Cracked chassis repair

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05 Sep 2018 16:08 #1 by tcgreen
tcgreen created the topic: Cracked chassis repair
Hi, I have discovered 2 cracks in the chassis of my Oka. Both are in the front passenger side wheel arch, fortunately on the outside of the chassis giving easy access for repair. One is along the weld of the semi eliptical cutout below the chassis number, and the other from one of the lower engine mount bolts extending up the outside of the chassis. I have read that cracks in these areas of the chassis are reasonably common, so am hoping that those of you who have experienced these problems can advise on the best way to repair.
I am wondering whether it would be best to plate the outside of the chassis in the area of the engine mounts, especially considering the engine is a 6bt. Perhaps even do the drivers side even though there is no cracking evident there? Any suggestions would be appreciated.
Cheers
Tony

Tony & Chris
Oka 334 motorhome.
Cummins 6bt, 4L80e auto, Nissan transfer.
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05 Sep 2018 17:57 #2 by Outback Jack
Outback Jack replied the topic: Cracked chassis repair
I think RoB 169 put in fish plates.

I have heard other doing engine conversion creating a cradle to support the engine. If that makes sense.

Fish plates add a lot strength in my opinion. But I am no engineer or boilermaker.

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05 Sep 2018 18:18 - 05 Sep 2018 18:21 #3 by Holmz
Holmz replied the topic: Cracked chassis repair
Generally a certified welder is required for that sort of work.
So I would probably find some rally/race type of welder, or some structural type of engineer that is local.

However it would not surprise me if the frame was welded and then a plate out over thatwhole section
How they keep rust out, or whether it is even an issue, is something I would find interesting to know.
If one ignores torsion, then normally a beam has most of the compression on the bottom, and the tension in the top just above the spring mounts...
Under the engine... or other load points between the mounts, then compression is at the top and tension at the bottom.
Usually loads are higher above and below, and the middle of the beam has less load.
So basically if they wanted straps at the top and bottom then it would not surprise me either.

Often doublers have a diamond or bow tie shape on the ends so that there is less of a load concentration.

All ^that^ is theory, and you need a practical solutions of the certified welder.
Last Edit: 05 Sep 2018 18:21 by Holmz.

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05 Sep 2018 18:58 #4 by Ralley
Ralley replied the topic: Cracked chassis repair
Mine was cracked around the engine mount plugs and up the outside amount half way up. When we put the cummins in we fixed the crack on the outside and extended the plate along the bottom of the chassis as far as we could. We then repaired the cracks on the inside and plated it. we let the plate in around the engine mount plugs and drilled and taped the other mount holes through the new plate. When I had it engineered the engineer was happy with what we had done.
The picture shows the plate on the inside and the plate along the bottom of the rail.

Rob

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07 Sep 2018 13:25 #5 by tcgreen
tcgreen replied the topic: Cracked chassis repair
Thanks for the info.I have had a qualified boilermaker look at it, and he will repair next week.
Cheers
Tony

Tony & Chris
Oka 334 motorhome.
Cummins 6bt, 4L80e auto, Nissan transfer.
The following user(s) said Thank You: Holmz

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