Saito Exhaust Comes Loose

[John Olsen 1]

Well BEB, that picture is useful to me since I will need to do something similar in my Fokker DVII. It is the Hangar 9 ARTF, and the Saito 91 mounts on an angle, but basicly upright, hopefully leaving room in the cowling for me to squeeze in the muffler. Of course , being in the antipodes, the local dealer doesn't have the right angle adaptor and flexipipe in stock, so I ordered them about six weeks back..... Now I am off to Australia next week, where there are shops that do have them in stock,leaving me with a slight moral dilemma...do I grab one when I get the chance or do I trust the local dealer to eventually deliver?

 

But anyway, I think I should be able to do something similar to your installation. I may not be able to use the standard muffler, but I have the gear here to make one if the need arises. Well, I could make the right angle adaptor too, the only reason I didn't was that the taps and dies for M12 x 1 cost considerably more than the list price of the adaptor. Mind you the egineering supplier does actually have them on the shelf, so maybe I should have gone that way.

 

regards

John

[oldSmithy]

Hi

 

I had the same situation with an SC91FS. Every time I tightened the locknut and flew the plane the thing would come loose until eventually the thread was knackered and when I threaded the pipe into the head it would jump a thread so the only answer was to replace the head. Since then I've had no trouble, it has never come loose since. I guess one of the important things is to thread the pipe in as far as it will go before applying the locknut and that should be as tight as possible. A torque setting for the lock nut would be useful. Not sure if high temp loctite would do the job or not as it is servicable up to 200 C. I suspect once the head thread has suffered some damage its pretty much a one way street after that. I have four 91 fs's and this has been the only one to have suffered a loose pipe. The right angled adapter certainly sounds like a worthwile option anyway.

 

 

Cheers

OldSmithy

[YakMad]

Peter,

 

 

Sorry to hear you had to return your engine to MacGregor's, my Saito 180 suffered from a sticky exhaust valve, polishing the valve stem sorts it out and returned the engine to full power.

[Peter Jenkins]

YakMad, that's very interesting. I shall have to see what MacGregors say about the engine shortly. Apparently they have stripped it down and re-assembled it but it is awaiting testing. In what did you have your Saito 180 installed and what was its all up weight? What prop did you use and what sort of vertical performance did you achieve?

[YakMad]

Peter,

 

 

It was in an Extreme Flight Yak-54 72 inch (I am keen on Yak's hence YakMad), I can't remember the weight as I have since sold it but I think it was around 11 lbs, vertical performance was good but not ballistic, it would hover with the 180 but there was not alot of power to pull out if you got it wrong, it would pull out slowly. After using an APC 18x6, 18x4W and 17x6 props I found that an APC 16x10 suited it the best and it ran the smoothest with this prop. I have since given up on four-strokes larger than 125 for aerobatic models and now use large OS two-strokes instead as the OS 1.60 produces alot more power than the Saito 180 and the OS 120 AX produces more power than my now expired Saito 150 (conrod came out of the bottom of the crankcase, another known problem with the Saito 150), don't get me wrong I am a very big fan of Saito engines and have years of service from current collection of my smaller one's from 1.25, .91, .82, several .72's and an old .65, just not very keen on larger four-strokes in aerobatic models.

[John Olsen 1]

Hi Guys, just had a thought about this, and presuming that what you have on these bigger engines is similar to my FA91S, the manifold pipe is threaded into the cylinder head and the pipe threads into the muffler itself near the front end. Well, if you point the exhaust backwards it is the front, I guess you can aim it any way you like. But presuming that it is mounted like that, the whole of the muffler is behind the screw thread. so the up and down vibration that comes with any single cylinder engine is trying to wiggle the thread loose in the cylinder head. That dioes seem like a very effective way of getting it to come loose, a bit like wiggling a fence post in the ground to free it up.

