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Discussion Starter · #1 ·
Just got home from where we keep our truck, having spent the evening putting acid etch primer on some of our suspension parts (axles, shackles etc), and bonnet.

Whilst spraying, I noticed that the gun is kinda going '... puh, puh, puh ...' as though there isn't enough paint getting through. Even though the gun is over half full.

There is plenty of air, and for the most part we're holding the gun upright as per normal, so I can't see a reason that it would be having trouble getting the paint through. Its the same gun and air pressure that we used last time, and I don't remember having the same trouble then.

Any ideas? :beuj:

Have we just mixed up the paint too thick? or done something else wrong?


For the record, my girlfriend (littletruck) and I are novices at this. Only had our truck just under a year, and the sum of our experience at spraying, is that we sprayed the chassis a few months back.
 

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Discussion Starter · #3 ·
Tons and tons of thinners. I give it a good clean so that there's no paint left in it, then spray a load of clean thinners through it, and leave it about half full of clean thinners, with the screw on nozzle parts inside, in the thinners.


I would say we was about 60/40 on the thick side. I'm pretty sure that's how we did it last time.

We did mix up a 50/50 solution, but it seemed well too thin (in our amateur opinions), so I put a smidgeon more of the thick stuff in, mixed it up, and poured it through a cone shaped filter into the cylinder thing.
 

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Have you actually stripped the gun down and cleaned it or just blown thinners through it ? ... secondly make sure the pot breather isn't blocked. Could be all sorts of reasons, sticky needle anything .....
 

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Discussion Starter · #6 ·
Just sprayed thinners through it. TBH I didn't realise there was much that can be taken off of it.

I'll have a look at dismantling it this weekend then. And work out which bit is the breather.


Paint is upoxy acid etch primer. It comes as a tin of thick brown paint and a separate (same size) container of activator. The guy in the paint shop said 50/50 as well.
 

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Mopars and Gassers
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The Upoxy etch primer should be quite thin mixed, ideally, you ought to buy yourself a viscosity cup (it's a Din spec cup with a hole in the bottom) and measure the viscosity.

It also sounds like you have a suction cup gun (paint pot at the bottom) and they can struggle a bit with high viscosity materials compared to a gravity cup (cup on the top).

Also I agree with the other guys, it's important to clean the gun thoroughly especially the breather hole, which should be in the top of the paint pot lid and make sure if it has an anti drip gasket inside, that's clear as well.

I'm assuming you've got plenty of air coming through your compressor, you probably need about 30 psi at the gun and the air volume to keep pushing the paint through.

HTH!
 

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This Put put put ,sounds like the gun is drawing air ,check the main kneedle jet retaining nut is tight,Bry
 

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I used to have the same problem, my solution now is to buy a £40 gun from Machine Mart & treat them as disposable, buying a new one every 3 or 4 years. No matter how well I think I've cleaned them after use, it just seems to do the same as yours after standing idle for a few months.
 

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Out of interest is it Upoxy Super Etch your using ??? If it is i've always had trouble with overcoating it, Better to use a Epoxy primer.
 

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ready salted
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Sounds like it's pulling air through where it shouldn't. Where the needle goes into the front part of the gun (behind the aircap, follow the needle forwards from the trigger) you'll see a small nut on the needle (hard to explain this lol) If not adjusted correctly, this nut will allow air to be sucked in, which in turn causes a spluttering at the aircap. The nut secures down onto a fibre insert. If not secured against the insert correctly or if the insert is damaged you'll get the symptoms described. Try tighteneing the nut bit by bit to see if the spluttering stops.

When using Upoxy or Epoxy, remember that they are both porous & will take in moisture if left for any length of time, contrary to what some believe. I've had this direct from the manufacturers hth, cheers.......Nige
 

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I used to have the same problem, my solution now is to buy a £40 gun from Machine Mart & treat them as disposable, buying a new one every 3 or 4 years. No matter how well I think I've cleaned them after use, it just seems to do the same as yours after standing idle for a few months.
Or just spend about £80 - 100 on a decent DeVilbiss JGA558, clean it properly and keep it for years. Benefits are that it will paint 1000 times better as well.

Getting back to paint problems, typical phut, phut, phut symptoms are;

loose aircap (even tho they feel tight, another nip will often cure this)

Paint too thick, test this by spraying some thinners through the gun, does it spray properly?

Muck in the aircap, not allowing free flow of the paint.

What size needle/tip are you using?

Do NOT leave thinners in gun, it damages the seals, also do NOT soak the trigger/needle area in thinners for the same reason.

Strip gun down completely every 3rd time (or less) that you paint, strip air cap off and wash needle/tip every time you paint.

Lubricate needle/tip/all seals with correct gun grease available from good paint factors.

