Engine Doctor

Posted by Merco 61 on 10/04/2015 12:01:18: Thanks,Engine Doctor,that is about the best description of likely four stroke problems I have read. I was helping my buddy yesterday.He was operating an old Chinese 80 four stroke.Started easily,adjusted easily,bags of power apart from an occasional splutter at full power in flight,probably due to a very old plug.After landing,we noticed a very obvious amount of fore and aft play in the crankshaft,almost as if it should have had a spacer washer. No vertical or horizontal play detectable. He says the play only appears when engine is hot.Your opinion please. Hi the fore and aft play or end float is bit more difficult to sort as it is usually due to bad machining tolerances.As said before the budget Chinese engines were unpredictable with QC, although later engines are generally much better apart from the head/valve issues. The camshaft is driven by a gear ground on the crankshaft. As the crank moves back and forth the valve timing changes . Not a problem at full power but at low throttle it can move changing the valve timing and cause sudden engine cut. It is only noticable when hot as the bearing will probably be sliding in the crank case .The cure is to find where the bad fit is . The last one I repaired had to have the crank machined just behind the front bearing .This allows the bearings to seat properly and the crank to nip the inner bearing race.The bearings can then be fitted with some"bearing fit" . This fix is time consuming and possibly not worth doing .They are a very powerful engine when running correctly. If it does what you require of it then carry on running it. Edited By Engine Doctor on 10/04/2015 18:43:53

Hi The majority of four strokes are ringed engines so will not hold compression .Compression should be felt when turning over but unlike ABC 2t they won't hold comp. To test for leaky valves (some but not every budget fs engines like ASP, SC and Magnum have poor quality control and valves leak...with no cure due to head distorsion) turn over engine while listening to the inlet and exhaust ports . Any leak will be heard as a light hissing/bubbling sound. Leaky valves , whatever the cause result in a loss of power at top end and unreliable idle and pick up.Yes bearings should be smooth but with the plug removed you may feel backlash in the valve gear ,this could be confused with bad bearings but is quite normal and nothing to worry about. Its espessially noticeable in Saitos. With the plug out corroded bearings will feel like a continuous series of ridges or roughness. If engine passes muster on these points then fit a prop so that its vertical with the engine at tdc. Hold engine firmly and try to rock the prop towards the cylinder and back. If any slack can be felt,feels like a slight click, then the rear main bearing is worn and will need replacement soon. This can be hard to spot if not shown how to check first, but it will caused a slight loss of power and failure of bearing can wreck an engine. While doing this also check for end float on the crankshaft. There shouldn't be any noticeable end float.

Posted by Sam Wragg on 07/04/2015 19:11:55: Ive seen this before and it's when another coat is applied outside the curing stage window of the previous coat could it be because the base coat at its curing stage And because of this its reacted with the top coat. Good luck Sam Agree with that . Some paint types are really critical with re-coat times.

Great shotgun it is then !!

They look terrific ! I guess it will be some years before they appear in the hobby. I must admit I did check the date on the caption as its THAT time of year.

Me and a few of my friends have had a serious loss of mojo this winter due I think to our changing (getting wetter) winters and longer periods of water logged fields. Now its warming and drying out interest is returning . You'll soon feel better after a good flying session with likeminde mates and some building sessions in a warmer workshop. But every cloud has a silver lining ,albeit a thin one ; the rabbits burrows have flooded so numbers are down . Less rabbit scrapes/holes on the patch. PS.How do you get rid of moles ?

Posted by Percy Verance on 05/04/2015 10:19:33: Who said that?????? Edited By Percy Verance on 05/04/2015 10:20:03 A few. Claims on the www. One is Mathew Henry a clergyman born 1662. Another is John Heywood in 1546 but seem to come from the Bible :Jeremiah 5:21. I'm not a religious type but there are some very relevant quotes for today's world.

" There's none so blind as those who will not see" or listen .

Simple formula = When you cant shut the shed door without damaging the last model in. Sheds should be SWMBO free zones ! Now duck or hide !!

Posted by Danny M2Z on 03/04/2015 11:45:07: A tip from the gunsmiths who use epoxy bedding for rifle barrels. Kiwi neutral boot polish is a really good release agent and it's cheap. * Danny M * Thanks for the tip .I'll try that the next time

They are good for electric powered models . I flew with one fitted last autumn and was amazed at how the sound traveled .. They also go off if the battery cant deliver the power and causes a voltage drop ;closing the throttle a bit usually sorts that . Look on line and they are just over a pound each ,I found four for under a fiver posted fromchina of course but only took about 12 days !

Hi I thought these pics might show the stages of making a cowling. I used polyester resin without the accelerator added, this gives plenty of working time .If you use the Davids resin from car accessory shops it will set much faster .Polyeste is fine for cowlings and cheaper than epoxy .It cures quicker but dont rush it,let it set fully before trying to remove from mold . I used an old wooden cowl as a plug to make a mold for my Luscombe Silvaire . The mode was bought from Avicraft , secondhand and hadn't been finished . As far as  I'm aware it's a home build so no glass parts available . The wooden cowl was a bit rubbish so some filler and sanding later it was a smooth plug .This was given many coats of release wax polished between coats and allowed to harden .Using polyester resin the mold was made by coating the plug with gel coat and allow to start to set then laminating chopped glass over that with normal resin . some stiffener plates from old ply was glassed onto the mold. When fully cured the plug was removed. this came out pretty clean . Any small marks in the mold were filled and the the mold was given lots of coats of release wax . The mold was given a coat of gel coat which was allowed to part cure before glass clothe was laid up inside . The edges where mounting screws were to be used were given some extra glass reinforcement.   Getting the cowl out of the mold was difficult considering it is a simple shape. The next time i do this I will spray the mold with PVA release agent Edited By Engine Doctor on 03/04/2015 11:18:57 Edited By Engine Doctor on 03/04/2015 11:19:33 Edited By Engine Doctor on 03/04/2015 11:32:15

