O.S. "F" plug won't keep ignition.

[John Wagg]

2 minutes ago, Denis Watkins said:

The F plug has a thicker gauge element to stay lit for the fourth stroke

To answer your question

A number 8 is a medium 2 stroke plug

A3 is a Hot 2 stroke plug

The F plug stays lit longer

You do have a problem if the tappets are set ok and the timing marks aligned

It does sound like you are one tooth out On timing

Thanks.. Would you happen to know how many degrees one tooth would make ?

There is a timing mark (TDC) on the prop' drive washer / crankcase and checked against piston at TDC.

The dot on the cam is inline with the pushrod tubes at this point. I will see if I can check the valves opening timings but can't find any information yet. I've looked for a revue, with no luck, which might have that information. There is nothing in the owners manual about the valve timing.

Cheers.

[Andy Stephenson]

John,

It's curious that the engine will run on a 2 stroke plug and not on an OS F. I suspect the fuel because when I have had fuel go bad it would first fail to run 4 stroke engines but seemed OK in 2 strokes. I wonder if this is why your engine will run only with a 2 stroke plug.

[John Wagg]

55 minutes ago, Andy Stephenson said:

John,

It's curious that the engine will run on a 2 stroke plug and not on an OS F. I suspect the fuel because when I have had fuel go bad it would first fail to run 4 stroke engines but seemed OK in 2 strokes. I wonder if this is why your engine will run only with a 2 stroke plug.

Andy - Could be fuel as that's about all that is left. Only one way to know so will be buying some new when I get chance. Must admit that the engine appeared to perform slightly better on what I think is the newer fuel. Funny that my other four stroke (SC30FS) with an O.S.F runs fine on the same fuels. 

I do have a couple of JP four stroke plugs which I'm going to try as well but it will be some time before I can get some new fuel.

Thanks everyone for the help.

John.

[Denis Watkins]

Fuel can be a let down, as we may believe we have had it for 1 year, but a shop may have had it 2 years, and the supplier may have held it 1 year before that.

We just don't know.

A good few years now have not been great weather most of the time, and fuel is just not getting turned over in shops.

Anyway John

Get a 2 stroke plug and a 4 stroke plug in good light, and just look at the difference in gauge of the element.

A 4 stroke plug has to maintain heat through more time without compression every second stroke, so you need to get the motor running on a 4 stroke plug.

Am looking for more info on timing marks on surpass.

 

[Martin Harris - Moderator]

I don't believe there's any practical limit to fuel storage as long as its tightly sealed and preferably kept out of sunlight - this was certainly the opinion of  Dave from Southern Modelcraft when we discussed the subject. 

 

I have fuel which I use in one particular engine (RCV91) which is probably around 10 years old and it still performs perfectly.  It's in a model which I tend to fly on good days and special occasions (a Sterling Stearman reputably dating back to the early 80s) and I'm on the last of the 3 gallons of Model Technics fuel which I inherited with the model. I promised the previous owner that I would use it in preference to my normal Southern Modelcraft everyday "cooking" fuel.

 

I do see people with bottles of fuel at the club left open all day or with what appear to be permanently open vents and I suspect these practices may contribute to the "old fuel" problems experienced by some.  My own set-up is to use an internal sealed cap in the container with 2 nipples, one connected to the feed tube and the other venting into the bottle. On starting to use fuel at the club, I remove the outer cap and a link pipe and connect my fuel pump, placing the filling nipple in the free end of the vent pipe when not in use, sealing the system between refuellings.  I believe this keeps the fuel in good condition with negligible chance of either FOD contamination or water accretion.

 

 

 

 

[J D 8]

Plus one on the above. I use the same system as Martin above, also a few years ago I "inherited" several gallons of fuel that was all still sealed. Still using it with no problems in OS 15, OS and IRVINE 46, RCV60sp, Webra 61, Enya 90 4st, even my old open rocker Enya 40 4st was popping away happy on it last Sunday.

Edited May 4, 2021 by J D 8
correction

[John Wagg]

 

Latest saga with the O.S. "F" plugs now its stopped raining.

Fitted idle-bar plug just to make sure motor behaves and runs fine.

Fitted a new JP 4 stroke plug - runs fine.

Fitted an "F" plug - started and ran but not well.

Fitted another "F" and that ran a lot better and good enough to be satisfactory.

Yesterday I found 1 off 3  of the "F" plugs glowed only dimly so that went in the bin. (using a 1.5v source same for all the others.) Possibly the one I tried originally and gave the original problem. The other 2 "F" plugs glowed as I would expect.

The 2nd "F" that works but not reliably - I want to try in my other 4 stroke to see how that performs but may end up in the bin as well.

The 3rd plug is still in the engine and behaved fine. So in all it seems to be the plugs. I have a couple of brand new "F" plugs in the box so I presume these will be O.K. in future.

Sorry for wasting peoples efforts when it seems, after all, down to a couple of duff plugs. 

Regards.

 

Edited May 5, 2021 by John Wagg

[Nigel R]

Ah we're all just pleased you tracked the fault down. 

 

Question is, does the F plug that runs OK, run as well as the JP plug?

 

 

[John Wagg]

2 hours ago, Nigel R said:

Ah we're all just pleased you tracked the fault down. 

 

Question is, does the F plug that runs OK, run as well as the JP plug?

