Mechanically mangled engines.
|Jon - Laser Engines||18/03/2020 16:11:48|
|5422 forum posts|
I have been meaning to start this thread for some time. The idea is to examine engines that have suffered mechanical drama, look at the reasons why, and then avoid doing the bad things!
On one of the fuel related threads i was talking about bearing cage failures and the process that causes them.
By pure chance i had a pair of engines returned today which clearly show how this can happen, and, what can happen as a result.
The following is a copy from that thread:
Bearing cage failures are often the symptom not the specific cause. Castor causes cage failures as it gums the balls up and they dont rotate. They then skid in the races, get all scored up, and when they eventually come free they transmit that damage back to the races as they roll round. This then puts damage on the other balls and loads start going through the roof. The rivets holding the cage together pop apart, the cage then starts to break up and eventually falls out into the crankcase where its gets pulverised. The engine wont stop, it will just keep eating itself.
Corrosion causes the same sort of failure mode as rust spots on the balls/cage/race do the same.
This is why any engine run on castor and left to go gummy needs to be stripped and its bearings replaced. Engines left in storage should also be stripped and bearings at the very least inspected before going further. I would even go so far as to replace bearings in any engine that has had a crash as the impact load on the front bearing could damage the balls, chip them, and even crack them clean in half. For the sake of a few quid in bearings and less than an hour's work its easy enough to just change them.
|Jon - Laser Engines||18/03/2020 16:18:33|
|5422 forum posts|
So, the photos.
Victim no1 is a 100 that suffered a cage failure and corrosion of the bearing is the suspected cause. Unfortunately, even though the engine sounded rough it was still used and this did it no favours at all.
Removal of the rocker cover shows metal particles in the oil
The conrod and crankcase show scars from smashing the bearing debris apart. The black marks in the crankcase are pieces of steel embedded in the aluminium.
As the engine rotated it threw material up the bore where it destroyed the cylinder and piston
The cause of all this mayhem..
The very small item at the end of the screw driver is a rivet that used to hold the cage together. The shrapnel on the right is the remains of the front side of the cage and as you can see a section of the rear cage is missing. This has been eaten by the engine and is floating around as glitter in all the oil.
|Jon - Laser Engines||18/03/2020 16:28:55|
|5422 forum posts|
This is why you dont run castor.
As you can see the bearing is well gummed with castor and although the castor in this example is just free enough that you might get away with it anything stiffer would result in bearing damage as described above.
What might not be clear immediately is the potential problem with the conrod. In the photo below you can clearly see the oil hole is totally plugged with congealed oil. This can prevent new oil reaching the bearing and can lead to conrod seizure on the crank pin.
Now i am using Laser's in my photos as i happen to have access to plenty of poorly ones, but these issues relate to all model engines.
The basic story is, dont run on castor and if you engine has run on castor in the past take it to bits and clean it before you run it again. Bearings gummed with castor cannot be saved, just get some new ones.
The same is true of engines left for a long time. The 100 at the top is only 4 years old but has not flown much and when it did, was flown a bit rich and at low power. This kills engines as they dont get hot enough to evaporate residual fuel left in the crankcase. Always tune for max power and try and give the engine a good blast to warm it up. Even if you just give it a minute at high power after the last flight of the day, that can really help.
If all that fails and you suspect your bearings are a bit gritty stop using the engine. Fix it, either yourself to send it to someone. Continuing to run an engine with duff bearings will only end one way.
|J D 8||18/03/2020 18:26:52|
1447 forum posts
Two years ago at the start of the flying season I was running up the Enya 90 in my Major Mannock in the back yard. Started with ease and ran well but after a couple of minuets I saw the prop start to wobble. Went to shut it down but as I did so the thing stopped with a bang. The prop flew off and shattered on the concreate. Bit's flew all over and I was lucky not to be hit.
Examination showed front bearing had gone to bit's. Engine has been pulling the Mannock around for twenty years, no castor and stored over winter in the dry with ATF fluid injected. There was no corrosion to be seen on the bearing bits or shaft. I think it just wore out. [ as other bearings do on my farm machines ]
|Steve Hargreaves - Moderator||18/03/2020 18:43:32|
6756 forum posts
I like to think I "know about" engines so my failures are few & far between. My last one was an ASP90 FS that stopped mid climb & would only turn half a turn or so when recovered.
Turned out the crank pin had sheared off....
Some "new parts" (crankshaft, con-rod & bearings) were obtained & fitted & the engine has been fine since.
Fuel used was Southern Modelcraft Mo-Glow 5% which is 15% synthetic & (whisper it) 2% castor oil
|Jon - Laser Engines||18/03/2020 19:21:51|
|5422 forum posts|
ASP pin failures are not uncommon. Most of their cranks use a separate pin which is pressed into the crank web. There are a number of possible failure modes here with an over hard pin cracking over time, a manufacturing defect or rust causing stress focusing, a pin being damaged on insertion causing a crack, or poor quality material.