It really depends on how porous the surface is . Apply one coat and see what happens if it soaks in then another will be needed to proof the surface. What varnish are you using ? Normal varnish is quite slow drying and could soak in more leaving a porous finish . Clear-coat by Solarlac is quick drying and would proof it ok . Thin coats will dry quicker and not soak in as much . whatever you use remember it all adds weight so keep coats thin. Edited By Engine Doctor on 02/04/2015 17:36:21

Posted by TinPot Pilot on 02/04/2015 13:58:24: Trebor, this thread ( 5th post down) shows a similar pump to the first one I listed as having been used as a fuel pump for many years. I have a similar pump but haven't got it wired up yet so I cannot personally recommend it but have seen the use recommended in a number of other forums The only likely problem I have seen mentioned is that some of them won't reverse so you have to change the pipes over to empty a fuel tank Edited By TinPot Pilot on 02/04/2015 13:59:52 Just checked that one out and its a lucas so should be ok .

Posted by TinPot Pilot on 02/04/2015 11:58:20: Could either this or this be persuaded to fit ? I dont know about the second (black pump) but the first one (orange and yellow are a bit rubbish . they run ok with washer liquid but mine seized with running fuel. They are really cheap copy of the orange and beige pumps that were available from lucas . They now offer a different type and dont knowhow good they are . I did find a similar type of better quality from a caravan spares shop on ebay that is still ok although not used very often .

Convincing dummy cyl . When I saw it in real life and up close I still had to really look. Its made from a turned down broom handle . The painting is really good and looks just like worn anodising would .It did fool (April type) someone on another forum .

I recently saw this great little twin diesel at club meeting . Looks like a DC but Dc didn't make a diesel twin as far as I know . Does anyone know different? Sorry for all the edits had trouble loading pics. Edited By Engine Doctor on 01/04/2015 09:01:49 Edited By Engine Doctor on 01/04/2015 09:04:02 Edited By Engine Doctor on 01/04/2015 09:05:57

No that's definitely an"engine running OUT" procedure. Its nearly April the first beware ! Or have you upset someone Years ago modellers used to add metal polish like Brasso to the fuel to speed up running in. Machining in those days was not cnc. And quality varied wildly as did somecofvthe materials used.If you over did it with the Brasso the engine was clapped _out before it was fitted to the plane. Grinding paste is much more aggressive and will destroy modern engines if it didn't block the fuel jets first. Just use good quality fuel run rich for a tank or so then fly it just slightly rich for a few more tank fulls an its done. Petrol engines take a bit longer but still use clean fuel /oil mix with no additives. Edited By Engine Doctor on 30/03/2015 15:51:09

I t might be worth checking the info you left when registering . The new system seems to work ok as have had a couple of calls re adds .

That would be Chinglish then

Posted by Allan Bennett on 27/03/2015 20:33:25: I'm not sure about oil-based enamel on foam Certainly I can vouch that water-based acrylics don't attack it -- I've used them on Depron, Elapor, and regular styrofoam or whatever it was the Mk 1 version of the Multiplex Hi yes paint like Humbrol enamel , the type in tins will/should be fine on foam but beware of the Humbrol aerosols as I believe they contain a solvent or possibly a propellant that will attack foam. Its still best to do a test piece as paint formulas seem to change quite a lot these days . Humbrol is I believe now made in China and it isn't the same as it used to be so probably best to stick to water based acrylic.

Hi Make sure the enamel is a oil based and not acrylioc type as it can eat the foam .You can get artist acrylic(water based) silver that sprays well . Its quite cheap on e-bay or from craft shops. I haven't used the silver but have used solid colours on foam and it works well. Once dry seal with Ronseal matt or Satin clear . I sprayed it straight from the can in a small touch in gun at 50psi .

That looks very much like our old club toffee bomber and is indeed a T 240 by President . The engine was a Magnum 108 and markings were MMFC (Medway Model flying Club ) that I painted on. If it is the same model as I cant see all the markings, then I was the keeper for more than a few years and still have the toffee bombing box that was slung underneath the fus. We sold it probably 5 or 6 years ago at one of our swapmeets I think, due to not being used  much and it taking up too much space in my workshop and no other club member would look after it. It used to be Yellow Profilm until a mishap probably 10 or 12  years ago when the fuslage was badly damaged . The wings were repaired and a second hand fus covered in olive drab was obtained and the wings recovered to match. It WILL need wing struts to fly. Have you got another pic of the side markings ? It is /was a pussy cat to fly but the engine used to over heat so ducts were fitted in the cowling that cured the overheating ..Hope you have some fun with it And would be interesting to know where its been . E.D. Edited By Engine Doctor on 26/03/2015 11:18:38 Edited By Engine Doctor on 26/03/2015 11:23:50

The Mystic is a great flying model The one I flew for a club mate  had a ST 90 for power that would keep cutting out suddenly .Not a problem though as it would glide on .........and ................on........ and...............on and always made it back to the patch  .Ive  never flown the smaller versions though . Edited By Engine Doctor on 26/03/2015 10:51:49

Hi Roger .Its not at all difficult . Do make sure you have some decent allen keys though as cheapies will round off and possibly damage the screw heads. Also have a clean plastic box/tray available to put the parts in as you remove them .Good luck and let us all know how you get on. Hears a you tube film of a OS 52 FS being stripped down . The OS is  almost identical to the SC so it should help .  . Edited By Engine Doctor on 26/03/2015 10:39:50