Cracked engine mount

[mike1948]

This should probably be directed to Ji, but if anyone can help, I'd appreciate it.
I have a cracked front engine mount on my Maico, and lacking a Tig, I need a skillful person with the right equipment to repair it.  I live on the north side of Brisbane, but have transport, so can anyone recommend a bike shop or workshop who does a good job on frame repairs?
I've got a welder, but am reluctant to try it out on a frame which I understand is chrome moly.

[GMC]

A TIG is ideal but any one competent with a MIG will also do.
Now when I say MIG I don’t mean the gasless systems, they are okay for an emergency repair but I wouldn’t use one otherwise.
Also be wary going to some engineering shops, while they may be very competent with their MIG machines, if they’re not used to thin stuff they will just end up pouring a reel of wire onto your frame as they try to fill the holes they have created.
Chrome moly will weld okay with ordinary MIG / TIG wire.
Is it just the mount itself or the tube it’s attached to that’s broken?
If your going to take it somewhere spend some time to get the paint from the area that needs to be fixed as this will benefit you by not having to pay some one to do it for you.

Any pictures?

[mike1948]

The front mount is attached to an oval crossmember of the twintube frame.  The whole mount has cracked out of the crossmember, leaving a hole the size of the original weld in the tubing.  Paint has been removed back 75mm from weld.

[GMC]

You may get away with welding the original mount back on but it may be better to make a new one.
If using the old mount then the welds will need to be ground down otherwise the welds just get bigger & bigger.
If you or someone tries to fix with a MIG and it doesn't quite go right, then don't keep welding over it again and again with out grinding down the poor welds otherwise things get ugly real quick.
Depending on the condition of the tube it may benefit from having a pad welded over the area and new mount brackets welded to the pad.
This is a common fix for the rear mounts on the oval tube as they fatigue through. I think Maico started doing this on the 75 models.

If TIG welding it can also do with a small hole (3mm) underneath the tube. Enclosed tubes suffer from pressure build up from the heat, the pressure wants to get out somewhere and the easiest spot is the soft core of the weld pool. When it pops out it will contaminate the tungsten and make an ugly spot in the middle of the weld.

[Ji Gantor]

Geoff that was fantastic.
It is always a pleasure to read your words.

Ji

[Ji Gantor]

Hi Geoff,
I know that Maico say that their frames were made from CrMo and
I remember that you from your experiances don't think their frames are made from CrMo.
I think you said that they were stronger than mild steel but no where near 4130.
Which I have no problems with.
What would you use as a filler rod for the job.
S70
ER80S-B2
Or a stainless steel rod.

Ji

[GMC]

Lots of manufacturers claim to have used Cro-Mo but very few stack up to the test of time the same way some aftermarket frames do that are made from 4130.
The hand built frames built by small companies in the 70's just seem to last a lot better and not suffer the same fatigue as the major manufacturers.
Just an opinion.

ER90 (Cro-Mo 1) is the better rod to use.
ER80 (Cro-Mo 2) is also suitable
Both these rods will produce strong welds in Cro-Mo however normal ER70 will weld fine it just won't be as strong a weld as with the other 2 rods. Most of the time this won't matter and an engine mount repair would be fine.
ER70 spec is commonly used in MIG wire.

I have heard some manufacturers use ER70 when welding roll cages for race cars as the heat affected zone is less critical as most roll cages are welded in the car and can’t be removed to be able to normalize in an oven.
I think nowadays they use a slightly lower spec. steel for roll cages that doesn’t suffer from brittleness from the HAV
BTW the heat affected zone is around 2 – 3 mm from the weld, right next to where the material has got to melting point.

I use ER90 when welding my frames, I can justify buying a packet as I use it all the time but if you just want to do the odd small repair on a frame I wouldn’t stress about it so just use some ER70

[Ji Gantor]

Thanks Geoff,
That is really great advise.
I have tried to find out what Maico did use but unable to pin point the metal yet.
I use ER80 rods when repairing CrMo frames.

When the push bike companies make titanium frames they use a stainless steel filler rod.
Interesting to see how frame manufacture has evolved.

Ji

[tony27]

Funny you should mention the stainless filler for titanium on pushbike frames, 1 of my workmates has an old titaniun framed bike for getting to work that cracked where the bracket for holding the rear axle attaches to the frame. He found that stainless was the only filler that we had that would last

[Ji Gantor]

If you are going to perform any kind of heat treatment out side of an oven you may need a thermometer like this one.
It reads metals temp to 1000 degs C without making contact with it.
With this you can raise the temp in a weldment to anealling temp and lower it slowly to achieve a ductile joint.

Ji

[Ji Gantor]

Hey Rocketfrog,
Can you upload those test images here so we can see them.

Ji

[rocketfrog]

Yeah,
 I was going to ask which would be the best way to do that. The images are embedded into a word doc. Which means I would have to insert each pic using photobucket and paste the text in between. Unless there is a simply way to upload the peice as a word doc? Alternatively I could send a copy to you on disc? There is quite a lot of info in the article, and the piccies would not mean a great deal without the guff.

[Ji Gantor]

Hi Rocketfrog,
The best way is to photobucket, but I would love to see the whole thing so please email me when you get time.

Thanks Ji