Engine basics > Four strokes only

Saito 72 with OS throttle

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ash:
Well, I've given it some test runs on the bench and it seems to go OK. Starts easily when choked properly, and runs about 9200 on a fat 23x6. I expected a bit more than that, but maybe the OS carb bore is smaller...

One thing I've noticed is that there is quite a lot of axial play in the crankshaft, both cold and hot. About 0.3mm (.012"). That would not be unusual on some engines set up for peak perfect at maximum running temperature, but I wasn't expecting it on this one. I don't think my Saito 62 exhibits any such play.

The bearings sound and feel clean and smooth. Could they be due for replacement?

Any thoughts on what is normal for crankshaft/bearing axial play on a Saito?

Air Ministry .:
6 thou. end float on a Commando ! . The 4 Strokes are notorious for dry bearings . Pre Lube is Std Proceedure - before use . The Oil Drian Tube set up is for flow thru , to keep em lubed .

So highly Likely inddeeeedddd that the bearings ARE SHOT . From the sound of it .

https://aerocirculairesainte.files.wordpress.com/2019/09/ic12.pdf there https://aerocirculairesainte.wordpress.com/plans/ there are Venturie drgs. 7 the Later Newsletters THERE . From the horses mouth. Beringer et. Co.

Not Operated one in a plane . However , let go of a few . The Propellors so big , when you let go IT stops & the aeroplane revolves !  ;D Well. One does wonder . Anyway .
Reg's latest Walker Mustang runs a 56 . Still authoritive thrust on the ground . The Discoverys sometimes have too .
THE POINT
being a small intake on a 72 might be enough , so you dont have to use twelve feet of propellor . Urtnowslis theorum was over 12 inch & youre in for a Rabe Rudder .

SOMEBODY was on about Wide Fuselages and tank INBOARD . Maybe Mr Zambilli himself ( in F. M . ) The Bloke with the .40 4 stroke profile at OneHunga centuries ago , the tank was INBOARD of the N V A COMPLETTELY
It did the Rich 4 stroke level , leaned off 2 stroke overhead . Maybe it might not have been two strokeing , BUT It Was ' down a gear ' ( up in power ) up there . Fuel Head level. Fuel Draw o. h. . With Tank INBOARD .

youd be wise to strip & access the 72 before it digests itself . Most R C flyers ARNT up on ' Engine Maintanace like their poorer breatheren .  VD~

https://www.     youtube.com/      watch?app=desktop&v=Ys6tWzR98iE probly plenty other Satio strip etc on SEARCH . The PRE LUBE bearings & Breather Hose CLEAR for oil circulation is a mandatory ritual .

Davids stuff ( on u tube )
Saito FA-72GK Customer Engine Disassembly
How to: Saito Engine Bearing Removal
PUT THAT HAMMER AWAY !

AFTER RUN oiling is mandatory too . ( after flying session ) Also , they wind them through backward - to ensure theyre ' clear ' . Dont Hydraulic .

so prime , pull through , 3 or six turns backward .  Turn untill AGAINST compression ( normal rotation ) Then flip back across ' clear ; so it hits comp. backward - and backfires forward - running .  :P I think it is .

The fuel in the cylinder , mounted iinverted , can throw itself into the combustion chamber . Dosnt Compress . Bent Rod & other malyadys . So check the rod for alignment while its apart , and all the other bits .
Some say a 5 or 10 x jewllers eye thing , and light . Check the ring land & ring . etc . A good find . A 72 .  H^^

Robert Zambelli:
Mr Ash: First off, you may have a carb for a smaller Surpass engine, like a 52.
Second, I hope you meant a 13-6 and not a 23-6!
Lastly, I checked a number of my engines and they ALL exhibited no crankshaft endplay that I could feel or see. Possibly a very very slight preload(?)
I would suggest not running your SAITO until you have identified/eliminated the axial play.
I will try and send a photo.
The spacer and cam drive gear determine the axial location of the bearings on the crankshaft.
If it is wrong or has been modified, the crank can move axially. NOT GOOD.

Bob Z.






--- Quote from: ash on November 22, 2023, 12:48:12 AM ---Well, I've given it some test runs on the bench and it seems to go OK. Starts easily when choked properly, and runs about 9200 on a fat 23x6. I expected a bit more than that, but maybe the OS carb bore is smaller...

One thing I've noticed is that there is quite a lot of axial play in the crankshaft, both cold and hot. About 0.3mm (.012"). That would not be unusual on some engines set up for peak perfect at maximum running temperature, but I wasn't expecting it on this one. I don't think my Saito 62 exhibits any such play.

The bearings sound and feel clean and smooth. Could they be due for replacement?

Any thoughts on what is normal for crankshaft/bearing axial play on a Saito?

--- End quote ---

Robert Zambelli:
Here is a diagram.

Air Ministry .:
Was in a Stunt News , Hoffman & his Firecracker Build .

Made the fuselage a touch wider , and considered tank should be as far inboard as you could get it .

Tecnically , side mounted , with the outer face of the tank level or inboard of the N V A ,

in level flight , all the fuel has a positive head .

dead overhead it is a negative head .

seems to work , if you set so not lean in the o. h. eights . or your doomed . the other aspect is in WIND the fuel head keeps it rich , so limits speed up . Drops the power as you go low .
2 strokes and 4 strokes . Just like the inboard tank on profiles , as a extreme example .

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