Engine knocking, hydraulic locking, overloading, and prop strikes are all likely to be contributory factors as well.
As the engine looks in great condition internally its likely a defect in the material or something along those lines
JD8, you are right that age can be a factor even on a well looked after bearing. In all of our engines its the front bearing that carries all of the load so it makes sense for it to wear out and not the rear. Normally something else finishes bearings off before they wear out but its not impossible. Contributory factors here would be things like prop strike or any other impact that would transmit load into the front bearing. An out of balance spinner or prop would also not help the poor thing out.
Edited By Jon - Laser Engines on 18/03/2020 19:23:31
|Don Fry||18/03/2020 20:05:12|
4557 forum posts
Thank you for the education. Not too sure I wanted it. I just run motors. My mate can do bearings, if needed. Perhaps , a lesson is needed, rather than wait for his expertise.
|Jon - Laser Engines||18/03/2020 20:45:46|
|5422 forum posts|
There is always something to learn Don. Its not especially difficult or time consuming. I can probably blitz through a 4 stroke in about half an hour-an hour depending on how stubborn its being...unless its an OS, it can take a week to get the flippin gudgeon pin out of that stupid hole in the crankcase!
That said, if you would rather hand the job to someone else there is nothing wrong with that as long as you know when it is time to give the engine some attention.
As a side note, its not just engines that suffer. I had a bearing cage fail on my 400 electric heli motor and that was...exciting
|2911 forum posts|
Had a 'new' ASP 120 FS's crankpin fail after under an hour's running. Cost me a new model after the resulting hard landing from low altitude in the rough outfield - busted paper thin glass fuz!. Also cost me fifty quid in spares (crankshaft and connecting rod) for the engine rebuild because although the engine was to all intents and purposes 'new', I'd had it stored on my bench in its box for a tad over the UK supplier's warranty period (two years from the date on the carton). The model it was intended for took so long to build because of some appallingly bad kit manufacturing, I got fed up with it and put it to one side for a while. Moral? perhaps don't buy your engine too soon if the build's going to take a while or give it a good run on the bench to shake out any bugs within warranty.
My one and only engine to suffer a catastrophic engine failure in over forty years of playing with models!
That was seven or eight years ago and the rebuilt motor has since ran fine with hours of running and gallons of Laser fuel through it in my H9 P47.
Edited By Cuban8 on 18/03/2020 21:04:02
|Martin Harris||18/03/2020 22:58:33|
9263 forum posts
The ASP/SC crankpin failures are certainly not uncommon but I witnessed just the same thing with a nearly new Saito 150 a few years ago. Apparently the importer was spectacularly unhelpful...
Another friend's Saito 50 munched its rear bearing, passing bits through the cam gears. Surprisingly, the cam and pinion gear were quite cheap at the time and with a bit of judicious stress relief where a bit of bearing had chipped the piston skirt and the con rod plus new bearings, from what should really have been an economic write-off, I rebuilt the engine for him and it's run fine in a succession of Magnattilas for many years afterwards.
|Jon - Laser Engines||19/03/2020 08:26:02|
|5422 forum posts|
Hydraulic locking has been only cause of crank pin failure that i have seen first hand. Two ASP 30fs's and an OS 52 surpass.
|J D 8||19/03/2020 09:31:00|
1447 forum posts
Have had two crank pin fails. DC Sabre in motor glider that I learned to fly RC with, had a lot of use.
OS max15 let go in a full power dive, it was underproped. Abuse I recon [ know better now ] A problem for model and full size engines of all types.
I have a mate who does a lot of work on Ford TDci engines [ Transit vans ] Any particular problems with these engines I asked ?
Yes he said, the ------- just don't service them.
|Jon - Laser Engines||19/03/2020 10:18:15|
|5422 forum posts|
To be honest, this is the cause of most model engine problems as well!
|Nigel R||19/03/2020 11:43:38|
3748 forum posts
I recently revived an old mk1 Irvine 46 helicopter engine. The engine was completely locked, carb and all, and sold as spares only. I soaked in IPA for a couple of days and it all felt free again. As it only cost a few quid I gave it a bench run. It ran perfectly well, but, the plug that came with it blew on the first run, which I just put down to age / use. I could see nothing in particular wrong with the plug when I pulled it so replaced and ran again, no further plug problems.
I opened the motor up again following the bench run, I could now see damage to the piston crown, and the main bearing, which had felt ok, was now rough.
Wish I'd read your post a few weeks ago!
