Time to check your clunk

[Keith Berriman]

Hi all and bear with me untill I have the time to down load some photos of a 5 year old Acro Wot that has given impecable sevice untill a flight last Friday when it suddenly developed an irrating noise from the OS 46 AX

[Keith Berriman]

Apologies for the delay too many visitors for a Friday Aft

Any way follow the pictures Con Rod Piston 1 Piston 2 and then the culprit

I feel sure this is the culprit but open to other suggestions

[Former Member]

[This posting has been removed]

[Keith Berriman]

The clunks is rusting all over and pieces missing

[Denis Watkins]

That's not rust, but maybe Castor Oil, or stored in moisture a long long time

And the bit could have been missing sometime

The conrod looks cracked, and may make a noise as it fails

Either way, you have been unlucky RC

1st time I saw a clunk to blame

 

Edited By Denis Watkins on 02/11/2018 20:30:34

[Levanter]

That type of clunk is made from chromed brass. The chrome is hard and if it has come off, it is conceivable that it could cause damage.

Levanter

[Martin Harris - Moderator]

A failing bearing can throw off small pieces of metal - it's worth checking the main bearing carefully, especially the ball retaining cage which can fail where it's riveted together.

[Former Member]

[This posting has been removed]

[nigel newby]

I always have a filter in my fuel line.

[cymaz]

The other culprit maybe pieces of metal fuel tube. This stuff has a nasty habit of degrading and falling to bit over time. Or grit getting in through the carb.

Edited By cymaz on 03/11/2018 05:35:17

[onetenor]

Do you mean the clunk was rattling due to vibration from the engine. That's the only reason I can think of for a noisy clunk. If so check bearings and conrod fits. The rod looks nudged not cracked but check carefully under a good magnifying glass Also prop for balance, cracks etc. Re the clunk give it a rubbing with wet and dry to clean it up. Clean out the holes by blowing through with an airline or a pump. to avoid any abrasive going into the engine.. It doesn't matter if the chrome comes off. Just as an afterthought are the engine mounts secure. That can cause vibes if not. Take care.

P.S. Just had a look at no 1 piston . Is that a vertical crack I see? That could be the problem if it is cracked.

Edited By onetenor on 03/11/2018 05:48:53

[Rich too]

OP, do you use an in line filter? I use that type of clunk and an in line filter as I like to see what is going on with the filter, rather than have it degrading inside the tank where I can’t see it.

[SIMON CRAGG]

This topic raises a few questions about fuel tanks!.

If they are left for any length of time it is worth taking the tank apart, as the brass type fuel tubes have a habit of disintigrating. This is not that obvious when you fill up, but potentially only half the tank is filled. I have seen this many times, and have replaced brass for aluminium or hard plastic.

Filters. Many years ago I started using "cintered" clunks. Much better than in-line filters which have an extra three places where thay can let in air (inlet-washer-outlet).

Without actually seeing the piston etc. On the face of it, it looks ok apart from a few wear marks. I have seen far worse that run perfectly. I would suspect bearings. They have only got to have a few rust spots, which can cause the engine to be difficult to tune and rumble like mad when they get really bad. They are not expensive to change. Local bearing companies usually supply them a LOT cheaper than the branded version.

Hope this helps & good luck!.

[Nigel R]

Clunk does look like congealed castor. Have you checked bearings yet? Always be first port of call for this sort of problem.

What sort of state is the crank in?

Either way the engine needs a few spares. Re: brass clunk lines, I've never personally seen that is it caused by high nitro?

Edited By Nigel R on 03/11/2018 07:44:05

Edited By Nigel R on 03/11/2018 07:44:40

[Keith Berriman]

Many thanks for the various responses and much appreciated. On closer inspection of the clunk it is not rust as expected but some congeled item. I only used Formula Irvine 5% untill recently and changed to Laser 5% so caster oil may be out ?? It looks like wet and dry could be the answer or another clunk from the toolbox. I did a finger check on the main bearing and it is rough to turn and specalled with rustmarks so this could be culpret, as suggested how did anything get through the main jet. I will check the bearing later although the cost of replacement parts is exorbitant. Luckely I drop on a brand new mark 1 some weeks ago so change the carb set up and refit Have had the tank out and all clean inside so fingers crossed for another 5 years. Just to finish I always run the engine dry of fuel after flying and dose with after run oil.

[Bob Cotsford]

Modelfixings can supply a pair of bearings for around £20, I'd never use OS branded ones!

[BackinBlack]

Why is everyone blaming the fuel?

As has been pointed out, debris would have to get through the needle valve, the usual result is that the needle gets blocked. Smaller particles that do get through might cause the minor score marks we see, the large score mark is a sign of something more substantial. The damage to the con rod could well be just fatigue.

Larger debris, the most likely cause of the damage seen on the piston, has most probably either been ingested with the intake air or comes from the breakdown of a bearing cage.

Repair will need new piston, liner, con rod, bearings and perhaps crankshaft. Cheaper just to buy a new engine?

