expo

My Feedback: (20)

Hi, I've got a .91 4 stroke which is ok now but I was wondering where to look for wear when it starts gets tired.

Is there something I can check compression with? Is there a compression psi rating like a car? What signs of wear should I look for on the piston, ring and sleeve? How about valves? Other than the seats being shiny is there anything else?

Thanks in advance for your answers.

MinnFlyer

My Feedback: (4)

In 20 years of using them I haven't worn one out yet.

But I have seen some that don't seem to have the punch that they used to. But by the time that happens, most people have usually accumulated a few others, so they can put the slow one in a plane that suits it.

onepern

Iv seen a compression gage some place for RC engines. as with any internal combustion engine compression is a good indicator of wear. on a 4 stroke make sure that you valves are set properly as that can effect your reading.
found one [link]http://centralhobbies.com/Tools/tool1.html[/link]

expo

My Feedback: (20)

More times than not, when I see a used YS .91 or 120 for sale they're "recently factory rebuilt" so something's up there.

That compression gauge looks just like the one I've got for car engines. All I need is an adapter for a smaller hole. What should it read though?

onepern

if it didn't come with the engine specs Yul have to contact the manufacture

DLVS2FLY

I ran my (90) OS 4-stroke for years untill it just didn't have very much power, I put in a new OS-91, but having had so much fun with the 90, I couldn't just put it up, plus I wanted to find out how it worked, so off came the head, boy what a mess it was full of carbon build-up from many gallons of fuel , took it all apart and cleaned everything up, everything looked real good so back togeather, setting the valves per specks, put it back in the same plane and it ran just like a new one with all the power back,
So as Minnflyer stated you'll have to go a long way to ware one out, In my32 years I haven't worn any out eather, keep e'm clean and ajusted, and they will run untill you sell them

scratchonly

If you don't use after run oil and some castor, you will feel play in your bearings when you wigggle your prop from side to side. This will indicate rusted bearings.