Dear folks,

A quick question without having access to the plane as we speak.

I turned the prop counter-clockwise for about 20-30 revolutions by hand and there was NO compression on the engine. After this ( and having checked that the prop/nut were tight) the engine started to show signs of compression.

This is a Saito 100 4-stroke engine as I am told... I bought the plane but not in my hands right now ...

What do you think may have been / is the issue?

Can't troubleshoot as its not in my possession as of yet.<br type="_moz" />

You should not feel the same amount of compression as you would on a two stroke ABC engine, but you should feel SOMETHING if the glow plug is in.

If the glow plug is out, you'll feel no compression at all nor any resistance.

If you are purchasing the plane/engine... don't do so until you see it running at all throttle settings.

Thanks for the quick reply. The glow plug was in the engine ... and it took 20-30 turns to feel ANY compression.

The seller had the same engine in a Hangar 9 AT6 and it had more compression than the P47 (when it started compressing)

Sometimes Saito 4 strokes seem to have little compression when turned cold but do just fine when they get hot. Especially older ones.

I have a 52 that does this but it flies well.

Tom

Thank you for sharing your experience Tom!

I will know by this weekend if the engine is working.

Your post made me feel a bit better about paying without seeing the plane run first.

G'day

I have about 14 Saitos and have had the "no compression" issue with a couple. The problem can be either that you have the throttle closed - the engine will then appear to have little compression or you have either a slightly stuck valve which is not closing properly or a small amount of some foreign matter is holding a valve slightly open causing it to leak. Also, a dry engine will feel as if it has less compression than it actually has. So will a new engine where the ring has not seated properly.

In the "closed throttle" case, all you need to do is open the throttle.

In the "stuck valve" case, I have removed the tappet covers, splashed some fuel or oil around and gently operated the valves with my finger and they have come good.

In the "foreign body" case, I flooded the engine with fuel and it cleared the problem.

One of my brand new engines did this too when I was first trying to start it. Once it was "wet" with a prime, it fired and the problem never came back.

I have had similar problems with other four strokes particularly with ASP/Magnum. I have one at the moment which has a leaking exhaust valve. It is not very old and you can hear the leak out the exhaust. I have tried to lap the valve (which has worked with other engines) but this one still leaks. It still runs though. I think I will just run it until it stops.

Hope this helps a bit.

Mike in Oz

This isn't a problem and it is felt with all brands, not just Saito. I have heard a lot of thoughts on this strange little quirk but none of them make a lot of sense. Last week it was doing that with one of my YS engines?? Started right up and ran great. Next flight it had plenty of compression?? I'm not going to repeat some of the reasons stated to me, some of them are just really stupid!! Peanut gallery reasons being stated!! Perhaps someone like Bill Baxter would come on and let us know what is really going on. I have my own thoughts but like the peanut gallery I won't state them because it could just be real stupid.

Thank you Mike.

We bought both the Hangar 9 AT6 with a Saito 100 and the P47 with another Saito 100.

I am confident that by the weekend I will have good news to report on the warbirds !!!!


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