Saito 100 stuck exhaust valve - RCCanada - Canada Radio Controlled Hobby Forum
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Old 05-17-2017, 07:18 AM   #1
Lieutenant Dan
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Saito 100 stuck exhaust valve


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Recently Acquired this Saito 100 with low compression wasn't run for a while seems to have not not have high time...the exhaust valve as you can see in pic is stuck open ..Tried soaking valve overnight not loosening yet ....I'm thinking heat from the heat gun and pull the head off completely? The side screws holding the mechanism are butcher tight too.
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Old 05-17-2017, 08:21 AM   #2
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Re: Saito 100 stuck exhaust valve

What are you soaking it in? I use automatic transmission fluid. Oil both ends.Try prying gently with a small screwdriver. Once it starts to move, keep oiling it and moving it. I have also used spray bomb carbon remover from Canadian tire.
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Old 05-17-2017, 08:35 AM   #3
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I was just spraying wd cleaned that out now and used a chemical from the states called. Piston Clean aluminum friendly and amazing on my vintage motorcycle pistons. Nothing moving as yet I'm almost thinking of taking the retainer off and spring out then replace retainer and gently pry up on that maybe
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Old 05-17-2017, 08:55 AM   #4
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Re: Saito 100 stuck exhaust valve

Great engines, (have 4 at last count). That and the 125a are my favorite 4-strokes.

That is pretty common if the engine sat during storage with the valve held open. Carbon and other contaminants can collect on the stem, valve face and seat and harden over time.

Best method I found to free it up without disassembly is to soak that area in raw fuel or methanol, (available in any pain department). You have to ensure that is completely submerged during the entire duration. May take a day or more.

WD will likely not work and others same chances. You want to use the same stuff that contained the lube and other compounds in the first place. Methanol forms the majority of the fuel so works very well in softening and cleaning it out.

You may be able to press on the end of the valve to help free it enough for the spring to return it to full closed after soaking. However, you MUST ensure the piston is at the bottom before doing so to prevent the valve from contacting the top and possibly bending the stem.

If you feel energetic you could pull the jug and drop that into raw fuel or hot glycol, (a subject for discussion all its own) but it takes some knowledge and experience to reassemble it correctly and at that point I would keep going and check the rest of the valve train.

NOTE 1: The spring can break or at least weaken over time. The exhaust is under much higher thermal stress and can suffer for it. Same with valve retainers and I just fixed an OS 120 I got with one that came apart.

NOTE 2: Ensure the rocker retaining screw center to the second pic does NOT move with the rocker. That should lock in the head boss and if not the bosses will wear rapidly. If that occurs the only option is an entire new jug assembly. That may be Loctited to the inner boss, but even a heat gun should soften it up enough to remove. A good driver should work in the slot without damage.

If you suspect the valve spring is weak you can order the spring and retainers for both.

Once you have the valve operating normally check the valve lash. I normally set mine to .001-2" on all my 4-strokes and they work fine. Do that at the beginning of each season and depending on run time once more part way through.

ps. From your pic the spring does not look corroded, the other negative that can weaken the spring. You have a good chance of normal service after freeing it up.
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Old 05-17-2017, 09:27 AM   #5
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Thanks for that wealth of information. Well used my piston clean and then the trans fluid as suggested and viaola and a few turns she popped right up and a little gentle pry. I'm letting booth soak a bit while doing other stuff today and will check clearance? as suggested. I'm hoping the plug threads going to be ok they seem a little tight ...
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Old 05-19-2017, 11:48 AM   #6
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Re: Saito 100 stuck exhaust valve

In addition to the above, I use a heat gun to free up a sticky motor. If not given a treatement with after-run oil, an engine sitting for a long time gets gummed and seizes solid. Heat gun and the use of more ATF oil/your favourite solvent gets things freed up in no time. Then dismantle and give a good cleaning.
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Old 05-19-2017, 11:53 AM   #7
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Yes last night cleaned it out and put the covers back on and she fired right up . Seems like the power is very nice too.
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Old 05-19-2017, 01:58 PM   #8
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Re: Saito 100 stuck exhaust valve

I've also used seafoam, take the valve cover off and fill the valve spring cavity with s/ foam, let sit for a while.
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