[J D 8]

That piston looks to have more than just wear marks,what is the bore like? Could be motor injested something through the air intake. We model flyers are just about the only people who operate small motors without an air filter. Even the most basic garden strimmer will have a bit of sponge to breath through.

[Bob Cotsford]

If the bearings are rusty then particles are coming UP the bore from within the engine. I've only experienced this with OS engines, in my case 61SFs. Paul Bardoe reckoned it was because I was leaving the tuned pipe connected leading to condensation running into the engine via the exhaust but I still had the problem when I changed to short exhausts. I think it's just something in the materials used in OS engines as the cranks often showed evidence of rust too. Oddly I never suffered this with 'cheap' ASP and SC engines.

[BackinBlack]

Posted by J D 8 on 03/11/2018 10:26:33:

That piston looks to have more than just wear marks,what is the bore like? Could be motor injested something through the air intake. We model flyers are just about the only people who operate small motors without an air filter. Even the most basic garden strimmer will have a bit of sponge to breath through.

At least 2 of us think along the same lines.

A simple air filter costs little in either money or power and could save a lot in the cost of damage to an engine.

[Martin Harris - Moderator]

Given the number of damaged components, the engine is probably beyond economic repair but good quality bearings shouldn't cost more than about £9 for the pair - delivered free the next day from a firm like Simply Bearings (no connection other than a satisfied customer). You could even opt for cheaper ones at less than £2 each but I wouldn't take the risk.

You just need a decent pair of vernier calipers to measure the 3 dimensions - bore size, outside diameter and thickness and specify C3 clearance if it's available. Almost all model bearings on modern engines are standard metric sizes although there were some odd sized ones in earlier years, e.g. some early Irvines used special mixed imperial/metric ones which are either unobtainable or would cost hundreds of pounds each! I think I recall that some OS engines used special sizes but I haven't come across any myself. It's unlikely that you would encounter these problems but if you have a particular attachment to an engine there are usually ways round this if you have some basic engineering facilities though.

Bearing failure is, in my experience, the number one killer of model engines. If an engine starts to sound mechanically noisy or develops any play or notchiness, that's the time to strip it and check the bearings. As you can see from the above, it's cheap insurance to change them if in any doubt.

[Former Member]

[This posting has been removed]

[Peter Beeney]

With regard to the brass tubes in fuel tanks failing, it’s actually the methanol that’s the culprit; methanol can attack brass, sometimes quite quickly and vigorously too. I discovered this many years ago and I replaced all the brass pipe with small bore copper tube; there’s also been a thread or two since on the forum chewing over this problem. As it happens, I’ve always used straight fuel anyway so it wouldn’t have been a nitro presence. When I was investigating this at the time I did read somewhere that the folks that go drag racing with high powered cars using methanol as hurry up stuff replace all the brass parts in the fuel system with stainless steel versions. I’d say very deep pockets are needed for drag racing…

When the OS .46 SX (the one after the FSX, as I remember) first appeared on the scene a friend bought one and it almost immediately failed; he sent it back and a new one soon materialised with unusually a letter stating the the new type of nickel plating lining the cylinder wall was faulty. I think this problem persisted for a while, indeed it might still occasionally be with us, I’ve seen at least two LA .46’s that have died very quickly because of this and yet another one didn’t.

My take would also be on the bearings causing the piston damage. I’ve seen similar a few times, I once had an Irvine .36 which got a bit noisy; being lazy I put off immediately sorting it and then one day there was suddenly no compression at all! If you didn’t know you’d have said the plug had been removed! Typically of course this happened when I was trying to start it as I was going to have a little burn up with a Frantic funfly at a local fete!! Quite remarkably a piece of a broken ball bearing had managed to embed itself in the piston’s skirt and had consequently cut a matching groove in the cylinder wall; this was quite deep so how it ever got to that point anyway I’ll never know. The rest of the piston and cylinder were also a matching mess… Unfortunately at the time I never thought to take any photos.

In those days I bought all the engines and bits from ‘The engine man from Devon’, John D. Haytree, and on speaking to him he said “It’s not your fault, these are being a bit of a problem all over.” It seemed as though Irvine had bought bought some bearings that were marginally not quite the right size to start with and were also not entirely the best quality either. Perhaps things were just starting to get tough modelling wise even back then? But he did remark too that it was amazing just how any bearings would last as long as they do in model engines…

I never met John but I did speak with him and his good lady many times. However, a good flying mate always that went to Devon for his holidays would always call in to see him for a chat and a cup of tea. On one occasion John was running a new version of an OS engine and it transpired that OS would often send him their newly designed models for his evaluation; the performance specification would then generally be based on his results. All in all he was a very nice and extremely knowledgeable bloke…

PB

[Keith Berriman]

Once again thanks for more comments, the engine is a right off apart from crankcase, head assembly, back plate and a silencer

I would be interested in the Air Filter option

[Denis Watkins]

Posted by RC Plane Flyer on 03/11/2018 15:18:25:

Once again thanks for more comments, the engine is a right off apart from crankcase, head assembly, back plate and a silencer

I would be interested in the Air Filter option

Look to the RC Car guys, they can teach us a thing or two about motors