Saito query

[David perry 1]

My son has had two separate failures of saito 180 fs pushrods now. I find this odd because my saito 180 was a beaut.

I suspect overheating but what else might cause this fault to repeat itself?₩

[Frank Skilbeck]

How have they failed, have they snapped or has the bronze bush bearing failed?

[Martin Arnold 1]

Sounds an odd one, can't really see how a pushrod can "fail", how have the pushrods failed, bent, broke, dislocated or worn out ?

[Brian Cooper]

More details are required.

It certainly is bizarre for a pushrod to fail, assuming it was straight (not bent) to start with.

[David perry 1]

Sorry, poor description. The pushrod or one at least bent.

its not my engine so i havent seen it but he says its bent. Ive seen it fly, plenty of smoke and it really didnt seem to get hot or bog down. One inverted pass and he says the engine made a clicking sound and stopped. Inspection revealed a bent rod

[Brian Cooper]

Curious.... and interesting.

Assuming the pushrod was 100% straight, it is difficult to see how it would bend in flight. However, it stands as a warning to the rest of us but, realistically, there is nothing we can do to prevent a similar failure.

Personally, I have been thrashing my Saitos mercilessly for the last 25 years or so and, so far, they have all stood up to no end of twisty-turny, high "G" flying.

How old is the "naughty" engine?  And has it suffered any crash damage in the past, or been rebuilt? 

Edited By Brian Cooper on 15/01/2021 09:38:33

[David perry 1]

Indeed Brian...as i say my own Saito never faltered.

This unit is less than six months old.

Makes me question manufacturing...

[Engine Doctor]

For a pushrod to bend something has to tighten up or run out of alignment. Have a look at the valve gear train from the followers to rockers and the valve guides. You say plenty of smoke from exhaust? That could mean oil has carbonised onto he valve stems causing them to stick if using castor based fuel. What fuel / oil was your son using ?

Like others I have had Saito engines that have run for hours and been thrashed mercilessly and never missed a beat.

[David perry 1]

He was on synth fuel no castor. Technics i think...pink stuff, smelled like a french knocking shop. Probably.

[Martin Harris - Moderator]

What size prop was he using - could he be over-revving the engine?

[Martin Arnold 1]

As everyone seems to have said, more info is needed, David you said "The pushrod or one at least bent" which one was it inlet or exhaust ? Where on the pushrod was the bend ? Was the pushrod unseated from the rocker arm on inspection after the motor stopped ?

[Jon H]

My suspicion is the valve clearance caused it.

If the clearance was quite large the pushrod might have jumped out of its adjustor and got wedged or it got stuck under the rocker and drove the valve into the piston. If it was the latter i would expect a fair bit more damage though so its probably the former but in either case, the rod could bend as it has nowhere else to go.

A clubmate had this happen to his engine (a 100? cant remember) but the rod didnt bend, it just jammed the valve open so the engine stopped with no other damage.

Martin's point about rpm is very valid in this case as a wide clearance with a bit of valve bounce, or perhaps a weak/broken valve spring would be contributory. A broken valve spring could also be the cause all on its own.