 

So what I wonder is if a bit of support at the other end would help? A little clamp around the tailpipe with a bit of rod down to the engine mount to stop any tendency for the thread to turn might do the trick.

 

regards

John

[Myron Beaumont]

There is a time proven solution to stopping vibration from loosening bolts or set screws . On full size airframes ,the bolt head is drilled from flat to flat and a length of stainless locking wire threaded through it and attached to the next bolt ad infinitum with the tension "tightening"if any vibration was present .ie pulling clockwise against the loosening direction.

The other method used on gas turbine engine casings might be locking /tab locating washers where a small tab fits in a bore close to the bolt perimeter and two tabs on the washer are bent back after tightening to end up squeezed onto two flats on the bolt head.

No loosening come what may .Does this give you any ideas maybe ? The only thing to watch out for is internal fretting on the thread and bolt hole bore with vibration normally shown up by "the black gunge" around the area .Suitable compounds are available ,maybe olde worlde copperslip would help .Giving my age away again !

[John Olsen 1]

Hi Myron,

The trouble is these are threaded tube, screwed into a threaded hole in the cylinder head, and with a lock nut fitted to lock it in the correct position. So if you drill through from flat to flat, you are going right through the exhaust passage. I have seen nuts cunningly drilled just at the corner, eg from one flat to the adjacent one, but that would be a bit tricky in this small size.

 

With these engines, in the normal upright position, the weight of the muffler is acting in the direction to undo the screwed connection. It is long enough to have good leverage, and with the vibration to assist, it seems that on the bigger engines it is quite well able to overcome the tightening forces. Mine hasn't been in the air yet, and will have an angle connection and flexi pipe when it does, so this will not be an issue for mine anyway, although fitting it all neatly inside the cowl may be.

 

Wasn't the copperslip more for the opposite situation, eg smear it on the exhaust nuts in the hope that one day you might be able to get them off again? I've got some Locktite nickel silver antiseize which is great for those situations.

 

regards

John

[Biggles' Elder Brother - Moderator]

This problem may be different case to case, but in my instance the problem was not with the cylinder head connection, it was with the muffler to stub connection - the muffler itself repeatedly came loose.

 

As I've said above I tried lots of solutions before hitting on the flexipipe answer. They included a variant of Myron's suggestion in that I drilled through the muffler at the neck, and through the stub and wired the muffler in place. No good - the muffler is aluminium and too soft, the hole just tears and the muffler comes loose!

 

At first, like you, I though it was the nut retaining the muffler that was coming loose - hence all the effort I put in to high temp lock-tite. But I concluded that this was not the mechanism as if you lock the nut in place - either with lock-tite or a lock nut - the muffler still vibrates loose but the nut is still locked in position!

 

So, what's happening? Well this is my explanation; the aluminium muffler thermally expands more than the steel. This means that no matter how tight you fasten it up the thread it develops "play". The vibration then causes the muffler to "travel" down the thread. This is born out but the presence of the "black gunge" which, as Myron says, is a result of the aluminium muffler "fretting". There is no black gunge upstream of the muffler/stub connection so we can conclude this is the source.

 

I believe the flexipipe solution works for three reasons:

 

1. the joint to the aluminium muffler is further from the engine and so runs cooler.

 

2. The joint is at least partially isolated from the engine vibration by the flexipipe and its mountings

 

3. The joint is supported as John has suggested.

 

This explanation would also fit with the fact that some folks have been able to solve the problem using plumber's tape - basically this "pads out" the thread and in some cases may do so just sufficiently to stop the fretting. But as Peter has found out it doesn't always work!

 

I think this isn'tt a problem for many if they have the stub to muffler joint "out in the breeze", that prbably cools the joint sufficiently to prevent the differential expansion being a problem. Its "in cowl" installations that tend to be most vulnerable. The only real solution of course is a redesign of the exhaust system!

