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Saito 80 GK blown up

Old 11-03-2008, 04:55 PM
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perdo
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Default Saito 80 GK blown up

I have been running a Saito .80Gk on and really old ugly stick for about a year, not all that much time on the engine. THe engine itself is probably 12 years old but it had never seen fuel until last summer. Now that being said Saturday evening I was out flying and on the third flight making an up wind pass just thinking about seting up to land on the next pass, and the engine stopped suddenly ( I mean right now with a resounding thump). I let it fly upwind and landed and retrieved the plane. the crankshaft was locked down, after some gentle rocking back and forth it started to turn but it was turning just the crank and cam, the connecting rod was obviously broken.

At dissassembly the crank pin end of the rod was broken into three pieces, no other damage occured to the engine. it didn't slap a valve or grind up the pieces of rod so I am lucky and have a new rod ordered.

Has anyone seen this before or was this a problem when the .80 was a modern production engine??

Prop was a MS 13 X 8 and the fuel was powermaster 15% with 20 % oil half castor and half synthetic.

when I opened up the crankcase it was still oily and there was no sign of gauling or excessive heat..
Old 11-03-2008, 05:19 PM
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w8ye
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Default RE: Saito 80 GK blown up

I have seen some variance in the big end bore of torn down Saitos. But I personally have not experienced one that let go. I experienced a new seized up 72 and therod was frozen to the crankpin.

The loose ones appeared to have always been that way.
Old 11-03-2008, 06:09 PM
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Ram Jet
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Default RE: Saito 80 GK blown up

I don't own a Saito and you will probably hear from members with a-lot of experience with your engine. If the bearing on the big end of the con rod isn't siezed I can't imagine why the rod let go. If it were my engine I would have the new con rod magnafluxed preferably by an aircraft certified technichian. You are lucky that there was no damage to the valve train. Stuff happens.

Bill
Old 11-03-2008, 06:13 PM
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Default RE: Saito 80 GK blown up

I know that on many of the Saitos, the big-end to crankcase clearance is *very* small to the extent that if the rear bearing wears then the conrod *will* touch the crankcase. I suspect that if the contact was sufficiently hard and prolonged, the result could be a broken rod.

I always change my bearings at the very first sign of wear or noise.
Old 11-03-2008, 06:18 PM
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Default RE: Saito 80 GK blown up

I go along with Xjet on the rod hitting the crankcase if the rear bearing is bad
Old 11-03-2008, 07:34 PM
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perdo
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Default RE: Saito 80 GK blown up

That is just the point of it all there are no wear marks on the case and the rear bearing is perfect, no slop at all.. and the brass bushing was still on the crank pin and not a mark on it either
Old 11-03-2008, 07:54 PM
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Default RE: Saito 80 GK blown up

Might have been a manufacturing defect then. Sometimes SHIrT happens.
Old 11-03-2008, 08:27 PM
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Default RE: Saito 80 GK blown up


ORIGINAL: XJet

I know that on many of the Saitos, the big-end to crankcase clearance is *very* small to the extent that if the rear bearing wears then the conrod *will* touch the crankcase. I suspect that if the contact was sufficiently hard and prolonged, the result could be a broken rod.

I always change my bearings at the very first sign of wear or noise.
I just put new bearings in a saito 150 and I guess the front bearing seated slightly deeper than the orignal because I now have rod contact with the backplate. I took care of that clearance problem with a pnumatic die grinder w/sanding disk on the backplate. No more interferance problem!
Old 11-03-2008, 08:32 PM
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Default RE: Saito 80 GK blown up

G'day. An idea from left field. I seem to remember seeing a post by Hobbsy in the Saito Club in which he said that his Saito 80 had too much compression to run as a diesel. I know that some earlier Saitos were made with high compression ratios so that they run very well with little or no nitro. If you have one of the older high compression engines, could it not be that the engine has been pre-igniting or pinging on your 15% nitro fuel? On a two stroke, this is easy to hear and sounds like a sort of crackle particularly in the mid range. A Leo 46 I have will not run on fuel with any nitro in it without pinging. It runs perfectly on FAI fuel.

As I understand it, an engine which is detonating prematurely puts very high stresses on the con rod and crank pin. Could it be that your engine has been damaged by this?

