By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Welding precautions

Welding sills

All Topics | Latest Posts

Search for:  in Thread Title in  
colin hawes16/07/2020 12:19:31
509 forum posts
18 photos

When garages weld on new sills do they remove the petrol tank or is this considered unnecessary? Colin

Martin Kyte16/07/2020 12:36:04
avatar
1903 forum posts
34 photos

Not sure, but full tanks are safer than empty.

regards Martin

Alan Waddington 216/07/2020 12:39:12
503 forum posts
87 photos

Not usually, suppose it depends on what vehicle it is and where the tank is located etc.

Bit of a thing of the past now welding sills on, but did loads in days gone by, never took tank out and lived to tell the tale.

not done it yet16/07/2020 12:39:41
4747 forum posts
16 photos

Doesn't it depend on the car?

Barrie Lever16/07/2020 12:43:58
653 forum posts
75 photos
Posted by colin hawes on 16/07/2020 12:19:31:

When garages weld on new sills do they remove the petrol tank or is this considered unnecessary? Colin

Colin

I have done restoration work on many cars over the years, got one on a slow burn at the moment and the fuel tanks have never been removed from the cars by any person welding.

The sills are a long way from the fuel tank on most cars.

In fact I think I have only once seen a fuel tank out of a car and I have done lots of work on cars.

B.

Dave Halford16/07/2020 12:52:10
804 forum posts
8 photos

The tank my need shielding if it's plastic and you weld very close to it. Taking the battery leads and the alternator lead off is much more useful insurance on modern stuff.

Chris Evans 616/07/2020 13:23:39
avatar
1702 forum posts

Plus 1 for battery and alternator leads if you are electric welding. Of more concern with sills is the interior trim/carpets.

My Daughter had her old Metro welded by a garage to pass an MOT and it set the trim on fire.

Nigel McBurney 116/07/2020 14:20:05
avatar
717 forum posts
3 photos

Many years ago ,a friend owned a garage,I got one of his men to do some "cash" welding on the front underside of my wifes morris traveller,I sat in the cars passenger seat with a bucket of water,then went up with the car ramp,with the welder under the car ,when things got a bit hot and smoky i sprinkled water on the hot bodywork, I always remember one thing I saw on that saturday afternoon,high up on the ramp i could see there was a mark 3 Cortina right over the back of the garage, a real cut and shut ,front an back were two different colours some doors and other panels were in further different colours.I had made up the sheet metal panel I wanted welded in place from good clean sheet metal formed up in a metal bender ,the welders comment " we dont see good material nicely bent like that,we usually cut up an oil drum and beat it flat to get some steel.

Nick Clarke 316/07/2020 14:45:05
avatar
812 forum posts
28 photos

If fitting skin sills over the top of the originals (NOT good practice!) beware of foam filled sills and petrol pipes running through or alongside the sill.

Sakura16/07/2020 15:11:53
46 forum posts
1 photos
Posted by Nick Clarke 3 on 16/07/2020 14:45:05:

If fitting skin sills over the top of the originals (NOT good practice!) beware of foam filled sills and petrol pipes running through or alongside the sill.

+1

Dave Halford16/07/2020 15:51:42
804 forum posts
8 photos
Posted by Nigel McBurney 1 on 16/07/2020 14:20:05:

,I sat in the cars passenger seat with a bucket of water,then went up with the car ramp,with the welder under the car ,when things got a bit hot and smoky i sprinkled water on the hot bodywork,

A trigger spray set to fine mist works best.

Peter G. Shaw16/07/2020 16:22:10
avatar
1121 forum posts
44 photos

I used to have a Maxi which had a slight petrol leak. Wasn't much, but when I went for a new exhaust and the people approached with a lit welding torch, I slowly drifted outside, just in case you understand. Fortunately, nothing did happen, but it was something of a worry.

Peter G. Shaw

J Hancock16/07/2020 17:12:02
420 forum posts

Those who remember the old BASEEFA standards for equipment mounted in hazardous atmospheres (EXd ) always wonder how car petrol tank level sensors were just a resistance wire and slider , in the tank.

Probably still are.

Yet never a mention of an explosion in normal use.

Incredible.

Nicholas Wheeler 116/07/2020 19:35:30
334 forum posts
19 photos
Posted by J Hancock on 16/07/2020 17:12:02:

Those who remember the old BASEEFA standards for equipment mounted in hazardous atmospheres (EXd ) always wonder how car petrol tank level sensors were just a resistance wire and slider , in the tank.

Probably still are.

Yet never a mention of an explosion in normal use.

Incredible.

Modern cars are even 'worse', because the electric fuel pump is installed inside the tank, and is often connected with uninsulated spade terminals. So that's many more million cars on the road with fitted even more dangerous parts that don't cause problems. Perhaps you worry too much?

Andy Stopford16/07/2020 20:09:13
33 forum posts
1 photos

I have a Fairway Taxi (the old-school London cab). Some previous owner, possibly the first, had it waxoyled in a totally futile attempt to prevent it rusting to bits.

I keep a small trigger spray full of water to hand during its yearly appointment with the oxy-acetylene torch, to snuff the inevitable waxoyl fires emanating from whatever box section is currently subject of attention (you don't need to be able to see the fire - just misting into the box section through some convenient opening towards the top does the job, a bit like putting out a chimney fire by throwing a cup or two of water on the hot grate).