A spraygun is a finely balanced instrument, dirt has no part in its use.
 

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Discussion Starter · #14 ·
Hi All,

Sorry I didn't reply to this sooner, didn't get round to painting again until today.

Anyway, just got back from doing another spraying session.

To answer a couple of questions

Out of interest is it Upoxy Super Etch your using ??? If it is i've always had trouble with overcoating it
Yes I think it is.

We used it on the chassis a few months back, and over coated it with a synthetic paint (I don't know what paint exactly, we just asked our local paint shop for one that work ok with this primer). So far we haven't noticed any problems with it.

loose aircap (even tho they feel tight, another nip will often cure this)

Paint too thick, test this by spraying some thinners through the gun, does it spray properly?

Muck in the aircap, not allowing free flow of the paint.

What size needle/tip are you using?
The gun had the same problem today. If anything I'd say its worse though.

We sprayed loads of thinners through it. The pattern it makes looks ok, but there is now a definite beating effect to the paint flow.

We tried adjusting the various adjusters, and the air pressure (both up and down) and it is still doing it.

It seems to only do it though when there is paint or thinners coming through the gun. If we hold the trigger when the gun is empty, the air comes through fine.

We made sure the aircap was as tight as it would go. and that the breather hole is clean and unblocked. We mixed the paint quite a bit thinner than before, but this made no difference.

Oh and the nozzle/needle thing is 1.8. according to the box it came in. (if that's what you meant ??).

Overall I'm beginning to think that this particular gun must have had it. :(

Guess we'll replace it and try not to bugger up the next one.

Incidentally, what type of gun is best? Gravity fed, or syphon type? Or is there more to it than that?

I'm a bit nervous at the though of upgrading to a much more expensive gun until I know I wont bugger it up like this one.
 

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Gravity or Syphon is personal choice really, you waste less paint with a gravity gun although i prefer syphon.
For topcoats I use DeVillbiss but Binks and Sata are up with them, For primer I use use a cheap Sealey or a cheap Ebay HVLP gun, They are god enough for primer.
As for the Super Etch primer i would never use it ever again, had too many problems in the past with overcoating it, although Synthetic over it seems to be fine, I used to use it for painting HGV's in Synthetic but when we switched to 2 pack we started having problems.

To clean a gun you have to strip it completely and use brushes to get it clean, Its the only way to do it properly i'm afraid.
 

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I agree with Steve,
gravity or siphon. I think siphon is a bit easier to clean as well.
A 1.8 tip is really a primer tip, 1.6 or pref 1.4 is best for topcoat. 1.8 will put too much paint on and will result in runs unless you are quite careful and turn the paint flow down quite a bit.
What air pressure are you running through the gun?
The 'pulsing' is because it is not drawing the paint up smoothly from the pot, which is because there is an air leak in the aircap area somewhere.
As for cleaning, its worth looking on ebay for a proper Devilbiss cleaning kit, this contains picks, various size bottle brushes and also tiny brushes for cleaning the airways, you can often get them for around £10-15 pounds.
Steve recommended to me the devilbiss JGA 558 guns, and they are truly a lovely gun to use.
I bought 2 from Ebay, one brand new and one that had been used about 4 times, both were about £90.00 though you can get cheaper ones that have been used more.

Strip your gun down completely and check that all parts are spotlessly clean and reassemble.

Then try spraying water through it to test it, to see if its ok. Air pressure should be approx 2.5 - 3 bar at the gun (35-50 psi) try varying it for the best results.
 

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Discussion Starter · #18 ·
Really strange, Today we did a touch up coat for the bits that were a bit thin.

Started out, the gun was doing the pulsating thing again, but not as bad as last time. But we figure, we're only doing primer so might as well get it finished.

Anyway, (to cut a very short but boring story even shorter) by the time we come to cleaning up again and spraying thinners through it, it seems to have stopped pulsating, and is spraying as normal. And I have no idea what changed. :confused:

Are spray guns usually temperamental like this? Or is it just that I've dislodged something that was causing the problem?
 

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They only get tempremental when not cleaned properly m8, Sounds to me like particle has been dislodged, Nows the time to strip completely and clean it to within an inch of its life :lol:

Really strange, Today we did a touch up coat for the bits that were a bit thin.

Started out, the gun was doing the pulsating thing again, but not as bad as last time. But we figure, we're only doing primer so might as well get it finished.

Anyway, (to cut a very short but boring story even shorter) by the time we come to cleaning up again and spraying thinners through it, it seems to have stopped pulsating, and is spraying as normal. And I have no idea what changed. :confused:

Are spray guns usually temperamental like this? Or is it just that I've dislodged something that was causing the problem?
 
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