I was just cleaning up my old trusty Saito 91 when I noticed low compression when I turn the prop over. I removed the valve covers and noticed that the exhaust side seems fine, but the intake side did not move at all. I figure stuck valve (been a hanger queen for some time).
The valve was not stuck. So I look at the push rod and it does not move at all, so I suspect, but could not figure how, the rod is broken. The rod is NOT broken, in fact it looks fine.

Any help would be much appreciated.

Jeff

The lifter or cam follower may be stuck in its bore

Quote:

ORIGINAL: w8ye

The lifter or cam follower may be stuck in its bore.

...Or, the cam lobe is worn flat...[:'(]

Yeah, could be either one of those, but more likely a stuck cam follower. I would try flowing a little penetrating oil down the push rod tube, or some fuel. Might try heating it up with a MonoKote blower or hair dryer, that might loosen it up.

Or tear it down and check it out.

Cheers,

Chip

Thanks guys, I appreciate your input. It must just be stuck, it ran fine the last time I flew, the day before my daughter came to us by the way. But now she is older and wants to learn to fly!! Doctor Z suggested a cam lobe could be worn flat, never heard of that in a Saito, but I have not heard much in a long time. Would there be a reason for the intake side to be worn flat and not the exhaust? Just curious.

Thanks again folks,

Jeff

Remember, Pay Attention not a tutor!!!!

Jeff,


A cam lobe can wear-away if it was galled by the cam-follower, as a result of improper machining, or tempering.

It can also happen if incorrect cam timing assembly was performed and the cam was forced to turn over, with a valve pressing against the piston...

Once galling has begun, the cam-lobe will keep wearing away...


A cam-lobe cannot become completely flat, while the engine is running, because with zero lift, the engine cannot run (obviously)...
With the lift diminishing as the lobe wears away, power will reduce until the engine cannot even keep idling...

Even then there will still be some lift...


As the un-experienced user keeps on grinding the engine with the starter, hoping for it to eventually start, the wear goes on until lift is zero...


If your engine ran well before it became a 'hangar queen'... it is more likely that the cam-follower is somehow stuck...

But that would hold the valve in an open position... Unless, that is, you re-adjusted the valve-lash...
I don't think there is enough room to cater for a complete loss of lift...


...I have a bachelor's degree... not a doctorate...

All this talk about the cam lobes . . . .

From my experience after having disassembled many Saito's, There is a high incidence of lifter or cam follower pitting and wear.

In my tear down and reassembly of a Saito I always plan on replacing the cam followers. (Or at least checking them) I have refaced them when I didn't have new ones. On a high time engine the face of the rocker arm where it contacts the valve stem will also have a wear indention and make it impossible to adjust the valves accurately.

The cams themselves seem to hold up well. There are areas that do show wear first are where there has been excessive valve lash and at the point on the cam where this lash is taken up, there will be a wear point. This is on the sides of the lobes, not the peaks.

There was a person on here that had a picture of a badly pitted cam lobe. I cannot remember the details but I do not remember the cause being excessive use. It was more of an improper storage situation.

Stuck lifter. WD-40.

Bill Robison had some good pics of cam wear. He had some run with castor and without, if you remember that.

I let the engine sit over night is a solution of wd-40 and liquid wrench, no good. Went ahead and dismatled the engine and indeed the lifter was stuck and stuck tight. I had to use some presuation to unstick it. It seems fine now with no pitting. Heres hoping that I can remember how to put it back together, the timing that is. The little mark on the cam goes straight up at top dead center right?

Jeff
Remember: Pay attention, not a tutor!!

Oh, I myself am an M.D., My wife just got her phd, so that makes me Mister Doctor George, doesn't it? Clear Skies everyone.

The timing mark can go up or down @ TDC it doesn't matter.

But it is a lot easier to set if you put it down. That way you can see it.

Also there is an oil hole in the intake cam lobe that aligns with the intake lifter hole when the timing dot is straight down.

You can use the small end of a push rod in this lifter guide hole to locate the cam while you set it on the engine at TDC.

The small end of the push rod goes towards the rocker arm during assembly

The valves are adjusted .002" to .004"

Quote:

ORIGINAL: skyratcalls

...The little mark on the cam goes straight up at top dead center right?

Quote:

ORIGINAL: w8ye

...The timing mark can go up or down @ TDC it doesn't matter.

Explanation, Jeff.


The camshaft rotates once per every two rotation of the crankshaft.

So, if you installed the camshaft with the timing mark straight-up and rotate the crankshaft one full turn, the timing mark will now be straight-down (Vice-versa if you start start straight-down...).
This is why either of these two exact positions is correct.

But dare not place the timing mark to either side of these two positions... The easy-to-solve problem is that the engine would just not run... The worse problem can be piston-to-valve clash...

...You don't want that, believe me...