cracked chassis/engine mount
Davey D - 10/8/14 at 11:16 PM
Has anyone with a vortx, or even any other make of bec with a solid mounted engine had their chassis crack before? I was under my car the other day
having a quick inspection ready for m.o.t and found this: 
Description
It is where the lower engine mount below the prop shaft is welded to the chassis. The crack starts on the top side of the chassis rail through the
weld h.a.z round the tube, and then starts to break away and round the tube.
If I had done my track day next weekend with it im sure it would have cracked further potentially snapping right in half.
So tonight I have been under the car sorting it out. Removed the powder coating. Drilled the ends of the crack. Welded up the crack, and welded in a
gusset for added strength, then to finish painted satin black to match the powder coat.
Tried to get a picture of the repair, but the battery on my phone was too low so it wouldn't let me, so I'll get a pic tomorrow.
It does make me concerned about cracks anywhere else so had a look around the chassis but couldn't find anything else.
Once I was done I went under the back to measure up for the diffuser I'm going to make for it. .... Only to find cv grease everywhere as one of
the boots had split. .. grrrr
CosKev3 - 11/8/14 at 09:36 AM
Not good 
How old is chassis?
was a thread on here with a MNR that had a snapped off rear wishbone mount around the weld iirc?
Pretty sure they were having the car in to check it out.
designer - 11/8/14 at 09:47 AM
This is the third MNR chassis I have heard of cracking!
mark chandler - 11/8/14 at 09:50 AM
That looks like a stress crack caused by vibrations, I once saw a lorry that had similar on its chassis, it was plated with 1/2" steel and the
crack followed the same path. Some things can be spooky, could just be overly hard engine mounts creating the issue not a reflection upon the
chassis.
Regards Mark
cliftyhanger - 11/8/14 at 09:56 AM
I would expect cracks around a solid mounted engine, unless there was substantial reinforcing. The vibrations will work harden the steel....
CosKev3 - 11/8/14 at 10:06 AM
quote:
Originally posted by cliftyhanger
I would expect cracks around a solid mounted engine, unless there was substantial reinforcing. The vibrations will work harden the steel....
All BEC engines are solid mounted, by all manufacturers I've seen, surely if cracks were 'expected' they would alter the designs?
Do bikes frames crack around engine mount points, or is there less vibes when solid mounted in a bike?
adithorp - 11/8/14 at 10:45 AM
quote:
Originally posted by CosKev3
quote:
Originally posted by cliftyhanger
I would expect cracks around a solid mounted engine, unless there was substantial reinforcing. The vibrations will work harden the steel....
All BEC engines are solid mounted, by all manufacturers I've seen, surely if cracks were 'expected' they would alter the designs?
Mine isn't and that's on mounts Fury supplied.
I think you should have spoken the MNR before getting stuck in repairing it. Their customer service is very well thought of by some on here, so
I'd expect they'd sort it out.
40inches - 11/8/14 at 11:08 AM
This has happened before on makes other than MNR. I think it may be possible that the mounts haven't been shimmed.
When I fitted my 9R there was a 2mm gap between the engine and mount, I fitted a tight washer to take up the gap.
If there is a gap, it may be possible that the strain on the mount caused by closing the gap, by distorting the mount, would cause a stress fracture.
CosKev3 - 11/8/14 at 11:25 AM
quote:
Originally posted by 40inches
This has happened before on makes other than MNR. I think it may be possible that the mounts haven't been shimmed.
When I fitted my 9R there was a 2mm gap between the engine and mount, I fitted a tight washer to take up the gap.
If there is a gap, it may be possible that the strain on the mount caused by closing the gap, by distorting the mount, would cause a stress fracture.
Good call 
And it would be the outer weld/area taking the strain as in above pic.
CosKev3 - 11/8/14 at 11:28 AM
quote:
Originally posted by adithorp
Mine isn't and that's on mounts Fury supplied.
Ah right, got any pics handy just to get an idea of how they have done them?
Has Cradle got mounts too?
Davey D - 11/8/14 at 12:10 PM
The chassis was made in 2007, and the car has been on the road since 2009.
I'm not overly concerned about getting MNR involved as there is nothing to achieve by doing so. And i cant see how they can do anything about it
better than I can.
