Sealing washers for CAV/Delphi water separator/sediment trap drain screw

[blackrose]

Does anyone know the diameter of the drain screw and what type of washers I should buy? Would dowty washers be suitable? I find that plain flat rubber washers just get squished out if you overtighten by just a tiny bit, and if you don't tighten sufficiently then vibration could cause a leak. 

 

Or could I use copper washers?

Edited September 1 by blackrose

[Tony Brooks]

Dowty will be the RR solution, but SOFT copper, fibre, or nylon have all worked for me.

 

Can't remember the size 

[blackrose]

1 hour ago, Tony Brooks said:

Dowty will be the RR solution, but SOFT copper, fibre, or nylon have all worked for me.

 

Can't remember the size 

 

Thanks Tony, I'll take the drain screw out of one today and measure it.

 

I thought fibre washers were only for water?

Edited September 2 by blackrose

[Tony Brooks]

1 hour ago, blackrose said:

 

Thanks Tony, I'll take the drain screw out of one today and measure it.

 

I thought fibre washers were only for water?

I carefully worded my reply to not recommend any type. Fibre may not be the best for diesel, but on many boats it would soon have been sealing rusty old water.

[Ex Brummie]

Whilst working as an oil boiler service engineer, all the oil filters I ever saw used rubber washers, but always with a steel washer between the plug and the filter. The washer still squashes but doesnot get any rotary distortion. The high pressure seals on oil pumps were either o rings on the neck of the plug, or 'crushable' aluminium washers under the hexagon head.

[blackrose]

4 hours ago, Ex Brummie said:

Whilst working as an oil boiler service engineer, all the oil filters I ever saw used rubber washers, but always with a steel washer between the plug and the filter. The washer still squashes but doesnot get any rotary distortion. The high pressure seals on oil pumps were either o rings on the neck of the plug, or 'crushable' aluminium washers under the hexagon head.

 

Ok perhaps I'll carry on with new rubber washer and add a stainless washer underneath. But would a metal washer below the rubber one actually make any difference? The screw has it's own flange and I'm not convinced a metal washer wouldn't start turning itself as soon as the screw flange begins to tighten onto it.

Edited September 2 by blackrose

[ditchcrawler]

I have a feeling when the topic of changing the plastic plug out someone said they were 8mm

[blackrose]

1 hour ago, ditchcrawler said:

I have a feeling when the topic of changing the plastic plug out someone said they were 8mm

 

That's what Google Ai says too. Seems odd that it's such a large thread dia for a small screw. I haven't taken it out to measure it yet. Been p*ssing down and drizzling all day and I have cruiser stern!

Edited September 2 by blackrose

[Ex Brummie]

I would have thought it would have been a BSP thread. If AI is just looking at the actual diameter, this would probably equate to 1/8" BSP. A 1/4"bsp is virtually 1/2" diameter. 

[Tony Brooks]

2 hours ago, ditchcrawler said:

I have a feeling when the topic of changing the plastic plug out someone said they were 8mm

That is typical for spin on filters. I thought the CAV filter drains were more like 6mm, 1/4 inch, but not sure. I suspect the thread altered over the years 

[blackrose]

1 hour ago, Ex Brummie said:

I would have thought it would have been a BSP thread. If AI is just looking at the actual diameter, this would probably equate to 1/8" BSP. A 1/4"bsp is virtually 1/2" diameter. 

 

Yes Ai said it was an imperial thread 5/16" UNC, but I'm not that interested in the actual screw thread type as I just need the approx thread diameter for some washers.

[ditchcrawler]

3 hours ago, Tony Brooks said:

That is typical for spin on filters. I thought the CAV filter drains were more like 6mm, 1/4 inch, but not sure. I suspect the thread altered over the years 

Its quite possible the thread was about spin on plugs

[Tony Brooks]

9 hours ago, ditchcrawler said:

Its quite possible the thread was about spin on plugs

Title says CAV/Delphi water seperator

[ditchcrawler]

3 hours ago, Tony Brooks said:

Title says CAV/Delphi water seperator

No the one I remembered , did a search and got this  

 

[blackrose]

Just measured the screw and it's 7.7mm dia with a 14mm flange. It's not a metric thread but that's not important for me as I'll order M8 x 14mm copper sealing washers.

Edited September 4 by blackrose

[ditchcrawler]

43 minutes ago, blackrose said:

Just measured the screw and it's 7.7mm dia with a 14mm flange. It's not a metric thread but that's not important for me as I'll order M8 x 14mm copper sealing washers.

