Loud crack heard then engine stopped.

[Former Member]

[This posting has been removed]

[Martin Harris - Moderator]

Posted by Percy Verance on 10/04/2016 08:21:55:

Hi again Craig

Looking at the Just Engines site, the spares costs are as follows: crankcase £27.55, crankshaft £27.55, and a new con rod (if yours is now bent) is £12.11 These spares prices are for ASP's, but as I mentioned earlier, those engines are identical in all respects to the SC range. Although I always thought it odd SC never did a .61fs

So Craig, a repair might well end up costing over half the price of a new engine. This is usually the point at which it isn't considered an economical repair, but that would of course be your choice.

...and a piston...and new bearings would be a wise investment...although he could consider bodging the crankcase with epoxy or ali soldering. The volume/sealing isn't critical on a four stroke as long as the airflow through the normal vent is sufficient to draw lubrication over the cam followers. Unless I had spares lying around, I wouldn't contemplate a rebuild.

Bob, I was always given to understand that rod failure on Triumphs was often due to people (quite possibly in the factories!) allowing them to knock against the crankcase lip while stripping the top end leading to a fine indentation where a crack could start. Con rods were always polished in serious applications.

[Adrian Smith 1]

Yeah know the feeling. Some years ago I had an OS 200 surpass F/S that did exactly that. Ripmax replaced two of them with new, one after the other without question. They both did it. The third new replacement I didn't touch it and left it in the box. It went to a deserving home soon after that. Ripmax never did say why it kept doing that.

[Bob Cotsford]

Posted by Martin Harris on 10/04/2016 13:05:34:

......

Con rods were always polished in serious applications.

Polishing should prevent conrod failures but they would still give in under sufficient abuse, though as teenagers I'd be hard put to classify ourselves as 'serious' tuners.

Edited By Bob Cotsford on 10/04/2016 15:34:34

[Jon H]

Looking at the colour of the crank pin it didn't seize. It would be a lovely blue colour if it had and it would have broken the conrod before the pin. There is a chance that some detonation was a contributory factor, but most likely there was a material defect somewhere in there and it was a fatigue type failure.

What you could do is either replace the crank, or buy another deceased engine and make something good from both. Or, drop kick both into the weeds and buy another pair.

As for the engine failing in the air, it should not have been an issue getting down as long as you maintained power on the other engine and kept your airspeed up.

[Peter Miller]

Posted by Percy Verance on 10/04/2016 09:22:32:

Hi again Peter

I had a .25 and a .36. Quite honestly I didn't rate them that highly. They seemed a very old design compared to OS's of the 70's. The .36 had a throttle arm on both sides of the carb though, which was handy. Even the way the silencers were held on was rather quirky. Four bolts on my .36

I don't think the UK modeller of today would accept such quirkiness.......

ONe of the big problems with Fox engines was that Duke Fox did not beieve in fancy finished on the outside. His engine were superb designs but very quirky in many ways.. Classic examples being the failuristic Split case 19 and the nice but strange barn door series. The little late 15s with the huge backplate were very powerul indeed on higher nitros.

Of course if you went into a shop and compared them with OS and Enya to name but two they looked poor and that was the problem. People buy on appearence .

As I said, we used a lot in the club back in the 70s and neve had any trouble with them. Mind you I would not buy one now apart from the famous 35 stunt which is still the best stunt engine for its size.

The silencer attachment was poor, espeiclaly the first version with only two. The silencers were not effective to be polite, especially the open ended one.

Recently a club member bought two brand new Fox 35s and found that the silencers did not haveany connection between the stack and the chamber.

[Cuban8]

Posted by Percy Verance on 10/04/2016 09:57:53:

You think ASP spares are expensive C8? Then whatever you do don't look at a Saito or OS spare part price list... .....

Yes, I know that OS and Saito are silly money prices for spares, it's profiteering, plain and simple when the customer has very little option other than to scrap an otherwise serviceable bit of kit.

 

Edit.

Just checked the price of a replacement crankshaft, piston, liner, and connecting rod for an OS 120 four stroke......comes to within a couple of quid of  half the cost of a new engine

And of course there would be labour charges if you couldn't fit the parts yourself.

