cracked frame (2023 Update)

if you weld it, you MUST use fish shaped plates over the crack . they are just oblong plates with a triangle shaped cut on each end. This will prevet a new crack. old john

I do not have oil in the crankcase.

WHY ?

I am

I think he meant no water in the crankcase :^), but oil in radiator, If this is the case, I would suspect a leaking transmission oil cooler in the radiator, not a engine oil leak. Engine oil in Radiator will always result in antifreeze in the crankcase..

JJ

Then he should have antifreeze in the Tranny fluid also

John, to clarify, do you mean plates shaped like this? ________________________ \ / \ / \ / / \ / \ /______________________\

Having a mechanical engineering tech background, you are going to have to explain that one.

Steve

Yes, I meant no water in the oil, sorry. I have a granny 3 speed so I don't think it is the oil cooler, don't think there is one. I did a compression test last night and it went like this... #1- 150 psi, norm plug, #3- 135 psi; norm. plug; #5- 135 psi, norm. plug;#7- 135 psi, norm. plug;#2 145 psi, norm. plug; #4- 135 psi, noprm. plug; #6- 85 psi, norm. plug;#8-120 psi, oily fouled plug. With this do you think it is possible I have a blown head gasket between 6 and 8?

It's called a double 'fish mouth' shape and it prevents a major discontinuity

in structural stiffness.. The fish mouth shown/could have a deeper

triangular trim.... and pulled back from trim corner weld ends may help too..

A discontinuity in stiffness may cause a Stress concentration.....

And major stress concentration can cause a metal fatigue crack...

Retired, ME

With Both Valves closed .. Piston on the Down stroke. Remove the Radiator Cap, Pump Compressed air into that Cyclinder Via the spark plug Hole. If the Head gasket is leaking u will Get Bubbles showing up at the RADIATOR cap HOLE in the radiator .

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Did I mention I graduated first in my class, with honours. You didn't need to explain what a stress concentration can do.

Do you know of any reference texts on this "double fish mouth." I don't see it in any of my texts and I'm interested in it. I've joined a many of tubes/channels/etc. on paper and have only used flat plate. I just want to read up on the application theory.

Steve

Fishmouths & shear ties are a way to blend stiffness between a box section

and a channel... which minimizes stress concentrations... Metal shape

as well as weld & weld ending details become equally important.

I've done this work in my younger Engr days via MTS test equipment, finite

element modeling, and PVC scale plastic modeling using Stresscoat paints.

It is a self acquired design/Engr skill that is used to solve structural Problems.

You just seem to be stating the same thing over and over. I have never used anything but plain rectangular plates and they have always met stress requirements. I want to read into the theory to see if changing the way I do it is worth it.

Steve

I know of no particular papers nor books on the subject, but

Technical Topics that may cover the general issue are:

Theory of Reinforcements...... or

Designing for Fatigue..... or

Lightweight Structure Design......... Amen

I have looked and looked for information on the NET about fish mouthed re-inforcing plates and there isn't much to be had.

Basically you can use a plate cut to form what looks like an open fish mouth on each end.

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Is the truck in fantastic shape, other than the issues you've mentioned? If not, it may not be cost effective to invest a lot of time and money to repair a cracked frame and engine in a truck that's 20 years old. Take a few minutes to do the math before you start throwing your hard earned bucks into a money pit.

Not always so. If you have a radiator with a engine oil cooler in the side tank. The oil cooler can leak/seep oil in to the cooliant, and not suck cooliant back in to the oil cooler.

Had this happen on a 1993 Buick Regal with a 3.8 V6. Charles

This looks to be a fatigue cracking matter...

Geordie seems to know from practical experience what does and doesn't work to avoid fatigue cracks or how to repair them when it happens.

Steve - you've read and all seems fine and from that basis you disbelieve and experienced practitioner.

Steve - you could do Finite Element Analysis modelling to see the stress concentrations. FEA for the general region of the structure. Here's a somewhat comparable example of me probing a feature I met while actually out there as a welder

I would bet is that you will see theory concurring with what Geordie is telling you already. Steve - you'd benefit from "treading the path" and seeing how where you come from can plug you into the deep knowledge out there.

I take it you are proposing some feature with an abrupt "right-angled in every way" change in thickness and possibly direction. That will be highly fatigue-prone.

Steve I think you are being given a chance to learn and you are not seeing it.

As best I can tell from message trail so far...

I take it you are proposing some feature with an abrupt "right-angled in every way" change in thickness and possibly direction. That will be highly fatigue-prone.

Steve I think you are being given a chance to learn and you are not seeing it.

As best I can tell from message trail so far...

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I vaguely remember learning in Strength of Materials class that the diagonal weld across the beam web reduced stress concentration. Maybe the reason for both diamond and fish-mouth plates is that one is scrap from cutting the other.