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Old Apr 14, 2008, 09:22 AM
Still a noob
London
Joined Mar 2008
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Saito 82a 4-Stroke Compression question and starting prob.

When I turn over the engine by hand there is virtually none (compression) I hear the piston rising but there is virtually no force needed on the prop to do it.

Is that how it is? (I'm new to glow) If memory serves this is how it was when I installed the engine anyway and it did run fine.

I ask because this is a new engine and after running it in (3 tanks, rich, 100% by the manual, used an optical tach) it no longer starts.

I have changed all hoses, plugs, reset needles to factory settings, blown through fuel hose to get small air from low end and more from high end. A tip I read here actually!

Glow start is good, fully charged etc.

I've tried everything I can think off to get this thing started.

Using an electric starter so any help on this would be great because I'm really starting to wish I stayed with Electric

Cheers Guys,

Alex
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Old Apr 14, 2008, 10:02 AM
Registered User
United States, TX, Weatherford
Joined Dec 2006
1,635 Posts
Well, is the glow plug any good? I have had glow plugs in four strokes get fouled in the second or third time I ran it because the oil content was so high. Had to keep the glow ignitor on just to keep it running, it was running so rich. So if it is not starting, your glow plug may be dead, open, or so coated with burnt oil it can not function.

Back to you original question, low compression. Since it is a four stroke, did you check the valve (tapet) clearance. If the gap has opened up, then the timing is off. Take the valve tappet covers off and check the clearance. Saito usually gives you the little feeler (go, no-go) gauges to make this adjustment. It also supplies the wrenches and the instruction manual gives the instructions on how to do this procedure.

Four stroke engines almost all have rings, and rings need to run in, or set, so to speak. Since our little four stroke engines use the "lost lube" process, where the lubricatiion is in the fuel - the oil - the ring gap is pretty large to allow by pass of fuel (thus oil) down into the crankcase to oil up the crank pin and bearings. There is a vent on the back of the back plate that allows the old oil to escape.

Because of the big ring gap, the new engine usually has very low compression but runs. As the ring sets, the compression goes up. Sometimes after a prolong period of non use, the compression goes down until the engine is run and oil seals up the piston/ring/sleeve assembly again.

Cheers,

Chip
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Old Apr 14, 2008, 10:28 AM
Still a noob
London
Joined Mar 2008
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Thanks, I did change the glow plug, first thing you do

I'll set the tappets and see how that goes as I know they need adjusting after an hour or so's run time.

Would that stop it from starting altogether though?

Thanks for taking the time,

Alex
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Old Apr 14, 2008, 10:41 AM
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If you have no compression it will not start. You need to determine why there is no compression. Make sure you are checking it with the carb open. Many four stroke engines will appear to have no compression with the carb closed.

Chances are a valve or cam follower is stuck.
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Old Apr 14, 2008, 11:14 AM
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Thanks again guys,

Well, I have adjusted the valve clearance and I now seem to have a decent compression stroke

I'll let ya know if it starts later...


Alex
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Old Apr 14, 2008, 12:05 PM
Still a noob
London
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It's running

Turned over first go and just needs tuning now.

without this place and the guys here I'd have been lost.

Thanks so much, now all I have to do is maiden her and hope all is still well after that

Alex
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Old Apr 14, 2008, 12:21 PM
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It's pretty unusual for the tappet clearance to tighten up like that.
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Old Apr 15, 2008, 07:22 AM
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I have to agree with you bro. It seems very unusual to adjust the tappet valve clearance just after 3 tanks.I only adjusted the tappet valve clearance at a rich setting after a gallon of 15% nitro. Since then, I have not adjusted it at all. I have been running at least about 3 gallons of nitros since then and the Saitos will always starts on the first flip
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Old Apr 15, 2008, 07:35 AM
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I could see loosening up so that the gap is larger but tightening up so there is no clearance makes me worry that there is dirt or something inside.

Greg
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Old Apr 15, 2008, 08:12 AM
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I've seen Saitos that got loose (in the valve train) and kicked the pushrod out of the little "cup" in the valve adjusting screw on the rocker arm. From there, it tends to hang the valve partially open.

