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Member postings for Engine Doctor

Here is a list of all the postings Engine Doctor has made in our forums. Click on a thread name to jump to the thread.

Thread: Radio, servo malfunction
19/04/2019 10:50:45

They must make millions of these so a few dodgy one must creep in from time to time . As Denis says If they work from new, then they will usually last their lifetime without trouble You did test them before installation didn't you ?

Possibly the heavier current drian from the duff servo will affect the other servos ?

Thread: Zenoah 38 conundrum
17/04/2019 09:30:11
Posted by Alan Gorham_ on 16/04/2019 11:02:15:

How important is crankcase compression on a sideport engine like a ZG38?


Extremely important . its extremely important on ANY two stroke engine The compression generated in the crankcase when the piston descends is used to propell/transfer the fuel mixture into the cylinder when the ports are opened and the subsequent vacuum when the piston ascends the cylinder is used to draw a fresh charge into the crankcase. Even a tiny leak will cause poor idle , low power and poor starting . The pulse of compression and vacuum is also used by the carb to pump fuel from the tank . The seals are affected by many things . probably the most common is the wear on bearings . They can also  harden with age or be affected by using cheaper oils . As its an older engine the seals are a prime suspect . Renew them and enjoy the reliability once again .


Edited By Engine Doctor on 17/04/2019 09:40:41

16/04/2019 10:55:20

Hi Martin just another thought. When yo stripped it down didi you re assemble with the old gaskets ? The symptoms you describe definitely sounds like poor crankcase or secondary compression. This is more important than primary compression on a two stroke as its the only way the fuel air mixture can transfer from c/case to the cylinder; hence it starting with a crank case prime that givies a rich or wet mix that can temporarily block any small leaks while starting.

16/04/2019 09:53:34

Just a couple of thoughts as you seem to have covered most causes of non starting When it had the heavy landing did the engine/ prop take a knock/ If it did then check the gap in the pick up, that's the gap between the coil and the flywheel . The coil gets its energy from the magnet and if the gap is too big or the touches the coil the it wont spark . The gap should be the thickness of a piece of thick paper and is adjusted by slackening the screws holding the coil . Check that the shaft isn't bent or twisted before adjusting while your there check to make sure no metal filings have got onto the coil or magnet ..Might also be time for a new plug as its had a couple of knocks and whiskered . Whiskering can cause a carbon track to be arced onto the plug insulator that causes the spark to leak to earth under pressure. If you have access to a sand blaster then give the plug inwards a clean , this should remove the carbon track if that's the cause if it then starts ok replace the plug as it will probably foul again . Let us know what you find .

ps When you stripped the engine did you make sure that the gasket and insulator block hole all lined up with the pulse hole in the cylinder ? Often overlooked .


Edited By Engine Doctor on 16/04/2019 10:42:47

Thread: 1912 blackburn mono
15/04/2019 13:45:36

I would do as Don says but before that give all the edges of the parts that you want covering to stick to ie; spars and ribs a good coat of Solarlac "Claercoat " full strength and allow to dry thoroughly if you have any left . Failing that a coat of De-Luxe materials "Cover Grip" These are heat sensitive adhesives . Once covering is fixed to the spar work out along the ribs keeping the covering as tight as you can . When all of the bottom of wing is covered go over the ribs or glued covering again to secure firmly .You can now use either an iron or a heat gun (my preference ) to take out any wrinkles and make covering taught, but be careful not to overhear the bits that are stuck down .

Thread: Lost radio contact
09/04/2019 11:18:38

Re OP . Its the very reason that welded packs came into fashion back in the late 60's early 70's as the spring contacts could often loose contact without warning and zinc carbon batteries of the day often leaked and damaged the contacts. Most radio gear especially low to middle range sets like the Futaba Challenger and similar were made for use with dry cell connectors fitted and were converted or ordered from the makers with welded packs by the distributors like Ripmax etc . The higher end sets back then were made for re-chargeable batteries with no evidence of connector mountings in the cases Only the cheap two channel surface use radios used for boats and cars continued to be supplied for use with dry cell batteries. Welded packs every for me . Using dry cells in the much improved radios of today is a fundamental backward step., Dry cells might be ok for small cheap rc toys but with continued use the connections will fail Converting to welded re-chargeable packs is usually a simple conversion

Thread: MDS 148 piston
08/04/2019 20:20:03

Engine came in job lot and looked and felt ok . A quick check revealed that about 1 cm of the circumference of the piston above the ring is missing. Ring appears ok ?

Yes still looking for a cheap c/case for a 49 .


06/04/2019 18:00:56

I'm still looking for a piston for the MDS 148 .

Thread: Pre-Ignition?
03/04/2019 11:08:16

Hello Roger The FP 40 was a good easy to run engine . It has a head Gasket /shim . If engine has been stripped these were often left off or lost. They were also removed back in the day in an attempt to get more power . If not fitted it will caused advanced timing /pre ignition and backfire /prop throwing . Its only six screw to check its fitted . If it doesnt have one then you may have trouble getting one and will have to make one from some Litho plate . Other possible cause for prop throwing is using a soft plastic spinner . The plastic compresses when tightened and then loosens . If your using a plastic spinner make sure its really tight or try an alloy spinner , they are better but may need balancing.

Thread: Mills 0.75 piston and conrod replacement
01/04/2019 08:45:52

Hello Ian I'm sure it will be fine . I had a Mills p 75 made up from bits and pieces from a few Mills and it ran really well . Enjoy your return to the hobby.

Thread: Spring is here. Who is flying?
31/03/2019 17:26:34

Ouch ! Hang in there and persevere .