Re. petrol tanks: in theory the mixture inside the tank is too rich to ignite. Furthermore, petrol is non-conductive (a dielectric I presume?), so I suppose there's no need to insulate the terminals of pumps, etc. - though the submerged pumps that Jaguar used on early Mark 10s were quite carefully earth bonded to the tank if I remember rightly.

Oily Rag16/07/2020 20:16:46
avatar
117 forum posts
57 photos

No problem with electrics in fuel tanks! You have all been watching too many Hollywood films where a car has a crash and explodes like an Exxon fuel tanker. Petrol is not that easy to light, as demonstrated to me on my first days induction working in a car factory. The instructor flipped a lighted match into a bucket of petrol and it just fizzled out. Apparently the most dangerous place for fire outbreak in a car factory was the trim shop with all the glue vapours, second most was the glycol anti freeze store, then the grease store and finally the petrol.

On the engine test beds we often had neat petrol dripping onto red hot exhaust manifolds! The biggest fire I saw was when a V8 engine broke a conrod and the sump oil exited the engine over the exhaust pipes, that was a fire!

To ignite petrol needs an air to fuel ratio of between 10:1 to 20:1 outside of this range it is pretty safe, that is why the electrics in a fuel tank (remember the fuel pump motors are brush type and liable to spark) are considered intrinsically safe.

Meunier16/07/2020 20:28:17
324 forum posts
1 photos
Posted by Barrie Lever on 16/07/2020 12:43:58:
Posted by colin hawes on 16/07/2020 12:19:31:

snip/ In fact I think I have only once seen a fuel tank out of a car and I have done lots of work on cars.

B.

I too have only taken one fuel tank out - a 1972 Corvette with a history of running fine until it didn't.
Car would stop randomly after half-mile or fifty miles and take between half-hour and twenty-four hours before it would re-start.
Friends wife alerted me to the problem and so bought the car as a steal because of this.
Long story short - after blowing through all three lines from tank to engine and replacing mechanical fuel pump, took tank down wearing my diving gear to counter seven years of Saudi sand.
Drained /emptied tank and when shaken it rattled ! only two things were shaken out - the gauze pick-up filter and a plastic bottle-top insert seal
Evidently the plastic seal was flotation neutral in petrol and occasionally would come up against the unprotected pick-up pipe and adhere with the suction and only when the suction eventually decayed and the seal dropped off could the car be restarted.
I gave myself a notional pat on the back when that proved to have resolved the problem and decided I never wished to repeat the exercise, especially as it was performed on granite chippings in the street.
DaveD

Nicholas Farr16/07/2020 21:34:31
avatar
2318 forum posts
1137 photos

Hi, there was a chap who run his own garage who was on the same advanced welding course that I was on and he had to drain and remove the petrol tank on a car, but only to get access to a part that needed welding which had to be done with oxy-acetylene, but he did have a proper pit to work in. After he removed the tank and put it a safe distance away, he proceeded to do the work, but no sooner he lit his blow torch he was engulfed in a fireball and suffered some vary serious burns and put him off work for a few weeks for recovery. Now you may think he had missed a pipe or something that had petrol in it, but it wasn't the case, in fact is was the petrol vapour lingering in the pit that flashed over. I think during the time of draining and removing the tank, he'd become used to the smell and could not smell it when he went back down into the pit, something he didn't forget about when he went back to work.

I've never taken a tank off when welding sills, but always did disconnect the battery and make sure trim etc. inside the car, couldn't catch fire. Haven't done such jobs for years and probably never will again.

Regards Nick.

Edited By Nicholas Farr on 16/07/2020 21:36:12

Mike London16/07/2020 21:59:32
13 forum posts
1 photos
Posted by colin hawes on 16/07/2020 12:19:31:

When garages weld on new sills do they remove the petrol tank or is this considered unnecessary? Colin

In the early 1970's I used to run a 1948 Triumph Roadster ( same car as in the Bergerac TV series ) which was a real wreck. It had a proper chassis with a corroded rear jacking point right next to the petrol tank about 1" away.
I approached a welder about welding it up and enquired about whether he wanted the tank removed especially when I discovered he only did gas welding. His reply was " No. Fill it right to the brim with petrol. Hot petrol will only boil. It's the vapour that explodes" And he duly welded it up.

Following up on the Corvette story. The same car had a bout of cutting out and stalling, which didn't impress my girl friend of the time. (The leaking roof didn't either!) But it had a manual lever to the mechanical fuel pump so taking her home late one night about every half mile had to climb out and manually pump some fuel up to get going. Could I find the fault. After blowing down the copper fuel pipe and dismantling virtually everything including the copper fuel line with a brass union in the middle found a little round pebble just big enough to go down the pipe till it met the union and then acted as a perfect one way valve.

I learnt a great deal about car maintenance with all the faults that car had, till I wrote it off on the M4. The joys of student motoring!

not done it yet16/07/2020 22:47:54
4747 forum posts
16 photos

... To ignite petrol needs an air to fuel ratio of between 10:1 to 20:1 outside of this range it is pretty safe, ...

Too true! The fuel connector into the carb came adrift and spraying petrol over the engine, while at over 100mph, back in 1977. The only time I ever turned off the ignition key at that speed. Fuel was still boiling on the engine after stopping and baling out. The first thing I knew of a problem was when the car filled with petrol fumes. Lucky escape, which I put down to one hell of a draught and a cross-flow cylinder head keeping the fuel away from the sparks. A good job we were not smokers, either!

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
ChesterUK
Allendale Electronics
Eccentric July 5 2018
emcomachinetools
Warco
EngineDIY
cowells
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest