Saito Exhaust Comes Loose

[Peter Jenkins]

I have run 2 Saito 100s and now a Saito 180. All three suffer from the exhaust pipe retaining lock nuts coming loose despite tightening them as much as possible. I've also tried loctite (ordinary and not high temperature) but that made no difference either.

 

I am considering running the engine up to operating temperature and then tightening the lock nuts. Alternatively, to find a high temperature loctite but the best I can find is Loctite 278 that only guarantees performance up to +200C.

 

What do others do to keep the Saito exhaust in situ?

[YakMad]

Peter,

 

 

The solution I use is to clean the oil from the manifold threads and apply high temp silicone gasket seal, put it on the manifold threads before inserting into the head or the exhaust and tighten the lock nuts, it works best if you apply enough silcone that it squeezes out under the lock nut, allow it to cure and the exhaust should stay in place. All my larger Saito 100, 125 and 150 suffered from the exhaust coming loose until I did this, but the exhausts on my smaller Saito's, 72's and 82's have never come loose without the fix. Hope this helps

[Peter Jenkins]

Thanks YakMad, I'll give your suggestion a try.

[Ed Darter]

not had problems on my 82a, but I did as you are suggesting and ran it up to temperature, then tightened the nuts up once more.

[Peter Jenkins]

Ed

 

It would be useful to know if you were suffering from exhausts coming loose on your 82a or whether you are merely taking precautions. YakMad reported that he had not had problems with his 72s and 82s so I was interested in learning if you had experienced problems.

[Biggles' Elder Brother - Moderator]

I can't speak about Saitos but I have experienced the problem on an OS91FS. The basic problem there was that the aluminium muffler was expanding more than the steel manifold - result the thread becomes loose. Vibration from the engine then finishes the job off - damaging the muffler thread in the process.

 

Are you getting any black oily residue around the joint Peter? If so its a sure sign that the muffler thread is being damaged.

 

BEB

[ken anderson.]

for years i have used 'fish tank' silicone on all 4st's and 2 st's.......0n the 2 st's i cover the nut or the hex end...and it stay's put...but is easy to get off if reqd....same also on the check nut of the 4 st........

 

 

ken anderson ne...1.(tech dept)

[YakMad]

The smaller Saito's run smoother than the larger sizes and don't appear to loosen the exhaust. I have five 72's and one 82a and the exhaust never comes loose, but on my 100's, 125, 150 and 180 (now sold), the exhaust's always came loose until I did the silicone fix, in fact on the 100's, two manifolds sheered off at the the end of the threads, the manifolds on Saito are made of a lighter grade metal than OS which I persume is done to save weight but may contribute to the problem. Still I am very keen on my Saito's, they can't be beat for the amount of power they produce unless you want to buy YS (I could'nt afford the fuel bill, 30% nitro only)

[Steve Hargreaves - Moderator]

I wrap PTFE tape around the manifold threads before inserting & tightening them up. They don't leak & they don't come loose!!

 

Just ordinary plumbers tape does it for me!!!

[Peter Jenkins]

I've just bought some Loctite 5920 Premium Copper Silicone sealer from Halfords (£5.49 a tube). The panel on the side says it is good for 200C continous and 350C intermittent. So based on Steve Hargreaves good experience using humble plumbers tape, I should be OK with the stuff I've bought. I'll let you know how I get on this weekend when I run the engine again.

 

BEB - I've only run in the Saito 180 and had 2 x 5 min flights. The engine stopped on the second flight which I put down to the silencer coming loose and the tank depressurising. No nasty black oily residue - so far. In fact, neither of my Saito 100's has displayed this residue either despite the exhaust coming loose a couple of times.

 

Thanks everyone for your inputs and advice.

[Ed Darter]

Peter - I just did it from 1st fitting, so guess as a precaution.

 

The other thing is to make sure you are screwing the threads into the manifold far enough, as many turns as possible! A friend bought a 2nd hand 82a that hadn't had this done and must have suffered the same fate as yours a few times as the threads were shot. Tried helicoiling etc but to no avail. Had to buy a new top end in the end which made it rather expensive as a 2nd hand buy!

 

So basically, its a good idea to sort it before you do any long term damage to the engine. The sealant is a good 1st effort to doing this I guess.

[Peter Jenkins]

Ed,

 

Thanks for the caution. Yes, I have screwed the manifold into the head as far as it will go and then backed out less than a turn to get the exhaust pointing in the right direction. I've put the silicone on both ends of the manifold pipe and am due to run the engine tomorrow - so we shall see how it goes!

[Biggles' Elder Brother - Moderator]

Let us know Peter, I would be interested to hear how it goes.

 

BEB

[Peter Jenkins]

Hi folks, I took the Saito 180 up to the field (in the Capiche) to check the exhaust and for a noise test. I had used the high temp Loctite silicone on the threads put on on Thursday evening. I ran the engine for a couple of minutes and ..... the exhaust came loose! So, cowl off, tighten up the exhaust lock nut again. The nut holding the pipe to the cylinder head was fine. I then ran the engine again and stopped it and while still cooking tightened the locknut from the pipe to the muffler as much as I could. I then put the aircraft through the noise test which meant full throttle running for approximately 30 secs on each direction - 2 mins total with a lot of idling in between. Nothing came loose but I failed the noise test! 89 db recorded with the prop facing the mike! Hmmm - have to check the forum on others expriences on this issue.