If someone was to tell me that this hasn't happened to any other cars then I would find it very hard to believe due to the nature of a vibrating
high revving engine being solidly mounted in a frame.
I am an engineer/fabricator/coded welder and see stress fractures and damage to equipment day in day out, so this is nothing new to me.
As said above. If I hadn't quite shimmed the gap enough where the engine bolts up, and there was some loading due to nipping the bolt up tight,
the that could have been a factor in this.
The crack started in the h.a.z, and the mounts have no bracing or gussets, so is in a position ripe for cracking
micksalt - 11/8/14 at 01:00 PM
Feed what information you can back to MNR though, they'll appreciate the feedback.
adithorp - 11/8/14 at 02:02 PM
quote:
Originally posted by CosKev3
quote:
Originally posted by adithorp
Mine isn't and that's on mounts Fury supplied.
Ah right, got any pics handy just to get an idea of how they have done them?
Has Cradle got mounts too?
They're more like traditional pair engine mounts and a tie bar, rather than a cradle like you often see with a bike engine and have a metalastic
bush between the mount and chassis. I'll see what pictures I can find later.
40inches - 11/8/14 at 06:27 PM
quote:
Originally posted by adithorp
quote:
Originally posted by CosKev3
quote:
Originally posted by adithorp
Mine isn't and that's on mounts Fury supplied.
Ah right, got any pics handy just to get an idea of how they have done them?
Has Cradle got mounts too?
They're more like traditional pair engine mounts and a tie bar, rather than a cradle like you often see with a bike engine and have a metalastic
bush between the mount and chassis. I'll see what pictures I can find later.
Some photos in this build blog.
Rather neat, I like the idea of mounting it similar to a car engine
cliftyhanger - 11/8/14 at 06:46 PM
quote:
Originally posted by CosKev3
quote:
Originally posted by cliftyhanger
I would expect cracks around a solid mounted engine, unless there was substantial reinforcing. The vibrations will work harden the steel....
All BEC engines are solid mounted, by all manufacturers I've seen, surely if cracks were 'expected' they would alter the designs?
Do bikes frames crack around engine mount points, or is there less vibes when solid mounted in a bike?
Bike manufacturers will have designed the frame with it all in mind. The picture looks like a normal welded joint, no reinforcing or allowances built
in.
I have seen car chassis split/fracture when people have decided to re-mount engines in a "better" position, and that is using rubber mounts.
Its all about the design......
Davey D - 12/8/14 at 07:06 AM
Here is a picture of my repair. I have taken this picture from above so that you can see more of the engine, and how it all fits together.
Description
I have welded in a 3mm plate gusset to the front edge round where it cracked, and have ground out, then run multiple passes over where the original
weld was on the tube.
The paint is Halfords Satin black which is a really good match to the black powder coat. Once ive done a few miles, and its got some road grime on it
you wont see the difference 
[Edited on 12/8/14 by Davey D]
micksalt - 20/8/14 at 09:40 AM
Nice work there, were those shims in place originally or have you added those to minimise the strain?
Davey D - 20/8/14 at 09:47 AM
they have always been installed from day 1
amalyos - 27/8/14 at 10:04 AM
Looks like same type of bracket as mine, I've been racing it in RGB for 4 years with no problems.
I don't tighten up against the bracket, I have a rod through the bottom engine mounts and engine that sits just proud of the brackets, then I
just put a Cap head into each end of the rod to captivate it. This means the lower mount is just used to stop the twist of the engine, there are no
side loads on the brackets in the direction that yours has cracked. It does look like it's been clamped against to close a gap up.
pewe - 27/8/14 at 10:33 AM
Interesting that.
No1 son had a very near escape whilst passengering in an S2000 Westie at Combe not so long ago.
Car span off backwards into the tyre-wall at something over 40mph completely destroying the left rear corner - good job Westie mount their fuel tank
inboard!
They had been braking heavily into a corner when the left lower front wishbone fractured clean apart right where Westie had put a
"strengthening" plate under the wishbone at the upright end.
It looked as if the weld had caused some rusting inside the tube weakening the wishbone.
So these two similar events lead me to ask - is tube wall thickness, especially on critical components, being under-specced to save weight and not
allowing for the fact that welds, long-term, can affect strength?