That'll give you a sudden loss of clearance, and zero compression. On the spot.

Not saying it happened in this case...but it's a possibility nonetheless.
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Old Apr 16, 2008, 05:42 AM
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Swindon UK
Joined Sep 2005
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This past Sunday, I found my Saito 82a had no compression. I removed the rocker covers and found the exhaust pushrod was out of its cup. I put it back in and still had no compression.

When I got it home, I found that the exhaust rocker was not moving at all when I turned the crank over. I stripped down the engine and found that the exhaust cam follower (called tappets in UK) was stuck in its guide. It took a little effort to remove it. When I did, I found that there was a burr on the end of the follower / tappet. I filed it off and it now runs smoothly.

I am very disappointed that this fault occurred. I had always thought of Saito as very high quality engines. Perhaps there was a bad batch Alex?

I now need to re-assemble the engine and I am having difficulty getting the timing right. I guess that the factory and engine maintenance guys use some kind of special tool. Does anybody have a source of information to help me get the timing right?

Cheers

Nick
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Old Apr 16, 2008, 06:40 AM
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Inspect the valve adjusting screw "cup" with an eye loupe before putting the motor back in service. If the pushrod came out....it tends to destroy the edges of the cup. It's brittle. Heaven knows where the metal bits go.

Getting the valve timing correct: It's really too early for that, but here goes in a nutshell.

1) Crankpin at TDC. Assuming the jug is off....I use a rubber band to hold it in position.

2) Cam gear timing mark at BDC. I made a .030" plastic shim with a channel cut in it to engage the teeth of the gear, and allow assembly of the cam cover without rotating the gear. When the cam cover is in place...slide the shim out, and the timing gear *SHOULD* be in the right spot.

3) Installing the pushrods: Make sure the pointy end is UP.

Perhaps I TOBOR has some photos of his procedure for same. One picture is worth a thousand words.

CV
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Old Apr 16, 2008, 07:34 AM
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Remove the cam followers when installing the cam onto the crank housing. If you set the cam gear with the timing mark down and look into the follower bores you will see a hole in the cam. Make sure it is centered on the bore as you install the cam assembly. They undoubtedly have a tool that slips into the bore and locks the cam in place during this step. There is only one hole, and right now I can't remember if it's on the intake or exhaust cam, intake I think. Regardless, if the dot is facing down it will be very clear.

Tappets hang up often. I bought an a Saito .80 off Ebay cheap. When I got it, it had no compression. I contacted the guy and he was really good about it and offered a few bucks for any needed parts. I freed the corroded follower and polished it, and replaced the bearings. The engine runs great.

Engines occasionally have problems. Minor problems don't bother me. When I can't fix it myself, it's a problem.
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Old Apr 16, 2008, 05:30 PM
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Quote:
Originally Posted by Nick Reffold
I am very disappointed that this fault occurred. I had always thought of Saito as very high quality engines. Perhaps there was a bad batch Alex?
Nick
I had a saito FT60 twin with which I just couldn't seem to keep the tappet clearances adjusted. It turns out that the camshaft was BROKEN in half at the rear support bearing. Replacing the cam fixed the problem. It's a wonder that the engine ran at all under the circumstances.
The instructions clearly state: "Avoid unnecessary dissasembly of your engine." Makes one wonder what the best course of action should be when something doesn't seem right.
BTW, I dicovered this fault long after the warranty had run out.
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Old Apr 16, 2008, 05:37 PM
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XJet's Avatar
Tokoroa
Joined Mar 2004
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Quote:
Originally Posted by gkamysz
Remove the cam followers when installing the cam onto the crank housing. If you set the cam gear with the timing mark down and look into the follower bores you will see a hole in the cam. Make sure it is centered on the bore as you install the cam assembly. They undoubtedly have a tool that slips into the bore and locks the cam in place during this step..
Last time I worked on my 100 I used the tapered end of a pushrod to position and hold the camshaft (there is a small hole into which it goes) while the cambox was reassembled. That's the way lots of folks do it -- no special tool or shims required.
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