 

BEB

[Peter Jenkins]

John Olson - you make an interesting point on the weight of the muffler driven by the vibration (and the Saito is a pretty rough engine) lead to the head connnection coming loose. But it would appear that both BEB and I have had the muffler come loose. Now on the standard Saito muffler, the mechanism John refers to would still apply. I have also used a Just Engines (Weston UK made) muffler which is screwed onto the Saito exhaust pipe in a symetric manner i.e. it does not have an offset mounting method. This also came adrift so it is more likely to be the problem of dissimilar metal expansion. As BEB says (stop smirking there BEB!) the only solution appears to be his! Mind you, I have yet to try the epoxy trick that Weston have recommended to me. I'll let you know how I get on with that in due course.

[Biggles' Elder Brother - Moderator]

Smirk? Moi? Nah - just

 

I would be interested to hear now you get on with the epoxy - if it works its a lot less hassle and much cheaper!

 

BEB

[Peter Jenkins]

BEB, I had sent my Saito off to MacGregors for them to check why it was down on power. It is now back, valve timing, clearances corrected and new piston ring fitted. I decided to use epoxy when fitting the exhaust. I've had an extended ground run, and 2 flights and the thing has stayed in place! Flying again on Friday so will let you know if it is still attached after that.

 

Peter

[YakMad]

Peter,

 

 

Good to hear you have you're 180 back, it's interesting that they said the valve timing was off. I do all my own maintenance on my Saito's. I purchased a Saito 100 in the US when on holiday one year but the engine was a pig to start, I decided to strip the engine to see if there was a problem but could find none, after re-builing it and setting the cam gear timing correctly (piston top dead centre and dot on timing gear facing straight down) the engine started first time and never missed a beat, the only conclusion I could come to at the time was that the valve timing was off.

[Biggles' Elder Brother - Moderator]

Hi Peter,

 

good news! Let's hope it stays there. I'm just about to fit a Saito 82B into my Extreme Flight Extra. I'm bucking the trend, converting an electric model to IC! So I hope the silencer stays on that one. Its a funny thing but it doesn't effect all engines even of a specific make and size - just some.

 

Anyway - fingers crossed for you.

 

BEB

Edited By Biggles' Elder Brother - Moderator on 12/08/2011 12:55:27

[Steve Hargreaves - Moderator]

Interesting (& worthwhile..) conversion there BEB....have you beefed up the firewall/front end or did it seem OK as it came out of the box...? I understand Saito motors are pretty light but probably still heavier than an electric motor....

[Biggles' Elder Brother - Moderator]

Considerably beefed it up Steve. I'll post some details in couple of days when I have it finished.

 

BEB

[YakMad]

BEB,

 

 

I had one of those when they came out first, good flier, mine had a Saito 72 in it, could have done with the 82, I just used ply doublers on the engine box and firewall, the only weak area is the landing gear mount as there is little supporting structure, try to beef it up before flying if you can to save on future repairs.

[Peter Jenkins]

Just returned from flying my Saito 180/Capiche. I am delighted to say that after a session of ground running and 3 flights, the silencer remains in place! The only problem is that I have a bigger silencer that I want to replace the standard Saito one with and just hope that I can get the existing one off! I'll let you know how I get on!

[YakMad]

Good news..

[Biggles' Elder Brother - Moderator]

You shouldn't have too much trouble getting the old one off. Generally the epoxy goes sort of "gooey" becuase of the temperatures.

 

BEB

[Engine Doctor]

It seems quite a few engines have this problem? I cant understand why . Nearly all my glow powered models are Fourstoke and I really cant remember the last time an exhaust came loose. I use the following method . Clean the thread and screw the exhaust tube into the head as far as it goes then back off to the angle required. Now tighten the lock nut up really snug. Run the engine up to tempereature stop and re-tighten the lock nut while engine is still hot . It works for me every time . I also make sure that the prop is correctly balanced as this will induce serious vibration and loosen your filling let alone the silencer and can also damage the airframe ! Even the props that claim to be prebalanced or or very expensive props can be seriously out of balance . All this works assuming that the threads have not been previously damaged by crash or running while loose . Once the head is damaged or worn the only real cure is replacement.

