Sealey 3HP twin not building pressure

[carrera]

Ah it is becoming clearer now

Starting at the top from memory

<snip>

There are no cheap wheels on mine as it's static in a belly locker in a truck with the tank mounted alongside, which isn't making access any easier

I have just looked at the parts diagram again and I think you are onto something. I only found one metal gasket. That's probably because I failed to separate the head from the first valve plate - I think you can see this in the photo above. Time for another

Thanks

 

[carrera]

At rest the pin should be in under pressure from the spring. When pressure reaches about 20psi the pressure overcomes the spring and the pin should pop out. During this period you should feel a good stream of air from the valve, this air flow stops when the pin pops out. The valve doesn't divert the air.

OK, that makes sense to me

With a faulty cylinder the air will be going from the good cylinder to the bad one and out through the inlet, but this may not happen until some pressure has built up in the manifold.

I was thinking along the same lines, a bit like a head gasket failure between two cylinders on a car engine

Does the pin pop out again once you've pushed it in?

Yes

I take it the 'bad' piston does move up & down when the pulley rotates? Although I think a broken crank would make its presence heard!

The piston and crank seem to be moving fine - the first time I tried to fit the barrel the crank rotated and the piston withdrew into the crankcase. I managed to pull it back and the movement seemed smooth

 

[normspanners]

It would not pump air out of the inlet if the crank/rod was broken. the reed valves are a pain to get right it doesnt matter which way you do it gravity still works on one, when I have done mine they used to fall out of the machined slot, now I use a thin feeler gauge to hold, the one gravity is working on, to keep it up in place, then tighten the head down down evenly till it JUST nips the feeler gauge back off the nuts slightly slide the feeler gauge out, that then ensures the reed stays in its slot, then tighten the head down evenly, I have made head gaskets out of aluminium coke cans, seems to work very well, but they have to be the exact shape of the old one, to stop the reeds moving.
the valve you are playing with is just a symptom of one cyl not working properly as soon as you get that one pumping that will work IMO.
as said the reeds hold debris under them from blown gaskets.

 

[normspanners]

Doesn't the plate that is stuck to the head not come off.
You need to check gasket no6 in your pdf.

Yes it should, that is where it will be blown on the bridge piece.

ALL The plates need removing from the head and block and checking the various gaskets .

 

[carrera]

Tonights little update is........... drum rolll....... it's fixed

The gasket between the head and the first valve plate is paper and it had failed along the web that divides the intake / exhaust tracts.

The material itself is very thin, I had some thicker gasket material on the shelf so have used that along with a smidgen of gasket sealer.

I found a useful technique to retain the reeds valves in the correct place when assembling the head was to use a welding magnet that kept the upside down reed valve in place until the bolts were nipped up.

The delay valve is working correctly. Pin in when off, out with no leak when the pressure is being generated. I think what was happening before was that my finger was performing the seal to allow pressure to flow to the tank, rather than past the delay valve. There probably was insufficient pressure to fully close the delay valve because the flow from the right cylinder was almost completely flowing into the left hand cylinder, hence no flow to the tank.

Many thanks to everyone who helped me track down the problem and fix it, much appreciated

 

[rtbcomp]

Great! Thanks for letting us know.

Your theory about what was happening with the delay valve sounds good, it's been bugging me all day as to what was happening.

There's one of those valves on my Clarke compressor and I thought it was faulty when I first switched on, there's nothing in the manual to tell you what it does.

 

[the snooper]

the delay valve on my compressor relies on a certain amount of air flow to close it, which you get one the motor / pump is upto speed

 

[normspanners]

The gasket between the head and the first valve plate is paper and it had failed along the web that divides the intake / exhaust tracts.

on the bridge piece across the gasket,that sound familiar,
Strange that, re- reeds I tried a magnet but it didnt have the power though the head to hold it.

Well done men,

as said previously, just be careful for the future if valve plate gaskets goes I wrongly used thicker gasket stuff on the valve plate gaskets, and it did work but it allowed the reed valves to move out of place eventually that is why I used allumium can, which is thin enough but stronger than original.

 

[carrera]

Fortunately it was only the top paper gasket that failed on mine, rather than the metal middle gasket - I suppose I have that to look forward to !

On the reassembly, my magnet was not strong enough to go through the head, but was strong enough to be effective through the bottom valve plate. If you look at my second picture and imagine the lower valve plate being placed on top of the upper valve plate using the magnet I think you may get the idea. Sorry I didn't take a picture.

That to me was the advantage of removing the barrell and assembling the components upside down. It was easy to slide the barrell back over the piston using a jubilee clip as a piston ring compressor. It's probably not the approved method, but worked well for me.

 

[normspanners]

edit

Up's -------cant do that with just smilies well done chap, with mine the cyl is one part with the crankcase.

I thought the delay valve was just a symptom of your cyl problem.

 

[normspanners]

Fortunately it was only the top paper gasket that failed on mine, rather than the metal middle gasket - I suppose I have that to look forward to !

Funny today was looking for something and came across these;-
the one on the left is clearly original with the bridge piece blown out, the middle is my replacement that was too thick ( due to the colour you can see that it worked fine, BUT allowed the reeds to move out of their slots slightly after a period of time ) and the third is first practice coke can attempt, I made the next ones a little better shape,

But if you notice I managed to make the bridge piece slightly wider than original to give it more lateral strength

 

[carrera]

Some good examples there - the middle one looks very close to the original. I note that your head has 6 bolts compared to just the 4 on mine, perhaps because you have alerger single cylinder than my twin ?

 

[normspanners]

No it still only has 4 studs 2 holes are for alignment dowels IIRC