31/03/2019 12:16:23

Spring was here yesterday working on a roof in a T shirt helping my son , but what happened today ?frown

One step forward three steps back !

Edited By Engine Doctor on 31/03/2019 12:18:33

Thread: Irvine MK111 piston and liner
29/03/2019 14:36:08

Mk 2 and Mk 3 are totally different engines and you will be wasting your money . The Mk111 is the red one and the last ones were made by OS . Let me know if your stuck I have a couple of Mk 3 40's in my spares box . Piston and liner , if ok will be a used one . Pm me if you cant find one .

Thread: Crash resistant electric motor mounting suggestions please
22/03/2019 13:10:58

Hi Alan . Build it to fly and not to crash . Mods that are too strong only pass the force of a cash further down the line. The Mamselle is a brilliant flying model so why should it crash ? Mine is now with it's second owner and about 15 yes old. I flew it hundreds of times with an old Mills 75 . Covered in light span the only signs of its age is some slight discoloration and a few tiny patches on the covering due to a bit of hangar rash. With electric power it should last indefinitely. Good luck .

Thread: Merco Engines
20/03/2019 10:25:09
Posted by Peter Christy on 20/03/2019 09:14:26:

unlike the .49 that I bought a year or two later, which was a disaster! Ran fine on the ground, but would die without warning in the air - usually on take-off. Model went into the hedge many times as a result before I got shot of it. None of the local experts managed to sort it.


I had a Merco 61 that did the same thing . I cost me a nice model Spitfire . I tried everything with that engine to no avail . I decided it was just scared of hieghtssmiley . I converted it to a water cooled engine as they are excellent boat engines .

Thread: Saito r33
17/03/2019 17:42:34

Could it be that the petrol versions suffer from ignition timing problems causing the bottom end to fail ? If as is suggested the glow version doesn't suffer any bottom end problems then my bet would be on the ignition setting/ module fault causing knocking and eventual big end failure.

Looking at the pics again there is a lot of black sludge probably caused by the crankpin moving about in con rod.....not good. Did it not knock or show an symptoms ?

Back in the 1960s the Triumph Tiger cubs and BSA C15 s occasionally broke crank pins  and was almost invariably found to be caused by  poor ignition setting causing engine knock. Even poor fuel could damage engines back in the good old days . Pinking or ignition knock could and often did blow holes in piston crowns but f pistons survived damage could be done to the bottom end.


Edited By Engine Doctor on 17/03/2019 17:57:02

Thread: Castor oil in 4 stroke engines
16/03/2019 17:01:03

Hello brokenenglish . I didn't make that very clear . Diesel engines obviously have to have good piston liner  fits to run and as they virtually all use iron piston liner technology then and Castor was /is fine for them . Although some of the engines from that period had plain main bearings that were just a reamed bush and had a fair amount of rock or a poor fit and needed a rich mixture to start them . Model diesel fuel also seems to prevent the castor from forming a varnish .

Earlier Vintage engines like the petrol engines and some of the low production run engines from the 1920/ 30's up to the war had terrible fits by today's standards . They needed a good drop of castor to make a seal . In fact as the varnish built up it improved their running . Modern Diesels are fine and don't varnish like modern glow units again perhaps its the fuel that prevents the varnishing.


Hello Dave Davis . Enya two strokes that used iron pistons /liners , I have to admit that I have never had one affected by the castor oil varnishing. Perhaps its the iron technology that prevents the varnish build up ? but the four- strokes suffer from varnished pistons and clogged valves /exhaust as do the ringed two strokes with alloy pistons that gum up and varnish .

ps John -Laser Engines . Sorry I din't mean to hijack you post , just got carried away



Edited By Engine Doctor on 16/03/2019 17:10:41

16/03/2019 11:56:09
Posted by Wihtgar on 16/03/2019 10:15:37:

When you say old Jon, do you mean an old design or actual age? Can these engines be run on modern synthetics with no adverse effects.

Old engines , as in Vintage had poorer tolerances and most had iron piston liner technology so Castor oil is probably the best option for them . Diesels don't generate the heat and have such a large large ammount of cooling fuel flowing through them that they will be fine on castor . An old vintage engine if its fits are ok would also be fine on synthetic based fuel

15/03/2019 15:24:48

With modern synthetic oil you don't need the castor, even at 2% it will either varnish on pistons or build up on valves .

As John says modern engines get much hotter than earlier versions due to producing a lot more power.

Remember when car engines had to be de-coked or re-built every 30,000 miles or so due to burnt on fuel and inferior oil . Modern oil is far far better so why do people persist in using castor oil ? On model diesel or a vintage engine with poor clearances or iron pistons and much lower power then yes use it but not on modern engines. On Model diesels there is little heat generated and with high fuel volume passing through none or very little build up will occur .

We had a member in our club , now retired from modeling who would load up with gallons of straight castor fuel at the shows because it was cheap . During the year he would loose model after model and moan about his engines stopping or breaking. This was all down to his modern engines being clogged up with varnish and muck.He couldn't see that spending a little more on his fuel would have saved him £'s in the long run .

Thread: Thanks for everybody’s time to reply
12/03/2019 11:14:16

DB is a very like-able man . Yes his commentary was a bit of a Marmite thing- you either loved it or hated it , but that can be said for all of us . I found his commentary entertaining most of the time . He also contributed to the show scene by organising the Plumpton show for many years. A brilliant family show and he insisted that the ice-cream sellers had to sell cheaper ice creams for the children .

The commentators Iv'e heard of late especially here in the south are rubbish by comparison

Dave Bishop Thanks for all the years you gave to the hobby

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