JNorton

My Feedback: (2)

I bought a new Magnum XL 91 RFS from Hobby People on sale in March. I was going to install it when I noticed there is no crankcase vent. Instead there is a fitting behind the cam housing on the crankcase with a hose going to the carburetor inlet.

Does this have any advantages or disadvantages compared to the crankcase vented to the atmosphere? I am unfamiliar with this setup.

Thanks,
John

lrb75

My Feedback: (12)

It is probably to get a little more oil to the camshaft. The cam shaft housing is still open to the crank case so it should still vent the pressure to the atmosphere.

w8ye

My Feedback: (16)

This has been a on going change to the Magnum four strokes which started with the 120 size.

People have played with removing the vent from the manifold and plugging the hole but it didn't change the rpm any.

Enjoy,

Jim

JNorton

My Feedback: (2)

If the carb inlet is low pressure wouldn't it be drawing from the camshaft? If so how would it get more lube? The only thing I could think of was reducing emissions which seems kinda crazy for model motor. Which is why I posted this. I can't see the reason for it.

John

JNorton

My Feedback: (2)

Bit more thought. Draw from the camshaft will bring fuel containing lube past the camshaft lobes. Takes me a while sometimes.
John

*JCB*

My Feedback: (9)

I was at a magnum engine clinic and a rep from the company said the MAIN reason for the return tube was to have a cleaner engine and hence a cleaner plane. he said that the power gain is minimal if even noticeable at all. nothing more nothing less

JNorton

My Feedback: (2)

Thanks JCB. At least I know why they did it now.
John

w8ye

My Feedback: (16)

Internal corrosion is a big problem in four strokes, especially in the camshaft area. The engines with the crankshaft vent near the camshaft fair better. But they seem to do a little better yet if the oil a drawn by the camshaft.

The OS 120 and 91 engines had this feature before the Magnums adopted it also.

None of the Saito single cylinder engines have this feature.

Enjoy,

Jim

JNorton

My Feedback: (2)

Ok so it's a good feature. Which bring up another question.

So now how do I put in after run oil in a cowled engine? I used to take the plug out and put a good healthy squirt of after run in the crankcase vent hose and crank the motor until I got a mist out of the glow plug hole. Tee off the camshaft to carb inlet line, or simply squirt it in the glow plug hole and hope for the best? If squirting it in the glow plug hole should the piston be at BDC?

John

w8ye

My Feedback: (16)

I would put it in the glow plug hole. It doesn't matter TDC or BDC.

I replace the plug but carefully turn the engine through a compression stroke or two by hand to make sure that it's not hydrolocked? You want to work the oil past the piston and into the crankcase. I just flip it through by hand a few times.

I'd be careful about putting a starter on it if the plug is in the head while there is oil in the cylinder?

Enjoy,

Jim

JNorton

My Feedback: (2)

w8ye,
Thanks for the information Jim. I bought the Magnum because it was on sale and there are a lot of people on this forum that like them. I thought I'd give them a try. The vent line location threw me however. I'll try your advise on using after run oil and be sure to hand prop it.
Thanks again everyone,
John

Flypaper 2

If you notice on your lawn mower, the same vent tube is on it from the valve cover to the carb. Purpose is for the environment and to keep the engine cleaner. No bearing on engine RPM. Negligable oil would leak past the piston if you put it in the glow plug hole. Over time very little leaks past it while the engine is running, just enough to keep the engine lubed. More oil would get to the engine innards if you put it in the vent tube.

JNorton

My Feedback: (2)

Flypaper2,
If I use the vent line to add after run oil it seems to me I'll have to break the line and only add oil to the side that goes to the cams. The other side that goes to the intake would fill the carburetor up with oil. I'll connect both sides when running the engine to help oil the cam bearings. Complications.
John

JNorton

My Feedback: (2)

After thinking more about this it would be easier to simply plug the intake and use the camshaft end of the hose as a vent. Then I could just use it to add after run oil -- the same as on other 4 strokes that use the crank case vent. If I use after run oil (50% ATF 50% Marvel Mystery Oil) after each run as is my practice the cams should always be well lubed.

John

w8ye

My Feedback: (16)

John,

That will be fine. Others have done that. My Magnum 91 does not have the line going to the carb. The vent spud is on the bottom of the engine.

Enjoy,

Jim

JNorton

My Feedback: (2)

Thanks Jim