Andy J Posted July 4, 2022 Share Posted July 4, 2022 Looking for a pair of OS 25's for a current project and note many for sale on ebay appear to have two forms of fixings for the exhaust. The first type is a U shaped strap whilst the second method are two bolts interfacing with the manifold. Which type of fixing is preferred for this engine and which type indicates an older engine? Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted July 4, 2022 Share Posted July 4, 2022 Straps/ U clamps are from the early 1970s Andy. Quote Link to comment Share on other sites More sharing options...
Andy J Posted July 4, 2022 Author Share Posted July 4, 2022 Thanks Denis. Am I correct in assuming that latter 25 engines used a gasket between the manifold and silencer? Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted July 4, 2022 Share Posted July 4, 2022 Yes but Many lads swear by epoxy. Thin layer applied to clean surfaces and the mating parts tightened up. Quote Link to comment Share on other sites More sharing options...
Paul De Tourtoulon Posted July 4, 2022 Share Posted July 4, 2022 I resurface all my engines and exhausts with wet and dry glued to a piece of flat glass, then with any sort of fine grinding paste, a smear of locktite on the surface and it should never leak, joints are only for bad mating surfaces,,, Quote Link to comment Share on other sites More sharing options...
kc Posted July 4, 2022 Share Posted July 4, 2022 I think the original 25 Max may all have had the U shaped strap - my one from 1985 was possibly one of the last and had a strap. The FP series came soon after 1985 Possibly only the FP series had just bolts. Is it really worth buying OS 25 Max? The two I have were really low power and when I last used used them I couldn't wait to get something better! Of course the ball race OS25 FSR was a much better engine. A couple of Enya 25 SS plain bearing would be a better bet and far more powerful. The bigger Enya 30SS ( but in a 25 sized case) was as powerful as a .40 and would be even better buy, although less common. At the last Old Warden model event the 'junk' stands had a number of Enya SS 25 or 30 looking dirty and unloved, but possibly a good buy if the price is right. Nobody seemed to take much interest in them so they will probably be still on sale at the next Old Warden! Quote Link to comment Share on other sites More sharing options...
Andy J Posted July 4, 2022 Author Share Posted July 4, 2022 How does the Enya 25 or 30ss compare with say the OS 30 Max in terms of power / reliability? Quote Link to comment Share on other sites More sharing options...
Andy J Posted July 4, 2022 Author Share Posted July 4, 2022 Well looking at what's currently available on ebay a OS 40 may be a better option in terms of price as they seem to be cheaper than 30''s for some reason.. Quote Link to comment Share on other sites More sharing options...
Nigel R Posted July 5, 2022 Share Posted July 5, 2022 (edited) 40fp are very common. And reliable. If they are what you are looking at? Also light. Might be a touch big for the GTC though? Enya SS are really nice motors. I note there are a few os 25 la engines on ebay. Also many 25fp. They could work well? Edited July 5, 2022 by Nigel R Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 5, 2022 Share Posted July 5, 2022 I would recommend the fp over the la any day of the week. The la series was far more vulnerable to the OS liner plating rot issue than the fp ever was. All of the fp engines my dad ever owned are still working fine but all of the la series are long since dead. The enya 25, asp 25 etc would be good though. Just be aware that with 2nd hand engines you might struggle to find two than run nicely together. Quote Link to comment Share on other sites More sharing options...
kc Posted July 5, 2022 Share Posted July 5, 2022 (edited) The OS Max came in several types - the Max and the Max FP. The Max 25 etc were plain bearing while the Max 40 was ballraced but the Max 40 FP was plain bearing. Max 40 is considered much better than the 40 FP, although it is older & has ballraces to get corroded etc. the Max 40 was not schneurle ported and neither was th Max 25. Schneurle makes a big difference in power. The FP were all schneurle. FP came in two types of cyl liner/ piston material - original and a later type. Enya SS plain bearing are very long lasting and very powerful- far better & more powerful than OS in my experience. My Enya 30SS plain bearing was much more powerful than my OS 40FP - used in the same plane. The OS 40FP wouldn't rev so was much better on a 11 by 7 than on a 10 by 6 - engine tests of the time showed this. Edited July 5, 2022 by kc Quote Link to comment Share on other sites More sharing options...
kc Posted July 5, 2022 Share Posted July 5, 2022 I finally found my OS data sheets from 1985 -1990. They show that the OS Max 25 had the type 702P strap type silencer while the 25 FP had just bolts into the type 842 silencer. Thats the difference - the strap type is the older Max 25, while the later & more powerful (schneurle) Max25FP has the bolt into silencer. Also shows the original Max 25 and Max 40 ball race were not schneurle ported. Quote Link to comment Share on other sites More sharing options...