[Peter Eve]

I can confirm absolutely all of the Doctor's diagnosisi! I have a Saito 100 which is on its 3rd cylinder the first 2 having been damaged in crashes and the manifold ripped out the thread. The answer to that, apart from not crashing which doesn't seem to be an option for me yet (!), is to make sure that the mauffler angles back from the vertical as far as the design of plane/cowl will allow.

 

I, too, have inadequately screwed the manifold into the cylinder which exacerbated the problem. On the third attempt I hope I have got all this right. So far, with the manifold as far in as poss, so good, but I did have to re-tighten the lock nut to the cylinder when the engine was hot and I had to have two goes at it. Now it seems OK and that has been the case in the past, always the need to re-tighten. Plumbers tape made no difference, I haven't tried epoxy but that's becasue I didn't need to.

 

So, take your spanners to the field, warm up, tighten up - and enjoy the day!

[Biggles' Elder Brother - Moderator]

Sorry guys, but in some cases it really isn't that simple. In my own case that technique works fine on all my 4 strokes bar one - and on that one nothing other than the technique I refer to several pages back works - believe me, I tried everything!

 

Tightening up when hot

Tightening up when cold

Putting locknuts on the head and muffler joint

Epoxy

Using high temperature lock-tite

Wiring the joint

Supporting the exhaust

Swapping the exhaust type

Using elbows instead of the curved manifold

 

You name it - I tried it. And bear in mind I always balance not only my props but my spinners as well. Only using the flexi-pipe did it for me.

 

BEB

 

I stress its only one engine that has the probelm - others are fine.

[Peter Jenkins]

Engine Doctor and Peter Eve - I've done all the things you have suggested to no avail till I tried the 5 min epoxy - which, by the way, Weston UK swear by!

 

This evening, I had the devil of a job getting the Saito silencer off but nothing like the problem getting the head to pipe joint separated! Managed it eventually, and then fitted the Weston 180 Four stroke big silencer again using 5 min epoxy.

 

Will let you know how I get on with that once I've flown it. If that doesn't work, then BEB's solution might be the only remaining option! ....and BEB;s just waiting for me to do that so that he can say ...... told you so!

[Peter Jenkins]

Well, removing the standard Saito silencer, which proved very difficult, was a great mistake! The Weston Saito 180 can just would not stay connected despite using 5 min epoxy. So, I returned to the Saito 180 standard silencer. Despite using 5 min epoxy, and tightening up after the ground run, the silencer still worked loose and led to a succession of dead sticks.

 

Then decided to run the Saito without exhaust pressure and the first flight showed that it needed to be richer for vertical climbs. Second flight with the engine set richer resulted in the silencer unwinding itself completely. Since none of us noticed a sudden increase in noise I can only surmise that it fell off during the low throttle recovery phase!

 

Saito had sent me a Saito 150 new silencer (same as for 180) and I had noticed that this was of a different design, material and finish to the original one. Basically a cylinder with a boss at each end for input and exhaust and not with the intake set at an angle as the original. I thought this might be the result of difficulties in retaining the original exhaust so decided to fit and fly! As this new silencer does not have flats on its mounting boss, I could only grip it by hand and tighten up the lock nut. I had cleaned the thread and the face of the nut that would abut the silencer. I did not use any epoxy or plumbers tape - just au natural.

 

The ground run showed that the silencer had not loosened so I flew it twice and flew two aerobatic schedules. Result was that the silencer was still firmly attached! Well, I rather suspect that Saito has done us a favour by redesigning this silencer to make it stay on without resorting to any special techniques.

 

I will be flying this set up at the Nats so will let you know whether the silencer has behaved itself while flying in competition.