Compair Jetair J15 problems & parts

[Paul99]

Been getting fed up lately of using the 25l compressor so thought I'd dig out the big jetair compressor from the back of the shed which I rescued from a scrap man years ago for parts as it was assumed broken. Anyway after fitting a new motor I find that it pumps but clearly there is something very wrong as it just doesn't build any pressure (rises very very slowly to about 10psi then builds no further no matter how long it's left.

I've sorted out the check valve with a new washer just to eliminate the simple things first and bypassed the pressure control valve temporarily just to eliminate that too. I'm now thinking that it must be worn piston rings (probably why it might have been scrapped all them years ago) - I can quite easily hold by thumb on the end of the air output pipe whilst running and suction is not all that great on the intake either to my mind.

I took the head off and cleaned the reed valves off but all seems ok and can't see anything obviously wrong above the pistons. There appears to be no lip at the top of the cylinder so hopefully a case of new rings and new gaskets. I assumed that there would be service kits easily available but no - half an hour of google ing and looking on ebay has thrown up a blank this far so does anyone here know of a source of parts for this compressor pump?

Hope someone has some ideas...
Paul

 

[piman]

Hello Paul,

even with bad rings given the lack of wear I would have thought that you would get more air pressure than that? Are you certain the reed valves are good and fitted in the right orientation, i.e. inlet and discharge are fitted in opposite directions to each other? Could some one all those years ago have taken the valves out and fitted one upside down?

Alec

 

[Paul99]

Anything is possible Alec - tbh I thought the same that it probably should build up a bit more pressure than that even if the rings are in a bad way. I'm pretty sure it looked right - but I will have another look at it in a minute just to be absolutely sure.

 

[Rig Pig]

If the rings or bores are shot it will probably be blowing badly from the crank case??

 

[Paul99]

OK managed to get one step further with it.... Took the cylinder head off again re-checked the valves and gave them a more thorough cleaning. Putting my hand over the cylinders and turning over by hand reveals that there seems to be a lot more suction than first thought - so valves definitely not working properly. Still couldn't see anything wrong and was at the point of giving up when I noticed that the gasket between the plates was a handmade job - much closer look at it and it seems the last owner was very lazy and didn't leave a section of gasket between inlet and outlet valves on both cylinders - hmm that's going to stop the valves from working right for sure. So 15mins and a trusty cornflakes box later I have a new gasket:

Old gasket on the right new on the left.

Re-assemble fire it up and for a moment I thought I'd cracked it when pressure built quickly to 50psi before slowing right down and failing to pass 60psi

I think now though the extra pressure me be possibly be causing the cylinder head gasket/s to leak between cylinders - they were a bit on the rough side but not bad enough to cause the earlier more catastrophic problem - I'll replace them tomorrow to see if that gets me any further along....

Thanks for the advice so far.
Paul.

 

[Paul99]

If the rings or bores are shot it will probably be blowing badly from the crank case??

Yep you'd have thought - but no sign of the crankcase being pressurised or oil blowing out the filler spout. Coupled with the last post maybe I was too quick to assume piston rings had to be the fault...

 

[piman]

Hello Paul,

I don't see how you can be sure those valve plates are sound, there seems to be no easy way of checking the seats and fingers?

Alec

 

[Paul99]

Hello Paul,

I don't see how you can be sure those valve plates are sound, there seems to be no easy way of checking the seats and fingers?

Alec

You're right of course - other than confirming the plates aren't warped with a straight edge I'm just going by eye as I couldn't think of any way to test them either short of swapping out with known good spares . I did think to smear the valve seats with some engineers blue re-assemble it all then turn the compressor over by hand a few times then take it apart again to check that the reeds are making a complete seal with the valve seat I'd probably need to repeat with the tank already pressurised as that is now when they are failing (if it is the valves)

At this point I would happily replace the valve plates, reed valves and all the gaskets but I'm back to square one with not being able to find any to buy. Even if it's an odd approach to overlook the most common / likely problem I might as well fix the bits that I can as at least it rules them out and narrows down the cause of the problem even more. The head gasket is in poor condition and would not trust it to hold much pressure and for the sake of another 15mins replacing it with another it's got to be worth trying whilst I'm still trying to track down parts.

 

[piman]

Hello Paul,

certainly it's worth the effort to eliminate any suspect areas. Just with my limited experience I am used to disc valves which are easy to check.

Alec

 

[Paul99]

Right New gaskets all round and it'll now reach around 115psi before rising no more Good news is the valves appear to be working fine and no more leaky head gasket. Bad news is the crankcase is definitely now being pressurised as there's a steady stream of air exiting the top of the oil filler plug and there's oil being forced out around the crankcase gasket so it looks like the piston rings are after all in need of replacement