A friend has an early Saito 120 which is also a high compression engine. To get it to run properly on larger props and with some nitro he had Brian Winch shim the barrel by about 15 thou inch to lower its effective compression ratio. It now happily swings larger props with no problems with nitro in the fuel.

The only other way to stop pre-ignition is to tune the engine richer but if the compression is just too high, the resultant rich mixture to avoid the pinging may be just too rich for it to perform.
Old 11-03-2008, 08:46 PM
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Default RE: Saito 80 GK blown up

rcdude7,

you either did not get the rear bearing seated correctly or have the wrong rear bearing. You need to determine which before you run the engine much.
Old 11-03-2008, 09:28 PM
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rcdude7
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Default RE: Saito 80 GK blown up

Nope, I have the exact NTN replacement rear bearing installed (same as OEM). I had to remove and reinstall the same (good) fwd bearing to get the rear out. The front bearing locates the crankshaft and takes all of the axial loading, the crankshaft meerly floats in the rear bearing race because it is a loose slip fit. When I installed a prop and tightened down the nut, there was NO binding whatsover and the crank would spin freely.

One thing I noticed about this 150 is that it took alot of heat to grow the case, and even then the bearings would not just drop out as is typical of every OS and Enya engine I have changed beraings in over the years, and I have done many, I'm no rookie.

I guess Saito must use a higher temp than I to install these bearings at the factory.
Old 11-03-2008, 09:49 PM
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Default RE: Saito 80 GK blown up

Sorry Pedro, I don't mean to hijack your thread here. It is possible that the replacement rod you get maybe a improved version if there was ever a problem with the 80 of the same vinatge as yours. I think Saito quietly updates the engine componets as problems occur over the years. There have been some great pictures of really blown up Saitos posted here in the past, mostly 150's and 180's probably before horizon became a advertiser here on RCU[:@] I have looked but, I can no longer find any of those old threads.

Despite all this, I love my saito engines and have a couple flying now..........

Old 11-04-2008, 12:17 AM
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Default RE: Saito 80 GK blown up


ORIGINAL: perdo

...and the brass bushing was still on the crank pin and not a mark on it either...
Pedro,


Are you sure of that?

First of all, if there is a bushing in the con-rod, it is not brass...

It is bronze! And this is true of all engines and is not particular to Saitos.


And as far as I knew, most Saito single-cylinder engines do not employ any bushing in the rod (see photo of 1.25 item)... It is made of high-silicon aluminium, which requires no bushing...


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Old 11-04-2008, 07:59 AM
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Default RE: Saito 80 GK blown up

Dar, here is my pre 1990 .80GK, it does have a bronze bushing and I believe my circa 1991 1.50 also has a bushed rod, I think they are the only ones I have with bushings.
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Old 11-04-2008, 08:41 AM
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Default RE: Saito 80 GK blown up

ORIGINAL: rcdude7

I just put new bearings in a saito 150 and I guess the front bearing seated slightly deeper than the orignal because I now have rod contact with the backplate. I took care of that clearance problem with a pnumatic die grinder w/sanding disk on the backplate. No more interferance problem!

That's an odd defect. You're positive the rear bearing was fully seated? I mean the parts are made to a certain size. If the bore for the front bearing was too deep, it should have been rejected before assembly. That problem just doesn't sound right. Either the bearings or the crank weren't seated correctly.

I had an NIB OS FS-26 that rubbed the backplate. It turned out the crank was an unusually tight fit in the bearings and wasn't fully seated.
Old 11-04-2008, 09:33 AM
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Default RE: Saito 80 GK blown up


ORIGINAL: gkamysz

ORIGINAL: rcdude7

I just put new bearings in a saito 150 and I guess the front bearing seated slightly deeper than the orignal because I now have rod contact with the backplate. I took care of that clearance problem with a pnumatic die grinder w/sanding disk on the backplate. No more interferance problem!

That's an odd defect. You're positive the rear bearing was fully seated? I mean the parts are made to a certain size. If the bore for the front bearing was too deep, it should have been rejected before assembly. That problem just doesn't sound right. Either the bearings or the crank weren't seated correctly.

