WacoNut

Hi Guys,
It has been a long time since I have messed with setting the valves on a 4-stroke and I do not remember the best clearance for the rocker arm gap? It is an old OS 61FS. I am getting ready to replace the bearings in this engine and get it back into flight condition. Any help would be appreciated.
Thanks!!
Anthony

ThumbSkull

My Feedback: (57)

.001-.003" generally speaking on valve clearance.

Ernie Misner

The clearance gets greater as the engine gets hot, just the opposite of many automotive applications. So you don't need much at all.

Ernie Misner

WacoNut

Thanks for the replies. I should get the new bearings sometime this week and I will tear into it.
Thanks Again!!
Anthony

Hobbsy

My Feedback: (102)

Its .004" for a Saito and that's what the guage is that comes with the engines.

Goinstraightup

My Feedback: (26)

Saito's really purr when set to .002 [8D]

Ernie Misner

It's interesting that on our model engines the intake and exhaust are set the same. Automotive exhaust valves need more clearance usually because the exhaust runs so much hotter than the intake on gasoline. What about the gasoline Saito's, still set the same?

At .002 they have a hair more duration. You definitely don't want to get zero clearance somehow and burn a valve though.

Ernie Misner

SrTelemaster150

I do mine @ .0015"

Hobbsy

My Feedback: (102)

Ernie, in my opinion the valve stems and the push rods are not long enough to expand or retract a measurable amount. No harm will come from doing it the way the engineers who designed it say to do it.

ThumbSkull

My Feedback: (57)

The head is aluminum, the pushrods, etc are steel and cooled in the propwash. The aluminum head expands while the pushrods do not.
As engine temp goes up, the gap increases, not much but some.
Remember we use silicone exhaust diverters on glow engines and they are good to around 500 degrees, and that's well under any temp that a valve would burn at or even glow hot.
As long as you have some actual gap, it will be fine.

Hobbsy

My Feedback: (102)

Actually the push rods, unless made of some backwards engineered exotic metal do expand when they get hot, they are not immune from the physical laws of nature.

ThumbSkull

My Feedback: (57)

In their location, the pushrods do not get hot until the engine is shut off.

littlera

WacoNut,

I still have the gages supplied with my old FS-61. The "no-go" gage is 0.01 mm (.00394 in.) and the "go" gage is 0.04 mm (.00157 in.) Therefore, the correct setting is less than .00394 in. and equal to or greater than .00157 in.

OS used to supply the feeler gages with every four stroke engine - before they got stingy.

As a practical consideration, I try to set the valves so that the thinner gage will just pass through the gap. As the valve train wears at all of the contact points with run time, the cold valve clearance will increase. This is most noticeable during the break-in porcess as the wear points in the valve train (cam, cam follower, push rod ends, etc.) I find that a correctly set engine will progress to the point the valves are out of clearance tolerance in the first 1 - 3 hours of running. Reset, and they will tend to remain in tolerance for a long time - maybe a year of normal use. Subsequent adjustments will last much longer as the engine becomes fully broken in.

I believe these same gages are applicable to all OS four strokes, and all Saito four strokes I have had have carried the same 0.01 - 0.04 specification, although Saito to my knowledge has never supplied a set of gages with an engine.

Hobbsy

My Feedback: (102)

Actually a .004" guage comes with every Saito as part of the tool package, this is the tool set that comes with 1.00 and under singles, 1.25 and larger comes with a 12/14mm wrench in addition to what you see here.

littlera

It has been a while since I bought a Saito. Looks like they are getting more generous as OS becomes less so. Odd.

By the way, I should have stated that the OS gage is 0.1 mm, not 0.01 mm. The convresion to 0.00394 is correct, however.

Hobbsy

My Feedback: (102)

Actually Saito used to be more generous, my 1991 Saito 1.50 came with a 17mm open end wrench, a 14mm box end and the above mentioned 12 and 14mm combo wrench.