 

 

The F plug seemed quite sensitive to full speed mixture setting and soon stopped when the mixture was weak. When I put the JP in I set the mixture easily but really it was just an in and out to see if it worked. Maybe a new F plug would be more tolerant ?

Feel a bit foolish in not checking the obvious when testing the engine in the first place. The thing that threw me was the engine would start and run fine with the battery connected but then stop as soon as it was removed.?

 

Edited May 5, 2021 by John Wagg

[J D 8]

     Hi John, Don't feel to bad, most of us have been there, done that, got the T shirt. Cheers John.

[John Wagg]

49 minutes ago, J D 8 said:

     Hi John, Don't feel to bad, most of us have been there, done that, got the T shirt. Cheers John.

I'm mad with myself for not seeing the obvious.  I've grown up in an environment of fault finding but plead that old age has now dulled the common sense. ?  

John

[Braddock, VC]

Go and sit on the naughty step ?.

[Braddock, VC]

Having said that os f plugs are normally robust, I have an OS 40 pre surpass 4 stroke I bought new in 83 or 84 and it's still on its original plug, I swapped an engine for an OS 52 surpass in the mid 90s that came with a saito plug complete with bent central post and it's still in there. Que sera, sera.

Don't lose sight of the fact it made us all look mugs and reinforces my belief that we always look for the worst case scenario when a quick cheap fix is the answer.

[Jon H]

In the past glow plug coils were pure platinum but these days there is a fair chance they are platinum plated. Naturally the plating will not be as robust and will degrade faster than braddock's example. 

 

a plug with a degraded coil will still glow nicely and will work fine while energised, but will fall over when it has to rely on itself to keep the reaction going. Its possible this is the problem you were seeing. 

[Robert Putley 1]

I also have been having problems with OS F plugs with my Laser 80, getting through several per season.  Am interersted to try the JP plugs that you mention.  I checked out SMC`s web site but no luck their.  

 

Can you tell me where I can obtain these plugs John?

[FlyinBrian]

I can only speak as I find but I find but I run all my four stroke engines - OS and clones - on 10% nitro and type F plug. This combo much improves the smoothness of running and idle.

[Jon H]

13 minutes ago, FlyinBrian said:

I can only speak as I find but I find but I run all my four stroke engines - OS and clones - on 10% nitro and type F plug. This combo much improves the smoothness of running and idle.

 

Lean off your slow run and they will idle fine at 5%. Slow run needles are shipped rich from the factory (especially ASP) to guarantee the engine will start. If you never lean it off it will be rich and lumpy. 10% nitro only masks this as you need a richer mix with the higher nitro so its closer to correct tuning. A tweak on the slow runner will make a fair saving to your fuel bill, increase flight duration, reduce the mess on the model and increase reliability. What's not to like about that? ? 

[John Wagg]

5 hours ago, Robert Putley 1 said:

I also have been having problems with OS F plugs with my Laser 80, getting through several per season.  Am interested to try the JP plugs that you mention.  I checked out SMC`s web site but no luck their.  

 

Can you tell me where I can obtain these plugs John?

Robert I think I got mine from Model Shop Leeds.

https://www.modelshopleeds.co.uk/catalog/product_info.php?products_id=30901

But other retailers are shown on Google.

As mentioned I only did a quick test with the JP. So in/run/tune/out. I don't know how long term use will be?

Regards

 

[Piers Bowlan]

Just wondered if your F plugs are copies and not the genuine article John? Where did you get them? Odd that so many seemed to be faulty.

[Don Fry]

I thought that, I’ve had two 80 size, and a 75 Lasers in pretty continuous use for years. Can’t remember when the OS F plugs were changed if they ever have been.

[John Wagg]

11 hours ago, Piers Bowlan said:

Just wondered if your F plugs are copies and not the genuine article John? Where did you get them? Odd that so many seemed to be faulty.

Sorry I don't know  (remember ?).

I got them last year and would have bought them from an shop in England.

All  know is they have an "F" on them.

I still have a couple in their packets so will have a look if there is the shop label on them.

[Martin Harris - Moderator]

Could you post a photo or two of the packages? Might provide a clue - when I suggested this as a possibility earlier in the thread I didn't really expect them to be counterfeit but it does seem odd that you've had problems that have proved to be due to faulty plugs with a proven record of reliability from many sources.

[John Wagg]

17 minutes ago, Martin Harris - Moderator said:

Could you post a photo or two of the packages? Might provide a clue - when I suggested this as a possibility earlier in the thread I didn't really expect them to be counterfeit but it does seem odd that you've had problems that have proved to be due to faulty plugs with a proven record of reliability from many sources.

Sorry my bad!

Not "F" type but the JPs that are in the packets.    

However found the bag that the "F"s came in and from Rapidrcmodels.com.

No reason to think they were counterfeit and no problem used in a couple of other four strokes.

Just must have been unlucky in having one that had obviously worn out and the other maybe getting tired. The last one I used worked as it should. 

Cheers

 

[Piers Bowlan]

Seems that you were just unlucky John and possibly just a slightly iffy batch that slipped through Chinese quality control on a Friday evening? Certainly not blaming Rapid RC Models as they are a top company and I have bought lots of items from them at the shows. Phew ?

[Don Fry]

Just remember, these modern plated plugs don’t stand up to abuse. 
I think they don’t like:

being left wet

being run on too many amps off the starter power supply

revved with the starter power supply on.

All of the above leave a matt white plug coil, and the motor does not want to tickover reliably.