Zman39

My Feedback: (6)

Hey All,

I have an OS .52 FS that is several years old. It ran good, but I could tell the bearings were getting bad and may have lost some of its compression so I decided to do a rebuild on it. I replaced both front and rear bearings and put a new head gasket on as well as an intake gasket. I reassembled it without problems, made sure the cam was aligned where it was suppose to be and set the valves to 2/1000". I ran about 4 tanks through pretty rich and then leaned it a little and flew it. The engine runs fine but it doesnt seem to have much compression. I can turn the prop and feel just a little bit of resistance and I go through compression. I am used to engines "popping" through compression. Is this normal for the OS 52 or should it have more compression then this?

Thanks for any help

Z

w8ye

My Feedback: (16)

I just rebuilt one and it will take a half gallon of fuel for the compression to return.

On a used engine like this you most probably moved the ring. It is no longer seated with the cylinder. The cylinder no longer has the ideal surface for seating a ring so it will take longer than on a new engine.

There is a possibility that you may have one of the valves too tight and you are loosing compression out the valve. You can hear this in the muffler or the carb.

There's no reason you can not just fly it and see of the compression returns?

Enjoy,

Jim

Zman39

My Feedback: (6)

Thanks for the reply. I was thinking (hoping) this will be the case but wanted to make sure I didnt miss something obvious. Only other thing I think I could have replaced was the sleeve but was hoping it wasnt necessary sinced it is a ringed engine. I will run some more fuel through it and see how it goes.

Z

w8ye

My Feedback: (16)

It is unlikely the sleeve will ever need replaced.

You may need a ring in the future but the piston and sleeve usually last a long time.

Enjoy,

Jim

Zman39

My Feedback: (6)

Speaking of valves. What is the ideal spacing on the valves when at room temperature?

Thanks again

w8ye

My Feedback: (16)

The tolerance works out to be .0015" to .004" but .002" is fine.

philfun

My Feedback: (58)

Hi Zman,

I have to reassemble an OS 48 FS.How to align the camshaft ?

Thanks

Phil

donkey doctor

Hello Phil; With the crank held at top dead centre, slide the camshaft into mesh with the crank gear so that the timing mark on the cam, aligns with the lifter and the push rod. It's easier to do it then to type it.

w8ye

My Feedback: (16)

The gear teeth are helical so the cam will twist as it goes into position. So you will need to lead the position a little when inserting so the cam will be correct when seated.

enjoy,

Jim

philfun

My Feedback: (58)

Thanks very much for your explanations.
Seems pretty straightforward
When I'll get a new connecting rod I'll reassemble.

Thanks again.

Phil