Creaking Saito

I've started to strip the Saito 125 that I was going to use to power the Hannibal. The engine creaked and was stiff to turn over. In order to get the cylinder off I had to cut down a standard Allen key. The four screws finally let go and I removed the cylinder. The piston was unmarked and the ring was free and undamaged. I took off the piston/con-rod assembly and straight away found the cause of the noise and stiffness. The con-rod, pin and piston are stuck fast, totally impossible to move the piston on the pin with my fingers. The plastic (PTFE?) caps on the pin wouldn't budge. I heated the piston thinking that I might be able to drift out the pin by using a piece of hardwood dowel.and a wood block with a clearance hole in it. I gave the heated assembly an experimental wiggle, but even though very hot it didn't move. I reheated it and there was a sharp cracking sound followed by the sound of something hitting the shed wall. It was one of the PTFE caps. I'm leaving the stuck piston in WD40, a few days might free it up.

Brian, I have an ultrasound cleaner which I use to unstick things. I put the item (e.g piston assembly) in a jar of kerosene and drop the jar into the water bath of the ultrasound cleaner, apply heat and vibes and the bits usually come loose. You are welcome to try it if you get nowhere.

Thank you JRI , if I can't get the pin out with heat and wiggling, I'd like to try your ultrasound kit. So far the pin has been moved about 2mm with a lot of heat and gentle tapping . I had to stop when the torch ran out of gas. I'm hoping that whatever is causing the seize up doesn't damage the mating surfaces, a new piston, pin and con rod costs quite a lot.

Fossilisied castor oil usually, it will soften but give it time!

Brian - If you need new bearings, following company are worth contacting, good prices
and super service :
ARB Bearings - Ferndown Ind Est - tel 07793 290625 - Web www.arbearings.co.uk
Hopefully you will not need their services.
Colin.

Thanks Colin and JRI, the engine is a bit of a mystery, there were rust spots on the crank web and the exhaust valve wouldn't close due to a big flake of rust. I've got most of it off with toothpicks, cotton buds and lots of WD40. The rusting is very odd. One screw holding the cylinder was very rusty the other three were perfect. Three screws holding the back plate were rusty, one was perfect.. Fortunately the cylinder bore and piston are unmarked, and the bearings are clean and turn smoothly. When I stripped the engine I found that the magnet holder on the prop driver hadn't been tightened, and the fixing for the sensor wasn't too good either, In a way its lucky that the engine didn't get fitted, it might have run, but not for long before the ignition system failed.

The gudgeon pin is out at last. The pin had some dark marks on it and fortunately, the bore in the con rod was OK. Cleaned the marks off the pin with fine Scotchbrite, cleaned the bores with WD 40 on a cotton bud. The pin was an easy fit in the piston but was impossible to push into the con rod by fingers alone. It appears that the seized con rod is a common fault with Saito engines, the usual failure being at the big end of the con rod. Re-fitting the pin to the con rod took a while. I mounted the pin on a long bolt secured with a nut. Holding the bolt in the chuck of a battery powered drill and using plenty of oil, turning the pin at low speed finally enabled the con rod to go on to the pin, it was extremely tight and the con rod heated up very quickly.It took about half an hour to get the pin turning freely. Now the pin can be pushed into the con rod, its firm but shows no sign of sticking. A lot of oil was used, it turned black after a couple of minutes, blotting up the blackened oil with kitchen paper and adding fresh oil kept it from getting stuck again. Now I have to re seat the valves, I poured some oil into the cylinder and overnight it has all drained out.

You have probably succeeded by now with the piston pin.

I would've suggested warming the con-rod in an oven or much to my wife's disgust a saucepan of oil at high temp and placing pin in a fridge or cool area for a while. Then insert. A common method (rather than force pushing it in) to heat up car and bike pistons to assist with removing the gudgeon pin, albiet these are also held in place with circlips too. Reverse to refit.

I know what you mean Phil, but the method is more suited to fitting bearings. The pin has to be free to move in the con rod, there's a cross hole in the top of the rod, it must be there to allow oil to reach the pin.

For info Brian

your namesake from down under, engine master "Winch" has written many articles about Saito motors including the Gas units. He has made reference to several suitable 2 - stroke oils, in particular
www.deluxematerials.co.uk/gb/rc-modellin...t-5060243901484.html
Because your motor uses several plain bearings, i think you should be using ITRO 20:1 mix.