Certainly when I was fabricating the F27 wishbones I went for relatively thick wall tubing (2mm) for the extra strength it gives.
Answers on a post-card.....
Cheers, Pewe10
Davey D - 27/8/14 at 10:40 AM
quote:
Originally posted by amalyos
Looks like same type of bracket as mine, I've been racing it in RGB for 4 years with no problems.
I don't tighten up against the bracket, I have a rod through the bottom engine mounts and engine that sits just proud of the brackets, then I
just put a Cap head into each end of the rod to captivate it. This means the lower mount is just used to stop the twist of the engine, there are no
side loads on the brackets in the direction that yours has cracked. It does look like it's been clamped against to close a gap up.
Mine too has a very long bolt all the way through the bottom of the engine to a mount the same on the other side. It has been shimmed with washers
from the day it has been built 5 years ago, so any pulling of the mount whilst nipping of the bolt up will have been nothing worth talking about.
I personally wouldnt leave the bolt slack though to let it move around. The movement/vibrations could end up causing damage to the mounts. would
perhaps be better with some rubber in there to take up the space, but stop any movement from vibrations
amalyos - 27/8/14 at 10:48 AM
quote:
Originally posted by Davey D
quote:
Originally posted by amalyos
Looks like same type of bracket as mine, I've been racing it in RGB for 4 years with no problems.
I don't tighten up against the bracket, I have a rod through the bottom engine mounts and engine that sits just proud of the brackets, then I
just put a Cap head into each end of the rod to captivate it. This means the lower mount is just used to stop the twist of the engine, there are no
side loads on the brackets in the direction that yours has cracked. It does look like it's been clamped against to close a gap up.
Mine too has a very long bolt all the way through the bottom of the engine to a mount the same on the other side. It has been shimmed with washers
from the day it has been built 5 years ago, so any pulling of the mount whilst nipping of the bolt up will have been nothing worth talking about.
I personally wouldnt leave the bolt slack though to let it move around. The movement/vibrations could end up causing damage to the mounts. would
perhaps be better with some rubber in there to take up the space, but stop any movement from vibrations
It's not that loose that it moves or vibrates, just a few thou so there's no clamping on the brackets. It's actually tight in the
holes. The cap heads are done up tight on the ends of the rod. All works no problems.
OliilO - 16/9/14 at 04:41 PM
quote:
Originally posted by CosKev3
quote:
Originally posted by adithorp
Mine isn't and that's on mounts Fury supplied.
Ah right, got any pics handy just to get an idea of how they have done them?
Has Cradle got mounts too?
My Mac#1 has a bushed engine cradle. It's basically as per any bike engine cradle, but instead of bolting direct into the chassis it has a bush
on each corner that sit in some u shaped brackets (same as those for wishbones). Can send you some pictures if you want?
britishtrident - 16/9/14 at 06:21 PM
quote:
Originally posted by Davey D
Here is a picture of my repair. I have taken this picture from above so that you can see more of the engine, and how it all fits together.
Description
I have welded in a 3mm plate gusset to the front edge round where it cracked, and have ground out, then run multiple passes over where the original
weld was on the tube.
The paint is Halfords Satin black which is a really good match to the black powder coat. Once ive done a few miles, and its got some road grime on it
you wont see the difference
[Edited on 12/8/14 by Davey D]
I wonder how long that repair will survive? From that picture it looks like the original fracture is cased by a design issue.The design puts the
loads in into the mid span (more or less) of an unsupported tube.
On a spaceframe loads should be applied at (or at least very close to ) a node. A node is a pont where at least 3 members (ie. tubes) in different
axis join.
[Edited on 16/9/14 by britishtrident]
[Edited on 16/9/14 by britishtrident]
Davey D - 16/9/14 at 06:36 PM
The mount is a long way from the middle of the tube. It's around 100mm from a node which is the end of the foot well/ transmission tunnel where
several tubes come together. The gusset is around 50mm so finishes less than 50mm from the node
Johneturbo - 12/10/14 at 04:40 PM
Good job you noticed that Davey before it was a big issue, i will be taking a good look at mine over the winter as my chassis is of the same age.
When i did my engine change/swap i did look in to rubber mountings but wasn't sure how to implement it into the current design.
