Hi there,

I need to drill and tap the crankcase on my os91 4stroke. I'm thinking of doing this to the center of the backplate. Will this be ok? Is there a better place to tap it?

Thanks

also, i'm told that the 4 strokes should already have a crankcase vent in it, but it doesn't... any idea why?

thanks

Davey,

The O.S. Max FS-91 Surpass engine has a crankcase vent on the bottom. This is so that air can move in and out as the piston moves up and down. This venting is essential.

The vent also serves the purpose of allowing the excess oil to be dumped overboard.

The vent is located on the bottom of the engine, forward of the rear bearing. This allows the oil to pass through the rear bearing before it's blown overboard.

An additional vent should not be needed on this engine.

Hi Bax and thanks for the reply.

While that may be true for the original OS Surpass series, I don't think this is true for the FS II Surpass Series. I've looked all over this engine and I just don't see any vent. Here are a few pics I took of the engine for your reference. Can you shed some light on how to handle this?

http://www.kulkarnicorp.com/~dms12/engine1.jpg
http://www.kulkarnicorp.com/~dms12/engine2.jpg
http://www.kulkarnicorp.com/~dms12/engine3.jpg
http://www.kulkarnicorp.com/~dms12/engine4.jpg

Hi.

Yes you have it, you can see it in the picture engine4...

Thanks very much. So all I have to do is T this instead of tapping the crankcase? This tube seems to lead back into the engine at the back of it...

Thx

David

With the O.S. Max FS-91 Surpass II, the crancase vent is ported back into the intake manifold. You don't need to tap the case for a vent. You also don't want to tap that line, either. If that line's not intact and connected, the engine usually runs poorer than when the line's intact.

If you need to tap the case, you can tap the rear cover, but you don't have a lot of metal to work with, so the tap may not be as secure as you wish. Also, tapping the case may degrade the engine's performance, much as tapping the line between the existing vent and the intake manifold.

How about if I tee that existing line though? All the pump needs to do is measure the positive and negative pulses from the engine. If I put a Tee in this line and still allowed it to enter back into the intake manifold would this be acceptable?

Since we've not used an after-market pump on the engine, we have no information that we can comment on.

The only pump we've used is the one that comes on the pumped version of the engine.