cracked frame (2023 Update)

I have an '86 Chevy pickup. I live in north Texas and the last 2 days went below freezing, I only had water in the radiator. I checked the fluid and I have oil in the radiator. I do not have oil in the crankcase. I am hoping it is a head gasket or something, because I have drained it a few times now and it is clearing out. Would the heater affect this, maybe it runs through a different gallery or something, because I stopped using the heater and it seems to have gone away. How can I check to see if I may have cracked the block or heads cheaply? Also, when I found out this, about the oil in the water, I also found out that my frame rail is cracked completely in two just aft of the passenger side motor mount. Is there a cheap repair for this? Do I need to weld the seam and then put braces on both sides?

Reply to
jmar595
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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

Reply to
<ajeeperman

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

Steve

Reply to
Steve Mackie

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

Reply to
Dennis Mayer

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

Reply to
Steve Mackie

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.

Reply to
Dennis Mayer

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

Reply to
Steve Mackie

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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You can also use a diamond shaped plate to give the same effect.

To weld the frame directly from the top to the bottom makes it likely to crack again for reasons which I am not qualified to try and explain. After over 30 years of working as a Millwright, I can say that once a crack has been welded it quite often cracks there again so a plate is used to bridge the repaired area and this plate is welded with stitch-welding so as not to make a continuous weld. This way, if one stitch was to crack it won't carry over to the next weld. The fish mouth (or diamond) allows you to place welds that are not in a direct line from top to bottom.

Since my explanation is wanting, and I am just a DIY repairman, I have cross posted this message to a welding NG to draw in some expert opinions for you - and for me :)

Reply to
The Nolalu Barn Owl

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

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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...

Reply to
Richard Smith

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.

Reply to
Jim Wilkins

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