As fate would have it, prior to running it, I had bought an aero head from a fellow forum member who wanted to move on a spare piston/liner with the head. I've now swapped out both bearing, head and piston...
|Braddock, VC||19/03/2020 12:37:20|
1647 forum posts
Back in 2004 I bought a stack of saito 82s at the Nats, I sold off three old diesels and got enough to pay for the three 82s and went on to buy 2 62s and 2 125s. I used to run them on southern modelcraft hi-lube 10% nitro and 20% synthetic oil.
One day one of the 82s stopped and couldn't be turned then a few months later another one did it. The conrod had seized onto the crankpin in both instances. I bought one new con rod and used some crocus paper on the pins and sold off the engines except for one 82 and one 62 which I still have.
I never used to run them lean and all my OS and OS clones continued to run perfectly as did my 3 lasers, all bar one of my OS + clones have had new bearings as they were just starting to brinel, same with the lasers. I found a source of stainless bearings that were well priced and most have those fitted. I did toy with the idea of using boca bearings ceramic bearings but I understand the races on them are steel.
One thing I don't understand is why Jon says the front bearing takes all the load in lasers, I've changed bearings in my 70 and 80 at least twice and the 100 once (the 70 and 80 are from about 2003/4 and the 100 is much earlier) and in those instances the rear bearing was showing signs of distress whilst the front one seemed to be as good as the day it was installed, I changed them anyway but it seems to me all of the firing loads and prop thrust are focused on the rear bearing and the only time any undue thrust is placed on the front one (unless it's a pusher) is when a starter is used or when you inadvertently stuff the plane in nose first at high speed.
On some of my OS types I've not been able to get the front bearing for one reason or another and the original has been recycled though I didn't remove the front bearing from the casting. One of those, a 52 surpass, has since been pulling a southerner major around since it replaced a 2 stroke in the 90s.
I always try to ensure that I run the engines at full throttle for a short while after flying and store them nose up so gravity drains any residue from the bearings onto the backplate. It seems to work.
|brian sylvester 1||20/03/2020 15:00:51|
|9 forum posts|
i have also suffered the asp91 fs crankpin falure along with a weston 52 2 stroke both happend last year. as far has i can remember i have not had any engines fail in the 60 years of model flying.neither engine had been flooded when being started ,both engines fitted with the correct size props and both being run on ivine 10nitro fuel.when it comes to model aircraft engines i guess fings are not wot they use,t to be.
|Steve Hargreaves - Moderator||20/03/2020 16:20:29|
6756 forum posts
Chaps, this discussion has strayed away from the original OP but is very interesting nonetheless. I am minded to start a new topic on Engine Bearings & move all the relevant threads over there thus leaving this thread for Engine Failures only....
The discussion on Engine Bearings has moved over to here **LINK**
If we can try & keep this thread for tales of mangled motors & exploding engines...
Edited By Steve Hargreaves - Moderator on 20/03/2020 19:58:17
|Jon - Laser Engines||06/04/2020 12:18:46|
|5422 forum posts|
I decided to practice what i preach over the weekend.
A few weeks ago i dug out my very sad and mostly ruined SC400 radial. Last time i stopped flying it i swore it was done due to lack of reliability, repeated mechanical failures, running like a dog and generally being rubbish.
But like a fool i decided to dig it out as i had been running it on 20% castor (it didnt like anything else due to poor compression) and didnt want it to gum up solid so intended to run it on my Laser fuel to flush it all out. Oop's, too late, it was a big sticky mess.
Being lazy and not really caring about the engine that much i just did all the things i told everyone not to. Fill it with fuel, free it up a bit, run. It ran...badly, so i nailed it to a plane and flew it a few times. By the 3rd flight it was running ok and i thought 'nice, job done'.
But then curiosity (and the fact that i knew it should have in the first place) got the better of me and i decided to take it apart.
The bearings, as expected, are dead. Castor has glazed the balls/clogged them up and they are all ruined. I also found some other interesting things like two rockers missing the E clips that stop them falling off their rocker shafts (i found them floating in the rocker cover) and the 3 screws that are supposed to hold the cam drum together...werent. Two were loose and one was broken so for a short time i had the only SC400 with variable valve timing! These loose screws have munched the crankcase a bit so that is not ideal. The front bearing is spinning in the housing again (its always done this) so the crank is floating about..no wonder it sounded awful.
Anyway, the whole thing is now buzzing in an ultrasonic cleaner. As i have to rebuild it again anyway im going to take the time to fully clean it and shot blast it to tart up the finish. Im also going to nick some twin ring pistons from a few dead Laser 75's and fit those to see if it runs better. If not, it will make a nice display item if its all shot blasted and nice.
Beyond that, dont be lazy. Take things apart!
Please login to post a reply.
Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!