Paul De Tourtoulon Posted July 5, 2022 Share Posted July 5, 2022 (edited) I had the .35Fp and the 40Fp ( in a contender ) yes plain bearing series which had air bleeds for the idle both never missed a beat, I also had both the max, not very powerful and the Fsr, std and the ABC ones really powerful for their sizes and better carbs, not like the Fp's I take it that you have visited here,,,, http://sceptreflight.com/Model Engine Tests/Index.html Edited July 5, 2022 by Paul De Tourtoulon visit Quote Link to comment Share on other sites More sharing options...
Andy J Posted July 5, 2022 Author Share Posted July 5, 2022 Thanks for all the info chaps now lost as to what to buy! Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted July 5, 2022 Share Posted July 5, 2022 Funny enough, just this Sunday I recommissioned an old club trainer that hadn't run for over 5 (and probably nearer 10) years, it has a Magnum GP25 in it, the guy who last owned the trainer and taken care not to allow the engine to become gummed up. Anyway some 5% nitro fully synthetic fuel and a quick dab on the starter and it was running away quite well. 1 Quote Link to comment Share on other sites More sharing options...
David Davis Posted July 5, 2022 Share Posted July 5, 2022 How big is the twin you intend to build Andy? I'm no expert but this 85" wingspan Bristol Blenheim apparently flew perfectly adequately on two OS 40 FPs. These engines were not particularly powerful but they were easy to start and very reliable. https://www.sarikhobbies.com/product/bristol-blenheim-7-plan/ Quote Link to comment Share on other sites More sharing options...
Andy J Posted July 5, 2022 Author Share Posted July 5, 2022 My twin is a 10% increase on the Grumpy Tiger cub so the wingspan will be 60inch. Did buy 2 OS 20 Max on the belief the original flew with 2 15''s but think I dropped a bit of a clanger as from what others have said they will be too small for a 60inch design. Quote Link to comment Share on other sites More sharing options...
David Ovenden Posted July 5, 2022 Share Posted July 5, 2022 Not sure if this helps, but I built a 62" span Doublet twin designed by Denis Tapsfield . That was quite adequately powered by 2 HB20 engines. So maybe 2 OS20 engines would be enough for your 60" model? Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted July 6, 2022 Share Posted July 6, 2022 As above, If this helps, not withstanding differences between a sleek model and a fully fitted bi-plane. Considering Weight, and getting this off the ground and into the air. 2x .20s should fly 5lb AUW comfortably, and 2x .25s should fly 6.25lb AUW Quote Link to comment Share on other sites More sharing options...
Nigel R Posted July 6, 2022 Share Posted July 6, 2022 I would go with 25FPs. They seem about right for the desired performance and likely end weight. And are reliable. Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted July 6, 2022 Share Posted July 6, 2022 (edited) Andy, I have 2 OS MAX 25FPs that came from a deceased modeller's estate if you are interested, they have different carbs but apart from that they are the same. I was going to take them to Woodspring this weekend and try to sell them on the club sale stand. I have given them a thorough clean-up and service but I haven't run them. They both flip over nicely with good compression. As far as I can see the cylinder liners are in good shape. ETA, I remembered that the one on the right had a JE carb so to make them identical it may be worth installing the other one with a JE carb. Edited July 6, 2022 by Andy Stephenson Quote Link to comment Share on other sites More sharing options...
Nigel R Posted July 6, 2022 Share Posted July 6, 2022 (edited) https://www.ebay.co.uk/itm/165561820394?epid=1323282985&hash=item268c40e4ea:g:eHIAAOSwTLhiw0w1 ^ complete engine, £20 https://www.ebay.co.uk/itm/165541363104?hash=item268b08bda0:g:Md0AAOSweopisNJh ^ carb, £12 JE now have different carbs these days - they are selling SH and Perry carbs as replacements, not the ASP ones. Edited July 6, 2022 by Nigel R Quote Link to comment Share on other sites More sharing options...
kc Posted July 7, 2022 Share Posted July 7, 2022 On 05/07/2022 at 21:11, Andy Joyce said: Did buy 2 OS 20 Max on the belief the original flew with 2 15''s but think I dropped a bit of a clanger as from what others have said they will be too small for a 60inch design. If they are the 20FP which are more powerful than the older Max20 then they may well be OK. If they have the bolt through into the silencer they should be the FP version ( schneurle port ) while the older type with strap on silencer are non schneurle and less powerful. If you have them test them and see if they run well and seem reliable. The 20 FP versions should have the angled type silencer exit pipe, while the older non scneurle do not have the angled exit pipe. ( if the data sheet is right and also if the silencers have not been changed) Only a dedicated engine person would fit 2 glow motors into a twin when electric is so easy now! Quote Link to comment Share on other sites More sharing options...
Nigel R Posted July 7, 2022 Share Posted July 7, 2022 Ah... using two electric motors would take all the fun out of having a twin! 1 Quote Link to comment Share on other sites More sharing options...
Andy J Posted July 7, 2022 Author Share Posted July 7, 2022 On 06/07/2022 at 10:23, Andy Stephenson said: Andy, I have 2 OS MAX 25FPs that came from a deceased modeller's estate PM sent Andy Quote Link to comment Share on other sites More sharing options...
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