rscarawa

Since I do not see an engine discussion forum, I figured I would post this here.

I have a Saito 91 that is about 6 years old and I noticed it does not have the power that some other's have. I did some rpm comparisons on many props just for some benchmarking and I always came up about 300-500 rpm short of other Saito 91's. This engine has about 15 gallons thru it (Omega 10-15%) and I also noticed that the compression was becoming weak on occasion.

I removed the cylinder liner from the crank case, pulled off the rocker arms and the exhaust. I blew into the cylinder and heard air coming out the exhaust side due to the valve not seating. I pulled that valve out, and it had a light amount of carbon on it. I cleaned it with a razor gently on all areas except the seat and the stem where it enters the guide. Then I rubbed it with a scotch brite pad until the carbon was thinned and shiney. I placed the valve back in the engine and all my compression came back.

Yesterday I had the opportunity to go flying and did the same rpm checks. I noticed that across all tested props, I got a 200-700 rpm increase. The props that tended to turn lower rpm had the least improvement.

Just an FYI is you burn castor oil.

Scot

Deadeye

Thanks for the info. I have also heard of guys using pencil eraser to remove the carbon. I cannot vouche for this method, however, as both of my 4 strokes (Saito 100 and Magnum 91) are too new yet. I would think a plastic brush on a Dremel would work well too.

rscarawa

I think the plastic brush would work well too. My guess is that if you run total synthetic oil, you would avoid these issue. I just feel more comfortable with a littel castor in the mix.



Scot

wcmorrison

My Feedback: (2)

It appears you did a valve job. You must be very careful as the valve faces are very small and delicate. I would shy away from a Dremel even with a plastic brush. Take it slow and avoid the risk of permanent and fatal damage. After six years and still getting the performance is great.

Cheers,

Chip Morrison

campbec

My Saito instruction manual states that the warranty is voided if you use castor oil. Mine run perfectly on 20% Coolpower Oil, 10% Nitro and 70% Methanol. When I adjusted the valves on a 90 (about ten years old with lots of work) I removed the valves to check for carbon build up and they were clean (albeit discoloured).

Cheers,

Colin

rscarawa

The Saito warranty is not voided for using castor. It states it is voided if you use 100% castor oil. Omega fuel is only 30% castor and 70% synthetic.



Scot

SDR-Hammer

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