

Something else I left out….
Mild pre heat between 200 and 400 would be beneficial and 9018 sticks are preferred, 11018 works to. As far as bothering the temper on the frame as long as it isn’t heated excessively it pretty much isn’t a problem. Generally speaking it takes about 800 to affect it and the area local to the weld kinda retempers itself from the welding.

 

This is exactly how my K100 was done, only difference was they inserted a 10’ piece of frame, they bolt it up(after drilling the pre-existing holes that mount to the front suspension hanger and same to the rear hanger and was bolt up the all the saddles for the fuel tank, battery box, flywheel housing and a couple of cross members. Ran it like a raped ape, loaded heavy, did a bunch of twisting and turning at job sites and never ever had any issues period. They thought about only adding a short section of a frame but I insisted I wanted a guaranteed I wouldn’t have any issues, so they went with the longer 10’ piece instead. I still have the truck parked. Only due to Commiefornia Emissions BS.

 

So you putting a insert in that’s good ! The frame bolts are grade 8 yes but they are made of different steel that the normal grade 8 bolt you buy at hardware store they are made to flex a bit more than a common grade 8 bolt before they shear. plus the threads won’t stretch as quickly plus the corrosion issue. You will have problem keeping a normal grade 8 bolt tight even if you use lock nuts also . I personally refuse to use common hardware store grade 8 bolts in a truck frame I have never had a good experience using them even if it’s just to plug unused bolt holes in a truck frame..

 

For clarification purposes, and I stand to be corrected:

10.9 is a metric bolt with a different rating metric than grade 8. They are very close in tensile strength. Grade 8 may actually be a bit stronger, I'm not sure. I did not look it up, but that is my understanding.

 

I think you’re most likely seeing the difference in manufacturing quality between a foreign made and loosely controlled bolt and one made to better standards. We have used grade 8 flange and non flange bolts from various vendors but have always specified USA or Canada produced. Never had a problem at all.

 

This isn't uncommon on the older W900Ls unfortunately. I've always had them welded back together and installed a partial liner and welded it inside the frame to brace it. Last one of these I had fixed we replaced the rear spring hangers with the Peterbilt style brackets with three horizontal bolts passing through the frame rail. Kenworth shouldn't have drilled through the bottom flange of the frame rails like they did. I think it's kind of funny that they put the little stickers on new truck frames saying not to drill or weld the top or bottom flange of the frame.