Brock Posted June 3, 2019 Share Posted June 3, 2019 For years my motorhomes have had metal dust caps without problems. When my rear tyres were replaced, I noticed that the garage had fitted all plastic caps. Didn't bother me until one of the caps lost its thread and wouldn't 'finger' tighten. My local Halfords (we have two) and local Europarts only sell plastic ones. Halfords say, "It is a safety issue in that they are easier to use, don't rust, and don't seize up - metal ones need copper grease". I can get metal caps from Iveco in Liverpool but I am wondering whether things have changed so much that plastic dust caps are better. Iveco metal ones are half the price of Halfords plastic ones. It's not going to keep me awake at night but I would like to know which are better for motorhomes. My valves are all metal to cope with the high tyre pressures. Link to comment Share on other sites More sharing options...
Geeco Posted June 3, 2019 Share Posted June 3, 2019 John The only reason I can think off to use metal rather than plastic is the effect that grit mixed with small pebbly material on the roads in winter could have on pulling the plastic cap off the valve stem. The pressure in the tyre should not IMO be a factor as the cusp is on the outside of the pressure area. Cheers, Link to comment Share on other sites More sharing options...
witzend Posted June 3, 2019 Share Posted June 3, 2019 I always use metal caps for all my tyres as they will hold air pressure if the valve develops a leak. In many years I've never had any problem removing them although some people seem to. £1 buys 4 on ebay Did they fitt metal valves as their recomended for pressures over 60 psi https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=208 Link to comment Share on other sites More sharing options...
colin Posted June 3, 2019 Share Posted June 3, 2019 At the last count I think we had 20+ vehicles, don't think any have metal caps. If the plastic ones have stripped threads you are over tightening them. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted June 3, 2019 Share Posted June 3, 2019 I’m not sure about ‘better’, but Schrader clamp-in tyre valves fitted as OE to Ducato-based camping-cars have (for some years) had plastic caps. These caps are pretty sturdy and have an internal seal, but many (most?’ of the plastic caps being sold will be ‘Schrader type’ not the genuine article fitted by Schrader to their ‘metal’ valves. If you can source good quality metal caps cheaply from Iveco, fit those. Link to comment Share on other sites More sharing options...
EJB Posted June 3, 2019 Share Posted June 3, 2019 Plastic is a lot cheaper than metal! ;-) Link to comment Share on other sites More sharing options...
Paul- Posted June 3, 2019 Share Posted June 3, 2019 I use plastic caps as I've seen the shiny metal ones stick fast, the tyre fitter cut the valve off dropped the tyre into the rim and fitted a new valve, up until then I also used the chrome caps Link to comment Share on other sites More sharing options...
Derek Uzzell Posted June 4, 2019 Share Posted June 4, 2019 The material normally used for metal clamp-in tyre valves (and for the stem of ‘rubber’ snap-in valves) is normally brass (plated or not). Alloy valves are also marketed, as are stainless-steel ones. When the valve has a metal cap, provided that the cap’s material is not dissimilar to that used for the valve’s stem, the cap should not corrode to the stem and there should be no need to lubricate the cap/stem threads as Halfords suggested to Brock should be done (and, if a lubricant were to be used, a ‘dry’ non-greasy product would be better than “copper grease”). The following link is to Schrader’s (large) catalogue https://tinyurl.com/ybvjz3vz and it will be seen that, although some of the tyre valves have metal caps, most have a plastic cap. The valve now (and in recent years) fitted as original equipment to the steel wheels of Ducato camping-cars is the 65765-68 product shown on Page 13 of the catalogue, and this valve has a plastic cap. https://tinyurl.com/y4yv9l25 Two things worth noting - the advised nut tightening torque differs according to whether the seal at a clamp-in valve’s base is an O-ring or a stepped washer, and the tubular ‘nut’ of the 65765-68 valve allows the standard Ducato plastic wheel trim to be fitted properly to the wheel, which may not be the case if a different valve is fitted. Schrader valve caps are shown on Page 80 of the brochure https://tinyurl.com/y4ahp6qh Some caps are made of polyethylene and have no internal seal (ie. have no ‘washer’) while those made of stronger polyamide have a seal. Obviously (as Colin said above) brutally overtightening a plastic valve cap will damage it, but it needs to be appreciated that some of the ‘car type’ snap-in valves used by tyre-fitting outlets are purchased by the outlet VERY cheaply and that cheapness extends to the quality of the plastic valve cap. Link to comment Share on other sites More sharing options...
Billggski Posted June 4, 2019 Share Posted June 4, 2019 I agree about the quality of the valves bought by tyre fitters. Personally I would always obtain my own high pressure valves and ask them to be fitted. Walking around dealers I often spot mohos, even on heavy chassis, with standard car valves fitted. Link to comment Share on other sites More sharing options...
Brock Posted June 4, 2019 Author Share Posted June 4, 2019 My Iveco metal dust caps were stolen yesterday in Edinburgh. My son had bought them for me earlier that morning. When he was unloading his van in Edinburgh, a carboard box on the front seat was snatched. Including my dust caps, the total value of the contents of the box was just under four pounds. The sat nav was not nicked so presumably the Scots, or their visitors, value dust caps over sat navs. I will have to wait for him to go to Iveco again. Link to comment Share on other sites More sharing options...