I had an NIB OS FS-26 that rubbed the backplate. It turned out the crank was an unusually tight fit in the bearings and wasn't fully seated.
I had the same problem with my Saito 65. Backplate rubbed after replacing bearings. Turned out the rear bearing was not fully seated on the crankshaft.
Old 11-04-2008, 09:47 AM
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Default RE: Saito 80 GK blown up


ORIGINAL: Hobbsy

Dar, here is my pre 1990 .80GK, it does have a bronze bushing and I believe my circa 1991 1.50 also has a bushed rod, I think they are the only ones I have with bushings.
I see where there has been rust?
Old 11-04-2008, 11:09 AM
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Default RE: Saito 80 GK blown up


ORIGINAL: Hobbsy

Dar, here is my pre 1990 .80GK, it does have a bronze bushing and I believe my circa 1991 1.50 also has a bushed rod, I think they are the only ones I have with bushings.
Dave,


Since I could not find the specific discontinued Saito .80 con-rod in the Horizon web site (what 'code' is it?), I reserved what I wrote...

...So, I used the term 'most'...
Old 11-04-2008, 06:44 PM
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Default RE: Saito 80 GK blown up

I had a 1.25 blow a rod on crank end with no marks in crankcase or on the crank pin. I did notice a little play in the crank bearings, which could have caused the rod to break. In any case i am replaceing them
Old 11-04-2008, 11:46 PM
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Default RE: Saito 80 GK blown up


ORIGINAL: FlyinAmos

...I did notice a little play in the crank bearings, which could have caused the rod to break.
Amos,


Radial play in ball bearings that amounts to 0.1 mm, or less, will not cause your con-rod to break...

You should use a machinist's dial indicator to measure the actual magnitude of this 'play'.


For a blow to be strong enough to cause any damage, the included 'play' must be large enough to allow relative speed between the pounding parts, to 'build up' sufficiently...

A clicking noise is nothing of the sort.


Besides, some clearance in the con-rod's sliding bushings is an utter necessity, if lubricant must enter the gap between the spinning parts, with no pressure assistance...

0.04-0.06 mm there is audible when dry, but completely harmless.


Old 11-09-2008, 09:55 AM
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Default RE: Saito 80 GK blown up

Sorry Dar, I was just showing you an "unmost" engine, no offense intended.
Old 11-09-2008, 10:07 AM
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Default RE: Saito 80 GK blown up


ORIGINAL: Hobbsy

Sorry Dar, I was just showing you an "unmost" engine, no offense intended.
Absolutely none taken, Dave.


Is that a 'generation gap' thing?
I.e. are earlier generation Saito single-cylinder engines with bushed con-rods and later generation ones with just the high-silicon aluminium con-rods?

I know the .72 I have here has the high-silicon type...


I know the Saito .80 is an earlier, big-block type...



Old 11-09-2008, 11:16 AM
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Default RE: Saito 80 GK blown up

A friend gave me an older high compression .80 GK....he said he bought it in the early or mid 90's. He gave it to me because it had a cam gear w/ a few broken teeth and was set-up from sitting for prob. a decade ...FWIW it had an un-bushed rod.

I say "had" because I replaced it along with the cam, lifters and bearings. The big end of the rod was .008 OOR. (IIRC he also said he used to run an all synth. oil fuel back then )
Old 11-10-2008, 10:57 AM
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Default RE: Saito 80 GK blown up

Hello; An old GK Saito 80 has come to me after a crash on pavement. With the barrel head off, it still feels like it has compression. The spinner is binding on the front bearing boss. There is lots of corrosion on the crank journal that the rod rides on. I popped the spinner off and everything freed up. This engine seems to have had a quite hard life in that; there is lots of visible wear below the piston on the bore and lots of corrosion stuck to the exhaust valve. The piston seems to have a crack in it in one of the valve pockets, but nothing shows through to the other side, os I think it's okay. It is a GK series engine and now that most of the black paint has come off, it looks terrible, I think i'll scrape the remainder black paint off and put it on my buuffing wheel after i change the bearings. I have two other Saito 80's, both the earlier high compression ones that have been serving me well for more then 10 years each with no problems whatsoever.

I will have to grind the spinner a bit, but Other then the corrosion, I don't see any problem with this engine, the big eng looks perfect.
Old 11-10-2008, 02:51 PM
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Default RE: Saito 80 GK blown up

Sounds like the crankshaft may be bent.

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