 

So, the lessons to be drawn are: use a high temp silicone but back it up by tightening the lock nuts when the engine is hot to make doubly sure that all remains fixed!

 

Thanks for all of your inputs.

[Martin Harris - Moderator]

I've never owned a Saito larger than a 40 but have several 90 and larger (up to 180) four strokes in regular use as well as smaller sizes. Other than one loose exhaust (on an SC52 in a second hand model) which I tightened and have had no problem with since, I don't recall ever having a problem - and all I've ever done is tightened the locknut - cold..

 

Just a thought, but have you balanced the prop - perhaps the problem is vibration?

Edited By Martin Harris on 07/05/2011 21:07:00

[Peter Jenkins]

Martin,

 

Actually, no! But that's only because the Graupner G-Sonic prop was perfectly balanced and didn't need any further fettling. First time for a Graupner prop in my experience! So, yes, the prop is balanced but the engine is not one of the smoothest running engines I have had. I suppose that is the penalty for a large single cylinder 4 stroke. The problem is vibration but not from the prop. I've had this with both my Saito 100s but they now seem to have beaten into submission. I suspect that Saito uses a coarser thread than OS and that is what is at the root of this problem.

[Biggles' Elder Brother - Moderator]

Peter, I really hate to bring a bit of pessimism into this story, but this is beginning to sound awfully familiar. When I had this problem I too eventually went down the tightening it up while hot route. And like you I found that it then didn't come loose - ooooh, for about 6 flights, then it did. In other words the tightening it up hot route only gave a temprorary solution.

 

You're right vibration is the problem - allied to to differential expansion rates. But there is nothing you can do about the vibration - I tried balancing props and even spinners to no avail.

 

In the end, the only solution that worked for me was to take the exhaust muffler off the engine, mount it on the firewall and connect it to the engine via a flexiable pipe, and make sure that the muffler gets some cooling air.That works.

 

I really hope that tightening it hot works for you - but if you are unlucky enough to have the same experience as me I offer the flexible pipe as the last hope! Let us know how you get on over the coming weeks.

 

BEB

[Peter Jenkins]

Thanks BEB. I'll let you know how I get on. I've left my Saito 100 alone as the muffler has stayed fixed in place for some time now. However, I will be looking at muffler security after every flight from now on - that is if it doesn't come adrift in flight and lead to a dead stick!

[Peter Jenkins]

Well, guess what? The Saito exhaust came loose despite the silicone sealer. In the course of a conversation with Weston regarding the Capiche, they said that they used 5 min epoxy on the threads of Saito exhausts, including that for the head. They assemble it wet and it never comes loose until you crack the joint with a spanner. Once undone, you can just chip off the epoxy and re-apply some more. I've not tried this yet as I am a little concerned with using epoxy but the folks at Weston apparently use this on both 4 stroke and 2 stroke exhausts!

[Biggles' Elder Brother - Moderator]

Sometimes don't you just hate being right  That exactly mimics my experience.

 

I tried the epoxy solution as well - and I have a clubmate who swears by it. But itdidn't work for me! The problem is the epoxy simply breaks down at the temperatures in the exhaust.

 

BEB

Edited By Biggles' Elder Brother - Moderator on 13/05/2011 21:31:23

[Peter Jenkins]

BEB is 30 min epoxy any better or even the good old 24 hr stuff?

[Biggles' Elder Brother - Moderator]

Hi Peter,

 

Well its worth a try, and some folks swear by it. But I must confess that when I was having this problem it didn't help. I tried 30min - no good. I spoke to a colleague in work who is an expert on resins, his view was that there was no epoxy that could remain mechanically strong at 200C - even so-called "high temperature" epoxies don't really go that far. My experience would bear him out - it just turns onto a soft putty-like substance. Don't worry about getting it off - mine just peeled off with a finger nail and had the consistency of chewing gum!

 

I think this works for some people if the problem is just vibration - then it acts as a sort of damper/filler and "gums things up". In my case I think I had both vibration and thermal expansion problems - and it can't cope then because once the muffler starts to thermally expand it breaks the epoxy joint (which as I say isn't strong).

 

Give it a go - you have nothing to loose. It might work.

 

You have my sympathy, I know how frustrating this can be. Let us know how you get on. If the epoxy doesn't work I'm happy to explain my flexible pipe solution. Best of luck!

 

BEB

[Steve Hargreaves - Moderator]

Give the PTFE tape a try!!!!!

[Peter Jenkins]

OK!! I'l give the PTFE tape a try Steve.

 

BEB, what's your flexible pipe solution mate? I've just received a Genesis pipe from Weston via JE and I'm firstly going to try Steve's suggestion and if, but only if, that doesn't work I'd like to hear your solution.

[Biggles' Elder Brother - Moderator]

Well let's see if the PTFE tape does the job - if not we'll start the flexible pipe approach!

 

BEB