John52 Posted June 16, 2019 Share Posted June 16, 2019 Brock - 2019-06-03 2:51 PM Halfords say, " metal (valve caps) need copper grease". As I understand it, the point of copper powder in the grease is when the grease burns off at high temperatures the copper powder is left to prevent threads seizing up. Use on exhaust bolts, spark plugs etc But why specify copper grease when its not subject to high temperature. - (tyre valve caps)? Copper grease I have is mineral based which attacks rubber (rubber stems / valve seals / tyre cap seals / tyres) If you put it on the caps its bound to get blown through over the valve seals and into the tyre when you inflate it. I've always used vaseline, silicone, lithium based grease, or candle wax on stuff that contacts rubber - whichever I found first. But never copper grease. Link to comment Share on other sites More sharing options...
Don636 Posted June 16, 2019 Share Posted June 16, 2019 I have metal dust caps on my van as supplied from new with no problem. First time I have ever heard of there being any problems using metal instead of plastic dust caps. Link to comment Share on other sites More sharing options...
John52 Posted June 16, 2019 Share Posted June 16, 2019 Don636 - 2019-06-16 9:27 PM I have metal dust caps on my van as supplied from new with no problem. First time I have ever heard of there being any problems using metal instead of plastic dust caps. Same here. It might be the fancy coloured aluminion valve caps that Halfords sell to boy racers (lol) In which case copper grease is an even worse idea because the copper grease can attack the aluminium as well - copper/aluminium galvanic corrosion :-S Link to comment Share on other sites More sharing options...
Don636 Posted June 16, 2019 Share Posted June 16, 2019 Just Googled this out of curiosity and there are lots of articles, forums and YouTube videos about metal caps fusing on, how to prevent this and how to get them off. I may be lucky in that the metal of the cap and the stem is the same on my van or as least not causing a reaction. The advice seems to be to apply copper grease or WD40 or use plastic caps. It seems this could be a more expensive problem if you have a TPMS fitted as you might need to replace the sensors along with valve stems. Based on this I would not think about replacing plastic caps with fancy shiny ones as I have done in the past, just in case although my current set up seems to be OK after 5 years. Link to comment Share on other sites More sharing options...
John52 Posted June 17, 2019 Share Posted June 17, 2019 Well I was taught mineral oil and grease rots rubber. Modern synthetic seals might be more resistant to it. But I still can't understand why they recommend copper grease for threads that don't get hot. Doubt if the average car driver would have any copper grease. Were they just trying to sell him some. (lol) Link to comment Share on other sites More sharing options...
flyboyprowler Posted June 18, 2019 Share Posted June 18, 2019 Don636 - 2019-06-16 10:51 PM Just Googled this out of curiosity and there are lots of articles, forums and YouTube videos about metal caps fusing on, how to prevent this and how to get them off. I may be lucky in that the metal of the cap and the stem is the same on my van or as least not causing a reaction. The advice seems to be to apply copper grease or WD40 or use plastic caps. It seems this could be a more expensive problem if you have a TPMS fitted as you might need to replace the sensors along with valve stems. Based on this I would not think about replacing plastic caps with fancy shiny ones as I have done in the past, just in case although my current set up seems to be OK after 5 years. We have had a TPMS fitted for 4 years, with no sign of corrosion on the metal valve stems. Link to comment Share on other sites More sharing options...
maldonmole Posted June 19, 2019 Share Posted June 19, 2019 To get back to the original question, we are talking about DUST caps, they are only there to protect the valve from moisture and dirt. Some metal ones may 'weld' themselves to the valve stem (especially if it is alloy), plastic ones wont do that. Shiny metal ones are attractive to the low life and will probably end up being repatriated on a citroen saxo with an exhaust tailpipe the size of Dartford Tunnel. Individual choice as always. Link to comment Share on other sites More sharing options...
Don636 Posted June 19, 2019 Share Posted June 19, 2019 My wife can’t believe you can have so much debate about what type of dust cap to have and thinks we must all have too much time on our hands and would I not be better getting on painting the spare bedroom - really!!! Link to comment Share on other sites More sharing options...
John52 Posted June 20, 2019 Share Posted June 20, 2019 maldonmole - 2019-06-19 11:52 AM To get back to the original question, we are talking about DUST caps, they are only there to protect the valve from moisture and dirt. And hopefully keep the pressure in if the valve leaks. (which I think might be more likely if you are using coppergrease because the mineral oil and powdered metal may harm the seals?) Tyres running at higher pressure have stronger metal valve stems to cope with the higher pressure. So its logical to ask if they need metal valve caps to keep the higher pressure in too. Link to comment Share on other sites More sharing options...
John52 Posted June 20, 2019 Share Posted June 20, 2019 Don636 - 2019-06-19 12:41 PM My wife can’t believe you can have so much debate about what type of dust cap to have and thinks we must all have too much time on our hands and would I not be better getting on painting the spare bedroom - really!!! Good Idea. Just buy her a foot pump for when the tyres go flat :-D Link to comment Share on other sites More sharing options...
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