 

[blackrose]

Well the copper washers don't work. There's no way you can get enough torque on that small screw to crush a copper washer. I tried tightening it with a pair of pliers on the finger tightening screw head but diesel is still dripping out. I thought about using a pair of grips but I'm worried I'll end up stripping the threads if I try to get it any tighter.

[ditchcrawler]

1 hour ago, blackrose said:

Well the copper washers don't work. There's no way you can get enough torque on that small screw to crush a copper washer. I tried tightening it with a pair of pliers on the finger tightening screw head but diesel is still dripping out. I thought about using a pair of grips but I'm worried I'll end up stripping the threads if I try to get it any tighter.

Maybe thats why they come with a rubber one as standard 

[blackrose]

5 hours ago, ditchcrawler said:

Maybe thats why they come with a rubber one as standard 

 

I think that's right. Interestingly I put the rubber washer back on and put a metal washer behind it as per Brummie's suggestion above, to allow the flange of the screw to slide on the metal washer rather than directly spinning on it and distorting the rubber washer. However, it wouldn't seal and let a drop out every few minutes. I was shocked. I couldn't understand why the thin metal washer behind the rubber one made any difference, so I then took the metal washer off and just used the rubber washer on its own and it sealed instantly! 🤔

Edited Wednesday at 14:02 by blackrose

[Tony Brooks]

1 hour ago, blackrose said:

 

I think that's right. Interestingly I put the rubber washer back on and put a metal washer behind it as per Brummie's suggestion above, to allow the flange of the screw to slide on the metal washer rather than directly spinning on it and distorting the rubber washer. However, it wouldn't seal and let a drop out every few minutes. I was shocked. I couldn't understand why the thin metal washer behind the rubber one made any difference, so I then took the metal washer off and just used the rubber washer on its own and it sealed instantly! 🤔

 

I would suggest that the rubber washer did not squeeze tightly enough onto the thread, so fuel could seep down it and down the hole in the washer. I had my doubts when I read Brummie's suggestion. At least you now know the diameter required so you can source a Dowty washer if you still want to.

[blackrose]

1 hour ago, Tony Brooks said:

 

I would suggest that the rubber washer did not squeeze tightly enough onto the thread, so fuel could seep down it and down the hole in the washer. I had my doubts when I read Brummie's suggestion. At least you now know the diameter required so you can source a Dowty washer if you still want to.

 

Could be, yes that makes sense.

 

I couldn't find a 5/16" dowty washer - I'm not sure they exist, and M8 seemed like it might be too loose on the thread as the ones I looked at were 8.3 - 8.7mm ID

Edited Wednesday at 16:33 by blackrose

[Tony Brooks]

8 minutes ago, blackrose said:

 

Could be, yes that makes sense.

 

I couldn't find a 5/16" dowty washer - I'm not sure they exist, and M8 seemed like it might be too loose on the thread as the ones I looked at were 8.3 - 8.7mm ID

 

Just found this, but I bet they only supply in large numbers.

[blackrose]

4 minutes ago, Tony Brooks said:

 

Just found this, but I bet they only supply in large numbers.

 

 

Thanks, I've just ordered a set of metric ones from Amazon for £7.99 and I'll try an M8. Your explanation made me think even loose Dowty washers will work for the same reason a loose plain flat rubber washer works. They don't need to grip the thread.

[Tony Brooks]

2 minutes ago, blackrose said:

 

Thanks, I've just ordered a set of metric ones from Amazon for £7.99 and I'll try an M8. Your explanation made me think even loose Dowty washers will work for the same reason a loose plain flat rubber washer works. They don't need to grip the thread.

 

Absolutely, sealing on the two surfaces and not the thread.

[jonesthenuke]

FWIW I have a new CAV filter assembly I bought about 5 years ago. The drain plug is brass with a copper washer. A shoulder on the plug centralises the washer and the mating surface on the filter bowl has been machined flat, thus it's made well. The thread is too coarse to be M8. It appears to be either 5/16 BSW or UNC; I cannot tell the difference when using thread gauges as both are 18 TPI and my eyes cannot see any difference re thread form.

 

There are a lot of cheap copies of these filter assemblies around which may have different threads. Similarly, older CAV units could be different though BSW or UNC strikes me as indicative of an older design thats been in production for decades.

 

Edited Friday at 11:09 by jonesthenuke