not so famous bob
Well-Known Member
no big deal to put them under the bolt /frame area , like I said , 68 hemi barracudas had the 1/2'' spacers under there from the Hurst factory .
Cracks in front frame rails under K frame mounting points
- Thread starter andrewwoz
- Start date
j-c-c-62
Well-Known Member
I'm not convinced yet the side plates will prevent future cracking in the area of the first crack.
I'm also wondering if inadequately torqued mounting bolts (4) might have played a part here in allowing some movement and the resulting extra shock loading?
The fact it appears one crack started at the spot weld indicates that possibility.
autoxcuda
Well-Known Member
That will change the relationship of the motor and LCA (lower control arm) to the body. Now 1/4" plate isn't much. But in my mind I didn't what to raise my center of gravity any, although realistically insignificant. It also slightly raises the UCA pickup point that I don't want for handling (again probably insignificant)
Trust me. Nothing gets the front end dropped out of the air as often as my racecar. It wheelies 1-2 foot most every pass. Nearly 1100 passes. Occasionally to high. It’s had the pan and the diaper repaired more than once. Last time even cracked the K frame. No damage to either rail. Weld areas are still perfect.
Doug
Doug
not so famous bob
Well-Known Member
they did it for engine clearance , worked well...
j-c-c-62
Well-Known Member
Actually, on further consideration and review of the pictures, IMO any drilling that goes thru the uncracked threaded inner backing plate would likely only weaken the entire mounting system, even after trying to weld back up the drilled hole, irrespective of any of the assumed benefits the drilled hole has in preventing additional crack propagation.
Meaning, don't bother to drill here at the end of the crack.
Meaning, don't bother to drill here at the end of the crack.
So I ended up designing some caps and got them from send cut send, .074" mild steel, I made them oversized so I could trim them to fit. After welding up the cracks I fit these up, welded the perimeter and plug welded the 4 holes. Happy with how it turned out, I'm sure it's overkill but now I won't worry about it.
Unrelated but I thought about getting some more caps (without holes) to put in places on the frame rails where I usually put jack stands, the rails always seem to get dented from the jack stands.
Unrelated but I thought about getting some more caps (without holes) to put in places on the frame rails where I usually put jack stands, the rails always seem to get dented from the jack stands.
j-c-c-62
Well-Known Member
I really like your solution. Specifically, the fact you did not oversize the thickness, and added plug welds.
However, one small suggestion for anyone else, I would have liked to slightly angled ends, ie trapezoid shaped in plan view, as all this metal flexes here under load no matter what we do, and the full straight across welds at end of your reinforcement are a prime spot for future fatigue cracking, if they ever begin. The longer weld of an angled end would spread out that stress concentration. Alternatively, the ends could be concave or convex shaped or even not or just partially welded, leaving the welded (upturned) sides, that are much longer, to absorb the stress. The issue with only partially welding the ends however makes for a good spot for water intrusion and its trapping leading to eventual rust issues.
All in all, I give the project an A- if asked.
There is some market potential here, that meets a need and works.
Oh, and don't use your grade 8 bolt as a grounding lug.
While we are on the topic, anybody seen or have a pic of what the threaded insert inside the rail looks like or size?
However, one small suggestion for anyone else, I would have liked to slightly angled ends, ie trapezoid shaped in plan view, as all this metal flexes here under load no matter what we do, and the full straight across welds at end of your reinforcement are a prime spot for future fatigue cracking, if they ever begin. The longer weld of an angled end would spread out that stress concentration. Alternatively, the ends could be concave or convex shaped or even not or just partially welded, leaving the welded (upturned) sides, that are much longer, to absorb the stress. The issue with only partially welding the ends however makes for a good spot for water intrusion and its trapping leading to eventual rust issues.
All in all, I give the project an A- if asked.
There is some market potential here, that meets a need and works.
Oh, and don't use your grade 8 bolt as a grounding lug.
While we are on the topic, anybody seen or have a pic of what the threaded insert inside the rail looks like or size?
Last edited:
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