spaceworm

Could it be that after the engine fully warms up, that the 0.002 clearance is reduced to less than zero and the valves are held slightly open? Would this account for the DROP in WOT rpms over the "supposed" to be initial clearance of 0.004? Or, does the clearance increase as the engine warms up? I don't know the answer to this, but I am curious.

Richard/Club Saito #635

mike early

The pushrods expand when hot and close the gap. if they are too tight, the valve will not seat and that's all sorts of bad.

Hobbsy

My Feedback: (102)

Hey Richard, the thing is we don't know the thermo dynamics of the engine, for example, we don't know if the pushrods get much heat from the cam area on the Saito. They are out in the breeze on most applications even in a cowl. The valve stems are not long enough to expand and contract much in differing temperatures. Compared to the cylinder temperature variances in fkight the pushrods are probably pretty stable once at their operating temperature. The cylinder length probably changes quite a bit because its aluminum but the pushrods are shorter, so, I choose to let Mr. Saito make the rules.

mike early

Manufacturers are always conservative....for a reason. Sir Bill Robison knew what he was doing.

hsukaria

You guys are going to spark another Inquisition!!

spaceworm

The 1.25 has been the specific subject of this discussion, but is the valve clearance issue applicable across the entire range of Saito engines?

Another thought: how about someone making the valve covers quickly removable on a Saito (1.25) engine, run it at WOT for long enough to stabilize the temps, then measure the valve lash compared to the original cold setting? I would, but I don't have a 1.25 (yet) and I don't have another Saito set up to run on the bench right now.


Richard/Club Saito #635

Hobbsy

My Feedback: (102)

If Saito cams have acceleration and deceleration ramps then running them too close defeats this. Bill could not quite determine whether they did or didn't. For those who might not know, these ramps gently lift the valve at first off its seat and then gently set it back down so it doesn't bag shut. By the same token setting them too loose also defeats this feature.

clytle374

I'd bet Saito says they need more gap than they really do for one reason, you can NOT trust the end user to do things properly and they don't want engines returned because people set improperly.

I'm also confident that the gap increases with heat. The aluminum cylinder expands more per degree than steel, and the aluminum definitely runs hotter than the steel push rods.

I just looked it up and Saito says .002" to .004" in the book I have for the 100. IMHO this means that Saito engineers believe that .001" to .005" won't hurt it, if they did any research on people using a feeler gauge.

Cory

earlwb

it is hard to say but I think the gap tends to close up with heat. The valve stem gets slightly longer when hot. The pushrods tend to grow in length as well. Not a lot because the engine is small. But the gap would close up slightly when the engine is hot.  Granted the cylinder grows a little bit longer too.  but I don't think it is enough to offeset the gap closing up a little bit.

clytle374

The cylinder and pushrods both mount to the block at almost the same place. If they heated up the same amount the cylinder would still get longer than the pushrods because aluminum expands faster than steel.

Aluminum 12.3 (10-6 in/in oF)
Steel 7.3 (10-6 in/in oF)

The aluminum is outrunning the steel quickly.

Cory

mike early

Good point. Even more reason to use a tighter tolerance when cold, perhaps.

Hobbsy

My Feedback: (102)

.004 has worked well for me for 22 years so I think I'll stick with it. I do run Enyas at .002"

clytle374

Anyone know what the valve lift is on a 100? Been wondering if .002" is a significant percentage of lift.

w8ye

My Feedback: (16)

All the Saito singles 62 through 125 have the same cam and rocker arms so the valve lift would be the same.

hsukaria

I'm considering purchasing a used Saito for a Sig Rascal 40. I just had a Magnum 52 RFS on it, but was not enough power to call it a sports plane. What would be a good Saito candidate? Realize that the Rascal 40 has a wood cowl integral to the fuselage, so I can't go too big.
Thanks.

clytle374

As long as the valves get bigger, Anyone know what it is? If not I'll measure it tomorrow.

A quote from Bill's article.
Gotta like the guy for mentioning using cigarette cellophane for setting lash, I sat tools on cnc mills that way for years.

w8ye

My Feedback: (16)

Try Bill's valve lash settings? The engine will not idle for toot and the high speed will be weak.

.002" cold is about it.

Rudolph Hart

I don't think you could go far wrong if you stick a used 62 in it providing it will fit,they rev really hard.

Rudolph Hart

I read what bill said and thought he may have said it back to front meaning .0005 was hot and vicky verky so to speak.Anybody here get stuck on the low speed needle because your engine idles and transitions so well then wind the heck out of the main to get a half decent top end?

clytle374

I'm not going under .002", I'm just wondering since I was lazy and used the stock gauge and I think it's on the very thick side.

Cory

Hobbsy

My Feedback: (102)

It is exactly .004" and Enya's is exactly .002, I miked them both.

OF, if you attach the prop to the HS needle and wind the heck out of it, it might have more power than the crankshaft.[8D]

Hobbsy

My Feedback: (102)

The reason Jim alluded to the ragged idle and weak top is that running the lash too close causes the valves to open sooner and close later. This would be fine if the load were reduced and the engines ability to breath were enhanced and it could turn higher rpms. This engine is a 1.20 ABITAR, the recommended prop is a 14x6 in lieu of the normal 1.20 sized 15x8. On 10% Wildcat it turned an APC 14x6 at 12,180 rpm. With four valves and bucket cam followers it was set up to rev and breath at those revs.

charlie1960

.001 works for me.
just my nickles worth.

clytle374

I just miked mine since .005" was stuck in my head, but calipers was all I used before. Mine is .004" on one end, and .0055" on the other.

Cory

Hobbsy

My Feedback: (102)

Cory, check the thick end and and see if the edges are ragged from the stamping process. I bought NAPA stainless guages removed the .002 and .004, in fact I cut them in two also.