Rudolph Hart

Hi dave if the engine is inverted the muffler will be pointing straight down ?

ALO 111

Correct,that's how it was and I don't run mufflers it's just the pipe.

SkyPilot101

Hydrolic lock, Why are you using a starter on a 125 four stroke, inverted to boot ? Learn how to start this engine with the backflip method, it's a dependable way to start four strokes.

ALO 111

Respectfully if you read through this entire thread I think it's apparent that it was not hydro lock.

the pope

Surely a hydro lock would show more damage than just the cylinder blowing off . I think it was a dud from the get go . Cheers the pope

1QwkSport2.5r

Thats what I've thought all along.

SkyPilot101

Respectfully... I Disagree !

I find it amazing that someone could make such a detailed evualation from a single picture of a cylinder, even if the OP disassembled the engine and photo'ed the internals, it might still be hard to determine the actual damage unless the parts were "in hand" photo's only show so much.

Hobbsy

My Feedback: (102)

Saying there would be more damage than is apparent is like saying that a chain will break at places other than the weakest link. For the cylinder to break instead of the crankpin or the rod just means it gave up first. It's common sense and easy to accept. A hydo lock is the most logical explanation. Even with a casting flaw it would require an unusual event to break it.

blw

My Feedback: (3)

Dave, people underestimate the pressures involved when an engine is hydrolocked and turned over with a healthy starter.

the pope

I think we need to get a constipated mathematician ( you know they could work it out with a pencil ) to give us the guts of the matter . It would be interesting to see the pressure required to blow the top off a healthy jug I imagine would be pretty big . Has anyone studied the fracture for tell tale signs of a flaw . This could have been discussed before but my memory is shot from to much of the good gear in my younger days ! Cheers from the fractured pope

ALO 111

The motor ran then died, started and ran four about 3 to 4 storkes then popped, so it blew while running. I have inspected the motor in great detail and there is no other damage, the crack shows signs of bad molding. I studied a fair bit of metal fatique and corrosion when i did my trade " helicopter fitter and later flight engineer"
By the way who is OP ???

the pope

OP is original post or something like dat . I would have thought that it would have been easier to put a dent in the piston or bend a rod rather than blow its top but ya never know . Cheers

ALO 111

So do i, how come one replys to the OP and then refers to Him as OP when you already used HIs Quote ? Strange I would think it more polite to use the OP,s name if your are already using His Quote.

Gizmo-RCU

My Feedback: (27)

I go with Hydro-lock. Hydrolocks exert tremendous pressures which is who there so many commercial uses for those systems. A shop once took apart one of my Caterpillar blade cylinders to replace the seals. The inexperianced
worker used 5 lbs. of air to push the rod/piston assembly out of the cyl. and did not restrain it. it shot about 20 feet across the shop hit the wall doing damage and came to rest undamaged it's self. He almost got fired over that stunt.
The part weighed about 75 lbs, and it only took 5 lbs. of air............
I suspect the break was in the weakest area of that engine and a lean condition may have assisted in the situation as I have had lean 4 strokes kick back violently!

blw

My Feedback: (3)

What may help is to have pictures of the piston top, con rod, crankpin on the crank, and more shots of the cylinder head.

OP is a very common term or shorthand used by almost everybody.

Hobbsy

My Feedback: (102)

The pressure at kick back is very high since it can undo the tightened prop nuts and even break prop blades in a hurry. This prop blade sheared off during a kickback caused by me having the timing set 40 degrees BTDC instead 35 as I had intended. When you think about that kind of pressure and the number of square inches inside the cylinder that the pressure had available to act on, you can see that happening. This is the second time this 1.50 has sheard off a prop blade during a kick back. It one of the first 1.50s manufactured and had in the neighborhood of 12.56 to 1 compression ration.

wingbolt

My Feedback: (5)

My saito 150 made a very loud bang last year as I went full throttle straight up to do a little roll at the peak. Got it down ok ,case cracked sent it to Horizon H. $235. Was fine after repair but I am presently having trouble with this same engine, stall stall otherwise the 150 is a good starting/running engine. Had trouble with the 125 and couple of 180`s (breaking in) good luck.....

willig10

To the op. If it was hydro lock the connecting rod will be bent, period. Looking at the break at the cylinder base if the metal is pourous it is a bad casting from manufacture. Since the engine is an older engine, although new it is probably going to be on your dime to repair.


good luck

Glenn

THERCAV8R

My Feedback: (283)

Sorry you are in south Africa. Here in the states we would send it back for warranty issue. Your Importer may be not be supportive but it is still a warranty issue and he should replace or repair the engine. That being said what kind of starter do you use because if it has enough torq to blow the cylinder off ANY engine I want one! Something else happened to cause this.

Javier-RCU

My Feedback: (6)

Some years ago i had same issue with a OS 120 fs engine. It exploded short after break in. The cause? some months before the engine fell off from my hands over concrete when nib while i was showing it to my buddy. I donīt saw visible damage at the time.

Proptip

My Feedback: (3)

I had a Saito 150 mounted inverted that was on an airplane I bought at a swap meet. I had flown it 3 or 4 times. It was easy to hydro-lock. It had been flown quite a bit before purchase by me. It was my first Saito. I quickly learned to be sure it or any other engine inverted is clear of fuel in the cylinder before applying an electric starter! It tried to run then a loud bang occurred. Upon removal I saw a crack in the bottom of the crankcase. Upon tear down I found the crankshaft sheared next to the counterbalance. It had been cracked part way around the shaft for sometime because you could see the brighter metal in the smaller break of the crank that was left waiting for me to finish it off. I since have made it a habit of opening the throttle before applying glow plug heat and cranking by hand backwards several times especially after filling with fuel. This eliminates any fuel that may have found its way into the cylinder during fueling process. I have watched others with similar problems especially after filling with fuel before first flight. The engine comes up against compression and stops because of excess fuel in cyl. head. Myself and fellow flyers have had no problem with hydro-lock when using this method.

the pope

I also turn the engine over a few times before starting .Why do I use a starter ? Because i don't have a ego and I like my fingers attached to my hands . Had to search for fingers once and that was once to often . The engine I fear most is a saito 82 , I will never attempt to hand start it and never need to prime it and its the 1st engine that put the fear in me on the test stand . Weird as I have bigger engines . Cheers the pope

ALO 111

Thanks for all the feedback, it has become very interesting. I must stress the point that themotor was already running when it blew..Its at the importer at the moment so other pics not possible. Will call them again today but until now they have said or done nothing. I they just would just reply to me I would accept what they say.

1QwkSport2.5r

I only have two 4-strokes, a .60 and a 1.20 and I won't hand start either one. I too check for hydro lock beforehand but my engines are usually mounted upright so I've no issues usually.

blw

My Feedback: (3)

That would make me stop using Graupner props!!!