seecomber Posted July 2, 2015 Share Posted July 2, 2015 I recently fitted new rings on my two OS Surpass 48 four strokes.I did not renew the liners. How long should I run them in? Is it a matter of running them in a test stand until they can run at peak revs,say 10,000.One of them,the newer one,is inclined to run hotter than the other at the moment. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted July 2, 2015 Share Posted July 2, 2015 No real reason why you would replace the liner..unless it was badly scored or extremely worn...they tend to last many hours. In the full size world it was common to hone the cylinder bore before fitting a new ring...the reultant cross hatching enabled the bore to "hold" a little oil. In the model world a light rub with some very fine wet & dry is usually sufficient to deglaze the bore (wash the liner well afterwards though.... Regarding running in then I would suggest very little really.....a few short runs a touch on the rich side & then go & fly. The newer one may be a little tighter with the resulting increase in friction increasing the running temp slightly but I wouldn't have expected it to be noticable....how are you measuring the temperature? A slightly leaner mixture would run hotter...is this a possibility? Quote Link to comment Share on other sites More sharing options...
Stuphedd Posted July 3, 2015 Share Posted July 3, 2015 The advice above is super I second/endorse the de-glazing , very important ! cheers Quote Link to comment Share on other sites More sharing options...
Stevo Posted July 3, 2015 Share Posted July 3, 2015 I 'third' it! Yes very little running in, I deGlaze with 1200 or 1500 wet 'n' dry, followed by a thorough wash. I always make sure the inside of the engine (as well as outside) is polished to perfection and sugically clean. I've re-ringed a few Saitos, Lasers and OS FS's and again little running in. Out of interest, where did you get your new rings? I get mine from a chap on eBay. Sounds bit dodgy but believe me they are worth every penny and perform like the originals. Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted July 3, 2015 Share Posted July 3, 2015 Done a few car engine rebuilds in my younger days when I was enthusiastic about crawling about under/inside cars, so I'm interested in how you chaps determined that your glow engines needed new rings. Pretty obvious with a car engine - smoke, low compression, ring gap test/worn bores etc. Unless there's zero compression (in which case I'd expect the liner to be shot as well), what other indicators would you use, or are you replacing rings as a matter of routine or just as a precaution? Always willing to learn something new! Quote Link to comment Share on other sites More sharing options...
seecomber Posted July 3, 2015 Author Share Posted July 3, 2015 Thank you Steve, Pete and Stevo,.I did not de-glaze the liners,do you think it is vital?After a bit of running in,two tankfulls,the older motor runs fine.I have just done the newer one and it runs a bit hot even with a rich mixture but has had little fuel through it so far. I could use a hone on it,the type used on car brake cylinders,do you think this will be OK?Will fine wet and dry be better? Stevo I got the rings from Gaviscool on EBay.Who told me about him?You did! On this Forum a week or two ago. Many thanks,you saved me a total of £30. Quote Link to comment Share on other sites More sharing options...
seecomber Posted July 3, 2015 Author Share Posted July 3, 2015 Cuban8 I replaced the ring on the older engine because it would not tick over although it was fine at high revs but it could not run slow enough for landing.The second motor suddenly lost compression but regrinding the valves solved that problem.A simple job but one often overlooked.I subsequently fitted a new ring because I had one although in retrospect I might have better left well alone! Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted July 3, 2015 Share Posted July 3, 2015 Hi its important to de-glaze the liner before fitting a new piston ring . As Steveo said Fine wet and dry will do the job anything from 1000 to 1500 grit . Wash well in plenty of soapy water after de-gazing to remove any traces of grit. De-gaze in a circular motion around the cylinder , not up and down . The fine scratches produced help bed down the new ring and trap oil to help the process . New rings , although turned round are not always perfectly round after they have been hardened and tempered so this bedding in really helps make a good seal that's vital for good slow running reliable engine . A hone isn't really necessary as a Mk1 finger will do the job fine .If the liner is badly scored then its a replacement job. Check valve seating and that the valve springs are ok at the same time as these are often overlooked .They shouldn't take too long to run in Three or four tanks running a touch rich with short runns allowing the engines to get thoroughly hot the allowed to cool will speed up the running in . After this fly them running slighty rich and they will be fine . Quote Link to comment Share on other sites More sharing options...
Stevo Posted July 3, 2015 Share Posted July 3, 2015 A point to note ... GavisCool on ebay will manaufacture a ring for you - just send him the older one and will measure it and go from there. I've had rings for OS 70FS, Laser 75 and 80, Saito 50... all no problem, using any techniques discussed here. Welcome to your new happy engines Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted July 3, 2015 Share Posted July 3, 2015 I've always used a circular but up and down action in both directions to produce a cross-hatched pattern - it feels kinder to the rings than having them hitting a series of horizontal sharp edges and follows larger engined practice - any reason for your method ED? Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted July 3, 2015 Share Posted July 3, 2015 A question on grinding in valves on a model engine. As far as I'm aware, model engines are not fitted with separate valve seats as in full size practice, but rely on the impact of the valve on the head material to work-harden it during running in. If lapping a valve in on a model four stroke, is there not a real risk of overdoing it and damaging the valve seat beyond use? What abrasive material would be best to use? I think I've got an old twin ended tin of valve grinding paste somewhere in the garage - but I don't think that would be a good idea to use. Quote Link to comment Share on other sites More sharing options...
Stevo Posted July 3, 2015 Share Posted July 3, 2015 On the contrary, use it Well the fine stuff anyway. When I do mine, I put some on the seat and valve. Insert the valve, then attach a small drill to the valve stem, rotate fairly slowly, and then pull on the drill until th evalve touches the seat, 3-4 times. Job done... however, CLEAN IT THOROUGHLY!! I beleive there are inserts into the head... but if they look nice and shinyas do the valves, there may be no point in regrinding... Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted July 3, 2015 Share Posted July 3, 2015 Posted by Martin Harris on 03/07/2015 11:27:59: I've always used a circular but up and down action in both directions to produce a cross-hatched pattern - it feels kinder to the rings than having them hitting a series of horizontal sharp edges and follows larger engined practice - any reason for your method ED? Hi Martin I didn't make that very clear did I ? Circular yes and vary the angle I meant not not straight up and down the bore . Using a digit to glaze bust our small engines does produce a cross-hatched effect as it very hard to keep the wet and dry in one place .Sharp edges , hardly , not from 1000 to 1500 grit . We are talking glaze busting not honing out machine marks . When lapping cylinders I use a back and forth motion to help maintain a parallel bore Its not critical . so long as the marks are not vertical . As for larger engine practice I would agreed with you entirely and use a honing tool but they do tend to have a courser grit and if they are not moved up and down the bore they can produce an un-parallel bore . Edited By Engine Doctor on 03/07/2015 21:16:51 Quote Link to comment Share on other sites More sharing options...
seecomber Posted July 5, 2015 Author Share Posted July 5, 2015 After consulting with your goodselves I took the newer of my re-ringed motors(OS48) down and honed the bore with a small motor car type brake cylinder hone as a glaze buster.I used only a few up and down passes with modest pressure. to remove the glaze.The motor still runs but at 10,000 rpm and a rich mixture it`s still inclined to cut out suddenly and I suspect is overheating on its test stand. but I have no heat measuring equiptment to check this.It ticks over at low revs and up to about 8000 very smoothly but the peak revs if sustained(a minute or two) bring it to an abrupt halt. Will further running- in solve the problem?.What other causes could their be.I have ground the valves and set the tappet clearances whilst cold.Can anyone suggest another reason for overheating other than the hot weather! Quote Link to comment Share on other sites More sharing options...
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