o.m.c cobra 3.0 lower unit

[steve 2]

While replacing a gear set, i noticed that the driveshaft pinion nut rests on top of the clutch dog,when turning the driveshaft by hand a rumbling can be heard,the driveshaft is shimmed correctly and bearings are excellent.What stops the driveshaft from floating in the casing as stims only control driveshaft from moving upwards.<br /> many thanks <br /> steve

 

[russthemuss]

Re: o.m.c cobra 3.0 lower unit

I havn't done a omc for quite a while but the pinion nut sits close, but not on the shaft. There is a taper roller bearing in the top which is preloaded by the shims and if there is a rumbling sound i would suspect this bearing is failing or the preload is to much (hence the shaft pulls down onto the lower unit )

 

[hondon]

Re: o.m.c cobra 3.0 lower unit

That pinion nut should not ride on the clutch dog. Disassemble and try again.

 

[steve 2]

Re: o.m.c cobra 3.0 lower unit

Thanks guys for info on o.m.c cobra,as what i can see, the pinion nut only rests on the clutch when the driveshaft is not turned,does the driveshaft move upwards,(due to centifugal force, acts like a screw)when the engine is started and then pushes against the shims.This gear box does not use taper bearings,unlike mercury lower units,and does not need shimming for backlash.exept on driveshaft.which only seems to control upward movement.

 

[russthemuss]

Re: o.m.c cobra 3.0 lower unit

mmmmmm yes the pinion will thrust upwards when in drive but wait untill you try reverse!! Something in there prevents the pinion from falling on the crown wheel.It may be something as simple as a circlip.I know it is a pain ,but i would remove the output shaft and pinion and check it out

 

[hondon]

Re: o.m.c cobra 3.0 lower unit

That pinion nut should not ride on the clutch dog ever. Something is not assembled right.

 

[steve 2]

Re: o.m.c cobra 3.0 lower unit

Thanks guys for your info,still seems close too the clutch dog,like what you say Russthemuss,but driveshaft only runs one way in forwards or reverse,there are some light score marks on old cluth dog,maybe the nut does come in contact with the clutch dog when the engine is at rest.Time i think to assemble, cross the fingers and wear the ear muffs,let you all know if i need a new lower unit,catch you all later ,steve.