SrTelemaster150

Saito recommends .1mm (.00394") to .04mm (.00157") valve lash.

The feeler gage Saito sends is actually .1mm & is a maximum gap.

I think they use .04mm as a minimum because it would be impractical to use anything less in a feeler gage.

The aluminum cylinder WILL expand more than the steel valve train even IF they were @ equal temperatures which they are not when the engine is running. The cylinder /head assembly will be much hotter than the pushrods/valve train when the engine is running.

ANY clearance when cold will increase as the engine gets to operating temperature.

Case in point: The old Harley Davidson big twin had a (solid lifter) valve adjustment procedure when cold of taking up the lash until the pushrods could just be spun W/slight drag W/the fingers. In other words, as near to .0000" lash as possible. The cylinders, even though they were iron, were greater in mass than the (sometimes aluminum) pushrods/valve train & would run warmer when operating thus the lash would increase as the engine reached operating temperature. The greater mass will expand more than the lesser mass @ simlilar temperatures even when made of the same material.

In the case of Saito engines, not only is the cylinder/head greater in mass, it is made of a material than has a larger expansion factor than the valve train.

Theoretically, the engine will run just fine W/.0000" lash cold as long as the valves are not held off the seats. As the engine warms to operating temperature, valve lash will increase.

Setting the lash @ the recommended minimum of .00157" (.0015 is close enough) will result in more power & less cam lobe/tappet wear.

I set valve lash on my Saito engines W/slight but noticable drag on the .0015" feeler gage AFTER THE ADJUSMENT IS LOCKED DOWN. I check for a slight "wiggle" in the rockers to assure that there is some (minimal) valve lash.

SrTelemaster150

Since I have a drawer full of all of the above, I would like to see them drop $10 from the price of the engines & ship them W/O tools. Sell the tool kits as an "accessory" item.

Hobbsy

My Feedback: (102)

Obviously you guys went to a better school than the Saito engineers. The pushrods probably run hotter than the cylinder since they are protected from the airflow and get heat from both ends, especially from the the exhaust rocker.

Guys grpie becdause OS fourstrokes don't come with tols so I'm sure they would gripe if Saitos didn't

SrTelemaster150

What are you talking about?

Saito engineers recommend .00157" valve lash. They send maximum valve lash feeler guages for the "Primitive Petes" that would probably have a hard time setting valve lash to their minimum recommendations.

If you want to set your valve lash @ the maximum recomended spec, then good for you.

If you think a pusrod that is in front of the cylinder gets hotter than a casting that is containing combustion I would like to know how that heat is migrating from the hottest part of the engine & picking up more heat in the prop wash.

Through the exhaust rocker? I'm sorry, but that thinking is just plain ludecrous. IMO

It can't possibly be hotter, & even if it is the same temperature, aluminum expands a lot more than steel @ ANY given temperature.

If those guys that gripe because of a $10 savings due to the elimination of redundant tools (for those of us that already own Saito engines) would just take that savings & buy a tool kit as an accessory, they would them be happy when they buy their 2nd Saito engine & pocket the $10 savings.

SrTelemaster150

Double post deleted.

WacoNut

I have feeler gauges in sizes from .0005 to .030. I will set the valve gap at .0015

Thanks for all the tips and advice and I didn't intend to open up a can of worms
Anthony

SrTelemaster150

It's a can of worms that need to be opened & clarified.

So many people are confusing .04mm W/.004".

SrTelemaster150

If these guys would stop setting their valve lash @ the maximum spec, maybe they wouldn't (feel the) need (for) castor oil to prevent cam lobe wear.

Hobbsy

My Feedback: (102)

If you looked at my micrometer above you can see its sitting dead on .004", if I put an Enya guage in there it reads .002"

I took this cam out of a then 20 year old Saito 1.50 thinking it was worn out, turns out the new one is exactly the same. Note nearly flat side on cam, I thought that was the result of wear.