 

 

Edited By Cuban8 on 10/04/2016 17:45:45

[Jon H]

The Laser spares are fairly priced :P

I try to keep them to a level that means repairs are a viable option for people. We also offer discounts on new engines if crash damaged or old engines are beyond economical repair.

As for labour, we again try to keep things under control price wise. Our £70 service gives new bearings, piston ring, valve springs, clean, test run, labour charge and return shipping. Its a pretty decent deal

[Former Member]

[This posting has been removed]

[Engine Doctor]

Budget engine won't stand abuse as well a a good brand. Even good brands will fail like this if runn with a larger prop than they can cope with . Fuel should be adjusted so that engine sounds smooth .If it sounds hard or is knocking then components like crank shaft or crank pin can fail wrecking the engine. It's not a common failure but budget engines like ASP ,SC or Magnum do have soft cranks that bend easily ,I've straightened loads of them. Looking at your engine it looks if it would be cheaper to replace rather than repair.

[Jon H]

ED is quite right. You can even kill a Laser with overloading/knocking over a long period. Its very uncommon, but one chap did kill his 180 by using a 24'' prop (20'' is the biggest we suggest) and 10% nitro for many years. I could see from the innards that it had been run hot and we suspected knocking had occurred. Anyway eventually the gudgeon pin broke in half which loaded the piston such that some time later the piston cracked. Incredibly, none of this was enough to stop the engine and it was returned to me as it was down on power and difficult to start!

Anyway, a new piston, gudgeon pin and rings had the engine back to normal and that was that.

I also agree that your engine is beyond economical repair, so unless you can build a good engine from 2 wounded ones i would get get another one. That or a pair if you want them matched for your twin. Personally i wouldnt worry though as i have tried to use ASP and SC engines as matched pairs in the past and they were too inconsistent for it to work.

[Engine Doctor]

Posted by Martin Harris on 10/04/2016 13:05:34:

Posted by Percy Verance on 10/04/2016 08:21:55:

Bob, I was always given to understand that rod failure on Triumphs was often due to people (quite possibly in the factories!) allowing them to knock against the crankcase lip while stripping the top end leading to a fine indentation where a crack could start. Con rods were always polished in serious applications.

I had a friend who back in the mid 1960's tuned his Triumph Bonneville it had done a few miles but was totally rebuilt . He polished the rods and they looked like chrome. One of the fitters in our workshop advised him to get them x-rayed before he refitted them . They both had fractures and would have quickly failed. Beezers were the same as you say but never seemed as powerful as the Triumphs unless the timing side main was converted to a ball or roller bearing. I run a A7 Shooting Star 500cc plunger frame later fitted with a A10 650cc unit for a few years . Sold that and bought a basket case Rocket Gold star for £45 ! Not a lot of money even then .Then proper work and a girlfriend who wanted a car ended the bike thing. Good old bikes, I wished I had kept the RGS and stored it .It would have been worth a few thousand by now !

[Craig Spence]

Thanks gents, I've already ordered a new one. Repressing new bearings in crankcase would be a bit out of my skill & toolset. I think now I could of perhaps overloaded them?, although not out of the reccomebdations!!.

They are old but barely flown, we'll run. They have always used xoar 11x6 after break in period. I then upped them to APC 11x7 for a little more thrust, well perhaps with the extra pitch & weight was enough to push it over the edge.

I'm just praying that the other one isn't suffering?, seems fine but then the other one did as well?.

Once the new one comes I'll put a good few tanks through it then try to tune them so there near the same again!, & then start flying again.

Cheers for the help fellas.

[Denis Watkins]

Would you believe a 12 x 6 would run better than an 11 x 7?

Like someone said, Detonation, Hydraulic lock? over propped BANG ! ! !

[Denis Watkins]

PM me with recommendations for por props and fuel when you select your alternate motors

[Tony Cook]

Don't forget to drain nitro fuel after a days flying and get some after-run into the crank when you get home (not too much) and when you re-start the next time out turn it over by hand a couple of times.

[Jon H]

11x6 is under propping them by quite a way. I would shoot for 12x6 as a start point after running in for about half hour on an 11x6.

I did this for a friend recently and after running in we switched to a 13x5 as they only have a trainer and it dosent need the speed 6 inches of pitch will give it